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3D Printing Latex: A Route to Complex Geometries of High Molecular Weight Polymers
Abstract
Vat photopolymerization (VP) additive manufacturing fabricates intricate geometries with excellent resolution; however, high molecular weight polymers are not amenable to VP due to concomitant high solution and melt viscosities. Thus, a challenging paradox arises between printability and mechanical performance. This report describes concurrent photopolymer and VP system design to navigate this paradox with the unprecedented use of polymeric colloids (latexes) that effectively decouple the dependency of viscosity on molecular weight. Photocrosslinking of a continuous-phase scaffold, which surrounds the latex particles, combined with in-situ computer-vision print parameter optimization, which compensates for light scattering, enables high-resolution VP of high molecular weight polymer latexes as particle-embedded green bodies. Thermal post-processing promotes coalescence of the dispersed particles throughout the scaffold, forming a semi-interpenetrating polymer network (sIPN) without loss in part resolution. Printing a styrene-butadiene rubber (SBR) latex, a previously inaccessible elastomer composition for VP, exemplified this approach and yielded printed elastomers with precise geometry and tensile extensibilities exceeding 500%.
... Currently, rubber is mainly printed by fused deposition modeling (FDM) [21][22][23][24], by vat photo-polymerization (VPP) [1,[25][26][27] using photo-curable precursors, and by direct ink writing (DIW) [28][29][30]. They have been used to successfully fabricate various complicated elastic rubber structures. ...
... Owing to the excellent interfacial compatibility between the printing layers (as shown in Figure 5), the mechanical properties of the 3D-printed rubber specimens are markedly superior to those reported in other studies (Figure 6f) [1,[24][25][26][27][28]42]. The surface and crosssectional morphology of the 3D-printed rubber specimen were examined using SEM. ...
... Owing to the excellent interfacial compatibility between the printing shown in Figure 5), the mechanical properties of the 3D-printed rubber spec markedly superior to those reported in other studies (Figure 6f) [1,[24][25][26][27][28]42]. Th and cross-sectional morphology of the 3D-printed rubber specimen were exami SEM. ...
Direct ink writing (DIW) is an economical, straightforward, and relatively energy-efficient 3D printing technique that has been used in various domains. However, the utilization of rubber latex for DIW remains limited due to its high fluidity and inadequate support, which makes it challenging to meet the required ink rheological characteristics for DIW. In this study, a concentrated pre-vulcanized natural rubber latex (CPNRL) ink with a high solid content of 73% without additives is developed for DIW 3D printing. The CPNRL ink is concentrated using superabsorbent polymer (SAP) beads, which demonstrates good colloidal stability, favorable rheological properties, and superior printability. The impact of printing angles on the mechanical properties of the rubber specimens based on the CPNRL-73 ink is explored in detail, wherein the tensile strength of the specimen printed at a 90° angle reaches an impressive 26 MPa and a strain of approximately 800%, which surpasses the majority of 3D-printed rubber latex specimens. Additionally, the CPNRL ink can be used to print a wide range of intricate shapes, demonstrating its advantages in excellent formability. The preparation of 3D printable ink using the absorption method will expand the application of elastomers in fields such as customized flexible sensing and personalized rubber products.
... 3D printing enables the creation of adsorbents with customizable pore sizes, shapes, and distributions that are difficult to achieve through traditional manufacturing methods. Materials such as activated carbon, zeolite, or modified biopolymers can be 3D-printed into adsorbents with optimized porosity and surface area, improving their contaminant uptake capacities [60]. Additionally, by customizing the shape and arrangement of adsorbent particles or structures, 3D printing enables the development of adsorbents that are more efficient in capturing targeted pollutants from leachate, potentially reducing the need for additional treatment stages and supporting material recovery. ...
... Adsorbents with certain properties were made using 3D printing technology to improve the efficiency of pollutants being absorbed by leachate. Material layer deposition, according to Scott et al. [60], is a unique kind of 3D printing that combines the capacity to produce objects with complex geometry with polymer recycling and reuse. The remediation of emerging pollutants and passive sampling has undergone a radical transformation due to 3D printing of complex materials. ...
