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Topological Design and Additive Manufacturing of Porous Metals for Bone Scaffolds and Orthopaedic Implants: A Review
Abstract
One of the critical issues in orthopaedic regenerative medicine is the design of bone scaffolds and implants that replicate the biomechanical properties of the host bones. Porous metals have found themselves to be suitable candidates for repairing or replacing the damaged bones since their stiffness and porosity can be adjusted on demands. Another advantage of porous metals lies in their open space for the in-growth of bone tissue, hence accelerating the osseointegration process. The fabrication of porous metals has been extensively explored over decades, however only limited controls over the internal architecture can be achieved by the conventional processes. Recent advances in additive manufacturing have provided unprecedented opportunities for producing complex structures to meet the increasing demands for implants with customized mechanical performance. At the same time, topology optimization techniques have been developed to enable the internal architecture of porous metals to be designed to achieve specified mechanical properties at will. Thus implants designed via the topology optimization approach and produced by additive manufacturing are of great interest. This paper reviews the state-of-the-art of topological design and manufacturing processes of various types of porous metals, in particular for titanium alloys, biodegradable metals and shape memory alloys. This review also identifies the limitations of current techniques and addresses the directions for future investigations.
... Conventional manufacturing methods, including casting, forging and milling, are challenging to use in complex designs for bioinspired cellular structures. This is due to the fact that the intricacies of the internal structures and geometrical arrangements exhibited in bioinspired designs are difficult to mimic using these manufacturing methods [59][60][61]. This is so except for a special group of alloy materials known as 'gasars', particularly lotos-like gasars [62]. ...
... Alternative manufacturing technologies that are more suited to bioinspired cellular parts have been investigated in order to solve these limitations. Among these advanced procedures is as follows: Additive manufacturing (AM), often known as 3D printing, which is advantageous for its ability in building complex designs of bioinspired cellular structures with high precision and customisation [37,40,[59][60][61]. This method builds structures layer by layer wise, and in doing so aids in fabricating complicated designs which mimic natural cellular structures [59]. ...
... Among these advanced procedures is as follows: Additive manufacturing (AM), often known as 3D printing, which is advantageous for its ability in building complex designs of bioinspired cellular structures with high precision and customisation [37,40,[59][60][61]. This method builds structures layer by layer wise, and in doing so aids in fabricating complicated designs which mimic natural cellular structures [59]. The combination of AM and bioinspired designs has enormous potential in industries such as automotive, aerospace, and biomedical [37]. ...
Natural cellular structures inspire numerous engineering applications due to their lightweight and good load-bearing capabilities. Variations in their structural configurations result in diverse mechanical properties, rendering them ideal for bioinspired designs. This review explores the occurrence, properties, and applications of cellular structures in nature and their engineering counterparts built via additive manufacturing (AM). Additive manufacturing technologies enable replication of natural cellular structures with enhanced geometrical complexity. However, they face challenges associated with scale-based geometrical constraints and minimum printable size of various features. Current constraints and techniques for overcoming these challenges, including advancements in nanotechnology, multiscale modelling, novel biomimetic designs, and improved mechanical testing methods are discussed in this paper. It is noted in the paper that it becomes increasingly possible with these advancements to optimise bioinspired engineering parts for complicated applications.
... Hydroxyapatite (CA10(PO4)6(OH)2, HAp) is considered one of the most attractive candidates. Research confirms that HAp significantly reduces the probability of fibrosis and increases adhesion between the implant and the host bone tissue [1][2][3]. ...
... In this case, the process of sedimentation is sufficiently slow to counteract the quick solidification of water in cryogenic conditions because of the high melting point. The sample with a suspension of isopropanol (2) shows no visible sedimentation. However, the very low melting point of isopropanol (185.2 ...
Hydroxyapatite (HAp) is one of the most widely studied materials for utilization in the development of artificial implants. Research is mainly aimed at the production and modification of HAp coatings for simplification of the deposition process, cost reduction, and increase in biocompatibility. In this paper, the authors deposited HAp synthetic microparticles by means of matrix-assisted pulsed laser evaporation (MAPLE) on Ti6Al4V alloy plate substrates and obtained uniform HAp coatings without further treatment or modifications. The authors utilized a tunable pulsed laser to adjust its wavelength to the selected solvents, in order to optimize the process for deposition speed and quality. The following solvents were used as matrices: deionized water, isopropyl alcohol, and a 3:2 mixture of isopropanol:acetonitrile. Obtained coatings were examined by means of scanning electron microscopy, Raman spectroscopy, X-ray diffraction, and profilometry in order to evaluate coating quality, uniformity, and structural integrity. MAPLE deposition allowed the acquisition of approx. 200 nm thick coatings for water and isopropanol matrices and approx. 320 nm for isopropanol:acetonitrile matrix, which indicates an increase in deposition rate by 37%. The obtained coatings meet requirements for further biocompatibility testing, material modification, and composite synthesis.
... On the other hand, the compressive strength determined by the yield stress (σ y ) ranges between 394 and 470 MPa depending on the channel size of samples, as listed in Table 3. Those values are also higher in comparison to the ones reported for the trabecular bones (5-200 MPa) by Wang et al. [64]. However, the values are in a low range compared to that of the fully dense materials actually used as bone implants and as noted, those values can be reduced by increasing the pore volume fraction in order to match the trabecular bone mechanical properties. ...
Nowadays, metallic bone replacement is in high demand due to different issues, like sicknesses and accidents. Thus, bone implants are fabricated with tailored properties and microstructure for long-term use in the human body. To improve such implants, 3D printing is the most promising technique. Therefore, this work aims to evaluate the fabrication of porous materials by extrusion 3D printing of Ti6Al4V. Cylindrical samples were fabricated from pellets for metal injection molding of Ti6Al4V powders, creating hexagonal channels with three different sizes. The densification kinetics was evaluated by dilatometry tests, which enabled following the densification of the samples during the sintering cycle. Subsequently, the samples were characterized by scanning electron microscopy and X-ray computed tomography to analyze their microstructure. Compression tests evaluated the mechanical strength of sintered samples. It was found that the hexagonal shape during printing is better defined as the channel size increases. The results show similar behavior for each of the channel sizes during sintering; however, greater densification is obtained as the channel size decreases. Additionally, microporosity is obtained at the particle level, which is completely interconnected, ensuring the passage of fluids through the entire sample. On the other hand, as the channel size increases, Young’s modulus and yield strength are considerably reduced. The main conclusion is that parts with two scales of porosity can be designed by the 3D printing extrusion process.
... [3] These implants, characterized by controllable external shape and internal porous structure, offer personalized repair solutions for di-verse patient needs and effectively mitigate the stress shielding problem commonly associated with metal implants. [38] Nevertheless, the bioinert nature of the widely utilized titanium and its alloys in clinical practice presents challenges in achieving vascularization within the interior of porous materials and promoting tissue ingrowth for stable osteointegration. [39] In this study, www.advancedsciencenews.com www.advmat.de ...
3D printed titanium scaffold has promising applications in orthopedics. However, the bioinert titanium presents challenges for promoting vascularization and tissue growth within the porous scaffold for stable osteointegration. In this study, a modular porous titanium scaffold is created using 3D printing and a gradient‐surface strategy to immobilize QK peptide on the surface with a bi‐directional gradient distribution. This design featured high peptide density in the interior and low peptide density on both ends, aiming to induce cell migration from ends to interior and subsequently enhance vascularization and osteointegration within the scaffold. In vitro results showed that besides the inherent bioactivity, the gradient distribution of QK positively correlated with endothelial cell migration and promoted angiogenesis. In vivo assay was performed by a segmental bone defect model in rabbit and a spine repair model in sheep. Various staining and Micro‐CT results demonstrated that compared to that with uniformly QK‐functionalized surface, the scaffold with bi‐directional gradient QK‐functionalized surface (Ti‐G) significantly encouraged new tissue growth toward the interior of the scaffold, subsequently facilitated angiogenesis and osteointegration. This study provides an effective strategy for enhancing the bioactivity of peptide‐functionalized scaffolds through the concept of bi‐directional gradients, and holds potential for various 3D printed scaffolds.
... These biomaterials are classified into three categories based on the body's response: biotolerant, bioactive, and bioinert materials. Bioactive materials are commonly preferred for joint replacements because of their superior bone integration and biocompatibility [1][2][3][4]. Metallic biomaterials, such as 316L stainless steel, cobalt chromium alloy, magnesium alloy, and titanium alloy, are primarily utilized in load-bearing applications. Among these, titanium alloys, particularly the Ti 6 Al 4 V alloy, stand out in the aerospace and biomedical industries due to their favourable combination of high strength, low density, and corrosion resistance [5,6]. ...
Titanium alloy is widely used as a biomaterial due to its strength, lightweight nature, and corrosion resistance. Despite its strength and lightweight nature, its low wear resistance limits its uses in prosthetic components. Laser surface texturing (LST) was used to improve the wear resistance of titanium alloys by creating textured surfaces before applying protective coatings. A biocompatible TiN composite protective coating was applied using physical vapour deposition (PVD) with a thickness of 4 µm. Response surface methodology (RSM) was used to predict the tribological properties by varying input parameters such as material type (TI, T2, T3, and T4), load in N, and sliding velocity in m/s. A pin-on-disc tribometer was used to conduct a unidirectional sliding wear test based on the RSM design. Tribological properties were studied to determine the impact of laser texturing on the bonding strength of the coating. As a result, material type T4 exhibits an improved coefficient of friction and specific wear resistance under varying sliding velocity and load conditions compared to other material types. The study was further supported by an ANSYS simulation, which revealed stress reduction affecting the coefficient of friction and, consequently, wear. The textured surface topography, wear mechanisms, and coating compositions were examined using scanning electron microscopy.
