No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
A hybrid additive manufacturing method for the fabrication of silicone bio-structures: 3D printing optimization and surface characterization
Abstract
The incremental trend in the practical applications of Additive Manufacturing (AM) brings up the challenge of developing novel methods for the fabrication of new materials. Thermoset polymers such as silicone are considered challenging materials in terms of the AM adoption. Printing silicone at a high speed may revolutionize multiple industries, specifically the medical sector. In this paper, a hybrid system that combines material jetting and material extrusion AM processes will be introduced. This method is not only capable of printing the non-Newtonian viscous silicone, but also increases the fabrication velocity between 10 to 20 times compared to the regular extrusion methods. Statistical optimization methods are employed to explore the optimum range of input parameters with the goal to maximize the 3D printing resolution, and improve the surface quality of 3D printed features. Finally, the working principle of the hybrid manufacturing method will be explained based on the surface characterization results.
... 5 Adaptations of this approach to bioprinting and curing via multipart mixing of the material enabled the development of multi-head deposition system (MHDS) [36]. 3D material extrusion is also the basis for several direct 3D printing of silicone approaches [11], two-photon polymerization processes [37]. ...
... Stansbury et al. [82] reported on a new generation of acrylic oligomers, introducing a block of other polymers, such as polyurethane, polyfluorocarbon, polysiloxane, etc., in polymer chain, which can eliminate the drawbacks of traditional acrylic copolymers and meet the requirements of a maxillofacial elastomer. 11 ...
... Direct approaches are based on the layer-by-layer extrusion, jetting, or polymerization of silicone. Despite the easy fabrication, direct 3D printing suffered from the visible layers from the progressive polymerization that did not meet aesthetics requirements [11]. Now, direct 3D printing approaches are actively developed for manufacture of silicon prosthesis with optimal characteristics. ...
Maxillofacial defects, arising from trauma, oncological disease or congenital differences, detrimentally affect everyday life. Prosthetic repair offers the aesthetic and functional reconstruction with the help of materials mimicking natural tissues, among which polymers take unprecedented role. The three-dimensional (3D) printing techniques based on the computer-aided design, where polymers are essential, provide a rapid and cost-effective workflow protocol to perfectly restore patient-specific anatomy for prosthetics. This review discusses the main 3D printing approaches to maxillofacial prostheses fabrication: extrusion and lithography, which are radically preferable to the traditional methods. The main assessment criteria, affording the polymer implementation in 3D printing of prostheses, as well as the characteristics of the key advanced polymers, are considered. The success of the prosthesis is shown to be largely dependent on the retention system, predominantly using polymers in the form of adhesives and osseointegrated implants as a support for the prosthesis. The approaches and technological prospects are also discussed in the context of specific aesthetic restoration on the example of the nasal, auricle and ocular prostheses. 3D printing techniques determine the development of personalized approaches to improve aesthetic and functional effect of prosthetics in patients with maxillofacial defects.
... The improvement of conductivity of the 3D-printed CNTs still needs to be addressed for the large-scale applications of 3D CNT structures as conductors in wearable electronics. Nevertheless, 3D-printed CNT structures can be widely used in scenarios [129] that do not request very high conductivity, such as pressure sensors [33,68], strain sensors [136], supercapacitors [135], and triboelectric nanogenerators [137]. ...
... c Top-view images of 3D-printed triboelectric generator insole. d Voltage profile of a 22 μF capacitor being charged by the 3Dprinted triboelectric generator insole and powering the electronic watch [137]. e 3D-printed flexible thermoelectric generator without the top electrode. ...
... Another triboelectric generator with a tailorable sophisticated 3D architecture was fabricated using a one-step 3D printing process without additional assembling processes [137]. In this work, the electricity is generated by the compressive deformation of the scaffold electrodes consisting of CNTs and PGS. ...
Four-dimensional (4D) printing, an innovative extension of three-dimensional (3D) printing, is defined as the additive manufacturing technology of intelligent components with controllable stimuli-responsive characteristics. The 4D-printed components can automatically and controllably change their shapes, properties, and/or functionalities with time in response to external stimuli, such as heat, moisture, light, PH, magnetism, and electricity. 4D printing integrates the design of structures’ intelligent behaviors into the fabrication processes, realizing integrated manufacturing of materials, structures, and functionalities. It has aroused worldwide attention in the academic and industrial communities since it was first proposed in 2013. Stimuli-response materials play a critical role in the relation of 4D printing. The stimuli-responsive characteristics of the 4D-printed components mainly depend on the properties of used stimuli-responsive materials and their combination and arrangement in 3D space. However, so far only limited stimuli-responsive materials for 4D printing have been developed, which greatly restricts to tap of the application potential of 4D printing. Thus, stimuli-responsive materials for 4D printing have become the hot and key spots of research in academia and engineering fields. In this chapter, after an introduction of the definition and prospect of 4D printing, the research advances in available stimuli-responsive materials for 4D printing were reviewed in detail in three categories: polymers and their composite materials, metals and their composite materials, and ceramics and their composite materials. This chapter may enhance our understanding of the 4D printing of stimuli-responsive materials and inspire further innovative ideas for the design of materials for 4D printing.
... Dual piezoelectric/pneumatic jetting valves have a much wider viscosity range (≥1 kPa s) 32 and high-viscosity jetting has been explored using Nordson Pico Pµlse printheads, using either reactive drop-on-drop jetting of a 2-part addition cure RTV 68 or a UV curable formulation with a dual UV/moisture cure system. 69,70 While resolution is lower than with inkjet -around ≥500 µm, similar to that achieved with electrohydrodynamic (EHD) 71 -piezo-pneumatic jetting valves can print 20 times faster than conventional inkjet. 70 Aerosol jetting has also been investigated: this technique has a low viscosity limit of up to 5 mPa s or 1000 mPa s, depending on the type of atomiser used. ...
... Mixed condensation/UV cure systems are increasingly used to enable fast shape retention (UV) with desired final mechanical properties (condensation). 69,[302][303][304] Orthogonal thiol-ene and condensation crosslinking was used to produce silicone double networks by vat photopolymerisation. 300 The mechanical properties of the inkjet-printed silicones were limited as non-viscous precursors were required for inkjet compatibility. 57 Typical hard silicone elastomers require ≥20 kg mol -1 precursors and soft elastomers ≥50 kg mol -1 precursors. ...
... Corning SE 1700, a commercial addition cure silicone with the correct rheological properties for RC/DIW, has been widely investigated 67 and vinyl-terminated silicone formulations currently dominate literature. Photopolymerisable reactions have been increasingly utilised for rapid, controlled curing, using commercial UV-curable silicones, 69,92,304,320,321 thiol-ene mechanisms, 295,296 and mixed moisture/UV cure systems. 69,302-304 1-part extrusion mixtures are typically prepared, regardless of whether they are based on 1-part or 2-part RTVs, as printing a single material is simpler than the deposition of two reagents; however, this limits the working-life. ...
There is a need for high-resolution and high-sensitivity temperature sensing in fields such as micro/nanoelectronics, integrated photonics, and biomedicine; however, non-invasive integrated sensing is difficult and expensive to achieve in miniaturised devices, as fabrication is greatly complicated by multi-step processes, heat treatments, and material compatibility. Inkjet printing (IJP) is a direct writing technique in the material jetting AM category that is effective for maskless multi-material printing with <50 µm resolution, which enables production of end-use devices and could simplify sensor integration. Existing inkjet-printed temperature sensors comprise simple circuit devices, which use the change in the electrical resistance of a sensing area to measure temperature. While current examples are well-suited to wearable sensors, they do not achieve the spatial and thermal resolutions desired for printed devices such as microfluidics. Development of inks for luminescence nanothermometry would enable inkjet-printable sensing geometries for planar and 3D thermal imaging with submicron and subdegree resolutions. Silicones are polymers suitable for optical sensing due to their ultraviolet (UV) and thermal stability, optical transparency, and high refractive indices. Composite inks for luminescence nanothermometry can be formulated with quantum dots (QDs), fluorescent semiconductor nanocrystals with intrinsic, reversible temperature quenching. Printable optical sensing materials would enable in situ temperature monitoring for applications and geometries that are otherwise impossible to monitor by conventional means. This thesis describes the development of the first inkjet-printable QD-silicone composite, and the first ink for luminescence thermometry, for integrated optical sensing; these may also have use in lighting applications . 2-part addition cure silicone inks and 1-part UV cure silicone inks were explored and QD-silicone composites were synthesised; inkjet printing of an addition cure QD-composite was demonstrated. Printing of reactive addition cure inks, where Ink A contained crosslinker and Ink B contained catalyst, was demonstrated using drop-on-drop IJP with the smallest average drop diameters reported for silicone IJP to date (33 36 µm). To overcome poor contact pinning, a pinned grid strategy was used for single printhead IJP and a line-by-line strategy for dual printhead IJP. Curing was the greatest challenge in reactive inkjet of QD-silicone composites, as labile ligands on the QDs poisoned the platinum catalyst despite low QD loading (0.005 wt% QD-Ink A). PtCl2 catalyst was added at low loading to enable curing and to explore the interactions between QDs and the catalyst. However, quenching was observed, with 70% decrease in emission intensity as PtCl2 concentration doubled; it was theorised that the QDs and catalyst competed for ligands, leading to metal-induced aggregation. Printing of fluorescent QD-silicone composites was demonstrated on a single printhead system using a pinned grid strategy; inks with no PtCl2 had stronger fluorescence but did not cure, highlighting their greater vulnerability to delays or fluctuations in heating. Novel UV curable silicone inks were formulated for inkjet using a high throughput screening method. Two photoinitiators (PIs) were trialled: DMPA (2,2-dimethoxy-2-phenylacetophenone) and TPO (phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide). DMPA was associated with rapid loss of fluorescence in QD-silicones, whereas quenching was not observed with TPO. Detachment of passivating ligands followed by photo-oxidation was suggested as a mechanism: TPO radicals are more susceptible to recombination with oxygen radicals than DMPA derived radicals, which might result in better shielding of the QD surface. Printing of 1 wt% TPO silicone inks without quantum dots was carried out under nitrogen to prevent oxygen inhibition. Jetting was demonstrated with 34-42 µm average drop diameter on silanised glass slides, while printing of continuous films was demonstrated on glass slides coated in a release agent. The temperature sensing performance of novel QD-silicone composites was assessed via fluorescence spectroscopy and imaging. 100 nm diameter QD clusters were observed in transmission electron microscopy and micron-scale QD aggregates in optical microscopy. QD emission appeared to be largely unchanged by immobilisation in silicone, although QD aggregation was expected to reduce photostability of the composite. Intensity- and spectral shift-based optical thermometry was demonstrated using well-plate reading and confocal laser scanning microscopy. Emission sensitivity at 627 nm was found to be approximately -0.7 to -1.2 % °C-1 between 30 50 °C and spectral sensitivity 0.07 to 0.08 nm °C-1, in agreement with other values in QD-sensing literature. Intensity decreased between thermal cycles of the same sample, although values at 60 °C were unchanged, while spectral shift appeared repeatable without redshift. Overall, fluorescent QD-silicone composites were produced via IJP for the first time and were shown to have temperature-sensitive emission. These materials are suitable for inkjet-printable devices with embedded optical temperature sensors using luminescence nanothermometry.
... The development of additive manufacturing (AM) has led to innovations in materials , processes & equipment [3][4][5][6], design [7], and systems [8]. Bio-additive manufacturing is a new growth point in additive manufacturing, bringing new possibilities in the fields of biomedical, biopharmaceutical, and rehabilitation medicine. ...
... Some scholars have developed integrated, new additive manufacturing processes and equipment [3][4][5][6] to expand the scope of the application of extrusion additive manufacturing. ...