Landfills contain valuable resources that can be recovered and recycled, contributing to a circular economy (CE). This article provides a critical review of landfill management techniques and its potential for climate change mitigation in the waste sector and identifies challenges, opportunities, and the potential of nutrient, energy, and material (NEM) recovery from landfills. This work also uncovers research gaps and the needs of unlocking synergies between CE-based landfill management and climate change mitigation through NEM recovery. A conceptual framework that integrates NEM recovery into landfill management based on CE principles and waste hierarchy is also presented. It is evident from a literature survey of 205 articles that CE-based landfill management (CEBLM) is a novel approach to minimize waste generation and maximize resource recovery from landfills. CEBLM can potentially unlock synergies between environmental protection, resource efficiency, and climate action simultaneously. CEBLM scenarios have the potential to decrease greenhouse gas (GHG) emissions by 56-95% in comparison to typical open dumps, and they have the capability to produce 0.8-3.2 kWh of energy and 0.4-1.6 kWh/ton heat of garbage. Additionally, they can recover 48% of metals, 32% of plastics, and 16% of glass from the landfill waste. Overall, integrating leachate treatment within CE landfill practices not only enables effective nutrient, energy, and material recovery but also offers a sustainable pathway for mitigating climate change impacts. This approach underscores the potential of innovative waste management strategies to contribute to environmental resilience and resource efficiency.
... 3D printing enables the creation of adsorbents with customizable pore sizes, shapes, and distributions that are difficult to achieve through traditional manufacturing methods. Materials such as activated carbon, zeolite, or modified biopolymers can be 3D-printed into adsorbents with optimized porosity and surface area, improving their contaminant uptake capacities [60]. Additionally, by customizing the shape and arrangement of adsorbent particles or structures, 3D printing enables the development of adsorbents that are more efficient in capturing targeted pollutants from leachate, potentially reducing the need for additional treatment stages and supporting material recovery. ...
... Adsorbents with certain properties were made using 3D printing technology to improve the efficiency of pollutants being absorbed by leachate. Material layer deposition, according to Scott et al. [60], is a unique kind of 3D printing that combines the capacity to produce objects with complex geometry with polymer recycling and reuse. The remediation of emerging pollutants and passive sampling has undergone a radical transformation due to 3D printing of complex materials. ...
Landfills contain valuable resources that can be recovered and recycled, contributing to a circular economy (CE). This article provides a critical review of landfill management techniques and its potential for climate change mitigation in the waste sector and identifies challenges, opportunities, and the potential of nutrient, energy, and material (NEM) recovery from landfills. This work also uncovers research gaps and the needs of unlocking synergies between CE-based landfill management and climate change mitigation through NEM recovery. A conceptual framework that integrates NEM recovery into landfill management based on CE principles and waste hierarchy is also presented. It is evident from a literature survey of 205 articles that CE-based landfill management (CEBLM) is a novel approach to minimize waste generation and maximize resource recovery from landfills. CEBLM can potentially unlock synergies between environmental protection, resource efficiency, and climate action simultaneously. CEBLM scenarios have the potential to decrease greenhouse gas (GHG) emissions by 56-95% in comparison to typical open dumps, and they have the capability to produce 0.8-3.2 kWh of energy and 0.4-1.6 kWh/ton heat of garbage. Additionally, they can recover 48% of metals, 32% of plastics, and 16% of glass from the landfill waste. Overall, integrating leachate treatment within CE landfill practices not only enables effective nutrient, energy, and material recovery but also offers a sustainable pathway for mitigating climate change impacts. This approach underscores the potential of innovative waste management strategies to contribute to environmental resilience and resource efficiency.
... NRL has been widely applied in dipping processes to produce products such as balloons, gloves, condoms, and other products like memory foam, coating (2D), and adhesives for centers. 2 Since 2017, a growing body of research has been on adapting this substance to additive manufacturing (3D). [3][4][5][6][7][8][9] Volume fraction is important parameter for understanding the fundamental properties of latex, including and viscosity and morphology. By definition, it represents the proportion of the total volume occupied by dispersed particles (solid particles) relative to the total volume of the colloidal system. ...
This study explores how three distinct preservation techniques affect the microstructure and rheological properties of natural rubber latex. Traditional ammoniated systems were compared against two emerging eco-friendly preservatives developed by AFLatex Technologies, which demonstrated enhanced latex properties reported in Ammonia-Free Latex Compositions, US Patent Application 63/267,167.2022. 2023. Rheological data were modeled using the Cross model to capture the non-linearity of viscosity and the Krieger–Dougherty (K&D) model to describe viscosity as a function of volume fraction. We also proposed an extended K&D model to better fit experimental observations. Additionally, Taylor–Couette flow simulation were performed to investigate shear-induced particle migration, providing insights into the dynamic behavior of particles under varied shear conditions. Our findings showed differences in critical volume fraction; the ammoniated system exhibited a critical volume fraction range of 0.6–0.7, while the ammonia-free systems had a lower range of 0.4–0.55. These values align closely with the predication from the Cross model, which suggests critical volume fraction of 0.4–0.5 for ammonia-free systems and above 0.6 for ammoniated systems. The extended and original K&D models corroborated these findings, with the ammonia-free systems typically reaching a critical volume fraction of 0.55 and the ammoniated systems approaching 0.7. Simulations under simplified assumptions revealed that shear-induced migration can maintain approximately 20% of the particles at a critical volume fraction of around 0.48, underscoring the complex interplay of particle dynamics and preservation technique in determining natural rubber latex material properties.