... Unlike soft tissues, hard bone is mineralized and has a dense and rigid matrix, providing structural support and protection to the body. [228] For bone repair, the biomaterial design should meet several key requirements: mechanical robustness, biocompatibility, and bone tissue integration. [229,230] The favorable properties of bio-based elastomers make them ideal candidates for bone regeneration. ...
To reduce carbon footprint and human dependence on fossil fuels, the field of bio‐based polymers has undergone explosive growth in recent years. Among them, bio‐based elastomers have gained tremendous attention for their inherent softness, high strain, and resilience. In this review, the recent progress of representative bio‐based elastomers derived from molecular building blocks and biopolymers are recapitulated, with an emphasis on molecular design, synthesis approaches, and mechanical performance. The performance‐advantaged properties of bio‐based elastomers, including immune modulation, biocompatibility, and biodegradability are also explored. Furthermore, their representative biomedical applications in wound dressing, cardiovascular, nerve repair, bone repair, and biosensors are exemplified. Lastly, the challenges and outlooks development of bio‐based elastomers are discussed. This review aims to offer readers valuable insights into the potential of bio‐based elastomers as viable alternatives to petroleum‐based counterparts, supporting the transition toward a more sustainable future.
... The architecture of a scaffold plays a pivotal role in its biological performance. Features such as pore shape, size, interconnectivity, open porosity, and surface curvature affect not only nutrient and waste diffusion, but also modulate cell behavior and functionality in vitro and in vivo [67]. To better elucidate which architectural feature of the bone-mimicking scaffolds could affect the in vitro mineralization, we plotted the normalized mineralization against the scaffolds' parameters presented in Table 1, and the permeability ( Figure 4B). ...
Bone tissue regeneration can be affected by various architectonical features of 3D porous scaffold, for example, pore size and shape, strut size, curvature, or porosity. However, the design of additively manufactured structures studied so far was based on uniform geometrical figures and unit cell structures, which often do not resemble the natural architecture of cancellous bone. Therefore, the aim of this study was to investigate the effect of architectonical features of additively manufactured (aka 3D printed) titanium scaffolds designed based on microtomographic scans of fragments of human femurs of individuals of different ages on in vitro response of human bone‐derived mesenchymal stem cells (hMSC). Four different types of titanium scaffold (33Y, 48Y, 56Y, and 63Y, where the number indicates the age of the individual) were fabricated using laser beam powder bed fusion (PBF‐LB) and characterized with respect to the dimensional features, permeability, and stiffness. hMSC were seeded onto the scaffolds and MTS, DNA, alkaline phosphatase, and alizarin red assays were used to study cell viability, proliferation, and osteogenic differentiation. Microcomputed tomography revealed that the largest average pore size was in scaffolds 63Y (543 ± 200 μm), which was nearly twice as large as the smallest pores in scaffolds 56Y. Moreover, scaffolds 63Y exhibited the highest porosity (~61%), while the other architectures had porosity of ~43%–44%. Scaffolds 63Y also had the lowest surface area‐to‐volume ratio (11.07 ± 0.05 mm ⁻¹ ), whereas scaffolds 56Y had the highest (14.80 ± 0.06 mm ⁻¹ ). Furthermore, scaffolds 33Y had the largest strut size (398 ± 124 μm), exceeding the size in scaffolds 56Y (the smallest strut size) by over 1.5 times. CFD simulations indicated that the hydraulic permeability was the highest for scaffolds 63Y (5.24 × 10 ⁻⁹ m ² ; order of magnitude higher than in the other architectures). Stiffness of the investigated scaffolds, determined by finite element modeling, ranged from ~29 GPa (63Y) to ~60 GPa (56Y). This study demonstrates that the highest manufacturing accuracy in 3D printed structures based on architectural designs inspired by cancellous bone could be achieved when the structures were characterized by moderate strut sizes, the largest pores, and the highest porosity and permeability. The scaffold with the highest porosity and permeability (i.e., 63Y) yielded the lowest cell retention. Regarding the osteogenic differentiation, a correlation was found between the mineralization of the deposited extracellular matrix and the hydraulic permeability, pore size, and surface area‐to‐volume ratio but not the porosity.
... In addition, these values are superior when compared to the work conducted by Abdian et al. [51], where they incorporated HAp into chitosan (CS); and the values are also higher than those of He et al. [52], where they coated scaffolds. Moreover, the improvement in the architectural configuration of the individual Voronoi cell affects the mechanical properties of the Voronoi scaffold [53]. Figure 3c displays the comparison between energy absorption and displacement for 3D elongated Voronoi scaffolds. ...
This study investigates the design and mechanical evaluation of hydroxyapatite (HAp) scaffolds for bone tissue engineering, using stereolithography (SLA) to fabricate homogeneous and hollow elongated Voronoi structures. HAp, known for its biocompatibility and biodegradability, was selected to create scaffolds with a structure that supports cell growth. Both scaffold designs were tested under compression to measure key properties, including compressive strength, Young's modulus, stiffness, and energy absorption. The homogeneous design demonstrated superior mechanical properties, achieving a maximum load of 913.6 N at a displacement of 0.166 mm and a stiffness of 5162.8 N/mm, indicating a higher load-bearing capacity and energy absorption compared to the hollow design. Despite these strengths, failure analysis revealed early fractures at strut junctions, particularly in slender areas, leading to fluctuations in the load-displacement curve and suggesting a risk to neighboring tissues in practical applications. These findings underscore the potential of Voronoi-based scaffolds for orthopedic use, while also highlighting the need for structural refinements to improve scaffold durability and clinical effectiveness.
... In the orthopaedic field, the metallic biomaterials used for the implant must be biocompatible and characterised by similar mechanical properties of the replaced and/or repaired bone. To avoid the so-called "stress shielding effect" that leads to bone resorption and, consequently, the necessity for further surgical operations, the stiffness of the metallic biomaterial must be close to the one of the human bones (<30 GPa) [4]. Ti-6Al-4V extra-low interstitial (ELI) is a widely used metallic biomaterial thanks to its high strength and corrosion resistance. ...
The metastable β-Ti21S alloy exhibits a lower elastic modulus than Ti-6Al-4V ELI while maintaining high mechanical strength and ductility. To address stress shielding, this study explores the integration of lattice structures within prosthetics, which is made possible through additive manufacturing. Continuous adhesion between the implant and bone is essential; therefore, auxetic bow-tie structures with a negative Poisson’s ratio are proposed for regions under tensile stress, while Triply Periodic Minimal Surface (TPMS) structures with a positive Poisson’s ratio are recommended for areas under compressive stress. This research examines the manufacturability and quasi-static mechanical behaviour of two auxetic bow-tie (AUX 2.5 and AUX 3.5) and two TPMS structures (TPMS 2.5 and TPMS 1.5) in β-Ti21S alloy produced via laser powder bed fusion. Micro-CT reveals printability issues in TPMS 1.5, affecting pore size and reducing fatigue resistance compared to TPMS 2.5. AUX 3.5’s low stiffness matches cancellous bone but shows insufficient yield strength and fatigue resistance for femoral implants. Biological tests confirm non-toxicity and enhanced cell activity in β-Ti21S structures. The study concludes that the β-Ti21S alloy, especially with TPMS 2.5 structures, demonstrates promising mechanical and biological properties for femoral implants. However, challenges like poor printability in TPMS 1.5 are acknowledged and should be addressed in future research.
... With the integration of ML, topology design for AM can be enhanced to create components with enhanced mechanical properties and reduced material usage. ML algorithms can analyze complex datasets of part geometries, mechanical properties, and manufacturing parameters to identify optimal topologies for specific loading conditions and performance requirements [102,103]. By leveraging ML, engineers can systematically explore design possibilities and arrive at innovative geometries that are well-suited for AM. ...
The article provides a detailed review of the utilisation of machine learning (ML) in various domains of additive manufacturing (AM) and highlights its potential to address key challenges in the industry. The article acknowledges the hurdles to widespread adoption of AM, including barriers in design for AM (DfAM), limited materials selection, processing defects, and inconsistent product quality. ML is increasingly being integrated into AM workflows, offering significant potential for classification, regression, and clustering to address the AM challenges. It can be used to generate new high-performance metamaterials and optimize topological designs, improving the efficacy and usefulness of the design process. It also optimizes process parameters, monitors powder spreading, and detects in-process defects, enhancing the overall quality and reliability of the manufacturing process. ML aids in streamlining the production processes and ensuring consistent product quality. There's recognition of the importance of data security in AM, with ML techniques potentially posing risks of data breaches if not properly managed. Therefore, a synergistic approach where ML assists in identifying critical conditions and human operators take action is likely the most effective way to ensure both efficiency and accuracy in AM processes. The paper summarises the key results from the literature and discusses some significant applications of machine learning in AM. It emphasizes the potential of ML to drive innovation and address critical challenges in the AM industry. Overall, the article underscores the significance of ML in advancing AM technology and its potential to overcome existing barriers to adoption, making way for broader implementation of AM in various industries.
... The regenerative performance of large bone defects primarily depends on the microstructure and chemical composition of biological materials, and the unique structure of porous scaffolds is vital for cell growth, differentiation and migration on its surface [32][33][34]. Before this, the use of porous Ti6Al4V scaffolds has been widely recognized in clinical practice. ...