Silicone material extrusion (MEX) is widely used for processing liquids and pastes. Owing to the uneven linewidth and elastic extrusion deformation caused by material accumulation, products may exhibit geometric errors and performance defects, leading to a decline in product quality and affecting its service life. This study proposes a process parameter optimization method that considers the mechanical properties of printed specimens and production costs. To improve the quality of silicone printing samples and reduce production costs, three machine learning models, kernel extreme learning machine (KELM), support vector regression (SVR), and random forest (RF), were developed to predict these three factors. Training data were obtained through a complete factorial experiment. A new dataset is obtained using the Euclidean distance method, which assigns the elimination factor. It is trained with Bayesian optimization algorithms for parameter optimization, the new dataset is input into the improved double Gaussian extreme learning machine, and finally obtains the improved KELM model. The results showed improved prediction accuracy over SVR and RF. Furthermore, a multi-objective optimization framework was proposed by combining genetic algorithm technology with the improved KELM model. The effectiveness and reasonableness of the model algorithm were verified by comparing the optimized results with the experimental results.
... The development of additive manufacturing (AM) has led to innovations in materials , processes & equipment [3][4][5][6], design [7], and systems [8]. Bio-additive manufacturing is a new growth point in additive manufacturing, bringing new possibilities in the fields of biomedical, biopharmaceutical, and rehabilitation medicine. ...
... Some scholars have developed integrated, new additive manufacturing processes and equipment [3][4][5][6] to expand the scope of the application of extrusion additive manufacturing. ...
The lack of direct process control of silicone material extrusion (MEX) limits the accuracy and design complexity of printed structures. In this paper, an iterative process monitoring system for silicone MEX that enables in-situ quality monitoring and optimization is presented and validated. To achieve in-situ quality monitoring, a laser profile sensor is integrated into the 3D printing platform to measure dimensional errors. The process includes virgin printing, scanning, analyzing, judging, and modified printing. Strands are initially printed and scanned step by step with the coordination of motion and sensing systems to obtain a point cloud with 3-dimensional coordinates. Data are corrected, standardized, and analyzed section by section instead of using an image process to improve efficiency and reserve information in the height direction. Centre, width, and height information are extracted for each strand cross-section. Noise and anomalies are then removed by a clustering algorithm for the center points to obtain the actual trajectory centerline and distribution of strand width along the trajectory. To achieve in-situ optimization for errors in trajectory, strand width, and height, the trajectory and process parameters are modified in the next print. The trajectory is corrected by applying the opposite trajectory deviation error vector. The feed rate is modified according to our previously proposed strand profile model that maps the process parameters to the strand cross-section geometry parameters. Compared with direct printing without in-situ quality monitoring and optimization, the overlap between the actual and the target strand was improved by 18%. The presented method demonstrates the feasibility and capability to improve accuracy and reduce errors.
... Several studies have developed neural network models based on the MVRA and GRNN in the field of AM [32][33][34][35][36]. The neural networking model is developed to determine the contribution of printing parameters and predict the accuracy of the SLS technique [32]. ...
... The GA optimization approach minimizes the effort required to perform experiments on all possible sets of input parameters [35]. The GA model's results on polyjet-manufactured dental models are reported to be more than 97% accurate against the original Polyjet AM data which highlights the capacity of the optimization technique to get the optimum outcomes [36]. This paper presents a novel fabrication and development of a predictive model for resilient, stable, chemical, and corrosion-resistant M8 thermoplastic fasteners manufactured using photopolymer jetting technology. ...
Polyjet Additive Manufacturing (AM) is gaining attention owing to its ability to manufacture intricate parts with microscopic resolution. While extensive research and development have optimized the accuracy and strength of 3D printed structures, however, only a few prediction models exist for predicting the accuracy of the thermoplastic-based components using Polyjet technique. The study presents an accuracy-based predictive model for polyjet AM of thermoplastic structures which significantly raises the fabrication standards and reduces the number of unnecessary experimental attempts. Multivariate Regression Analysis (MVRA) statistical approach and the Generalized Regression Neural Networks (GRNN) approach is carried out to evaluate the effect of numerous significant polyjet printing parameters such as Support Material, Print Mode, Print Orientation, and Thermoplastic resin on the dimensional stability of the printed structures, examined under an ultra-compact 3D laser sensor. The outputs are optimized using the Genetic Algorithm (GA), and the findings are found consistent with experimental trials. This study sets new standards for additive manufacturing of thermoplastic components by examining the influence of polyjet printing factors on the accuracy of the manufactured fastener along the X, Y, and Z axes, respectively. The study may eventually substitute metal fasteners in certain industrial applications such as in fluidics, electronics, biomedical engineering, food packaging, and automobile industries.
... Several studies have developed neural network models based on the MVRA and GRNN in the field of AM [32][33][34][35][36]. The neural networking model is developed to determine the contribution of printing parameters and predict the accuracy of the SLS technique [32]. ...
... The GA optimization approach minimizes the effort required to perform experiments on all possible sets of input parameters [35]. The GA model's results on polyjet-manufactured dental models are reported to be more than 97% accurate against the original Polyjet AM data which highlights the capacity of the optimization technique to get the optimum outcomes [36]. This paper presents a novel fabrication and development of a predictive model for resilient, stable, chemical, and corrosion-resistant M8 thermoplastic fasteners manufactured using photopolymer jetting technology. ...
Polyjet Additive Manufacturing (AM) is gaining attention owing to its ability to
manufacture intricate parts with microscopic resolution. While extensive research and
development have optimized the accuracy and strength of 3D printed structures,
however, only a few prediction models exist for predicting the accuracy of the
thermoplastic-based components using Polyjet technique. The study presents an
accuracy-based predictive model for polyjet AM of thermoplastic structures which
significantly raises the fabrication standards and reduces the number of unnecessary
experimental attempts. Multivariate Regression Analysis (MVRA) statistical approach
and the Generalized Regression Neural Networks (GRNN) approach is carried out to
evaluate the effect of numerous significant polyjet printing parameters such as Support
Material, Print Mode, Print Orientation, and Thermoplastic resin on the dimensional
stability of the printed structures, examined under an ultra-compact 3D laser sensor.
The outputs are optimized using the Genetic Algorithm (GA), and the findings are
found consistent with experimental trials. This study sets new standards for additive
manufacturing of thermoplastic components by examining the influence of polyjet
printing factors on the accuracy of the manufactured fastener along the X, Y, and Z
axes, respectively. The study may eventually substitute metal fasteners in certain
industrial applications such as in fluidics, electronics, biomedical engineering, food
packaging, and automobile industries.
... The piezoelectric-pneumatic material jet printing method (PPMJ), as a new generation of ink-based additive manufacturing technique, stands out in threedimensional fabrication with the ability to handle highly viscous inks (up to 1000 Pa·s) in high-speed conditions (up to 500 mm/s) [14]. The dual piezoelectricpneumatic nature of the printheads in the printing system for PPMJ provides adequate force for the stable jetting of uniform droplets of viscous fluids [15]. ...
Piezoelectric-pneumatic material jet printing (PPMJ), as a new generation of ink-based additive manufacturing, can be used to fabricate complex 3D structures with high-viscosity materials. In this work, a two-dimensional computational fluid dynamics model is presented to elucidate the multiphase aerodynamic phenomenon and deposition morphology of jet printing features. Based on the laminar and incompressible flow assumptions, governing equations are numerically developed to calculate crucial flow variables in the jet printing process. The fluid dynamics and deposition characteristics of droplets are investigated, and pressure and velocity distributions during the jet printing are also analysed. By comparing the numerical simulation with the experimental data, the operation mechanism of PPMJ shows good agreement, making the computational framework a valuable tool for predicting the morphologies of droplets. The results show that the material rheological properties and the fabrication parameters would influence the printing techniques and the formation of the printed droplets.
... Genetic Algorithm (GA) models are widely employed to achieve the optimised solution for collecting recorded data comprising several process variables [31]. GA approach is reported to be highly accurate for predicting the accuracy of the polyjet-printed tooth specimens utilising dental resins [32]. The GA-GRNN model accurately predicts the strength of FDM-printed components, resulting in superior design and enhanced product functionality [34]. ...
Reinforced polymers structures are widely used to fabricate intricate end-use parts due to their high durability, material-corrosion stability, low cost, and less weight. While extensive studies have focused on optimizing the compressive performance of fibre-reinforced structures; however, only a few have emphasised on compressive strength-based studies for reinforced multi-material structures to improve multi-functionality of end-use products. The study presents the universal compression strength-based predictive model employing material jetting technique which significantly optimizes the compressive performance of reinforced-thermoset structures precisely governing the material distribution of polymers controlling filler shape, filler volume concentration, and filler position considering full factorial Design of Experiments approach. Numerous prefabricating factors and fabricating constraints are considered to improve the accuracy of the model and identify complex correlations that are not apparent through empirical model. The compressive strength-prediction model is developed using machine learning algorithms where the Genetic Algorithm optimizes the compressive strength outcomes. The implementation of elliptical-reinforced filler networks, characterised by a Filler Aspect Ratio of 0.2938 and a Filler Volume Concentration of 30%, enhances the compressive strength by 146.41%. FESEM is employed to characterize the microstructural morphology at the interface of multi-material specimens. This study exhibits the replacement of metal stud gear with an elliptical-reinforced polymer stud gear in the Panther 1650 Series All Geared Lathe Machine, achieving a total of 2 million revolutions. The optical 3D measurement technique is used to visualise and examine residual stresses using displacement fields.
... Currently, a lot of pharmaceutical AM is still being developed in laboratories, and researchers are struggling with prophase research studies like developing the appropriate materials, standard operating procedures (SOP), as well as speculating on the handling window for various products as well as devices. To optimize the pharmaceutical AM process on a busy scale, the design of experiment has been used [47,48]. The QbD should be made available to guide pharmaceutical advancement to the center, the design of things, and treatments that maximize the product's efficacy and additionally, security and safety and security account while increasing item manufacturability if pharmaceutical AM has been industrialized or advertised. ...
... In order to guarantee a repeatable and reproducible printing process, a fine control of the volume and shape of the ink drop is required through the tuning of the printing parameters. As confirmed in [36], [37], the shape and size of the formed droplets depend on the piezoelectric force produced by the piezo actuator through the tappet and the pneumatic force generated by the pressure inside the syringe, and thus on the energy transferred to the droplet during the printing process. ...
Printed sensors offer unique benefits – highly customizable designs, low-cost prototyping, and a wide range of materials and properties - which can be exploited. Piezo-driven Jet Valve Dispensing is a printing technique suitable for the fabrication of sensors and electronics directly on the surfaces (both 2D and 3D) of smart objects and devices but needs additional analysis and study. In this work, we studied the influence of printing parameters on the performance of the Nordson PICO Jetting system mounted on the Neotech PJ15X machine by depositing a silver ink, typically used for the fabrication of sensors and interconnections, and a Ti
3
C
2
T
x
ink, a very promising 2D material in the sensing and electronics fields for its extraordinary physical, electrical, chemical, and mechanical properties. A tuning approach was proposed to tune the printing parameters correctly. The profiles of the cross-sections of printed lines were evaluated, including the process variability, when the values of the printing parameters were changed. In the case of Ti
3
C
2
T
x
, the improper setting of the printing setup caused undesired spots and irregular lines. The optimal settings for the printing setup were found for each ink, reaching a variability in the profile of 1.5%.
... SLS fabricated the sheets, while single-point incremental forming addressed the remaining geometry; this increased the variety of shape typology while improving accuracy and avoiding excessive sheets. Liravi and Toyserkani conducted a study to investigate combining jetting and extrusion processes for medical applications (Liravi & Toyserkani, 2018). The objects are printed using electromechanical, magnetic, and pneumatic nozzles. ...
... Currently, research on the quality of lines printed by HPJ is limited, with most studies focusing on inkjet printing for low material viscosities. Due to the similarities in the technical principles and forming processes, 23 the results in inkjet printing can provide a reference and research basis for the study of the HPJ line printing quality. Since the lines are printed by the coalescence of multiple droplets, some studies focused on the coalescence process to understand the formation of line contours. ...