... Vat photopolymerization, also commonly called stereolithography, is a promising avenue for fabricating advanced elastomers with complex geometries, as demonstrated with printed silicone [18] and latex [19]. Formlabs' Elastic 50A, a polyurethane-based resin, is one of the more common commercially available elastomeric materials for this process. ...
Due to its ability to achieve geometric complexity at high resolution and low length scales, additive manufacturing (AM) has increasingly been used for fabricating cellular structures (e.g., foams and lattices) for a variety of applications. Specifically, elastomeric cellular structures offer tunability of compliance as well as energy absorption and dissipation characteristics. However, there are limited data available on compression properties for printed elastomeric cellular structures of different designs and testing parameters. In this work, the authors evaluate how unit cell topology, part size, the rate of compression, and aging affect the compressive response of polyurethane-based simple cubic, body-centered, and gyroid structures formed by vat photopolymerization AM. Finite element simulations incorporating hyperelastic and viscoelastic models were used to describe the data, and the simulated results compared well with the experimental data. Of the designs tested, only the parts with the body-centered unit cell exhibited differences in stress–strain responses at different part sizes. Of the compression rates tested, the highest displacement rate (1000 mm/min) often caused stiffer compressive behavior, indicating deviation from the quasi-static assumption and approaching the intermediate rate response. The cellular structures did not change in compression properties across five weeks of aging time, which is desirable for cushioning applications. This work advances knowledge on the structure–property relationships of printed elastomeric cellular materials, which will enable more predictable compressive properties that can be traced to specific unit cell designs.
... Geleneksel üretim yöntemleri kullanarak imal edilmesi mümkün olmayan karmaşık geometrili ürünler, eklemeli imalat yöntemi kullanılarak üretilebilmektedir [1,2]. Bu yöntem sayesinde kişiye veya duruma özel parçaların üretimi mümkün hale gelmiştir [3,4]. ...
Recently, the fused deposition modeling, which is one of the additive manufacturing technologies, has been increasingly used. This method makes it possible to manufacture parts with light weight, less material waste and complex geometries thanks to additive manufacturing technology. However, the mechanical properties of the parts produced by the fused deposition modeling may be lower than the parts produced by the traditional production methods. In order to improve the mechanical properties, materials such as chopped glass, carbon, or Kevlar fiber are added to the matrix polymer. In this study, test samples were produced for the optimization of printing parameters (nozzle temperature, bed temperature and layer thickness) using chopped carbon fiber reinforced PLA. The produced samples were subjected to the three-point bending test and the effect on the mechanical properties was examined.
... These can create new properties in combination with other resins to result in new applications, such as degradable scaffolds. [31,32] ...
Direct Ink Writing (DIW) utilizes a wide range of ink formulations to produce desirable 3D-printed structures and properties. Styrene-butadiene rubber (SBR) is an attractive candidate for 3D printing owing to its commercial availability, rheology, excellent mechanical properties, good impact resilience, and chemical stability. The SBR-based sealant was 3D printed in a DIW process, even in an ambient environment. The rheological behavior was assessed and correlated with optimized printing parameters. Important physico-chemical properties of the 3D-printed material were reported showing excellent properties as an elastomer. This work should expand the potential applications of existing rubber-based materials in additive manufacturing.Graphical abstract
... The utilization of 3D printing [1,2] is becoming increasingly prominent in the fabrication of products with intricate geometries and tuneable properties [3,4]. Moreover, it is being employed to explore novel approaches for reusing various plastic wastes for developing engineering products [5][6][7]. ...
Recycled acrylonitrile butadiene styrene (RABS) has undesirable thermal properties that cause the material to shrink and not adhere to the printing bed during three-dimensional (3D) printing. In order to address this issue, virgin acrylonitrile butadiene styrene (VABS) of varying weight proportions (i.e., 10–50%) is blended with RABS to fabricate parts at various printing temperatures (i.e., 230 °C, 240 °C, and 250 °C). The study emphasizes to achieve proper inter-layer bonding and enhancing the physical and mechanical characteristics of the final product made from RABS. It was found that blending of VABS up to 40% in RABS with components fabricated at 240 °C resulted in the highest improvement in physical and mechanical properties. The 60% RABS/40%VABS sample printed at 240 °C exhibits improvements in Young's modulus (E), yield strength (σy), and ultimate tensile strength (UTS) by 13.69%, 13.37%, and 15.64%, respectively. Moreover, the RABS sample blended with 20% VABS exhibited comparable flexural results to the 100% VABS samples as blending VABS enhances molecular chain bonding and provides better elasticity to the material.