Due to the limited self-regeneration capacity of bone, medical interventions is often required for large segmental bone defects. In this study, the application of porous titanium alloy (Ti6Al4V) scaffold in bone defect repair was investigated. Owing to its excellent mechanical properties and biocompatibility, Ti6Al4V is a preferred choice for orthopedic implants. To reduce the negative impact of its high elastic modulus on bone tissue, 3D printing technology was utilized to manufacture porous structures to approximate the elastic modulus of human bone, reducing the stress shielding phenomenon. In addition, electrochemical deposition technology was employed to deposit CeO2 nanoparticles (CNPs) onto the scaffold surface, aiming to improve its biological activity. According to the experimental findings, adding CNPs significantly enhanced the scaffold osteogenic capability. In vitro experiments on proliferation and expression of osteogenic markers verified its biological activity, while in vivo experiments further confirmed its potential to promote bone regeneration. Through detailed material characterization and biological evaluation, this study demonstrated the application prospect of 3D printed porous Ti6Al4V scaffold combined with CNPs, providing a new idea for the clinical repair of bone defects.
... This can be done by removing material from the design or introducing porosity to the design [14]. The stiffness and the porosity of the material can be architecture according to the need [15]. The finite element approach is one of the vital tools to solve complex structures. ...
... Consequently, numerous studies have highlighted the advantages of lattice structures, particularly their improved biocompatibility. These structures support cell seeding, bone ingrowth, vascularization, permeability, and enhanced osseointegration (Alvarez and Nakajima, 2009;Melchels, 2010;Naghavi et al., 2022;Wang et al., 2016). Regarding mechanical properties, porous structures' elasticity modulus and yield strength can be customized by adjusting factors like pore size, porosity, or relative density. ...
... One of these strategies is additive manufacturing (ADM), a rapidly evolving technology that has revolutionized the fabrication of medical implants and scaffolds. 117,118 ADM allows for the creation of complex and customized structures that closely mimic the natural architecture of bone, providing optimal conditions for cell adhesion, proliferation, and differentiation. 119 In a recent study, researchers demonstrated the use of robotically aided printing (robocasting) to fabricate sintering-free BCP/natural polymer composite scaffolds for bone regeneration ( Figure 4E). ...
... However, such additively manufactured metal scaffolds for bone applications need to be evaluated for numerous physical characteristics and subsequently optimized during the scaffold designing stages. It is worth noting that several critical parameters, such as elastic modulus, relative density, permeability, wall shear stress (WSS), porosity, and pore size, may impact both the mechanical and biological efficacy of the scaffold [6][7][8][9][10][11][12]. ...
In recent years, additively manufactured metallic scaffolds have generated significant interest among researchers working in the field of bone tissue engineering and orthopaedic implants. Although such intricate, porous architectures are promising as bone substitutes, they need to be thoroughly tested for structural robustness as well as their capacity for bony integration. In this present work, we introduced and preclinically evaluated the biomechanical viability of Weaire-Phelan (WP) Ti-alloy scaffolds as bone replacement components. Two distinct groups of WP scaffolds, namely WPA and WPD, of varying porosities were examined for comparative assessment. Finite element (FE) analysis, computational fluid dynamics (CFD) and uniaxial compression tests were performed on 3D printed as-built scaffolds to comprehensively evaluate the structural, hemodynamic, fatigue and morphometric properties of the two groups. The mechanical performances of the WP scaffolds of 70%, 80% 90% porous group (relative density 0.3 and lower) were found to accord with the natural trabecular bone tissue. However, WPA scaffolds demonstrated slightly superior mechanical performances as compared to WPD scaffolds (22%– 63% greater compressive modulus depending on the porosity). On the other hand, WPD scaffolds showed improved hemodynamic properties thereby implying enhanced osteogenic potential. Moreover, the range of effective elastic moduli corresponding to the WP scaffolds was found to be in good agreement with that of the natural bone tissue. As such, these designs were categorized based on their suitability at different anatomical sites. The overall performance metrics of the WP scaffolds underscore its potential for improved osseointegration, structural conformities and greater capacity for customization with enhanced manufacturability.
... The on-demand control of mechanical properties opens up the possibility of using iron and its alloys as a biodegradable repair scaffold for bone implantation. [51][52][53][54] ...
Hierarchically porous‐structured metals show tremendous potential for mechanical applications in the aerospace, automotive, and healthcare sectors. Accurately controlling both the microstructural pore morphology and the macroscopic geometric shape presents a significant challenge and directly impacts its applications. Existing approaches involve combining 3D printing with sacrificial templating, where the introduction of templating agents restricts the control of the 3D printing process. Here, a template‐free process is developed for the manufacturing of hierarchical metallic structures from DLP 3D‐printed ion‐infused porous hydrogels. The porous structure of the hydrogel scaffold introduced by lyophilization not only induces the formation of microporous metallic structures during the sintering process but also helps reduce the internal stresses within the material to facilitate shape integrity. Hierarchically structured iron and iron‐based high‐entropy alloys with pore diameters ranging from sub‐micrometer to millimeter are fabricated to demonstrate the feasibility of this method. This work is anticipated to inspire the design and fabrication of high‐performance metallic structures for functional applications such as catalysts or metamaterials.
... The advancement of additive printing technology in recent times has made it possible to create bone tissue scaffolds that combine mechanical, biological, and physical qualities by realising structures with intricate topological features [88][89][90]. Of these structures, creating and designing triply periodic minimal surfaces (TPMSs) has emerged as a focus of research [91,92]. ...
Nanomaterials hold significant promise for the future of orthopaedic implants due to their ability to mimic the nanoscale components of the bone, such as collagen fibrils and hydroxyapatite. Nanomaterials can regulate cell behaviour while offering mechanical strength and biocompatibility, making them ideal for bone repair and tissue regeneration. This comprehensive review explores the key existing and potential applications of nanotechnology in orthopaedics, including bone tissue engineering, drug delivery systems, systems combatting implant-related infections, and the surface preparation of implants to enhance osseointegration. These innovations are poised to revolutionise orthopaedic care by improving implant durability, reducing infection risks, and promoting bone regeneration to deliver personalised treatment and create better patient outcomes.
This work aims to investigate the effect of pore size on the corrosion behavior of Ti6Al4V/25Ta composites. Samples with two different pore size distributions and similar pore volume fractions were fabricated using the space holder solid-state sintering technique. Results show that the microstructure of samples is similar regardless of the pore size, which mainly comprises β-Ti and martensite α’-Ti. The porosity was fully interconnected in both kinds of samples, with average pore size of 95 and 270 µm, respectively. The corrosion behavior was improved by adding pores and increasing their size, as Ecorr is higher and Icorr is lower compared to samples without large pores. This improvement is attributed to better distribution of corrosive liquid throughout the sample, thanks to fully interconnected porosity that inhibits the formation of corrosion pits.
Fabrication process of highly porous Ti64/25Ta composites, and their microstructure and corrosion behavior
The complex stresses experienced by medical-grade porous metals in the physiological environment following implantation as bone repair materials necessitate a comprehensive understanding of their mechanical behavior. This paper investigates the effects of pore structure and matrix composition on the corrosion behavior and mechanical properties of pure Zn. Porous Zn alloys with varying pore sizes were prepared via vacuum infiltration casting. The results showed that addition of Mg elements and an increase in pore size were observed to enhance the strength and elastic modulus of the porous Zn alloy (41.34 ± 0.113 MPa and 0.58 ± 0.02 GPa of the C-Z3AM). However, corrosion tests indicated that specimens with smaller pores and the addition of Mg elements exhibited accelerated corrosion of porous Zn alloys in Hank’s solution. Electrochemical test results show the corrosion resistance rank in order of C-Z5A > C-Z3AM > N-Z5A > N-Z3AM. Additionally, the mechanical retention of porous Zn alloys in simulated body fluids was found to be significantly reduced by the incorporation of Mg elements and smaller pore sizes, the yield strength declines rates of C-Z5A, C-Z3AM and N-Z3AM after 30 days of immersion were 16.7%, 63.7% and 78.2%, respectively. The objective is to establish the role of the material-structure-corrosion-mechanics relationship, which can provide a theoretical and experimental basis for the design and evaluation of Zn and its alloy implanted devices.
The extracellular matrix can be replicated by 3D scaffolds, providing a favorable environment for cell growth, proliferation, and differentiation. Despite their biocompatibility, biodegradability, and bioactivity, the poor mechanical strength of 3D scaffolds limits their use for heavy loads. This creates a bottleneck in the supply of scaffolds with enhanced mechanical strength and all the previously mentioned characteristics. Conjugated polymers have emerged as a promising option for 3D scaffold construction due to their electrical conductivity, adjustable surface qualities, and ability to transfer bioactive molecules. Moreover, metal-organic frameworks (MOFs) are a rapidly emerging class of nanomaterials due to their uniform porosity, excellent surface-to-volume ratio, variable and diverse configurations, as well as tuanble chemical structures. While both conjugated polymer-based and MOF-based 3D scaffolds suffer from drawbacks such as low mechanical stability and possible toxicity, their combination is an imperative strategy to construct desirable 3D scaffols for biomedical applications. Specific examples of investigated conjugated polymer-MOF 3D scaffolds are provided in each area, along with an explanation of their synthesis, fabrication method, and the physicochemical and mechanical properties. Finally, the biomedical applications of conjugated polymers/MOF 3D scaffolds in tissue engineering and cancer theragnostic are reviewed, along with current challenges and potential future directions are discussed.