The utilization of high-viscosity paste jetting technology has the potential to significantly expand the range of available materials and enhance the three-dimensional forming efficiency compared to inkjet printing. In this study, the threedimensional morphology and contour quality of lines printed using high-viscosity silver paste were investigated. Four types of lines were identified based on differences in the printing shape, and contour fluctuation evaluation indices were defined in both the transverse and longitudinal directions to establish quantitative distinction principles. Based on the research of inkjet printing, a modified theoretical model relating the dimensionless line width and droplet spacing was established considering the cross-sectional characteristics of the lines printed by high-viscosity paste jetting. With the establishment of mathematical models, distinction criteria between various line shapes were obtained and the printable range of uniform lines was determined. Finally, based on response surface methodology, the influences of single droplet jetting parameters, the line printing speed, and their interactions on the line contour fluctuation were analyzed. This study involved theoretical and experimental research on the line morphology and contour quality, which can provide support for control of the line printing quality in high-viscosity paste jetting technology.
... However, the low viscosity, long curing time, and low elastic modulus characteristics of silicone materials present significant challenges for the 3D printing of silicone. Currently, 3D printing technologies that can be directly used to manufacture silicone models include material jetting [12][13][14], binder jetting [15], hybrid methods [16,17], vat polymerization [18,19], and material extrusion [20], among others. Their main technical characteristics are shown in Table 2, and this article introduces several commonly used 3D printing technologies. ...
Personalized precision medicine is a new direction for medical development, and advanced manufacturing technology can provide effective support for the development of personalized precision medicine. Based on the layered accumulation manufacturing principle, 3D printing technology has unique advantages in personalized rapid manufacturing, and can form complex geometric shape parts at low cost and high efficiency. This article introduces the application progress of 3D printing technology in medical models, surgical navigation templates, invisible aligners, and human implants, analyzes their advantages and limitations, and provides an outlook for the development trend of 3D printing technology in precision medicine.
... In this way, the amount and size of voids between consecutive layers will be abruptly reduced, improving both the mechanical properties and the accuracy [ 42 , 43 ]. The force prediction through the proposed model is very appealing, especially for the fabrication of 3D printed silicone-based biomedical devices, requiring high accuracy and good mechanical performance, such as meniscus implants [44][45][46][47] . : overall extrusion force; Q: flow rate; ∅: nozzle outlet diameter; t: layer thickness. ...
Material extrusion (MEX) has become a highly desirable additive manufacturing technology for creating silicone-based structures in the biomedical and soft robotics fields due to its ease of fabrication of complex structure without molding or casting. However, the lack of models for the MEX process when extruding silicone has limited its application. This study seeks to bridge this gap by introducing semi-analytical and numerical models of the MEX process that can predict the extrusion force in practical scenarios, accounting the counterpressure force from the deposited silicone beads on a substrate. Using a custom-made MEX setup capable of extruding silicone, the two proposed models were validated through experimental tests. The models, semi analytical and numerical models, demonstrated maximum accuracy of 99.7% and 99.3% respectively in predicting the extrusion force based on the process parameters such as layer thickness, nozzle size and flow rate. The development of a tool capable of predicting the silicone printing force, such as the one proposed in this paper, can expand the role of MEX in the fabrication of silicone structures beyond the current limitations by improving the manufacturing process control, enabling the creation of thin-walled structures, and enhancing accuracy.
... The method has indicated applications in biomedical engineering for printing the matrix of a drug delivery system generated by SLA while placing several drugs independently in the matrix using MJ [123]. Within the bio family, the combination of material extrusion and MJ processes has enabled the production of silicone-based bio-structures earning the benefit of high printing quality of the extrusion system as well as high printing velocity of the jetting system [124]. Representative 3D parts processed by this method are shown in Fig. 14. ...
Additive manufacturing (AM) has a great potential to create complex parts and systems lighter and stronger compared to traditional manufacturing operations. So far, several polymeric materials including different types of thermoset polymers and recently fiber reinforced thermosetting composites have been used in different additive manufacturing processes. Printed parts have shown an enhanced performance compared to their counterparts made by conventional techniques. This review article presents the state-of-the-art in the field of polymer-based additive manufacturing processes employed for thermoset resins, their corresponding fiber reinforced composites, main process parameters, build strategies, and their effects on the mechanical behavior of printed parts. This paper enlightens the basics of material extrusion, vat photopolymerization, and hybrid AM processes. In particular, these techniques involve Direct Ink Writing (DIW), Frontal Polymerization (FP), Reactive Extrusion (RE), In-bath print and cure (IBPC) that fall under extrusion-based AM system, and Stereolithography (SLA), Digital Light Processing (DLP) falling under vat photopolymerization AM.
... The new generation of jetting printheads can print highly viscous inks up to 10 6 mPa.s. Dual systems such as UV-extrusion Ink jetting [19] and piezoelectric-pneumatic [20,21] systems demonstrated the possibility of fabricating silicone structures at a velocity of 100 mm/s with a resolution of 500-600 μm. Nevertheless, preparing the required ink is extremely challenging [22], and 3D printing of a large and complex structure made of silicone using the dual systems has not been demonstrated yet. ...
The direct ink writing (DIW) method of 3D-printing liquid resins has shown promising results in various applications such as flexible electronics, medical devices, and soft robots. A cost-effective extrusion system for a two-part high-viscous resin is developed in this article to fabricate soft and immensely stretchable structures. A static mixer capable of evenly mixing two viscous resins in an extremely low flow regime is designed based on the required mixing performance through a series of biphasic computational fluid dynamics analyses. The printing parameters of the extrusion system are determined empirically , and the mechanical properties of the printed samples are compared to their molded counterparts. Furthermore, some potential applications of the system in soft robotics and medical training are demonstrated. This research provides a clear guide for utilizing DIW to 3D print highly stretchable structures.
... Among them, MEX is becoming a popular approach to fabricating foams. It has been developed through a hybrid process of shell printing and infill injection to build closed-cell lattice foams [46], use of support materials [47], process optimization considering voids [48] and force [49], the hybrid process of MEX and MJ [50], etc. [7]. ...
This research demonstrates a Modeling idea using parametric Modeling and considering the process to predict coiling patterns effectively in open-cell foams material extrusion (MEX) with liquid rope coiling (LRC) effect. The model consists of three sub-models, including pneumatic extrusion model, liquid rope coiling model, and geometric model, considering material properties, material extrusion, falling, LRC, pattern formation process and device structure. The model uses four MEX process parameters (back pressure, moving speed, inner nozzle diameter, and nozzle height) to predict three geometric parameters of the coiling pattern. The capability to predict pattern shape (period length, width, and loop length) accurately is validated by comparing the fit of predicted and experimental values when adjusting the process parameters, with R-squared coefficients up to 0.957. Then, application value is demonstrated by printing silicone open-cell foams under the guidance of the proposed model and studying the compression properties of these foams. The obtained three-region stress-strain curves indicate the feasibility of variable stiffness foam fabrication by adjusting the process parameters according to the proposed model during the printing process. Based on the results, the proposed model demonstrates accuracy in predicting geometric parameters of translational coiling pattern, makes predictable manufacturing of complex cellular structures available, and provides a foundation for design and fabrication of load-based variable stiffness silicone open-cell foam.
... The research results showed remarkable improvements in the mechanical properties of the produced filaments, enhancing the ability of MEX 3D printing processes, thus showing the potential of such ceramic materials in nanopowder form. Additionally, the performance of the MEX 3D printed parts has been improved, in terms of their quality characteristics with post-processing procedures in hybrid material extrusion processes [66][67][68][69][70]. Attempts have also been made to improve the eco-friendliness of the 3D printing process [71,72], by optimizing the energy consumption [73,74], which as a result, affects the eco-friendliness of the produced parts. ...
Polycarbonate-based nanocomposites were developed herein through a material extrusion (MEX) additive manufacturing (AM) process. The fabrication of the final nanocomposite specimens was achieved by implementing the fused filament fabrication (FFF) 3D printing process. The impact of aluminum nitride (AlN) nanoparticles on the thermal and mechanical behavior of the polycarbonate (PC) matrix was investigated thoroughly for the fabricated nanocomposites, carrying out a range of thermomechanical tests. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) provided information about the morphological and surface characteristics of the produced specimens. Using energy dispersive spectroscopy (EDS), the elemental composition of the nanocomposite materials was validated. Raman spectroscopy revealed no chemical interactions between the two material phases. The results showed the reinforcement of most mechanical properties with the addition of the AlN nanoparticles. The nanocomposite with 2 wt.% filler concentration exhibited the best mechanical performance overall, with the highest improvements observed for the tensile strength and toughness of the fabricated specimens, with a percentage of 32.8% and 51.6%, respectively, compared with the pure polymer. The successful AM of PC/AlN nanocomposites with the MEX process is a new paradigm, which expands 3D printing technology and opens a new route for the development of nanocomposite materials with multifunctional properties for industrial applications.
... Polymers: (Cruz & Coole, 2006a), (Lopes, G., Miranda, R. M., Quintino, L., Rodrigues, 2007), (Tröger et al., 2008), (Höfer & Hinrichs, 2009), (Suwanprateeb et al., 2014), (Husár et al., 2014), (Short et al., 2014), (W. Z. Wu et al., 2014), (Vaezi & Yang, 2015), (Leonards et al., 2015), (Poh et al., 2016), (Jungst et al., 2016), (Stieghorst et al., 2016), , (Walker et al., 2017), (Pekkanen et al., 2017), (Shin et al., 2017), (Liravi & Toyserkani, 2018), (Kuo et al., 2018). Ceramics: (Cruz & Coole, 2006), (Yves-Christian et al., 2010), (Goffard & Sforza, 2013), (Lusquiños et al., 2014), (Gmeiner & Deisinger, 2015), (Falvo D'Urso Labate et al., 2017), (Nabiyouni et al., 2018), (Choi et al., 2018). ...
In order to describe the impact that the appropriation of additive manufacturing (AM) has on the supply chain (SC), a validated system dynamics model representing vectorially multiple products and multiple demands in different periods was used as a basis to apply to a case study of medical implant manufacturing, configuring three chain scenarios: 1. traditional supply chain with subtractive manufacturing, 2. centralized supply chain with additive manufacturing, and 3. decentralized supply chain with additive manufacturing. It was possible to notice that the production time is longer in additive manufacturing compared to traditional manufacturing and the cycle time and total demand closure were lower in traditional manufacturing. In addition, it was observed that the AM performance is significantly better in conditions of lower demand, which can be attributed to the characteristics of customization and small batches that this type of production approach implies.
... Beispielsweise zur additiven Fertigung von Silikonstrukturen existieren zahlreiche weitere Herstellungsansätze, welche sich, wie in [188] dargestellt, in verschiedene direkte und indirekte Verfahrensansätze unterteilen lassen. Bei diesen exemplarischen additiven Verfahren wird bereits bei der Betrachtung der realisierbaren Schichtdicken von minimal 50 µm bis 400 µm [189][190][191][192][193] deutlich, dass sich das Gros der Ansätze nur eingeschränkt oder gar nicht zur Herstellung von Dielektrischen Elastomeren eignet. Der zeitintensive Prozess der Ionen-Implantation mit einer Strukturierung mittels Polyamidmasken wird für Titan-Ionen in [194] und in [138] für die Herstellung von Goldelektroden auf einem mit Fotolack maskierten PDMS-Substrat vorgestellt. ...
Wesentlicher Gegenstand der Dissertationsschrift ist die Erforschung eines neuartigen additiven Fertigungsansatzes zur Herstellung elastischer mechatronischer Komponenten. Es wird die Kombination von Variationen und Weiterentwicklungen des Aerosol-Jet-Druck Verfahrens zur Produktion gestapelter Dielektrischer Elastomere beschrieben. Den Rahmen eines prototypischen Anwendungsfalls zur Ableitung der notwendigen und wünschenswerten Eigenschaften solcher flexiblen mechatronischen Systeme und damit letztlich der Anforderungen an ein Fertigungsverfahren bilden nachgiebige und damit anpassungsfähige Robotersysteme. Deren makroskopisch wirksame Kinematiken und Wirkflächen vereinen einen Merkmalskatalog hinsichtlich ihrer grundlegenden Konzepte und ihrer Anforderungen an einen Fertigungsansatz, der zukünftig auch einen Übertrag der gewonnenen Erkenntnisse auf andere Anwendungsdomänen flexibler mechatronischer Systeme erlaubt. Die dargestellten Methoden zur Herstellung von flexiblen Elektroden, Silikon-Dielektrika und integrierter Aktoren und Sensoren umfassen zum einen den Multi-Aerosol-Druck von RTV2-Silikonen zur programmierbaren Fertigung von Silikonlagen mit Schichtdicken im Bereich von 10 µm und deren Stapelung zu Volumenkörpern mit mehreren hundert Lagen. Weiterhin werden neuartige Ansätze zum zeiteffizienten Aerosol-Jet-Druck von elastischen Elektrodenstrukturen auf der Basis von reduziertem Graphenoxid vorgestellt. Der deren Herstellung erfolgt mittels eines neuartigen Hybrid-Atomizers, der die pneumatische und die ultraschallbasierte Aerosolerzeugung kombiniert. Daneben wird der Direktdruck von gefüllten Polymermatrizen durch die Kombination von drei Aerosolströmen beschrieben. Mit diesen neuartigen Ansätzen wird die Herstellung von prototypischen elastischen mechatronischen Komponenten in einem integrierten Prozessgerät demonstriert.