... Essentially, additive manufacturing (AM) is the broader category of techniques to which 3D printing belongs, where 3D parts composed of diverse materials such as polymers (including thermoplastics [4]), ceramics [5,6], metals [3,7], elastomers [8], thermosets [9], and compounds [10]) are manufactured layer by layer from computer-aided design (CAD) models. Three-dimensional (3D) printing (3DP) has a distinct advantage over traditional manufacturing procedures, such as plastic forming, CNC machining, and injection molding, in producing objects with various materials [11,12], complicated structures [13,14], and customized bulk properties, including thermal [15,16], mechanical [17], antimicrobial [18][19][20], often used in dental applications [66], implants and coatings [67], and optical applications [68]. Due to its popularity, it is applied in 3D printing, almost exclusively in medical treatments for dental and implant applications [69,70], employing the vat photopolymerization and material jetting techniques [71]. ...
The influence of nanoparticles (NPs) in zirconium oxide (ZrO2) as a strengthening factor of Polylactic Acid (PLA) and Polyamide 12 (PA12) thermoplastics in material extrusion (MEX) additive manufacturing (AM) is reported herein for the first time. Using a melt-mixing compounding method, zirconium dioxide nanoparticles were added at four distinct filler loadings. Additionally, 3D-printed samples were carefully examined for their material performance in various standardized tests. The unfilled polymers were the control samples. The nature of the materials was demonstrated by Raman spectroscopy and thermogravimetric studies. Atomic Force Microscopy and Scanning Electron Microscopy were used to comprehensively analyze their morphological characteristics. Zirconium dioxide NPs showed an affirmative reinforcement tool at all filler concentrations, while the optimized material was calculated with loading in the range of 1.0-3.0 wt.% (3.0 wt.% for PA12, 47.7% increase in strength; 1.0 wt.% for PLA, 20.1% increase in strength). PA12 and PLA polymers with zirconium dioxide in the form of nanocomposite filaments for 3D printing applications could be used in implementations using thermoplastic materials in engineering structures with improved mechanical behavior.
... Using water-soluble free radical photoinitiators with NVP and PEGDA as scaffold precursors, Long et al. produced green bodies with entrapped SBR latex particles ( Figure 13). 350 These reactive diluents ensured sufficient modulus (classically ranging from 10 4 −10 6 Pa) to maintain feature fidelity throughout the printing process. Upon greenbody formation, subsequent annealing above the T g of the latex promoted particle coalescence, forming a semi-interpenetrating polymer network (sIPN), ensuring the properties of the previously dispersed high molar mass polymer ( Figure 13). ...
Polymer colloids are complex materials that have the potential to be used in a vast array of applications. One of the main reasons for their continued growth in commercial use is the water-based emulsion polymerization process through which they are generally synthesized. This technique is not only highly efficient from an industrial point of view but also extremely versatile and permits the large-scale production of colloidal particles with controllable properties. In this perspective, we seek to highlight the central challenges in the synthesis and use of polymer colloids, with respect to both existing and emerging applications. We first address the challenges in the current production and application of polymer colloids, with a particular focus on the transition toward sustainable feedstocks and reduced environmental impact in their primary commercial applications. Later, we highlight the features that allow novel polymer colloids to be designed and applied in emerging application areas. Finally, we present recent approaches that have used the unique colloidal nature in unconventional processing techniques.
... These groups are employed as building blocks to develop bigger molecules due to their high reactivity upon light irradiation, well-established mechanisms and commercial availability [57]. A few examples of the most common monomers and oligomers according to their nature are shown in Fig. 2. Other functionalities can also be used, such as polyester, vinyl, vinyl ether, thio-ene/yne and even cationic-based systems (combining free radical systems) [58][59][60][61]. The selection of suitable monomers or oligomers for VP is based on the application and processing technology to be used. ...
In the last few years, 3D printing has evolved from its original niche applications, such as rapid prototyping and hobbyists, towards many applications in industry, research and everyday life. This involved an evolution in terms of equipment, software and, most of all, in materials. Among the different available 3D printing technologies, the light activated ones need particular attention from a chemical point of view, since those are based on photocurable formulations and in situ rapid solidification via photopolymerization. In this article, the chemical aspects beyond the preparation of a formulation for light-induced 3D printing are analyzed and explained, aiming at giving more tools for the development of new photocurable materials that can be used for the fabrication of innovative 3D printable devices.