This review presents the design and experimental analysis of metamaterials with tunable properties for biomedical applications. Five different metamaterials, such as lightweight metamaterials, pattern transformation metamaterials, negative compressibility metamaterials, pentamode metamaterials and auxetic metamaterials, are discussed in detail with emphasis on their mechanical and biological features that are primarily applicable in the field of biomedical technology. Various indigenous structures of the metamaterials are carefully analysed for metamaterial design and their influence on mechanical performance is studied. Thus, this review comprehensively summarizes the different additive manufacturing techniques implemented for biomedical metamaterials and their influence on their mechanical properties. Finally, the mechanical properties and deformation mechanisms for different geometries and structures of all the above-mentioned metamaterials are analyzed.
Scaffold represents important components of tissue engineering. Scaffold for bone tissue engineering needs to mimic bone structures that are heterogeneous and anisotropic. When using Triply Periodic Minimal Surfaces (TPMS) based unit cells to simulate bone structure for the additive manufacture of bone scaffolds, researchers frequently find a vast array of options for structural heterogeneity but not enough for material heterogeneity. The utilization of TPMS has led to a surge in the production of tissue engineering scaffolds by increasing the surface area to volume ratio, a crucial factor in vascularization and cell proliferation. Pore interconnectivity can be achieved more smoothly by using the TPMS unit cell for the making of scaffolds. This paper presents a comprehensive overview of TPMS-based (P-Primitive, Gyroid, and Double Diamond) bone scaffolds having both structural and material heterogeneity using composite material made of polymer Poly Lactic Acid (PLA) and ceramic Hydroxyapatite (HA) for 3D printing. As scaffolds should be biodegradable so polymer composites (PLA and Hydroxyapatite) have been studied to focus on their biodegradability and bioactivity. Material heterogeneity can be achieved by varying the composition of hydroxyapatite in PLA. Here, the hybridization of TPMS (P-Primitive, Gyroid, and Double Diamond) structures has been analyzed for making scaffolds that mimic human bone structures, and the best combination has been proposed.
Purpose
This study examines the accuracy of a homogenization scheme for the linear buckling analysis of structures assembled from beam-based lattice plates. Regardless of in-plane acting loads, the buckling behavior is characterized by the abrupt out-of-plane deformation. Apparently, if the lattice plates are modeled as homogenized ones, the out-of-plane effective material properties should be considered. However, as prevalently implemented in literature, the in-plane effective material properties are assigned to the homogenized plates for the linear buckling analysis, and thus, the results are erroneous.
Design/methodology/approach
The linear buckling analysis is performed by two finite element models, i.e. the high- and low-fidelity finite element models. In the former one, each strut of the lattice structures is modeled as an Euler–Bernoulli beam, and thus, all the geometrical features are explicitly simulated. On the other hand, the low-fidelity one involves the homogenized plates having the out-of-plane effective material properties determined from the lattice counterparts using an energy-based homogenization method.
Findings
The accuracy of the homogenization scheme is confirmed by the comparison of results obtained by the high- and low-fidelity finite element models. Six topological configurations of the unit cells are considered, and the first five buckling modes are inspected. In all examinations, the low-fidelity finite element model offers the acceptable level of accuracy, i.e. the relative difference between two finite element models is lower than 5%. Furthermore, it is recommended to use the out-of-plane effective material properties rather than the in-plane ones to ensure the precise simulation.
Originality/value
The current study is original. In literature, there are some studies regarding the buckling analysis of lattice plates or panels with out-of-plane material properties. However, these studies use the analytical approach, and consequently, they are confined to lattice structures whose geometry is simple. In the present paper, structures assembled from beam-based lattice plates are examined. It can be noticed that these structures can have complex geometry. Therefore, the feasibility and accuracy of using out-of-plane effective material properties with homogenized plates for the linear buckling analysis of lattice plates are validated.
Cavitation is a harmful phenomenon for hydraulic machineries such as pumps and valves etc., as it causes severe erosion by impacts at cavitation bubble collapses. However, the cavitation impacts can be utilized for mechanical surface modification in the same way of shot peening. A peening method using cavitation impact is called as “cavitation peening”, especially cavitation peening using a pulsed laser is named as “laser cavitation peening”. Laser cavitation peening can improve fatigue strength of additively manufactured (AM) metals. However, it takes time to treat, as the repletion frequency of Q-switched Nd:YAG laser is slow such as 10 Hz. In the present paper, laser cavitation peeing using a fiber laser whose maximum frequency was 50 kHz was demonstrated.
The emergence of bioabsorbable implant materials has generated significant enthusiasm in medical and engineering research. The present systematic review study thoroughly examines the development, characteristics, uses, and difficulties associated with bioabsorbable materials, specifically emphasizing magnesium, zinc, iron, and alloys. Bioabsorbable implant materials have become popular in orthopaedic and dental surgery because they enhance tissue regeneration while minimizing foreign body responses. Using bioabsorbable implant materials can lessen the requirement for implant removal operations while also improving patient outcomes. Developing bioabsorbable implant materials is a fascinating field of study with the potential to transform medical implant technology. The present systematic review study thoroughly examines the development, characteristics, uses, and difficulties associated with bioabsorbable materials, specifically emphasizing magnesium, zinc, iron, and alloys. The novelty of the present review is that a roadmap for future research is outlined. Thus, the present review thoroughly analyses the latest discoveries in bioabsorbable materials, providing valuable insights that could improve implant technology and significantly transform medical treatments and patient care.
This work presents the characterization of a prototype for a vertebral bone implant. The part was fabricated by extrusion 3D printing and sintering using pellets of Ti64 powders. Parts were consolidated by a debinding step at 500 °C and sintered at 1150 °C in a horizontal furnace under argon atmosphere. Microstructure characterization was performed by computed microtomography and scanning electron microscopy. Results showed that it’s possible to obtain a complex part by 3D printing, although different defects were detected. Part’s shape is consistent with the designed model, excepted for the finer details. Interparticle porosity was detected, resulting in a permeability large enough to possibly promote bone ingrowth. Final microstructure contains α + β Ti lamellas. The main finding is to develop a processing route to fabricate parts with tailored porosity by extrusion 3D printing, which is promissory for bone implants. However, optimizing the impression parameters to achieve an excellent final shape is necessary.
Development of prototype for vertebral implants from Ti64 feedstock with tailored interconnected porosity for improving osseointegration
In this paper, the mechanical behavior and compression deformation mode of three types of composite multilayer structures based on triply periodic minimal surfaces (TPMS) were conducted through experiments and finite element analysis. The results indicate that the load-displacement curves under varying stain rates manifest a double-platform characteristic for all three structure types. The P-G four-layer structure and P-G six-layer structure have no discernible extrusion of the structural layers during compression, and the entirety of the structure displays an almost regular cubic configuration after compression. Nevertheless, local separation was observed in the extruded portion of the P-H six-layer structure after the structural deformation at higher strain rates. For the other conditions, the structure exhibited a bulge but did not display any local detachment or separation phenomena. During the deformation of the P-H six-layer structure, a dome-shaped region emerges in the first and fifth layers. The “crown” layer displays an inverted bell-shaped failure mode for the first layer structure, exhibiting downward extrusion. In contrast, the fifth layer structure displays an upward extrusion and exhibits a bell-shaped failure mode. The P-H 6-layer structure has the best energy absorption performance under quasistatic compression conditions for the P-G 4-layer, P-G 6-layer and P-H 6-layer structure. However, the energy absorption performance of the identical structure remains largely consistent across varying strain rate conditions.
In this study, the changes in tensile strength of PLA and ABS specimens, the most commonly used materials in additive manufacturing with FFF, were investigated as a function of fill rate and print speed. Tensile specimens were fabricated for different fill rates and speeds and tensile tests were performed. Increasing the fill rate increases the tensile strength. Increasing or decreasing the print speed too much has a negative effect on tensile strength. Filament usage and printing times were also calculated. With the data obtained, an optimization model was created using response surface methodology. The aim of this study is to optimize the strength/cost of ABS and PLA, the two preferred FFF materials. The novelty of the study is to investigate the strength/cost optimization for different material types in terms of UTS, filament consumption and printing speed. For each material type, high tensile strength, low printing time and low filament used conditions were determined for the optimization model. The optimum parameters for PLA are obtained at 66.77% fill level and 78.43% speed rate. For ABS, optimum values are obtained at 79.5% fill rate and 135% speed rate. Then, samples were produced for optimum conditions and experiments and calculations were repeated. The numerical results obtained with the model were compared with the experimental results. It is found that the model estimates the output parameters with high accuracy. This proves the accuracy of the proposed optimization model.
Spinal fusion is the ultimate choice for most patients with severe disc degeneration, and bone tissue engineering offers novel strategies to improve intervertebral bone growth and fusion. In this study, we utilized graphene oxide (GO) and methacrylated gelatin (GelMA) to prepare GelMA/GO composite hydrogel scaffolds with different GO concentrations. By characterizing the various properties of the scaffolds, it was learned that the composite scaffold containing 1.2 mg/mL GO possessed the best overall performance, and we used it for subsequent experiments. GelMA/GO composite scaffolds containing different bone‐forming peptide‐1 (BFP‐1) concentrations were constructed and cocultured with bone marrow mesenchymal stem cells (BMSCs), and the results showed that GelMA/GO composite scaffolds containing 0.4 mg/mL BFP‐1 induced the cells to produce more ALP and mineralized matrix. The above scaffold was further investigated as a GelMA/GO@BFP‐1 composite, and the results showed that it promoted the production of ALP and mineralized matrix in BMSCs, and significantly enhanced the expression of osteogenesis‐related genes (ALP, Runx‐2, OCN, OPN) and proteins (Runx‐2, OCN). It suggests that the GelMA/GO@BFP‐1 complex promotes osteogenic differentiation of BMSCs and has the potential tobe used as a bone implant for improving intervertebral bone fusion.