... The printing of very soft polymers that do not exhibit any shear-thinning properties (which thereby falls out of the scope of DIW) is known as liquid additive manufacturing (LAM). It remains a rather marginal topic and has been only addressed so far in the case of non-functional materials (i.e., pure silicone) [40][41][42][43] with applications in biomedicine or pneumatic-based soft robotics. More recently, German RepRap (now innovatiQ) [44] has introduced a commercial printer for the 3D printing of liquid silicone rubber, though the proposed compatible material has a rather high viscosity (~150,000 cps) and lies in the "harder" range for very soft silicones (50 Shore A). ...
This work explores the use of liquid additive manufacturing (LAM) to print heterogeneous magnetoactive layers. A general method is proposed where, by studying the printing of pure silicone lines, the successful printing of closed shapes, open shapes, and a combination thereof, can be achieved while accounting for the continuous deposition that is specific to LAM. The results of this characterization are subsequently exploited for the printing of a heterogeneous layer composed of four magnetoactive discs embedded in a pure silicone square. Such a layer, when affixed to a softer silicone substrate, yields a system that produces truly three-dimensional surface patterns upon application of a magnetic field. Hence, this work demonstrates that LAM is a promising approach for the rapid 4D printing of morphing surfaces exhibiting 3D surface patterns that can be actuated remotely and reversibly via a magnetic field. Such heterogenous layers have a wide range of applications, ranging from haptics to camouflage to differential cell growth.
Additive manufacturing (AM), known as three‐dimensional (3D) printing, uses computer‐controlled materials deposition to fabricate 3D objects by selectively depositing materials, usually in a layer‐wised fashion, to build a 3D object using free‐form fabrication. Integrating silicone elastomers with AM deposition strategies has been of interest due to the important application characteristics of silicones such as excellent mechanical properties, thermal resistance, and chemical inertness. This work presents a study on the shear‐thinning properties of thermally‐curable liquid silicone feedstocks to describe ideal flow and shape‐retention properties for direct ink writing of liquid silicone rubbers. To complement the direct ink writing process developed in this work for silicone AM, flow properties of various silicone feedstocks were identified through measurement of rheological properties using the AM fluid dispenser under various pressures, supported by parallel plate oscillatory shear rheology. A systematic process for evaluating and investigating the AM performance of seven different grades of silicones is introduced. The shape retention, overhang, and dimensional accuracy of these silicones in 3D printing process have been compared and summarized. This systematic evaluation methodology can be applied for silicone material selection and printing of silicone parts with complicated architectures.
In this paper, a string of waterborne polyurethane (WPU) emulsions synergistically modified with PDMS and GMS were successfully prepared by incorporating Polydimethylsiloxane (PDMS) into the soft segments of waterborne polyurethanes, and using glycerol monostearate (GMS) as a chain extender. FTIR, TGA, SEM, particle size test, water contact angle and other tests were used to characterize the effects of variable GMS contents on the structure and function of WPUs. The experimental tests showed that the WPUs synthesised with 30% PDMS-8% GMS synergism had better overall performance. The water contact angle could reach 115.4°, and the water absorption was reduced to 10.52% at 72 h. Furthermore, this innovative WPU film had excellent thermal stabilization, and this study provided a new approach to improve waterproofing performance, hydrophobicity and thermal stability of waterborne polyurethanes, which is expected to be applied in coatings, adhesives and water-resistant agents.
A high‐strength metakaolin‐based porous ceramics are fabricated using slurry‐based material extrusion via optimizing four key process parameters, including nozzle internal diameter, height to diameter ratio, filling rate, and printing speed. The orthogonal experiments are used to adjust flexural strength and porosity, and the optimal process parameters are obtained by comprehensive scoring and range analysis methods. The predictive models of strength‐parameters, porosity‐parameters, and strength‐porosity are established and validated. The results show that the optimal process parameters for high‐strength and high‐porosity ceramics are 0.51 mm nozzle internal diameter, 70% height to diameter ratio, 100% filling rate, and 15 mm s⁻¹ printing speed. The correctness and predictability of three predictive models are proved by two methods, which are the mutual validation and comparison between theoretical and actual values. And the error rates between theoretical and actual results are less than 7%. This work provides guidance for the rapid fabrication of ceramics with adjustable strength and porosity by material extrusion, and the established predictive models can pave the way for its wider application in the practice.
In this paper, a string of waterborne polyurethane (WPU) emulsions synergistically modified with PDMS and GMS were successfully prepared by incorporating Polydimethylsiloxane (PDMS) into the soft segments of waterborne polyurethanes, and using glycerol monostearate (GMS) as a chain extender. FTIR, TGA, SEM, particle size test, water contact angle and other tests were used to characterize the effects of variable GMS contents on the structure and function of WPUs. The experimental tests showed that the WPUs synthesised with 30% PDMS-8% GMS synergism had better overall performance. The water contact angle could reach 115.4 °, and the water absorption was reduced to 10.52% at 72 h. Furthermore, this innovative WPU film had excellent thermal stabilization, and this study provided a new approach to improve waterproofing performance, hydrophobicity and thermal stability of waterborne polyurethanes, which is expected to be applied in coatings, adhesives and water-resistant agents.
3D-printed implantable drug delivery systems (DDSs) are a class of novel therapeutic approaches with promising characteristics for developing personalised therapies. The pharmacokinetic and pharmacodynamic profile of long-acting implantable drug release scaffolds provide significant potential in reducing treatment limitations, like patient compliance, therapeutic threshold, drug bioavailability, and side effects. The manufacturing process of 3D-printed implants involves an initial selection of materials, techniques, and a rational formulation process design. Physico-chemical characteristics of materials, material compatibility, and manufacturing techniques are critical in developing diverse and multifunctional scaffolds defined by a long-acting drug release rate. In this chapter, an overview in manufacturing techniques, DDSs classification, critical design parameters, and prospects of 3D-printed implantable DDSs is given.
Maxillofacial defects, arising from trauma, oncological disease or congenital abnormalities, detrimentally affect daily life. Prosthetic repair offers the aesthetic and functional reconstruction with the help of materials
mimicking natural tissues. 3D polymer printing enables the design of patient-specific prostheses with high
structural complexity, as well as rapid and low-cost fabrication on-demand. However, 3D printing for prosthetics
is still in the early stage of development and faces various challenges for widespread use. This is because the most
suitable polymers for maxillofacial restoration are soft materials that do not have the required printability,
mechanical strength of the printed parts, as well as functionality. This review focuses on the challenges and
opportunities of 3D printing techniques for production of polymer maxillofacial prostheses using computer-aided
design and modeling software. Review discusses the widely used polymers, as well as their blends and composites,
which meet the most important assessment criteria, such as the physicochemical, biological, aesthetic
properties and processability in 3D printing. In addition, strategies for improving the polymer properties, such as
their printability, mechanical strength, and their ability to print multimaterial and architectural structures are
highlighted. The current state of the prosthetic retention system is presented with a focus on actively used
polymer adhesives and the recently implemented prosthesis-supporting osseointegrated implants, with an
emphasis on their creation from 3D-printed polymers. The successful prosthetics is discussed in terms of the
specificity of polymer materials at the restoration site. The approaches and technological prospects are also
explored through the examples of the nasal, auricle and ocular prostheses, ranging from prototypes to end-use
products.
Elastomers play a significant role across different fields including healthcare. They have similar mechanical properties to some of the soft tissues of the human body, which makes them useful in applications such as implants and prosthetics. However, forming elastomers for tailored-fit medical devices using 3D printing is still not yet widely utilized because of the current problems seen as innate to the elastomer properties, and the principles of 3D printing techniques. With a focus on silicone and polyurethane, this review details the state-of-the-art 3D printing techniques that are being modified over the years to allow its printability for medical applications. The paper also discusses the manufacturing challenges faced by the researchers in printing elastomers, and how these challenges are currently being addressed. This review paper shows further research direction and hopes to initiate further development of these solutions. This will allow the 3D printing of elastomers to gain widespread use in patient-specific medical devices and components with optimized functionality in the near future.
Aerogel‐based biomaterials are increasingly being considered for biomedical applications due to their unique properties such as high porosity, hierarchical porous network, and large specific pore surface area. Depending on the pore size of the aerogel, biological effects such as cell adhesion, fluid absorption, oxygen permeability, and metabolite exchange can be altered. Based on the diverse potential of aerogels in biomedical applications, this paper provides a comprehensive review of fabrication processes including sol‐gel, aging, drying, and self‐assembly along with the materials that can be used to form aerogels. In addition to the technology utilizing aerogel itself, it also provides insight into the applicability of aerogel based on additive manufacturing technology. To this end, how microfluidic‐based technologies and 3D printing can be combined with aerogel‐based materials for biomedical applications is discussed. Furthermore, previously reported examples of aerogels for regenerative medicine and biomedical applications are thoroughly reviewed. A wide range of applications with aerogels including wound healing, drug delivery, tissue engineering, and diagnostics are demonstrated. Finally, the prospects for aerogel‐based biomedical applications are presented. The understanding of the fabrication, modification, and applicability of aerogels through this study is expected to shed light on the biomedical utilization of aerogels.
Direct additive manufacturing (AM) of commercial silicones is an unmet need with high demand. We report a new technology, heating at a patterned photothermal interface (HAPPI), which achieves AM of commercial thermoset resins without any chemical modifications. HAPPI integrates desirable aspects of stereolithography with the thermally driven chemical modalities of commercial silicone formulations. In this way, HAPPI combines the geometric advantages of vat photopolymerization with the materials properties of, for example, injection molded silicones. We describe the realization of the new technology, HAPPI printing using a commercial Sylgard 184 polydimethylsiloxane resin, comparative analyses of material properties, and demonstration of HAPPI in targeted applications.
This research investigates the spatial structure of periodic titanium alloys. The response surface optimization method is used to optimize the weight reduction structure of combined model parameters. Under the condition of unidirectional load, the stress and strain results of each model group of a 3D structure with weight reduction rates of 30 %, 50 %, and 70 % are obtained through simulation analysis. Furthermore, the characteristics of the selective laser melting (SLM) forming process are incorporated, and a comparative analysis of the maximum equivalent stress of each group of models under unidirectional load is performed. The optimal structural form and its parameters suitable for multi-directional loads are screened. By using SLM to form the optimal model and carry out a loading test, the ultimate load of the model under different weight reduction rates is obtained to provide a theoretical basis for the next step of 3D printing process research.
Additive manufacturing (AM) has attracted increasing attention from the scientific community due to its huge potential to fabricate ceramic components without the use of expensive tooling. In addition, it has a layer-by-layer building principle, making it a suitable candidate for the creation of geometrically complex, functionalized, customized architectures that could not be realized at all, or could only be produced at great cost, using conventional technology. However, there has been a slower industrial adoption of additively manufactured ceramic components compared to polymers and metals. Several limitations must be addressed to extend the widespread adoption of AM by industrial end-users. This study provides a review covering the current state of the AM of advanced ceramics, culminating in a comprehensive evaluation of both the advantages and the limitations of each AM process and emphasising the achievements of advanced ceramics and ceramic matrix composites made using AM in terms of characterization and applications. The outcome is the provision of guidelines for ceramicists for optimal AM process selection considering a given material, and most suitable ceramic materials for AM specialists considering a specific application. Furthermore, this chapter also presents case studies illustrating the advantages of ceramic AM.