Graphical abstract
... More specifically, 3DP is an additive manufacturing (AM) technology, in which 3D objects consisting of different materials, e.g., metals [3,4], ceramics [5,6], polymers, i.e., thermoplastics [7], thermosets [8] and elastomers [9], and composites [10] are constructed in a sequential layer-by-layer manufacturing approach directly from computer-aided design (CAD) models. As such, 3D objects consisting of different materials [11,12], complex geometries [13,14], and by-design and tailored final component bulk properties, i.e., mechanical [15], thermal [16], electrical [17], magnetic [18], catalytic [19], antimicrobial [20], etc., could be easily realized due to the unique nature of 3DP, compared to traditional manufacturing methods (injection molding, plastic forming, CNC machining, etc.) To that end, several high-end applications have been reported; namely, in the biomedical field [21], e.g., implants [22], scaffolds for tissue engineering [23], surgical equipment [24], medical diagnostic tools [25], tissue and organ printing [26], etc., up to 4D printed structures for robotics applications [27,28], all employing 3DP as the main manufacturing and fabrication technology alternative to traditional manufacturing methods. ...
The effect of aluminum oxide (Al2O3) nanoparticles (NPs) as a reinforcing agent of Polyamide 12 (PA12) and Polylactic acid (PLA) in fused filament fabrication (FFF) three-dimensional printing (3DP) is reported herein for the first time. Alumina NPs are incorporated via a melt-mixing compounding process, at four different filler loadings. Neat as well as nanocomposite 3DP filaments are prepared as feedstock for the 3DP manufacturing of specimens which are thoroughly investigated for their mechanical properties. Thermogravimetric analyses (TGA) and Raman spectroscopy (RS) proved the nature of the materials. Their morphological characteristics were thoroughly investigated with scanning electron and atomic force microscopy. Al2O3 NPs exhibited a positive reinforcement mechanism at all filler loadings, while the mechanical percolation threshold with the maximum increase of performance was found between 1.0-2.0 wt.% filler loading (1.0 wt.% for PA12, 41.1%, and 56.4% increase in strength and modulus, respectively; 2.0 wt.% for PLA, 40.2%, and 27.1% increase in strength and modulus, respectively). The combination of 3DP and polymer engineering using nanocomposite PA12 and PLA filaments with low-cost filler additives, e.g., Al2O3 NPs, could open new avenues towards a series of potential applications using thermoplastic engineering polymers in FFF 3DP manufacturing.
... 3D printing is gaining increasing prominence to fabricate products with complex geometries (Scott et al., 2020) or to implement new approaches to reuse and recycle plastics (Sanchez-Rexach et al., 2020). 3D printing is generally defined as the production of components by successive deposition of layers of materials; fused filament fabrication, in particular, uses thermoplastic filaments as feedstock material. ...
Over the years, our oceans have witnessed an enormous accumulation of marine plastic waste resulting from ocean‐related economic activities. As plastic pollution adversely affects marine wildlife and habitat, our society requires urgent solutions to address this increasingly alarming dilemma. Here, we turn our attention to circular economy principles to reduce the amount of nonbiodegradable petroleum‐based marine litter. We consider a production process based on 3D printing to fabricate products for the marine industry, which uses marine plastic waste as a source material. Additionally, the suitability of virgin bio‐based polyamide (bio‐PA), polylactic acid (PLA), and polyhydroxybutyrate (PHB) is explored. PHB is selected due to its extraordinary rapid biodegradation in aquatic environments. To quantify the environmental impacts of the proposed processes, a cradle‐to‐grave life cycle assessment (LCA) is applied according to ISO 14040:2006 and ISO 14044:2006 standards. Different end‐of‐life alternatives are proposed, including landfill deposition, thermal degradation, and composting. LCA results reveal that the use of marine plastic waste is environmentally preferred in comparison with bio‐PA, PLA, and PHB. Specifically, the global warming indicator, considered a prime driver toward sustainability, shows a 3.7‐fold decrease in comparison with bio‐PA. Importantly, the environmental impacts of PHB production through crude glycerol fermentation are quantified for the first time. Regarding the end‐of‐life options with a composting scenario, PLA and PHB are preferred as they yield biogenic carbon dioxide (CO2), which can be used as a renewable energy source.
... Such reactive groups are employed since they present high reactivity upon light irradiation, well-established mechanisms of reactions, and a wide range of (meth)acrylate-based are commercially available [196]. A few examples of the most used (meth)acrylate-based monomers and oligomers are depicted in Fig. 3. Other functionalities can also be employed, such as unsaturated polyester, vinyl, vinyl ether, thiol-ene/yne, and even cationic-based systems (in combination with free-radical systems) [197][198][199][200]. In general, the selection of suitable monomers or oligomers for vat polymerization is based on the specific application and the processing technology to be used. ...