Advancement in medicine and technology has resulted into prevention of countless deaths and increased life span. However, it is important to note that, the modern lifestyle has altered the food habits, witnessed increased life-style stresses and road accidents leading to several health complications and one of the primary victims is the bone health. More often than ever, healthcare professionals encounter cases of massive bone fracture, bone loss and generation of critical sized bone defects. Surgical interventions, through the use of bone grafting techniques are necessary in such cases. Natural bone grafts (allografts, autografts and xenografts) however, have major drawbacks in terms of delayed rehabilitation, lack of appropriate donors, infection and morbidity that shifted the focus of several investigators to the direction of synthetic bone grafts. By employing biomaterials that are based on bone tissue engineering (BTE), synthetic bone grafts provide a more biologically acceptable approach to establishing the phases of bone healing. In BTE, various materials are utilized to support and enhance bone regeneration. Biodegradable polymers like poly-(lactic acid), poly-(glycolic acid), and poly-(ϵ-caprolactone) are commonly used for their customizable mechanical properties and ability to degrade over time, allowing for natural bone growth. PEG is employed in hydrogels to promote cell adhesion and growth. Ceramics, such as hydroxyapatite and beta-tricalcium phosphate (β-TCP) mimic natural bone mineral and support bone cell attachment, with β-TCP gradually resorbing as new bone forms. Composite materials, including polymer-ceramic and polymer-glasses, combine the benefits of both polymers and ceramics/glasses to offer enhanced mechanical and biological properties. Natural biomaterials like collagen, gelatin, and chitosan provide a natural matrix for cell attachment and tissue formation, with chitosan also offering antimicrobial properties. Hybrid materials such as decellularized bone matrix retain natural bone structure and biological factors, while functionalized scaffolds incorporate growth factors or bioactive molecules to further stimulate bone healing and integration. The current review article provides the critical insights on several biomaterials that could yield to revolutionary improvements in orthopedic medical fields. The introduction section of this article focuses on the statistical information on the requirements of various bone scaffolds globally and its impact on economy. In the later section, anatomy of the human bone, defects and diseases pertaining to human bone, and limitations of natural bone scaffolds and synthetic bone scaffolds were detailed. Biopolymers, bioceramics, and biometals-based biomaterials were discussed in further depth in the sections that followed. The article then concludes with a summary addressing the current trends and the future prospects of potential bone transplants.
Magnesium (Mg) and its alloys are revolutionizing the field of interventional surgeries in the medical industry. Their high biocompatibility, biodegradability, and a similar elastic modulus to natural bone make porous Mg-based structures potential candidates for orthopedic implants and tissue engineering scaffolding. However, fabricating and machining porous Mg-based structures is challenging due to their complexity and difficulties in achieving uniform or gradient porosity. This review aims to thoroughly explore various fabrication procedures used to create metallic scaffolds, with a specific focus on those made from Mg-based alloys. Both traditional manufacturing techniques, including the directional solidification of metal-gas eutectic technique, pattern casting, methods using space holders, and modern fabrication methods, which are based on additive manufacturing, are covered in this review article. Furthermore, the paper highlights the most important findings of recent studies on Mg-based scaffolds in terms of their microstructure specifications, mechanical properties, degradation and corrosion behavior, antibacterial activity, and biocompatibility (both in vivo and in vitro). While extensive research has been conducted to optimize manufacturing parameters and qualities of Mg-based scaffolds for use in biomedical applications, specifically for bone tissue engineering applications, further investigation is needed to fabricate these scaffolds with specific properties, such as high resistance to corrosion, good antibacterial properties, osteoconductivity, osteoinductivity, and the ability to elicit a favorable response from osteoblast-like cell lines. The review concludes with recommendations for future research in the field of medical applications.
Tissue biofabrication mimicking organ-specific architecture and function requires physiologically-relevant cell densities. Bioprinting using spheroids can achieve this, but is limited due to the lack of practical, scalable techniques. This study presents HITS-Bio (High-throughput Integrated Tissue Fabrication System for Bioprinting), a multiarray bioprinting technique for rapidly positioning multiple spheroids simultaneously using a digitally-controlled nozzle array (DCNA). HITS-Bio achieves an unprecedented speed, ten times faster compared to existing techniques while maintaining high cell viability ( > 90%). The utility of HITS-Bio was exemplified in multiple applications, including intraoperative bioprinting with microRNA transfected human adipose-derived stem cell spheroids for calvarial bone regeneration ( ~ 30 mm³) in a rat model achieving a near-complete defect closure (bone coverage area of ~ 91% in 3 weeks and ~96% in 6 weeks). Additionally, the successful fabrication of scalable cartilage constructs (1 cm³) containing ~600 chondrogenic spheroids highlights its high-throughput efficiency (under 40 min per construct) and potential for repairing volumetric defects.
This paper provides a thorough analysis of recent advancements and emerging trends in the integration of metal additive manufacturing (AM) within orthopedic implant development. With an emphasis on the use of various metals and alloys, including titanium, cobalt-chromium, and nickel-titanium, the review looks at their characteristics and how they relate to the creation of various orthopedic implants, such as spinal implants, hip and knee replacements, and cranial-facial reconstructions. The study highlights how metal additive manufacturing (AM) can revolutionize the field by enabling customized implant designs that take patient anatomical variances into account. The review discusses the drawbacks of conventional manufacturing techniques and emphasizes the benefits of metal additive manufacturing (AM), such as increased design flexibility and decreased material waste. Important material selection factors, including mechanical qualities and biocompatibility, are covered in relation to metal additive manufacturing applications. The work ends with a summary of the issues facing metal AM today, such as surface finish and material certification, and suggestions for future developments, like the creation of advanced materials and the application of AI to design optimization.
Highlights
Exploring personalized biomedical metal implants through additive manufacturing (AM).
Presenting new load-bearing and biodegradable alloys for implants.
Showcasing AI and 4D printing advancements in material properties.
Exploring AM’s roles in various medical fields.
Highlighting perspectives of implant technology for improved patient care.
Bone tissue engineering (BTE) has emerged as a promising approach for the regeneration and repair of bone defects caused by trauma, disease, or aging. This review provides an overview of recent advancements in BTE, with a focus on the development and application of biomaterial‐based scaffolds, including natural (e.g., collagen, chitosan), synthetic (e.g., polylactic acid [PLA], polycaprolactone [PCL]), and composite materials (e.g., hydroxyapatite‐based composites). It discusses their properties, benefits, and limitations. Additionally, this review examines innovative fabrication strategies such as 3D printing, electrospinning, and freeze‐drying, which enhance scaffold customization and performance. This review aims to provide insights into future directions of BTE research and its potential applications in regenerative medicine. Functionalization strategies, including surface modifications, coating, and the incorporation of growth factors and cells, are reviewed for their roles in improving scaffold bioactivity. In vivo and in vitro research have demonstrated the therapeutic promise of these scaffolds, while current clinical trials offer insights into their translational use. Challenges facing the translation of these technologies into clinical practice are also highlighted.
This work presents the application of a topology optimisation method to the hip implant design. A three-dimensional implanted femur is modelled and defined as a design domain. The implant, modelled as type 1, is optimised while other materials i.e. cement (type 2) and bone (type 3), are not being optimised. The domain is subjected to a load case, which corresponds to the loads applied when walking. Loads are employed at the proximal end of the implant and the abductor muscle. Loads from other muscles are not considered. The goal of the study is to minimise the energy of implant compliance subjected to several sets of volume reduction. Reductions are set to be 30%, 40%, 50%, 60%, and 70% from the initial volume (Vo). The result of each set is cut into several sections about x-y plane in z-direction in order to observe the topology inside the stem. It was found that implants with 30% Vo, 40% Vo, and 70% Vo had developed open boundaries whereas 50% Vo and 60% Vo had closed boundary and produced possible shape. Therefore, these designs (50% Vo and 60% Vo) are chosen and refined. Both are analysed using the same boundary conditions as before they were optimised. Results of stresses along medial and lateral line are plotted and compared.
Additive manufacturing (AM) is expanding the range of designable geometries, but to exploit this evolving design space new methods are required to find optimum solutions. Finite element based topology optimisation (TO) is a powerful method of structural optimization, however the results obtained tend to be dependent on the algorithm used, the algorithm parameters and the finite element mesh. This paper will discuss these issues as it relates to the SIMP and BESO algorithms. An example of the application of topological optimization to the design of improved structures is given.
Today, laser additive manufacturing (LAM) is used in more and more industrial applications. Due
to a new freedom in design it offers a high potential for weight saving in lightweight applications,
e.g., in the aerospace industry. However, most design engineers are used to design parts for
conventional manufacturing methods, such as milling and casting, and often only have limited
experience in designing products for additive manufacturing. The absence of comprehensive
design guidelines is therefore limiting the further usage and distribution of LAM. In this paper,
experimental investigations on the influence of part position and orientation on the dimension
accuracy and surface quality are presented. Typical basic shapes used in lightweight design have
been identified and built in LAM. Thin walls, bars, and bore holes with varying diameters were
built in different orientations to determine the process limits. From the results of the experiments,
comprehensive design guidelines for lightweight structures were derived in a catalog according to
DIN 2222 and are presented in detail. For each structure a favorable and an unfavorable example is
shown, the underlying process restrictions are mentioned and further recommendations are given.