Using additive manufacturing technology, objects can be created layer wise by a single machine rather than utilizing molds and dies. A digital-projection light source is used to cure the surface of a liquid photopolymer in digital light processing (DLP) technique. This method is best for items with complicated structures and small cross-sectional areas that demand a high level of surface finish and strength. Objects are created for variety of angles using a variety of input parameters. 3D printing technologies based on DLP printing are commonly utilized to fabricate complex items without the use of tools or machining. Numerous variables influence the design of 3D printed parts, and they differ for each design and process. The layer thickness, pattern diameter, pattern spacing, and hollow thickness are the initial factors to be considered for DLP printed test coupons. In the present paper, DLP 3D coupons are printed using ultraviolet sensitive resin (λ = 405 nm). The primary objective of the work is to study the influence of support orientation on the surface finish and toughness of the DLP 3D printed test coupons as per ASTM standards.KeywordsAdditive manufacturingDLPHardnessSurface roughnessImpact strength ultraviolet-sensitive resin
In this work, a biocompatible Ti6Al4V titanium alloy was selected as a clad for a pure magnesium substrate. The laser cladding technique was used to clad Ti6Al4V alloy on the pure magnesium substrate. The 600 watts laser power, 200 mm/min scan speed, and 5 g/min powder feed were the cladding parameters. The microstructure of samples was analyzed through a scanning electron microscope (SEM), and hardness was evaluated through the Vickers microhardness test with the test load of 0.5 kg in 10 s dwell time. Wear resistance of the samples was investigated with the dry sliding pin on disk wear testing. Wear testing parameters are applied load (30 and 50 N), sliding velocity (1 and 2 m/s), and sliding distance of 1000 m. Results revealed that the microstructure contains α + β phases with Fe2O3Ti phases in the clad zone and cellular dendrites with Al12Mg17 phases in HAZ. Microhardness increased ~20 times and wear rates have reduced by 30–40% than the un-affected substrate.KeywordsLaser claddingTi–6Al–4V titanium alloyMagnesiumMicrostructureWear resistance
The CAD (Computer-aided design) and CAM (computer-aided manufacturing) have most applications in the manufacturing of fully automated, personalized dental devices and tailor-made treatment plans. 3D printing is one of the most rapidly expanding and new methods of manufacturing different things because of its on-demand and high productivity within the cost-effective manner which have a variety of applications in healthcare, pharmaceuticals, orthopaedics, engineered tissue models, medical devices, defence industries, automotive and aerospace sectors. Due to its emerging applications in the various sectors, the healthcare, Industries, and academic sectors are attracted towards the 3D printed materials.This review talks about the dental implants, polymers that are employed in concocting dental implants, critical parameters, and challenges which are to be considered while preparing these implants, advantages of 3D printing in the field of dentistry and the current trends. it discusses the variety of applications of 3D printed materials in the field of dentistry. Along with their method of fabrication, their critical process parameters (CPPs) are also discussed.
Electrohydrodynamic inkjet printing-based micro-additive manufacturing technology is a nano-manufacturing process using fluid jet printing, influenced by an electric field through nano-scale nozzles. This method helps to achieve higher resolution and control which is way better than that of traditional processes. This paper focuses on a fuzzy logic-based neural networking system, also known as ANFIS which has been used to predict and model the output parameter, i.e., droplet frequency for three controllable processes like nozzle-substrate gap, ink flow rate, and applied voltage. Since it is difficult to maintain constant operating conditions, the jet frequency and droplet diameter fluctuate. In order to stabilize this fluctuating jet frequency, a second-order non-linear regression equation has been implemented. In the proposed adaptive neuro-fuzzy predictive system, hybridization and backpropagation were used to predict the values. To do a comparative study in the accuracy of prediction of the characteristics of the deposited droplet, triangular, Gaussian and bell-shaped membership functions have been considered after a careful study. The comparative study indicates that, for predicting the droplet frequency, the optimal data base and the rule base of the expert system can be designed by the proposed methodology.
Polydimethylsiloxane (PDMS) elastomer is used in a wide range of biomaterial applications including microfluidics, cell culture substrates, flexible electronics and medical devices. However, it has proved challenging to 3D print PDMS in complex structures due to its low elastic modulus and need for support during the printing process. Here we demonstrate the 3D printing of hydrophobic PDMS pre-polymer resins within a hydrophilic Carbopol gel support via freeform reversible embedding (FRE). In the FRE printing process, the Carbopol support acts as a Bingham plastic that yields and fluidizes when the syringe tip of the 3D printer moves through it, but acts as a solid for the PDMS extruded within it. This, in combination with the immiscibility of hydrophobic PDMS in the hydrophilic Carbopol, confines the PDMS pre-polymer within the support for curing times up to 72 hours while maintaining dimensional stability. After printing and curing, the Carbopol support gel releases the embedded PDMS prints by using phosphate buffered saline solution to reduce the Carbopol yield stress. As proof-of-concept, we used Sylgard 184 PDMS to 3D print linear and helical filaments via continuous extrusion and cylindrical and helical tubes via layer-by-layer fabrication. Importantly, we show that the 3D printed tubes were manifold and perfusable. The results demonstrate that hydrophobic polymers with low viscosity and long cure times can be 3D printed using a hydrophilic support, expanding the range of biomaterials that can be used in additive manufacturing. Further, by implementing the technology using low cost open-source hardware and software tools, the FRE printing technique can be rapidly implemented for research applications.
The application of a maxillofacial prosthesis is an alternative to surgery in functional-aesthetic facial reconstruction. Computer aided design/computer aided manufacturing has opened up a new approach to the fabrication of maxillofacial prostheses. An intelligentized rapid simulative design and manufacturing system for prostheses was developed to facilitate the prosthesis fabrication procedure.
The rapid simulation design and rapid fabrication system for maxillofacial prostheses consists of three components: digital impression, intelligentized prosthesis design, and rapid manufacturing. The patients' maxillofacial digital impressions were taken with a structured-light 3D scanner; then, the 3D model of the prostheses and their negative molds could be designed with specific software; lastly, with resin molds fabricated by the rapid prototyping machine, the prostheses could be produced directly and quickly.
Fifteen patients with maxillofacial defects received prosthesis rehabilitation provided by the established system. The total clinical time used for each patient was only 4 hours over 2 appointments on average. The contours of the prostheses coordinated properly with the appearance of the patients, and the uniform-thickness border sealed well to adjacent tissues. All of the patients were satisfied with their prostheses.
The rapid simulative rehabilitation system of maxillofacial defects is approaching completion. It could provide an advanced technological solution for the Army in cases of maxillofacial defect rehabilitation.
Additive manufacturing, otherwise known as three-dimensional (3D) printing, is driving major innovations in many areas, such as engineering, manufacturing, art, education and medicine. Recent advances have enabled 3D printing of biocompatible materials, cells and supporting components into complex 3D functional living tissues. 3D bioprinting is being applied to regenerative medicine to address the need for tissues and organs suitable for transplantation. Compared with non-biological printing, 3D bioprinting involves additional complexities, such as the choice of materials, cell types, growth and differentiation factors, and technical challenges related to the sensitivities of living cells and the construction of tissues. Addressing these complexities requires the integration of technologies from the fields of engineering, biomaterials science, cell biology, physics and medicine. 3D bioprinting has already been used for the generation and transplantation of several tissues, including multilayered skin, bone, vascular grafts, tracheal splints, heart tissue and cartilaginous structures. Other applications include developing high-throughput 3D-bioprinted tissue models for research, drug discovery and toxicology.
The numbers of patients needing facial prostheses has increased in the last few decades due to improving cancer survival rates. The many limitations of the handmade prostheses together with rapid expansion of prototyping in all directions, particularly in producing human anatomically accurate parts, have raised the question of how to employ this technology for rapid manufacturing of facial soft tissue prostheses.
The idea started to grow and the project was implemented based on CAD/CAM principles – additive manufacturing technology, by employing layered fabrication of facial prostheses from starch powder and a water based binder and infiltrated with a silicone polymer (SPIS).
The project aimed to produce a facial prosthesis by using 3D colour printing, which would match the patient’s skin shade and have the desirable mechanical properties, through a relatively low cost process that would be accessible to the global patient community. This was achieved by providing a simple system for data capture, design and reproducible method of manufacture with a clinically acceptable material. The prosthesis produced has several advantages and few limitations when compared to existing products/prostheses made from silicone polymer (SP).
The mechanical properties and durability were not as good as those of the SP made prosthesis but they were acceptable, although the ideal properties have yet to be identified. Colour reproduction and colour matching were more than acceptable, although the colour of the SPIS parts was less stable than the SP colour under natural and accelerated weathering conditions. However, it is acknowledged that neither of the two methods used represent the natural life use on patients and the deficiencies demonstrated in terms of mechanical properties and colour instability were partially inherent in the methodology used, as the project was still at the developmental stage and it was not possible to apply real life tests on patients. Moreover, deficiencies in mechanical and optical properties were probably caused by the starch present, which was used as a scaffold for the SP.
Furthermore, a suitable retention system utilising existing components was designed and added to the prosthesis. This enabled the prosthesis to be retained by implants with no need for the addition of adhesive. This would also help to prolong the durability and life span of the prosthesis.
The capability of the printer to produce skin shades was determined and it was found that all the skin colours measured fall within the range of the 3D colour printer and thereby the printer was able to produce all the colours required. Biocompatibility was also acceptable, with a very low rate of toxicity. However, no material is 100% safe and each material has a certain range of toxicity at certain concentrations.
At this stage of the project, it can be confirmed that facial prostheses were successfully manufactured by using 3D colour printing to match the patient’s skin shade, using biocompatible materials and having the desirable mechanical properties. Furthermore, the technology used enabled prostheses to be produced in a shorter time frame and at a lower cost than conventional SP prostheses. They are also very lightweight, easier to use and possibly more comfortable for the patients. Moreover, this technology has the capability of producing multiple prostheses at the time of manufacture at reduced extra cost, whilst the data can be saved and can be utilised/modified for producing further copies in the future without having to going through all the steps involved with handmade prostheses.
Based on the mechanical properties and colour measurements the prostheses will have a finite service life and the recommendation is that these prostheses will need replacing every 6 to 12 months, depending on how the patient handles and maintains the prostheses and whether the prosthesis is being used as an interim or definitive prosthesis. This was largely comparable to existing prostheses but without the time and cost implications for replacement.
However, it is acknowledged that further investigations and clinical case studies are required to investigate the “real life” effect on the prostheses and to get feedback from the patients in order to make appropriate improvements to the mechanical properties and the durability of the prosthesis.
In this study, a new 3D colour image reproduction system is proposed for the automated and accurate additive manufacturing of soft tissue facial prostheses. A framework of 3D colour image reproduction was defined and a protocol for each sub-process was developed for this specific application. Colour management processes were developed and integrated into the proposed 3D image reproduction system; colour profiles for both the 3dMD photogrammetry system and the Z Corp Z510 3D printer were established utilising conventional colour reproduction techniques for 2D images. The soft tissue prototypes of both nose and ear prostheses were produced using the proposed system. The quality of prostheses was evaluated. The results show that the protocol used in the 3D manufacturing process was capable of producing accurate skin colour with fine textures and 3D shape, with significant savings in both time and cost.
Polydimethylsiloxane is a translucent and biologically inert silicone material used in sealants, biomedical implants and microscale lab-on-a-chip devices. Furthermore, in membrane technology, polydimethylsiloxane represents a material for separation barriers as it has high permeabilities for various gases. The facile handling of two component formulations with a silicone base material, a catalyst and a small molecular weight crosslinker makes it widely applicable for soft-lithographic replication of two-dimensional device geometries, such as microfluidic chips or micro-contact stamps. Here, we develop a new technique to directly print polydimethylsiloxane in a rapid prototyping device, circumventing the need for masks or sacrificial mold production. We create a three-dimensional polydimethylsiloxane membrane for gas-liquid-contacting based on a Schwarz-P triple-periodic minimal-surface, which is inaccessible with common machining techniques. Direct 3D-printing of polydimethylsiloxane enables rapid production of novel chip geometries for a manifold of lab-on-a-chip applications.