During the last two decades, 3D printing technology has emerged as a valid alternative for producing microfluidic devices. 3D printing introduces new strategies to obtain high precision microfluidic parts without complex tooling and equipment, making the production of microfluidic devices cheaper, faster, and easier than conventional fabrication methods such as soft lithography. Among the main 3D techniques used for this purpose, fused filament manufacturing (FFF), inkjet 3D printing (i3Dp) and vat polymerization (VP) are of the greatest interest since they are well-established techniques in the field and are cost-affordable both in equipment and material. However, there are still some barriers in terms of technology and materials to overtake for definitively establishing 3D printing as a truly microfluidic production method. For example, the level of resolution and precision of 3D printed microfluidic parts still does not reach the level of conventional fabrication techniques, and, from a materialistic point of view, few materials present the desired characteristics (e.g., biocompatibility, optical transparency, and mechanical properties) for target areas such as medicine, analytical chemistry, and pharmaceuticals. This review intends to evaluate and analyze the current state of polymeric 3D printing techniques and materials to manufacture microfluidic chips. The article will show and discuss the latest innovations, materials, and applications of such 3D printed microstructures. The focus of this review is to provide an overview of recent and future developments in 3D printing and materials in the branch of microfluidics fabrications, showing that the selection of the right materials together with the design freedom afforded by 3D printing will be the cornerstone for microfluidic development.
... functionalities can also be employed, such as unsaturated polyester, vinyl, vinyl ether, or thiol-ene/yne systems.[93][94][95] The selection of acrylate-based reagents for vat polymerization is based on the specific application and the processing technology to be used. ...
3D printing technology is changing how objects are designed and manufactured by gradually introducing novel production concepts. Indeed, 3D printing is considered as one of the fundamental pillars of the so-called Industry 4.0. It enables the fabrication, in a short time, of bespoke parts with quasi any geometry from a digital model and without requiring tooling or expensive equipment. 3D printing techniques are based on the layer-by-layer spatial-controlled joining of materials, a concept that can be applied to metallic powders, ceramic slurries, polymers, and composites in different conditions, i.e., liquid, gel, powder, or solid filaments. Moreover, 3D printing allows the fast production of customized objects and, at the same time, a better way of using raw materials, generating economic savings.
In the biomedical field, 3D printing has found a particular ground for producing customized goods such as medical implants, biological models, and biomedical analytical systems. In this scenario, polymers' 3D printing is largely exploited for medical applications thanks to the relatively wide availability of printable polymers, offering a palette of different properties. Furthermore, they can also be processed by cost-affordable printer machines. All this has gradually led doctors, experts, and scientists to approach 3D printing for many particular biomedical purposes where personalized devices or implants are promptly required. A clear example was observed during the recent pandemic outbreak related to COVID-19, where customized pieces were on-demand and rapidly produced near hospitals, demonstrating how polymeric 3D printing can play a fundamental role in crisis moments. Nevertheless, to keep up with the rise of 3D printing in the biomedical field, new materials must be developed to satisfy basic biomedical properties, e.g., biocompatibility. The current market for printable polymers shows that only a few are considered biocompatible, and post-printing treatments play a crucial role in reducing the potential toxic agents.
The investigations presented in this dissertation focus on the development of custom-made photosensitive polymers or photopolymers for light-based 3D printing applications, also noted as vat polymerization, intending to produce bespoke objects with biomedical features. By combining appropriate materials during the printable polymer preparation and the freedom of design given by 3D printing, unique structures can be produced with interesting bioproperties; the following chapters will present different approaches to achieve such purposes. An overview of the 3D printing technology, its achievements, and challenges, focusing on the light-induced techniques, is first reported in Chapter 1 of this thesis. It follows in Chapter 2, a literature review on polymeric 3D printing applications in the biomedical field. The first experimental part is based on preparing and testing commonly-used photopolymers for vat 3D printing to produce parts for biological studies (Chapter 3, Part I). Post-printing treatments will also be explored to eliminate the potentially toxic elements from the printed parts, thus enhancing cell lines' biocompatibility. Other polymeric systems based on acrylate‐polydimethylsiloxane (PDMS) resins are also presented to print complex‐shaped and three-dimensional structures with good printing resolution (Chapter 3, Part II). In this case, the specific idea is to fabricate 3D printed PDMS-based microfluidic chips with characteristics similar to the conventional PDMS material used for microchip fabrication. The final goal consists of obtaining parts with great optical features, high chemical stability, and good mechanical properties. Chapter 4 reports the second experimental contribution based on the investigation of specific post-printing protocols to induce surface modification on the printed parts, intending to expand their bioproperties. The changes in the printed objects' properties
will be assessed by taking advantage of some reactive functional groups exposed on their surface after 3D printing. These functional groups can be used to link additional molecules of biological interest. The surface functionalization can proceed during the necessary post-curing step via UV-induced grafting polymerization techniques, even in close microfluidic devices (Chapter 4, Part I), or via microwave radiation (Chapter 4, Part II). The last experimental part focuses on exploiting an exclusive additive during the photopolymer preparation for increasing the printed parts' functionality (Chapter 5). A custom-made photopolymer is prepared by integrating a functional dye to obtain 3D printed structures with inner properties such as convenient optical characteristics, adequate light-guiding performances, and high sensitivity to different environments.