This paper introduces a two-scale topology optimization approach by integrating optimized structures
with the design of their materials. The optimization aims to find a multifunctional structure composed
of homogeneous porous material. Driven by the multi-objective functions, macrostructural stiffness
and material thermal conductivity, stiff but lightweight structures composed of thermal insulation materials
can be achieved through optimizing the topologies of the macrostructures and their material microstructure
simultaneously. For such a two-scale optimization problem, the effective properties of
materials derived from the homogenization method are applied to the analysis of macrostructure. Meanwhile,
the displacement field of the macrostructure under given boundary conditions is used for the sensitivity
analysis of the material microstructure. Then, the bi-directional evolutionary structural
optimization (BESO) method is employed to iteratively update the macrostructures and material microstructures
by ranking elemental sensitivity numbers at the both scales. Finally, some 2D and 3D numerical
examples are presented to demonstrate the effectiveness of the proposed optimization algorithm. A
variety of optimal macrostructures and their optimal material microstructures are obtained.
While calcium phosphate–based ceramics are currently the most widely used materials in bone repair, they generally lack tensile strength for initial load bearing. Bulk titanium is the gold standard of metallic implant materials, but does not match the mechanical properties of the surrounding bone, potentially leading to problems of fixation and bone resorption. As an alternative, nickel–titanium alloys possess a unique combination of mechanical properties including a relatively low elastic modulus, pseudoelasticity, and high damping capacity, matching the properties of bone better than any other metallic material. With the ultimate goal of fabricating porous implants for spinal, orthopedic and dental applications, nickel–titanium substrates were fabricated by means of selective laser melting. The response of human mesenchymal stromal cells to the nickel–titanium substrates was compared to mesenchymal stromal cells cultured on clinically used titanium. Selective laser melted titanium as well as surface-treated nickel–titanium and titanium served as controls. Mesenchymal stromal cells had similar proliferation rates when cultured on selective laser melted nickel–titanium, clinically used titanium, or controls. Osteogenic differentiation was similar for mesenchymal stromal cells cultured on the selected materials, as indicated by similar gene expression levels of bone sialoprotein and osteocalcin. Mesenchymal stromal cells seeded and cultured on porous three-dimensional selective laser melted nickel–titanium scaffolds homogeneously colonized the scaffold, and following osteogenic induction, filled the scaffold’s pore volume with extracellular matrix. The combination of bone-related mechanical properties of selective laser melted nickel–titanium with its cytocompatibility and support of osteogenic differentiation of mesenchymal stromal cells highlights its potential as a superior bone substitute as compared to clinically used titanium.
The precipitates formed after suitable thermal treatments in seven Ni-rich Ni–Ti–Hf and Ni–Ti–Zr high-temperature shape memory alloys have been investigated by conventional and high-resolution transmission electron microscopy. In both ternary systems, the pre-cipitate coarsening kinetics become faster as the Ni and ternary element contents (Hf or Zr) of the bulk alloy are increased, in agreement with the precipitate composition measured by energy-dispersive X-ray microanalysis. The precipitate structure has been found to be the same in both Hf-and Zr-containing ternary alloys, and determined to be a superstructure of the B2 austenite phase, which arises from a recombination of the Hf/Zr and Ti atoms in their sublattice. Two different structural models for the precipitate phase were optimized using density functional theory methods. These calculations indicate that the energetics of the structure are not very sensitive to the atomic configuration of the Ti–Hf/Zr planes, thus significant configurational disorder due to entropic effects can be envisaged at high temperatures. The precipitates are fully coherent with the austenite B2 matrix; however, upon martensitic transformation, they lose some coherency with the B19 0 matrix as a result of the transformation shear process in the surrounding matrix. The strain accommodation around the particles is much easier in the Ni–Ti–Zr-containing alloys than in the Ni–Ti–Hf system, which correlates well with the lower transformation strain and stiffness predicted for the Ni–Ti–Zr alloys. The B19 0 martensite twinning modes observed in the studied Ni-rich ternary alloys are not changed by the new precipitated phase, being equivalent to those previously reported in Ni-poor ternary alloys.
Custom implants for the reconstruction of craniofacial defects have gained importance due to better performance over their generic counterparts. This is due to the precise adaptation to the region of implantation, reduced surgical times and better cosmesis. Application of 3D modeling in craniofacial surgery is changing the way surgeons are planning surgeries and graphic designers are designing custom implants. Advances in manufacturing processes and ushering of additive manufacturing for direct production of implants has eliminated the constraints of shape, size and internal structure and mechanical properties making it possible for the fabrication of implants that conform to the physical and mechanical requirements of the region of implantation. This article will review recent trends in 3D modeling and custom implants in craniofacial reconstruction.
Background
The development of novel biomaterials able to control cell activities and direct their fate is warranted for engineering functional bone tissues. Adding bioactive materials can improve new bone formation and better osseointegration. Three types of titanium (Ti) implants were tested for in vitro biocompatibility in this comparative study: Ti6Al7Nb implants with 25% total porosity used as controls, implants infiltrated using a sol–gel method with hydroxyapatite (Ti HA) and silicatitanate (Ti SiO2). The behavior of human osteoblasts was observed in terms of adhesion, cell growth and differentiation.
Results
The two coating methods have provided different morphological and chemical properties (SEM and EDX analysis). Cell attachment in the first hour was slower on the Ti HA scaffolds when compared to Ti SiO2 and porous uncoated Ti implants. The Alamar blue test and the assessment of total protein content uncovered a peak of metabolic activity at day 8–9 with an advantage for Ti SiO2 implants. Osteoblast differentiation and de novo mineralization, evaluated by osteopontin (OP) expression (ELISA and immnocytochemistry), alkaline phosphatase (ALP) activity, calcium deposition (alizarin red), collagen synthesis (SIRCOL test and immnocytochemical staining) and osteocalcin (OC) expression, highlighted the higher osteoconductive ability of Ti HA implants. Higher soluble collagen levels were found for cells cultured in simple osteogenic differentiation medium on control Ti and Ti SiO2 implants. Osteocalcin (OC), a marker of terminal osteoblastic differentiation, was most strongly expressed in osteoblasts cultivated on Ti SiO2 implants.
Conclusions
The behavior of osteoblasts depends on the type of implant and culture conditions. Ti SiO2 scaffolds sustain osteoblast adhesion and promote differentiation with increased collagen and non-collagenic proteins (OP and OC) production. Ti HA implants have a lower ability to induce cell adhesion and proliferation but an increased capacity to induce early mineralization. Addition of growth factors BMP-2 and TGFβ1 in differentiation medium did not improve the mineralization process. Both types of infiltrates have their advantages and limitations, which can be exploited depending on local conditions of bone lesions that have to be repaired. These limitations can also be offset through methods of functionalization with biomolecules involved in osteogenesis.
The area of implant osseointegration is of major importance, given the predicted significant rise in the number of orthopaedic procedures and an increasingly ageing population. Osseointegration is a complex process involving a number of distinct mechanisms affected by the implant bulk properties and surface characteristics. Our understanding and ability to modify these mechanisms through alterations in implant design is continuously expanding. The following review considers the main aspects of material and surface alterations in metal implants, and the extent of their subsequent influence on osseointegration. Clinically, osseointegration results in asymptomatic stable durable fixation of orthopaedic implants. The complexity of achieving this outcome through incorporation and balance of contributory factors is highlighted through a clinical case report.
Customised implants manufacture has always presented difficulties which result in high cost and complex fabrication, mainly due to patients' anatomical differences. The solution has been to produce prostheses with different sizes and use the one that best suits each patient. Additive manufacturing (AM) as a technology from engineering has been providing several advancements in the medical field, particularly as far as fabrication of implants is concerned. The use of additive manufacturing in medicine has added, in an era of development of so many new technologies, the possibility of performing the surgical planning and simulation by using a three-dimensional (3D) physical model, very faithful to the patient's anatomy. AM is a technology that enables the production of models and implants directly from the 3D virtual model (obtained by a Computer-Aided Design (CAD) system, computed tomography or magnetic resonance) facilitating surgical procedures and reducing risks. Furthermore, additive manufacturing has been used to produce implants especially designed for a particular patient, with sizes, shapes and mechanical properties optimised, for areas of medicine such as craniomaxillofacial surgery. This work presents how AM technologies were applied to design and fabricate a biomodel and customised implant for the surgical reconstruction of a large cranial defect. A series of computed tomography data was obtained and software was used to extract the cranial geometry. The protocol presented was used for creation of an anatomic biomodel of the bone defect for the surgical planning and, finally, the design and manufacture of the patient-specific implant.
Titanium and its alloys are successfully used in aerospace through to marine applications. Selective laser melting (SLM) is an additive manufacturing technique, which promises to allow production of novel Ti structures. However, there is still a paucity of accepted methods for quantifying build quality. The viability of using X-ray microtomography (μCT) to quantify and track changes in morphology of SLM Ti porous structures at each stage of the post-laser melting production was tested, quantifying its quality through process. Quantification was achieved using an accessible volume tool to determine pore and strut sizes. Removal of partially sintered struts by cleaning was visualised and quantified. 88% of the struts broken by the cleaning process were found to have connecting neck diameters of less than 180 μm with a mean of 109 μm allowing build criteria to be set. Tracking particles removed during cleaning revealed other methods to improve build design, e.g. avoiding low angle struts that did not sinter well. Partially melted powder particles from strut surfaces were quantified by comparing surface roughness values at each cleaning step. The study demonstrates that μCT provides not only 3D quantification of structure quality, but also a feedback mechanism, such that improvements to the initial design can be made to create more stable and reliable titanium structures for a wide variety of applications.