In prosthodontics, conventional methods of fabrication of oral and facial prostheses have been considered the gold standard for many years. The development of computer-aided manufacturing and the medical application of this industrial technology have provided an alternative way of fabricating oral and facial prostheses. This narrative review aims to evaluate the different streams of computer-aided manufacturing in prosthodontics. To date, there are two streams: the subtractive and the additive approaches. The differences reside in the processing protocols, materials used, and their respective accuracy. In general, there is a tendency for the subtractive method to provide more homogeneous objects with acceptable accuracy that may be more suitable for the production of intraoral prostheses where high occlusal forces are anticipated. Additive manufacturing methods have the ability to produce large workpieces with significant surface variation and competitive accuracy. Such advantages make them ideal for the fabrication of facial prostheses.
Additive manufacturing (AM) is a production method that enables the building of porous structures with a controlled geometry. However, there is a limited control over the final surface of the product. Hence, complementary surface engineering strategies are needed. In this work, design of experiments (DoE) was used to customize post AM surface treatment for 3D selective laser melted Ti6Al4V open porous structures for bone tissue engineering. A two-level three-factor full factorial design was employed to assess the individual and interactive effects of the surface treatment duration and the concentration of the chemical etching solution on the final surface roughness and beam thickness of the treated porous structures. It was observed that the concentration of the surface treatment solution was the most important factor influencing roughness reduction. The designed beam thickness decreased the effectiveness of the surface treatment. In this case study, the optimized processing conditions for AM production and the post-AM surface treatment were defined based on the DoE output and were validated experimentally. This allowed the production of customized 3D porous structures with controlled surface roughness and overall morphological properties, which can assist in more controlled evaluation of the effect of surface roughness on various functional properties.
The ability to three-dimensionally interweave biological tissue with functional electronics could enable the creation of bionic organs possessing enhanced functionalities over their human counterparts. However, current electronics are inherently two dimensional, preventing seamless multidimensional integration with biology as the processes and materials used to structure synthetic tissue constructs and conventional electronic devices are very different. Here, we present a novel strategy for overcoming these difficulties via additive manufacturing of biological cells with structural and nanoparticle derived electronic elements. As a proof of concept, we generated a bionic ear via 3D printing of a cell-seeded hydrogel matrix in the precise anatomic geometry of a human ear, along with an intertwined conducting polymer consisting of infused silver nanoparticles. This allowed for the in vitro culturing of cartilage tissue around an inductive coil antenna in the ear, which subsequently connects to cochlear-like electrodes. The printed ear exhibits enhanced auditory sensing for radio frequency reception, and complementary left and right ears can listen to stereo audio music. Overall, our approach suggests a means to intricately merge biologic and nanoelectronic functionalities via 3D printing.
Purpose
The purpose of this paper is to propose and discuss a definition and a classification scheme for direct writing (DW) technologies.
Design/methodology/approach
Both the definition and the classification are developed based on the perspectives of the growing DW community in the UK, through consultation with members, workshops and a survey across the community. In addition, current DW technologies and literature on classification techniques are reviewed.
Findings
The classification is structured in order to encompass current technologies, but also to be expandable to accommodate new ones that could be identified in the future as belonging to the DW remit. It is developed considering three dimensions related to DW: “Technology” to encompass all the processes, apparatuses, principles and tools which allow DW manufacturing; “Applications” to consider all the “types of manufactured goods” which could be produced with the DW technologies; and “Materials” which could be employed in DW manufacturing. The classification scheme is visualised into navigation maps and used as the basis of a software tool which can allow the community to exchange information on DW.
Research limitations/implications
The paper proposes a classification as a tool for knowledge exchange and to support knowledge organisation and retrieval. However, the classification proposed in this paper might not be the only possible solution.
Practical implications
The definitional framework is proposed to the DW community as a language tool to help communication among members with different perspectives and to be used to support the creation of information databases. It is embodied in a software tool through which they could file personal profiles (i.e. their expertise and interests) and hence map the community.
Originality/value
It is evident that, due to the heterogeneity of the community of scientists and practitioners interested in these technologies, many perspectives coexisted and that a communication platform is required. The authors decide to develop a classification which could be flexible enough to encompass new emerging technologies as the use of classifications as tools for supporting communication across the scientific community is well known and as the authors could not identify in literature any other DW technology classification which could satisfy these requirements.
BACKGROUND: Additive manufacturing (AM) is being increasingly used for producing medical models. The accuracy of these models varies between different materials, AM technologies and machine runs. PURPOSE: To determine the accuracy of selective laser sintering (SLS), three-dimensional printing (3DP) and PolyJet technologies in the production of medical models. MATERIAL: 3D skull models: "original", "moderate" and "worse". SLS, 3DP and PolyJet models, and a coordinate measuring machine (CMM). METHODS: Measuring balls designed for measurements were attached to each 3D model. Skull models were manufactured using SLS, 3DP and PolyJet. The midpoints of the balls were determined using CMM. The distances between these points were calculated and compared with the 3D model. RESULTS: The dimensional error for the PolyJet was 0.18 ± 0.12% (first measurement) and 0.18 ± 0.13% (second measurement), for SLS 0.79 ± 0.26% (first model) and 0.80 ± 0.32% (second model), and for 3DP 0.67 ± 0.43% (original model, first measurement) and 0.69 ± 0.44% (original model, second measurement), 0.38 ± 0.22% (moderate model) and 0.55 ± 0.37% (worse model). Repeatability of the measurement method was 0.12% for the PolyJet and 0.08% for the 3DP. CONCLUSION: A novel measuring technique was developed and its repeatability was found to be good. The accuracy of the PolyJet was higher when compared with SLS or 3DP.
Purpose
The purpose of this paper is to determine the most‐practical means of transforming computer‐aided‐design models of custom clubfoot pedorthoses into functional pedorthoses for testing on patients in a clinical trial.
Design/methodology/approach
The materials used in conventional orthosis fabrication are not yet available for solid free‐form fabrication; therefore, to fabricate the pedorthoses, several approaches were considered, including direct manufacturing, additive‐based moulding, laser cutting of foam and combinations of several of these approaches.
Findings
The chosen approach of additively manufacturing the custom hard shell, and moulding the polyurethane‐foam insert, resulted in accurate, durable and effective pedorthoses that fit well, and could be adjusted as needed. The pedorthoses that were produced are currently being tested on the respective patients for their improvement in mobility and degree of clubfoot correction, and will continue through early 2010.
Practical implications
Additive manufacturing provides an ideal approach for generating the custom, end‐use hard‐ and soft‐layer patterns: each pedorthosis is truly unique; and the soft layer has regions of variable thickness. The advantage of this approach is the reduction in labour and the increase in degrees of design freedom available, compared to conventional methods of fabricating orthotic devices. Replacement inserts can be moulded in a matter of hours using this silicone‐moulding approach.
Originality/value
Several new approaches for fabricating custom orthotic devices were explored, and the related results are discussed. The goal of this paper is to convey the potential of the fabrication procedure used and lessons learned on this project to the rapid prototyping and orthotic communities.
This study was designed to evaluate pulse sequences and patient positioning for MR imaging of silicone breast implants in patients. One hundred forty-three patients (281 silicone implants) underwent imaging over a 21-month period. The combination of a T2-weighted fast spin echo technique (SE), T2-weighted fast SE with water suppression, and T1-weighted SE with fat suppression is recommended to reliably differentiate silicone from other breast tissues and to identify intracapsular and extracapsular ruptures or leaks. Seventy of the 143 patients underwent removal of their silicone implants. The sensitivity for detection of silicone implant rupture was 76%, with a specificity of 97%. Positioning the patient prone improved image quality.
A technique for controlled deposition of biomaterials and cells in specific and complex architectures is described. It employs a highly accurate three-dimensional micropositioning system with a pressure-controlled syringe to deposit biopolymer structures with a lateral resolution of 5 microm. The pressure-activated microsyringe is equipped with a fine-bore exit needle and a wide variety of two- and three-dimensional patterns on which cells to be deposited can adhere. The system has been characterized in terms of deposition parameters such as applied pressure, motor speed, line width and height, and polymer viscosity, and a fluid dynamic model simulating the deposition process has been developed, allowing an accurate prediction of the topological characteristics of the polymer structures.
Additive manufacturing (AM) of highly viscous materials, e.g., polysiloxane (silicone) has gained attention in academia and different industries, specifically the medical and healthcare sectors. Different AM processes including micro-syringe nozzle dispensing systems have demonstrated promising results in the deposition of highly viscous materials. This contact-based 3D printing system has drawbacks such as overfilling of material at locations where there is a change in the direction of the trajectory, thereby reducing the printing quality. Modeling the continuous flow of a highly viscous polysiloxane in the nozzle dispensing AM system using finite element analysis will be the first step to solve this overfilling phenomenon. The results of simulation can be used to predict the required variation in the value of pressure before the nozzle reaches a corner. The level-set method is employed for this simulation, and the results are validated by comparing the flow profile and geometrical parameters of the model with those of the experimental trials of the dispensing of polysiloxane. Comparisons show that the model is able to predict the location of the droplet before it reaches the substrate, as well as the height of the droplet generated on the substrate accurately. To predict the width of the droplet, adjustment factors need to be considered in calculations based on the value of the pressure.
This paper presents a support-free fabrication method for three-dimensional soft structures by creating a hydrostatic condition. The hydrostatic force inside the polymer resin can, theoretically, keep a soft structure in position and shape. The key technology behind this method is the low one-photon polymerization (LOPP), which can initiate polymerization at the focusing spot under the resin surface, as opposed to the surface one-photon polymerization in stereolithography (SLA). To prove the concept of LOPP, an optics setup for a wide beam gradient along with a low-absorption wavelength was built for this study. An ultraviolet (UV) curable silicone was adopted as the soft material. The experiments consisted of a qualitative observation for LOPP phenomenon and a quantitative study on the cured geometry and volume under various UV exposure conditions. Results have demonstrated the “in-liquid” polymerization using LOPP and also unveiled the challenges of geometrical resolution and accuracy as a function of UV beam gradient, intensity, and exposure time. Further investigation is required for better control over this method.
In this contribution we present recent findings of our efforts to qualify the so called Aerosol-Jet-Printing process as an additive manufacturing approach for stacked dielectric elastomer actuators (DEA). With the presented system we are able to print the two essential structural elements dielectric layer and electrode in one machine. The system is capable of generating RTV-2 silicone layers made of Wacker Elastosil P 7670. Therefore, two aerosol streams of both precursor components A and B are generated in parallel and mixed in one printing nozzle that is attached to a 4-axis kinematic. At maximum speed the printing of one circular Elastosil layer with a calculated thickness of 10 μm and a diameter of 1 cm takes 12 seconds while the process keeps stable for 4.5 hours allowing a quite high overall material output and the generation of numerous silicone layers. By adding a second printing nozzle and the infrastructure to generate a third aerosol, the system is also capable of printing inks with conductive particles in parallel to the silicone. We have printed a reduced graphene oxide (rGO) ink prepared in our lab to generate electrodes on VHB 4905, Elastosil foils and finally on Aerosol-Jet-Printed Elastosil layers. With rGO ink printed on Elastosil foil, layers with a 4-point measured sheet resistance as low as 4 kΩ can be realized leaving room for improving the electrode printing time, which at the moment is not as good as the quite good time-frame for printing the silicone layers. Up to now we have used the system to print a fully functional two-layer stacked DEA to demonstrate the principle of continuously 3D printing actuators.
Polysiloxane (silicone) has been widely used in production of in-vivo prostheses due to its unique properties such as biocompatibility. Traditional methods of producing polysiloxane prostheses are mostly based on casting. These methods are time consuming and require high technical expertise. Moreover, the process can be tedious for the patients as it requires their presence in the design and fabrication steps. Using additive manufacturing for production of polysiloxane prostheses eliminate the need for presence of patient and reduce the production time. However, additive manufacturing has been mostly used for production of moulds for polysiloxane casting. In this study, a nozzle dispensing method for rapid manufacturing of polysiloxane products is assessed. Owing to importance of dimensional accuracy of prosthetic products in micro-scale, the effects of process parameters on final dimensions of printed parts have been investigated using design of experiments to optimise parameter values. A t-test is also employed to validate optimisation model.