The research findings reported in this manuscript describe the efforts to shorten distances between the potential medical application of 3D printing and the available polymeric materials to produce more reliable and suitable biomedical parts. This doctoral dissertation's main idea is to enlarge the palette of the processable polymers with biological characteristics; each of the developed materials and methods reported here might be used as novel tools for biomedical purposes, particularly in point-of-a-care medicine.
... It is now used to transform digital models into real-world objects for applications in catalysis [2], medicine [3], gas adsorption and storage [4,5], etc. [6] by layer-by-layer deposition of a polymer [7]. Of the many 3D printing processes [8], the most popular are polymer extrusion (fused deposition modeling, FDM, or directly ink writing, DIW) [9,10] and vat polymerization (stereolithography, SLA, or digital light processing, DLP) [11]. They can both produce functionalized objects from composite materials [12] containing the polymer matrix with a filler that provides the needed functionality. ...
Here we report new porous carbon materials obtained by 3D printing from photopolymer compositions with zinc- and nickel-based metal–organic frameworks, ZIF-8 and Ni-BTC, followed by high-temperature pyrolysis. The pyrolyzed materials that retain the shapes of complex objects contain pores, which were produced by boiling zinc and magnetic nickel particles. The two thus provided functionalities—large specific surface area and ferromagnetism—that pave the way towards creating heterogenous catalysts that can be easily removed from reaction mixtures in industrial catalytic processes.
Vat photopolymerization (VPP) is one of the most successful additive manufacturing modalities, offering high printing resolution and a wide selection of photo‐resins for applications in aerospace, electronics, soft robotics, and biomedical devices. However, conventional photo‐resins, primarily derived from fossil resources, present sustainability challenges. They often rely on short‐chain oligomers that form brittle, dense polymer networks, limiting their performance in high‐demand applications, especially for elastomeric materials. In this study, we developed an ammonia‐free natural rubber latex‐based photo‐resin featuring an ultra‐high molecular weight polymer with low viscosity (<10 Pa·s) and rapid curing speed (~11 s, corresponding to gelling point), making it highly suitable for VPP. The printed green parts underwent a two‐step process of crosslinking and coagulation, resulting in semi‐interpenetrating polymer networks with unique structural properties. Two curing intensities were investigated: 18 and 35 mW/cm². Lower intensity resulted in lower 9×10−5mol/cm3 in crosslinked density and higher intensity, 1.4×10−4mol/cm3 in crosslink density. We systematically investigated multiscale structure–property relationships using spin–lattice (T1) and spin–spin (T2) relaxation analysis via inversion recovery and Carr‐Purcell‐Meiboom‐Gill. 18 mW/cm² with 30 s of curing and drying resulted in two regimens of motion for Rubber polymer with intermediate crosslinking density and intermediate entanglements dominating the network. Also, 35 mW/cm² with 30 s of curing and drying resulted in two regimes of Rubber polymer: however, one with a higher crosslinked and a mobile polymer phase. Optimized curing parameters enabled the fabrication of highly stretchable elastomers with 5–7.8 MPa tensile strengths and breaking strains of 750%–900%. These results highlight the potential of biomass‐based photo‐resins to advance sustainable 3D printing technologies. Furthermore, we demonstrated the feasibility of this formulation by printing complex geometries using a commercially available SLA printer.
Highlights
Ammonia‐free latex resin cures rapidly at <10 Pa·s for sustainable 3D printing.
NMR reveals distinct rubber motions under 18 versus 35 mW/cm² curing.
35 mW/cm² raises crosslink density to 1.4 × 10⁻⁴ g/mol for tougher parts.
Printed elastomers achieve 5–7.8 MPa and 750%–900% strain in minimal time.
Complex 3D prints validated on a standard Form 2 SLA printer.