Highly ordered TiO2 nanotubes (NTs) were synthesized by the electrochemical anodization of Ti foils. We extracted the effect of the Ti surface roughness (applying different pre-treatments prior to the anodization) on the length, growth rate and degree of self-organization of the obtained NT arrays. The mechanisms subjacent to the TiO2 NTs formation and growth were correlated not only with the corresponding anodization curves but also to their appropriate
derivatives (1st order) and suitable integrated and/or obtained param eters, to revel the onset and
end of the different electrochemical regimes. This enable s an in depth interpretation of such
details (and physical- chemical insight), for different levels of surface roughness and
topographic features. We found that pre-treat ments that lead to an extremely small Ti surface
roughness and offer enhanced NT length and also provide a significant improvement of the
template organization quality (highly ordered hexagonal NTs arrays over larger areas) , due to
the optimized surface topography. We present a new statistical approach of evaluate highly
ordered hexagonal NTs arrays areas. Large domains with ideally arranged nanotube structures
represented by a hexagonal closed -packed array were obtained (6.61 µm^2), close to the
smallest grain diameter of the Ti foil and three times larger than those so far reported in the
literature. The use of optimized pre-treatments then allowed avoiding a second anodization
step, ultimately leading to highly hexagonal self ordered samples with large organized domains
at reduced time and cost.
We used selective laser melting (SLM) and hot pressing of mechanically-alloyed beta-type Ti-40Nb powder to fabricate macroporous bulk specimens (solid cylinders). The total porosity, compressive strength, and compressive elastic modulus of the SLM-fabricated material were determined as 17% +/- 1%, 968 +/- 8 MPa, and 33 +/- 2 GPa, respectively. The alloy's elastic modulus is comparable to that of healthy cancellous bone. The comparable results for the hot-pressed material were 3% +/- 2%, 1400 +/- 19 MPa, and 77 +/- 3 GPa. This difference in mechanical properties results from different porosity and phase composition of the two alloys. Both SLM-fabricated and hot-pressed cylinders demonstrated good in vitro biocompatibility. The presented results suggest that the SLM-fabricated alloy may be preferable to the hot-pressed alloy for biomedical applications, such as the manufacture of load-bearing metallic components for total joint replacements.
Open-porous scaffolds made of W4 and WZ21 fibres were evaluated to analyse their potential as an implant material. WZ21 scaffolds without any surface modification or coating, showed promising mechanical properties which were comparable to the W4 scaffolds tested in previous studies. Eudiometric testing results were dependent on the experimental setup, with corrosion rates differing by a factor of 3. Cytotoxicity testing of WZ21 showed sufficient cytocompatibility. The corrosion behavior of the WZ21 scaffolds in different cell culture media are indicating a selective dealloying of elements from the magnesium scaffold by different solutions. Long term in-vivo studies were using 24 W4 scaffolds and 12 WZ21 scaffolds, both implanted in rabbit femoral condyles. The condyles and important inner organs were explanted after 6, 12 and 24 weeks and analyzed. The in-vivo corrosion rate of the WZ21 scaffolds calculated by microCT-based volume loss was up to 49 times slower than the in-vitro corrosion rate based on weight loss. Intramembranous bone formation within the scaffolds of both alloys was revealed, however a low corrosion rate and formation of gas cavities at initial time points were also detected. No systemic or local toxicity could be observed. Investigations by μ-XRF did not reveal accumulation of yttrium in the neighboring tissue. In summary, the magnesium scaffold´s performance is biocompatible, but would benefit from a surface modification, such as a coating to obtain lower the initial corrosion rates, and hereby establish a promising open-porous implant material for load-bearing applications.
Statement of significance
Magnesium is an ideal temporary implant material for non-load bearing applications like bigger bone defects, since it degrades in the body over time. Here we developed and tested in vitro and in a rabbit model in vivo degradable open porous scaffolds made of sintered magnesium W4 and WZ21 short fibres. These scaffolds allow the ingrowth of cells and blood vessels to promote bone healing and regeneration. Both fibre types showed in vitro sufficient cytocompatibility and proliferation rates and in vivo, no systemic toxicity could be detected. At the implantation site, intramembranous bone formation accompanied by ingrowth of supplying blood vessels within the scaffolds of both alloys could be detected.
A simple chemical method was established for inducing bioactivity of Ti and its alloys. When pure Ti, Ti‐6Al‐4V, Ti‐6Al‐2Nb‐Ta, and Ti‐15Mo‐5Zr‐3Al substrates were treated with 10M NaOH aqueous solution and subsequently heat‐treated at 600°C, a thin sodium titanate layer was formed on their surfaces. Thus, treated substrates formed a dense and uniform bonelike apatite layer on their surfaces in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. This indicates that the alkali‐ and heat‐treated metals bond to living bone through the bonelike apatite layer formed on their surfaces in the body. The apatite formation on the surfaces of Ti and its alloys was assumed to be induced by a hydrated titania which was formed by an ion exchange of the alkali ion in the alkali titanate layer and the hydronium ion in SBF. The resultant surface structure changed gradually from the outermost apatite layer to the inner Ti and its alloys through a hydrated titania and titanium oxide layers. This provides not only the strong bonding of the apatite layer to the substrates but also a uniform gradient of stress transfer from bone to the implants. The present chemical surface modification is therefore expected to allow the use the bioactive Ti and its alloys as artificial bones even under load‐bearing conditons. © 1996 John Wiley & Sons, Inc.
By slowly removing inefficient material from a structure, the shape of the structure evolves towards an optimum. This is the simple concept of evolutionary structural optimization (ESO). Various design constraints such as stiffness, frequency and buckling load may be imposed upon a structure. Depending on the types of design constraints, different rejection criteria for removing material need to be used. For each type of constraints, the corresponding rejection criteria will be discussed in detail in the subsequent chapters. This chapter describes the simplest rejection criterion based on local stress level. Several examples are included to illustrate how the ESO process works.
Selective laser melting (SLM) is characterized by highly localized heat input and short interaction times, which lead to large thermal gradients. In this research, nine different materials are processed via SLM and compared. The resulting microstructures are characterized by optical and scanning electron microscopy. Residual stresses are measured qualitatively using a novel deflection method and quantitatively using X-ray diffraction. Microcracking, surface oxidation and the anisotropy of the residual stress are discussed. The different phenomena interacting with the buildup of residual stress make it difficult to distinguish the possible correlations between material parameters and the magnitude of residual stresses.
This is a comprehensive and accessible overview of what is known about the structure and mechanics of bone, bones, and teeth. In it, John Currey incorporates critical new concepts and findings from the two decades of research since the publication of his highly regarded The Mechanical Adaptations of Bones. Crucially, Currey shows how bone structure and bone's mechanical properties are intimately bound up with each other and how the mechanical properties of the material interact with the structure of whole bones to produce an adapted structure. For bone tissue, the book discusses stiffness, strength, viscoelasticity, fatigue, and fracture mechanics properties. For whole bones, subjects dealt with include buckling, the optimum hollowness of long bones, impact fracture, and properties of cancellous bone. The effects of mineralization on stiffness and toughness and the role of microcracking in the fracture process receive particular attention. As a zoologist, Currey views bone and bones as solutions to the design problems that vertebrates have faced during their evolution and throughout the book considers what bones have been adapted to do. He covers the full range of bones and bony tissues, as well as dentin and enamel, and uses both human and non-human examples. Copiously illustrated, engagingly written, and assuming little in the way of prior knowledge or mathematical background, Bones is both an ideal introduction to the field and also a reference sure to be frequently consulted by practicing researchers.
Essentials of 3D Biofabrication and Translation discusses the techniques that are making bioprinting a viable alternative in regenerative medicine. The book runs the gamut of topics related to the subject, including hydrogels and polymers, nanotechnology, toxicity testing, and drug screening platforms, also introducing current applications in the cardiac, skeletal, and nervous systems, and organ construction. Leaders in clinical medicine and translational science provide a global perspective of the transformative nature of this field, including the use of cells, biomaterials, and macromolecules to create basic building blocks of tissues and organs, all of which are driving the field of biofabrication to transform regenerative medicine.
This chapter discusses the biomechanics of human vertebral trabecular bone. It also describes aging, disease, and repetitive loading. This chapter addresses the behavior of the whole vertebra, including discussion of the role of the cortical shell, intervertebral disc, and posterior elements. Detailed knowledge of the biomechanical behavior of vertebral bone is necessary in order to design robust implants. Design of orthopedic implants for the spine is particularly challenging because vertebral trabecular bone is so weak and the cortices are so thin. As a result, failure of the bone-implant system often originates in the bone. The problem is compounded because the bone properties vary so much across individuals and over time and with disease. The development of minimally invasive surgical repair techniques for vertebral fractures such as vertebroplasty and kyphoplasty also invites biomechanical analysis of vertebral trabecular bone and the whole vertebral body in order to refine those procedures. Subsequently, computational models are in use to refine and indeed develop designs of new implants for the spine.
For reutilizing the cement sludge as a concrete waterproofer, the sludge was treated with stearic acid by chemical method. And we compared the performances of the new waterproofers with those of two others which have been used in demostic area. The particles of the new waterproofer are finer than those of standard sand but larger than those of cement. And the surfaces of the particles are coated with metallic soaps which have strong water repellency. Also the exess stearic acid and metallic soaps coated on the sludge react with the Ca++ or Al+++ when mixed with cement mortar. Therefore, the watertightness and the physical properties of the new waterproofers in cement mortar were superior to those of the others.
Degradable biomaterials constitute a novel class of bioactive biomaterials which are expected to support healing process of a diseased tissue and to degrade thereafter. Two classes of metals have been proposed: magnesium- and iron-based alloys. Three targeted applications are envisaged: orthopaedic, cardiovascular and pediatric implants. Conceptually, biodegradable metals should provide a temporary support on healing process and should progressively degrade thereafter.