Salivary glands are required for oral health and general well-being. In patients suffering from irreversible salivary hypofunction secondary to therapeutic radiation exposure or Sjögren’s syndrome, available therapies are limited to salivary gland substitutes or parasympathetic stimulants, both of which show limited efficacy. The pathophysiologic basis of radiation-induced damage involves a reduction in viable acinar cells required for physiologic function, as well as a deterioration in acinar cell morphology. Together, these alterations lead to irreversible salivary gland dysfunction. Therefore, it is imperative to prevent damage to these acinar cells and to recover lost function of those cells after exposure to radiation. This chapter provides a brief overview of the current strategies being implemented for the prevention of radiation-induced damage, current strategies for the regeneration of acinar cells, and concludes with a basic review of salivary gland anatomy and development.
Over one million patients per year undergo some type of procedure involving cartilage reconstruction. Polymer hydrogels, such as alginate, have been shown to be effective carriers for chondrocytes in subcutaneous cartilage formation. The goal of our current study was to develop a method to create complex structures (nose bridge, chin, etc.) with good dimensional tolerance to form cartilage in specific shapes. Molds of facial implants were prepared using Silastic ERTV. Suspensions of chondrocytes in 2% alginate were gelled by mixing with CaSO(4) (0.2 g/mL) and injected into the molds. Constructs of various cell concentrations (10, 25, and 50 million/mL) were implanted in the dorsal aspect of nude mice and harvested at times up to 30 weeks. Analysis of implanted constructs indicated progressive cartilage formation with time. Proteoglycan and collagen constructs increased with time to approximately 60% that of native tissue. Equilibrium modulus likewise increased with time to 15% that of normal tissue, whereas hydraulic permeability decreased to 20 times that of native tissue. Implants seeded with greater concentrations of cells increased proteoglycan content and collagen content and equilibrium and decreased permeability. Production of shaped cartilage implants by this technique presents several advantages, including good dimensional tolerance, high sample-to-sample reproducibility, and high cell viability. This system may be useful in the large-scale production of precisely shaped cartilage implants. 2001
Most AM processes require post-processing after part building to prepare the part for its intended form, fit and/or function. Depending upon the AM technique, the reason for post-processing varies. For purposes of simplicity, this chapter will focus on post-processing techniques which are used to enhance components or overcome AM limitations. These include:
Purpose:
To establish an alternative method to design and fabricate an obturator prosthesis within the maxillectomy defect using a computer-aided design (CAD) and rapid prototyping (RP) technique and to evaluate the functional results of this technique.
Materials and methods:
Eleven patients with acquired maxillary defects resulting from head and neck cancers were treated using a protocol based on three-dimensional (3D) reconstruction, CAD, and RP technologies to fabricate obturator prostheses. To evaluate the quality of the obturator prostheses and the patients' satisfaction, the Obturator Functioning Scale (OFS) of the Memorial Sloan-Kettering Cancer Center was applied.
Results:
Each patient received an individualized obturator that exactly matched the static shape and fit of the defect. Clinical modifications were required to improve border contours. The patients showed good results in all fields of functional outcomes and social acceptance. The OFS scores were comparable with those reported in other studies using traditional maxillectomy impression methods.
Conclusions:
This study combined CAD with RP technology to explore an alternative and feasible method for manufacturing individualized obturators for patients after maxillary resection. It has shown significant clinical value, especially for use in developing countries.
Three-dimensional printing of viscoelastic inks to create porous, elastomeric architectures with mechanical properties governed by the ordered arrangement of their sub-millimeter struts is reported. Two layouts are patterned, one resembling a “simple cubic” (SC)-like structure and another akin to a “face-centered tetragonal” (FCT) configuration. These structures exhibit markedly distinct load response with directionally dependent behavior, including negative stiffness. More broadly, these findings suggest the ability to independently tailor mechanical response in cellular solids via micro-architected design. Such ordered materials may one day replace random foams in mechanical energy absorption applications.
This work addresses the characterization of a UV-based micro-syringe deposition (μSD) system utilized in the micro-dispensing of photopolymers on particulate ceramic substrates. This methodology is used in embedding functionally graded and interconnected micro-features within constructs produced by a novel combined powder-based additive manufacturing (AM) and UV-based micro-syringe deposition (μSD) technique. The process is experimentally characterized using SEM and optical microscopy to study the effect of a wide range of process parameters on the geometrical quality of deposited tracks. Experimental data show that the system can produce features ranging from 200 to 575 μm in width and from 20 to 200 μm in height on particulate ceramic surfaces. To gain insight into the proposed micro-deposition process, a two-tier model is also developed. The first framework describes an analytical model for predicting the flow rate of the dispensed photopolymer fluid based on the piston displacement. The second model is a stochastic framework for predicting the line width of the features deposited on the substrate using a Monte Carlo probabilistic simulation to compensate for uncertainty in the system input parameters. A comparison between experimental and modeling line width predictions shows that the modeling results are 14–38% higher than the experimental results, depending on the system input variables. The proposed model is enhanced by introducing adjustment factors to compensate for UV exposure delay, fluid migration, and imbibition.
New microproducts need the utilization of a diversity of materials and have complicated three-dimensional (3D) microstructures with high aspect ratios. To date, many micromanufacturing processes have been developed but specific class of such processes are applicable for fabrication of functional and true 3D microcomponents/assemblies. The aptitude to process a broad range of materials and the ability to fabricate functional and geometrically complicated 3D microstructures provides the additive manufacturing (AM) processes some profits over traditional methods, such as lithography-based or micromachining approaches investigated widely in the past. In this paper, 3D micro-AM processes have been classified into three main groups, including scalable micro-AM systems, 3D direct writing, and hybrid processes, and the key processes have been reviewed comprehensively. Principle and recent progress of each 3D micro-AM process has been described, and the advantages and disadvantages of each process have been presented.
The medical grade silicones are probably the most widely used of all the synthetic polymers for permanently implanted subdermal devices. This paper reviews the chemistry of these materials from the original polymer manufacturing through the various stages necessary to obtain the types of heat vulcanizing silicone rubber, room temperature vulcanizing silicone rubber, and silicone rubber adhesive most commonly used in medical applications.
Purpose
This paper aims to present a novel rapid prototyping (RP) fabrication methods and preliminary characterization for chitosan scaffolds.
Design
A desktop rapid prototyping robot dispensing (RPBOD) system has been developed to fabricate scaffolds for tissue engineering (TE) applications. The system is a computer‐controlled four‐axis machine with a multiple‐dispenser head. Neutralization of the acetic acid by the sodium hydroxide results in a precipitate to form a gel‐like chitosan strand. The scaffold properties were characterized by scanning electron microscopy, porosity calculation and compression test. An example of fabrication of a freeform hydrogel scaffold is demonstrated. The required geometric data for the freeform scaffold were obtained from CT‐scan images and the dispensing path control data were converted form its volume model. The applications of the scaffolds are discussed based on its potential for TE.
Findings
It is shown that the RPBOD system can be interfaced with imaging techniques and computational modeling to produce scaffolds which can be customized in overall size and shape allowing tissue‐engineered grafts to be tailored to specific applications or even for individual patients.
Research limitations/implications
Important challenges for further research are the incorporation of growth factors, as well as cell seeding into the 3D dispensing plotting materials. Improvements regarding the mechanical properties of the scaffolds are also necessary.
Originality/value
One of the important aspects of TE is the design scaffolds. For customized TE, it is essential to be able to fabricate 3D scaffolds of various geometric shapes, in order to repair tissue defects. RP or solid free‐form fabrication techniques hold great promise for designing 3D customized scaffolds; yet traditional cell‐seeding techniques may not provide enough cell mass for larger constructs. This paper presents a novel attempt to fabricate 3D scaffolds, using hydrogels which in the future can be combined with cells.
The efficacy of computer-aided technologies in the design and manufacture of maxillofacial prostheses has not been fully proven. This paper presents research into the evaluation of direct and indirect additive manufacture of a maxillofacial prosthesis against conventional laboratory-based techniques. An implant/magnet-retained nasal prosthesis case from a UK maxillofacial unit was selected as a case study. A benchmark prosthesis was fabricated using conventional laboratory-based techniques for comparison against additive manufactured prostheses. For the computer-aided workflow, photogrammetry, computer-aided design and additive manufacture (AM) methods were evaluated in direct prosthesis body fabrication and indirect production using an additively manufactured mould. Qualitative analysis of position, shape, colour and edge quality was undertaken. Mechanical testing to ISO standards was also used to compare the silicone rubber used in the conventional prosthesis with the AM material. Critical evaluation has shown that utilising a computer-aided work-flow can produce a prosthesis body that is comparable to that produced using existing best practice. Technical limitations currently prevent the direct fabrication method demonstrated in this paper from being clinically viable. This research helps prosthesis providers understand the application of a computer-aided approach and guides technology developers and researchers to address the limitations identified.
The effect of plasma surface treatment on the dried diameter of droplets inkjet-printed on the PI substrate was investigated by varying the plasma process parameters. The sequential design of the experiments technique combining a factorial design with a response surface method was introduced to systematically estimate an accurate empirical response model for two independent design variables: radio frequency (RF) power and gas pressure. C4F8 gas was used for the plasma surface treatment of 90 mm × 90 mm polyimide substrates. Ag ink droplets ejected from a 30 µm nozzle were printed on the plasma-treated substrates, and their measured diameter and standard deviation were used as the response variables. The plasma-treated substrate was also characterized by contact angles and x-ray photoelectron spectroscopy. The results indicate that the droplet diameters and their uniformity are sensitive to changes in both RF power and gas pressure, lower droplet diameters on PI substrates correspond to lower surface energies, and the process condition producing higher F content results in more hydrophobic surface. The resolution of the inkjet printing can be precisely controlled by varying the droplet diameter and uniformity through the C4F8 plasma surface treatment.
Dentists have used rapid prototyping (RP) techniques in the fields of oral maxillofacial surgery simulation and implantology. With new research emerging for molding materials and the forming process of RP techniques, this method is becoming more attractive in dental prosthesis fabrication; however, few researchers have published material on the RP technology of prosthesis pattern fabrication. This article reviews and discusses the application of RP techniques for prosthodontics including: (1) fabrication of wax pattern for the dental prosthesis, (2) dental (facial) prosthesis mold (shell) fabrication, (3) dental metal prosthesis fabrication, and (4) zirconia prosthesis fabrication. Many people could benefit from this new technology through various forms of dental prosthesis production. Traditional prosthodontic practices could also be changed by RP techniques in the near future.
Silicone rubber poppets, apparently without exception, will absorb lipid from the blood stream. In most cases, absorption is quite low and confined to simple lipids like cholesterol and cholesterol esters. A small percentage, however, absorb an unknown material in quantities sufficient to render them variant. This material appears to be an oxidation product of polyunsaturated fatty acids formed after their absorption into the poppet by the action of molecular oxygen. In vitro experiments supporting the in vivo findings are described.
The surface finish of Fused Deposition Modeled (FDM) parts can be improved by performing chemical dipping based on immersion in a dimethylketone-water solution. The authors aim to gain a more in-depth knowledge of this process, by analyzing and comparing the mechanical properties and the surface quality of treated and untreated FDM parts. Tensile and bending mechanical properties have been investigated by designing and performing four Central Composite Designs (CCDs) of experiments, totalizing about two-hundred tests. The results have been verified by testing an FDM marine turbine blade employed to generate energy
Regenerative medicine seeks to repair or replace dysfunctional tissues with engineered biological or biohybrid systems. Current clinical regenerative models utilize simple uniform tissue constructs formed with cells cultured onto biocompatible scaffolds. Future regenerative therapies will require the fabrication of complex three-dimensional constructs containing multiple cell types and extracellular matrices. We believe bioprinting technologies will provide a key role in the design and construction of future engineered tissues for cell-based and regenerative therapies. This review describes the current state-of-the-art bioprinting technologies, focusing on direct-write bioprinting. We describe a number of process and device considerations for successful bioprinting of composite biohybrid constructs. In addition, we have provided baseline direct-write printing parameters for a hydrogel system (Pluronic F127) often used in cardiovascular applications. Direct-write dispensed lines (gels with viscosities ranging from 30 mPa s to greater than 600 × 10⁶ mPa s) were measured following mechanical and pneumatic printing via three commercially available needle sizes (20 ga, 25 ga, and 30 ga). Example patterns containing microvascular cells and isolated microvessel fragments were also bioprinted into composite 3D structures. Cells and vessel fragments remained viable and maintained in vitro behavior after incorporation into biohybrid structures. Direct-write bioprinting of biologicals provides a unique method to design and fabricate complex, multicomponent 3D structures for experimental use. We hope our design insights and baseline parameter descriptions of direct-write bioprinting will provide a useful foundation for colleagues to incorporate this 3D fabrication method into future regenerative therapies.