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:
Bone is dynamic, highly vascularised tissue with a unique capacity to heal?and remodel. Its main role is to provide structural support for the body. Furthermore the skeleton also serves as a mineral reservoir, supports muscular contraction resulting in motion, withstands load bearing and protects internal organs [1]. Hence, it is logical to say that major alterations in its structure due to injury or disease can dramatically alter one?s body equilibrium and quality of life. There are roughly 1 million cases of skeletal defects a year that require bone-graft procedures to achieve repair. Socioeconomic consequences in treating these patients with bone fractures is a major concern in both the USA and EU, which are likely to increase due to the ageing of their populations. Bone repair may be treated by grafts taken from either the patient?s own existing bone from other sites (autografts) or donor sources (allografts). The use of synthetic substitutes eliminates the need for further surgery for autografts and the risk of infectious disease transmission from allografts. The significant limitations of current treatments have compelled researchers to develop synthetic alternatives for bone reconstruction. In the early 1950s Swedish orthopaedic surgeon Per Ingvar Branemark began studying the healing process of titanium anchoring screws, which proved to be a seminal point for modern dental and orthopaedic implants [2]. Current bone substitutes using metal, ceramic, polymer and composites, though far from ideal, are commonly implanted materials, second only to blood products. Currently, bone tissue engineering is being researched including scaffolds, growth factors and engineering cells which may provide next-generation bone substitutes. Production of such bone implants and scaffolds requires complex structures that would provide the necessary bone shape and morphology. In general, current orthopaedic prostheses are modular in nature and, although scalable, adhere to a range of basic generic designs. The surgeon, therefore, must select the best size fit based upon preoperative evaluation of radiographs. Current production methods for these devices, which are made from metal/ceramic/ polymers, include casting, compression moulding, sintering, and bar stock milling. These approaches have some inherent restrictions, these include the use of static moulds/tooling which do not allow rapid design changes or one-off patient-specific devices to be produced, or they have geometry restrictions, and high material wastage. One school of thought believes that patient-oriented devices have the potential to enhance the longevity of a device by providing a securer fit, especially in those cases where the devices are not cemented. Closeness of fit aims to aid the distribution and normalization of the stresses incurred in the remaining skeletal system, thereby reducing stress shielding, micromotion, and sinkage. Accurate fits are typically achieved by removing the patient?s bone stock to accommodate the prosthesis, thereby destroying valuable viable bone and making any revision surgery more difficult. It would be preferable to produce custom prostheses for individual patients that required little or no healthy bone stock removal to increase the device stability, especially in young patients, and thus increase the options for a successful revision surgery if required [3]. Today reverse engineering (RE) and medical image-based modelling technologies allow the construction of three-dimensional (3D) models of anatomical structures of human body based on information from imaging data such as computerized tomography (CT), magnetic resonance imaging (MRI), and laser (or structured light) scanning [4]. Based on 3D models, advanced mouldless manufacturing techniques, commonly known as solid free-from fabrication (SFF) or rapid prototyping (RP) have been used to build 3D physical models for surgical training, preoperative planning, surgical simulation andmore recently applied to fabricate customised implants and scaffolds for individual patients. This chapter gives a background on bone structure and properties, biomaterials for bone implants and requirements for bone implant and scaffolds. It then introduces state-of-the-art reverse engineering and rapid prototyping techniques to assist in the manufacture of customised bone implants and then focuses on current research on the techniques to fabricate bone implants and scaffolds directly.
The effects of laser surface remelting (LSR) on the microstructural evolution and surface mechanical properties of Ti-Zr beta titanium alloy were investigated. The surfaces of the Ti-Zr alloy was re-melted using a CO2 laser. X-ray diffraction, Scanning electron microscope, Transmission electron microscope, nanoindentation, and microhardness analyses were performed to evaluate the microstructural and mechanical properties of the alloy. The results showed that the alloy microstructure in the remelting region was greatly refined and homogeneous compared with that in the base material because of the rapid remelting and resolidifying. Meanwhile, the metastable hexagonal x phases with the size of 20-50 nm was found and uniformly distributed throughout the b matrix after LSR. Phase transformation and microstructural refinement were the major microstructural changes in the alloys after LSR. The microhardness and elastic modulus in the remelted region clearly increased by 92.9% and 21.78%, respectively, compared with those in the region without laser processing. The strengthening effect of LSR on the mechanical properties of the Ti-Zr alloy was also addressed. Our results indicated that LSR was an effective method of improving the surface mechanical properties of alloys.
Novel ultrafine lamellar (α + β) microstructures comprising ultrafine (∼200-300 nm) α-laths and retained β phases were created via promoting in situ decomposition of a near α′ martensitic structure in Ti-6Al-4V additively manufactured by selective laser melting (SLM). As a consequence, the total tensile elongation to failure reached 11.4% while maintaining high yield strength above 1100 MPa, superior to both conventional SLM-fabricated Ti-6Al-4V containing non-equilibrium acicular α′ martensite and conventional mill-annealed Ti-6Al-4V. The formation and decomposition of α′ martensite in additively manufactured Ti-6Al-4V was studied via specially designed experiments including single-track deposition, multi-layer deposition and post-SLM heat treatment. The essential SLM additive manufacturing conditions for Ti-6Al-4V including layer thickness, focal offset distance and energy density, under which a near α′ martensitic structure forms in each layer and then in situ transforms into ultrafine lamellar (α + β) structures, were determined. This is the first fundamental effort that has realized complete in situ martensite decomposition in SLM-fabricated Ti-6Al-4V for outstanding mechanical properties.
Unlike conventional materials removal methods, additive manufacturing (AM) is based on a novel materials incremental manufacturing philosophy. Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet demanding requirements from aerospace, defence, automotive and biomedical industries. Laser sintering (LS), laser melting (LM) and laser metal deposition (LMD) are presently regarded as the three most versatile AM processes. Laser based AM processes generally have a complex non-equilibrium physical and chemical metallurgical nature, which is material and process dependent. The influence of material characteristics and processing conditions on metallurgical mechanisms and resultant microstructural and mechanical properties of AM processed components needs to be clarified. The present review initially defines LS/LM/LMD processes and operative consolidation mechanisms for metallic components. Powder materials used for AM, in the categories of pure metal powder, prealloyed powder and multicomponent metals/alloys/MMCs powder, and associated densification mechanisms during AM are addressed. An in depth review is then presented of material and process aspects of AM, including physical aspects of materials for AM and microstructural and mechanical properties of AM processed components. The overall objective is to establish a relationship between material, process, and metallurgical mechanism for laser based AM of metallic components. © 2012 Institute of Materials, Minerals and Mining and ASM International.
Topology optimisation enables profound insight into the optimal material distribution for a given structural objective, applied loading and boundary conditions. The topologically optimal geometry is often geometrically complex and incompatible with traditional manufacturing methods. Additive manufacture can accommodate significantly more complex geometries than traditional manufacture; however , it is necessary that specific design rules be satisfied to ensure manufacturability. Based on identified design for additive manufacture rules, a novel method is proposed that modifies the theoretically optimal topology as required to ensure manufacturability without requiring additional support material. By assessing the manufacturing time and component mass associated with feasible orientations of the proposed geometry, an optimal orientation can be identified. A case study is presented to demonstrate the usefulness of the proposed method.
Computer-aided tissue engineering (CATE) integrates advances of multi-disciplinary fields of Biology, Biomedical Engineering, Information Technology, and modern Design and Manufacturing. Application of CATE to the design and fabrication of tissue scaffolds can facilitate the exploration of many novel ideas of incorporating biomimetic and biological features into the scaffold design. This paper presents some of the salient applications of CATE, particularly in the modeling and design of scaffolds with controlled internal and external architecture; with vascular channels of different sizes; with modular and interconnecting subunits; with multi-layered heterogeneous dense and compact regions; and the scaffolds with designed artificial chambers for drug delivery, embedded growth factors and other sophisticated features.
Natural structural materials are built at ambient temperature from a fairly limited selection of components. They usually comprise hard and soft phases arranged in complex hierarchical architectures, with characteristic dimensions spanning from the nanoscale to the macroscale. The resulting materials are lightweight and often display unique combinations of strength and toughness, but have proven difficult to mimic synthetically. Here, we review the common design motifs of a range of natural structural materials, and discuss the difficulties associated with the design and fabrication of synthetic structures that mimic the structural and mechanical characteristics of their natural counterparts.
Additive manufacturing provides an attractive processing method for nickel–titanium (NiTi) shape memory and pseudoelastic parts. In this paper, we show how the additive manufacturing process affects structural and functional properties of additively manufactured NiTi and how the process parameter set-up can be optimized to produce high quality NiTi parts and components. Comparisons of shape recovery due to shape memory and pseudoelasticity in additively manufactured and commercial NiTi exhibit promising potential for this innovative processing method.
Selective laser melting (SLM) process allows fabricating strong, lightweight and complex metallic structures. To successfully produce metallic parts by SLM, additional structures are needed to support overhanging surfaces in order to dissipate process heat and to minimize geometrical distortions induced by internal stresses. However, these structures are often massive and require additional post-processing for their removal. A minimization of support structures would therefore significantly reduce manufacturing and finishing efforts and costs. This study investigates the manufacturability of overhanging structures using optimized support parts. An experimental study was performed to identify the optimal self-supporting overhanging structures using Taguchi L-36 design. Experimental results revealed that with optimized supports it is possible to build non-assembly mechanism with overhang surfaces. However, it is necessary to correctly orientate the part in the SLM machine in order to build it with a minimal support structure so to obtain the best trade-off between production time, cost, and accuracy.