Conventionally, fabricating a facial prosthesis requires complicated steps and sophisticated skills. Particularly, the facial impression can be uncomfortable for the patient and can cause compression because of the weight of the material. The new approach presented in this report could simplify the fabrication of facial prostheses using a noncontact three-dimensional digitizer and binder multinozzle inkjet printer, without computed tomography or making a conventional impression. Treatment time was reduced, and the patient expressed satisfaction after 6 months follow-up.
Purpose
– Maxillofacial prosthetics is faced with increasing patient numbers and cost constraints leading to the need to explore whether computer‐aided techniques can increase efficiency. This need is addressed through a four‐year research project that identified quality, economic, technological and clinical implications of the application of digital technologies in maxillofacial prosthetics. The purpose of this paper is to address the aspects of this research that related to the application of rapid prototyping (RP).
Design/methodology/approach
– An action research approach is taken, utilising multiple case studies to evaluate the current capabilities of digital technologies in the preparation, design and manufacture of maxillofacial prostheses.
Findings
– The research indicates where RP has demonstrated potential clinical application and where further technical developments are required. The paper provides a technical specification towards which RP manufacturers can direct developments that would meet the needs of maxillofacial prosthetists.
Originality/value
– Whilst research studies have explored digital technologies in maxillofacial prosthetics, they have relied on individual studies applying a single RP technology to one particular aspect of a prosthesis. Consequently, conclusions on the wider implications have not been possible. This research explored the application of digital technologies to every aspect of the design and manufacture of a series of maxillofacial prostheses. Unlike previous research, the cases described here addressed the application of RP to the direct manufacture of substructures, retention components and texture. This research analyses prosthetic requirements to ascertain target technical specifications towards which RP processes should be developed.
Artificial scaffolds play vital roles in tissue engineering as they provide a supportive environment for cell attachment, proliferation and differentiation during tissue formation. Fabrication of tissue scaffolds is thus of fundamental importance for tissue engineering. Of the variety of scaffold fabrication techniques available, rapid prototyping (RP) methods have attracted a great deal of attention in recent years. This method can improve conventional scaffold fabrication by controlling scaffold microstructure, incorporating cells into scaffolds and regulating cell distribution. All of these contribute towards the ultimate goal of tissue engineering: functional tissues or organs. Dispensing is typically used in different RP techniques to implement the layer-by-layer fabrication process. This article reviews RP methods in tissue scaffold fabrication, with emphasis on dispensing-based techniques, and analyzes the effects of different process factors on fabrication performance, including flow rate, pore size and porosity, and mechanical cell damage that can occur in the bio-manufacturing process.
Production survey and seed analysis are presented, and biochemical properties are investigated. Future research aims are stated.
Sixty-six patients who had a total of eighty-six double-stem silicone implants in the first metatarsophalangeal joint were followed prospectively for an average of 5.8 years (range, two to fifteen years). There were two groups of patients: thirty-four patients (thirty-seven implants) who had degenerative joint disease (including those who had hallux rigidus or in whom a previous operation on a bunion had failed) and thirty-two patients (forty-nine implants) who had rheumatoid arthritis. The implants were used only if the patient was a candidate for an excisional arthroplasty or an arthrodesis; they were not used in patients who wished to maintain or adopt very active use of the foot (such as in running, jogging, and tennis) or to wear very high heels. Twenty-eight (82 per cent) of the thirty-four patients in the first group were completely satisfied and three (9 per cent) were somewhat satisfied. However, three patients (9 per cent), all of whom had had a failed bunionectomy, were dissatisfied; the ages of these three patients were less than the average age of all patients in the first group. Radiographs showed a fracture in three implants, but the patients had a good clinical result and an additional operation was not warranted. Twenty-seven (84 per cent) of the thirty-two patients in the second group were completely satisfied, four (13 per cent) were somewhat satisfied, and one (3 per cent) was dissatisfied. Radiographs showed a fracture in five implants. Four of the implants caused no symptoms, and the result was good; the fifth one was fragmented and was removed because of symptoms. Radiographs showed radiolucent areas around the implant and hypertrophic changes in many patients. There was no evidence of synovitis, such as that caused by silicone, either clinically or radiographically. We found that the double-stem silicone implant was effective in reconstructing the first metatarsophalangeal joint but emphasize our belief that it should be used only in carefully selected patients.
Radial head resection is the accepted treatment of comminuted radial-head fractures in adults, but the results are not always satisfactory. This study examines the results of silicone replacement arthroplasty of the radial head in acute fractures and as a salvage procedure after failed resections of the radial head. The first group of patients was evaluated both before and after silicone replacement arthroplasty had been done as a salvage procedure following a previous radial head fracture. This group comprised twelve patients with an average follow-up of 3.8 years. Improvement was found in a number of parameters, including supination and grip strength. The second group of patients had had a primary silicone replacement arthroplasty following a comminuted radial-head fracture. This group was composed of six patients with an average follow-up of 3.6 years. The radial head implant was found to provide a spacer effect that maintained good radiocapitellar contact and prevented radial shortening. Silicone replacement arthroplasty has a role as a useful, safe, and reliable alternative in the treatment of comminuted radial-head fractures in adults and as a salvage procedure in patients with failed radial-head resections. This is especially true in young, active individuals, who were found to be at the greatest risk of failure after radial head resection alone. This was attributed to greater demands being placed on the involved extremity.
A first approach to laparoscopic placement of the adjustable silicone gastric band (ASGB) was begun in our institution in 1992. This work started on an animal model first. In the animal lab, details of laparoscopic dissection around the stomach have been defined. A new prototype of the adjustable silicone band for laparoscopic use has been devised. Four voluntary patients underwent this operation on the 1st, 2nd, and 3rd of September 1993. All the patients were female and the average weight was 116 kg (102-120 kg). The mean body mass index was 43 kg/m2 (36-49 kg/m2). No major operative difficulty was encountered. Immediate postoperative outcome was uneventful.
A computer-aided designing and manufacturing (CAD/CAM) technique for clinical fabrication of facial prostheses was developed. Laser surface scanning was applied to acquire three-dimensional imaging data of the patient's facial defect. The three-dimensional imaging data was then transferred to a CAD/CAM interactive program for image processing, which then mathematically designed and produced a model for fabrication of the facial prosthesis. This CAD/CAM technique has the potential to simplify the procedure and decrease the laboratory work required compared to that required for the conventional plaster-cast method. This new technique also provides a novel approach to the fabrication of prostheses for the reconstruction of facial defects. Two alternative three-dimensional modeling processes, laser lithographic modeling and numerically controlled milling modeling, were integrated in this study. The possibilities and current limitations of the techniques are also discussed.
Over one million patients per year undergo some type of procedure involving cartilage reconstruction. Polymer hydrogels, such as alginate, have been shown to be effective carriers for chondrocytes in subcutaneous cartilage formation. The goal of our current study was to develop a method to create complex structures (nose bridge, chin, etc.) with good dimensional tolerance to form cartilage in specific shapes. Molds of facial implants were prepared using Silastic ERTV. Suspensions of chondrocytes in 2% alginate were gelled by mixing with CaSO(4) (0.2 g/mL) and injected into the molds. Constructs of various cell concentrations (10, 25, and 50 million/mL) were implanted in the dorsal aspect of nude mice and harvested at times up to 30 weeks. Analysis of implanted constructs indicated progressive cartilage formation with time. Proteoglycan and collagen constructs increased with time to approximately 60% that of native tissue. Equilibrium modulus likewise increased with time to 15% that of normal tissue, whereas hydraulic permeability decreased to 20 times that of native tissue. Implants seeded with greater concentrations of cells increased proteoglycan content and collagen content and equilibrium and decreased permeability. Production of shaped cartilage implants by this technique presents several advantages, including good dimensional tolerance, high sample-to-sample reproducibility, and high cell viability. This system may be useful in the large-scale production of precisely shaped cartilage implants.
Maxillofacial prosthetic materials are used to replace facial parts lost through disease or trauma. Silicone rubbers are the materials of choice, however it is widely accepted that these materials do not possess ideal properties. The objective of this study was to assess the properties of a range of commercially available silicone rubber maxillofacial materials and make recommendations for improvements.
Specimens of five commonly used maxillofacial materials were prepared in dental flasks according manufacturers instructions. Tear strength, tensile strength, percentage elongation, hardness, water absorption and water contact angles were determined for each material.
The tear strength of Factor II, Cosmesil HC and Nusil were all comparable and significantly higher than Cosmesil St and Prestige (p<0.001). Nusil had a significantly higher tensile strength and elongation in comparison to the other materials (p<0.001) and Cosmesil St and Cosmesil HC were significantly harder (p<0.001). Factor II was significantly less wetted and Prestige and Cosmsesil St had a significantly higher water absorption in comparison to the other materials.
None of the commercially available silicone rubber materials possessed ideal properties for use as a maxillofacial prosthetic material. Factor II, however, showed more favourable properties due to it's high tear strength, softness and ease of manipulation.
This work presents a new molding process for photo-crosslinked, degradable polymeric networks of poly(propylene fumarate) (PPF) and the crosslinking agent poly(propylene fumarate)-diacrylate (PPF-DA). Transparent room temperature vulcanizing silicone molds were fabricated for parts ranging from simple test coupons to orthopaedic implants. The PPF/PPF-DA resin blend was injected into the cavity and photo-crosslinked as light was transmitted through the mold wall. The volumetric shrinkage, mechanical properties, and the effects of gamma sterilization were reported for molded PPF/PPF-DA networks prepared with varying compositions of the two polymer components. The shrinkage decreased while the mechanical properties displayed a general increasing trend when more of the crosslinking agent was incorporated into the network. Gamma irradiation resulted in an improvement of the mechanical properties. In addition, PPF/PPF-DA replicates of a 70:30 poly(L/DL-lactide) biodegradable fixation plate and a bone allograft interbody fusion spacer were produced to evaluate the performance of PPF/PPF-DA as an orthopaedic implant and allow for a comparison to be made with materials that have been established for clinical use.
Silicone rubber has been used safely and effectively for facial augmentation for nearly 5 decades in eastern Asia. We have used silicone rubber nasal implants in primary ethnic rhinoplasty and have found consistent and long-lasting results with low complication rates. Silicone dorsal nasal augmentation in primary rhinoplasty avoids donor site morbidity and implant resorption as seen with autogenous implants. Silicone nasal implants have a low extrusion and infection rate. In the appropriate patient with proper placement, silicone nasal implant is nearly the ideal implant material.
Maxillofacial prostheses are usually fabricated on the basis of impressions made with dental-impression material. The extent to which the prosthesis reproduces normal facial morphology depends on the clinical judgment of the individual fabricating the prosthesis. This paper describes a computer-aided design and manufacturing (CAD/CAM) system for the fabrication of maxillofacial prostheses. This system will provide a more consistently accurate reproduction of facial morphology.
Facial measurements were taken using a non-contact three-dimensional laser morphological measurement system. The measurements were sent to a computer numerical controlled (CNC) milling machine to generate a cast of the patient's face for the fabrication of prosthesis.
Facial contours were measured using a laser. This method minimizes patient discomfort and avoids soft tissue distortion by impression material. Moreover, the digital data obtained is easy to store and transmit, and mirror-images can be readily generated by computer processing.
This method offers an objective, quantified approach for fabricating maxillofacial prostheses.