Vat photopolymerization (VP) has emerged as a promising additive manufacturing technique to allow rapid light-based fabrication of 3D objects from a liquid resin. Research in the field of vat photopolymerization spans across multiple disciplines from engineering and materials science to applied chemistry and physics. This perspective brings together early-career researchers from various disciplines in academia and national laboratories around the world to summarize the most recent advancements with special emphasis on the research highlighted as part of the Gordon Research Conference (GRC) 2024 meeting on Additive Manufacturing of Soft Materials. We provide an outlook on next-generation polymer processing methods from synthesis of novel materials to multimodality manufacturing and performance engineering. Further, this article combines the ideas of many of these junior researchers to present a vision for the future of the field by highlighting the challenges and opportunities that lie ahead.
Vat photopolymerization (VPP) of highly aromatic polyurethanes (PUs) expands the library of additive manufacturing (AM) materials and enables a vast array of ductile thermoplastics, rigid and flexible thermosets, and elastomers. Aromatic diisocyanates and various diols enable printing of rigid, highly aromatic cross‐linked parts, which offer high glass transition temperatures and tunable thermomechanical performance. The judicious control of molecular weight of the photo‐reactive telechelic oligomers allows for a fundamental study of the influence of cross‐link density in highly aromatic 3D PU printed objects. VPP AM produces objects with high resolution, smooth surface finish, and isotropic mechanical properties. Thermal post‐processing is critical in maintaining excellent thermomechanical properties with semi‐crystallinity as a function of cross‐link density. Due to the presence of two ester carbonyls in the bis(2‐hydroxyethyl) terephthalate chain extender, the printed parts are readily amenable to depolymerization with methanolysis to produce difunctional dimethyl dicarbamates under modest reaction conditions. Dimethyl dicarbamates serve as suitable monomers for subsequent polycondensation.
Silica is a reinforcing filler commonly used in the production of environmentally friendly tires, because tires reinforced with silica have lower rolling resistance that translates into reduced energy consumption and improved fuel economy. However, achieving the optimal dispersion of silica within the rubber matrix is crucial for maximizing its reinforcing effects. In this study, a three-dimensionally networked silica (NS) was introduced in various amounts to rubber inks to improve their tensile strength and increase miscibility to enable their use in additive manufacturing. The results show that synthetic rubber ink with a high content of SBR (90%) and reinforced by NS possesses adequate viscosity for use in the direct ink write (DIW) process. NS was confirmed to have an impact on the rheological properties and printability of the rubber ink as well as improve the tensile strength of the printed parts. Different formulations were tested to study and facilitate the vulcanization process and identify the optimal curing conditions as well as the print parameters to use in DIW printing. The successful printing and vulcanization of various printed structures demonstrate the potential for using the developed printable ink in additive manufacturing. This study opens up new possibilities for creating rubber products (such as tire treads) with adequate flexibility and high tensile strength.
Additive manufacturing (AM) involves creating prototypes by depositing and solidifying material by the placement of material in X, Y, and Z axes in a 3D space. The emergence of AM using elastomers has allowed the production of complex and
customised parts with intricate geometries and modified properties as per specific needs of engineers cum designers. For successful 3D printing (3DP), it is crucial to use a material that is suitable for the specific application and printing process.
Elastomers are unique polymers that are resilient, flexible and capable of deforming under stress. Fused deposition modelling,
stereolithography and selective laser sintering printing are the most common 3DP techniques for elastomers. The use
of elastomers in AM is limited due to technological, material and processing constraints. Despite challenges, elastomers have great potential in AM and can be applied in various industries namely automotive, aerospace, healthcare and consumer goods. However, there is a growing interest in expanding the range of elastomers that can be 3D printed. Researchers are experimenting with different approaches to enhance the printability of elastomers such as modifying material composition, material design, optimising printing parameters, control of chemical composition and 3DP techniques. Recent advancements in the structure, properties and printing techniques of elastomers show wide scope for improving their printability. Several elastomeric materials that can be 3D printed include thermoplastic elastomer, thermoplastic polyurethane, liquid silicone rubber, etc. This review paper aims at providing an overview of the current state of AM of elastomers, including the challenges and limitations. It discusses recent advancements and suggests ways to enhance the printability of elastomers in near
future, which can help researchers and industry professionals to explore new and unique AM applications.
Polyurethanes are remarkably versatile materials that offer exceptional control over structure–property relationships, making them the subject of extensive research and exploration across diverse applications. These materials have garnered significant attention due to their inherent chemical, mechanical, thermomechanical, biological and physical properties, further fueling interest in their potential uses. However, conventional processing methods, involving molds, high temperatures or solvents, impose limitations on geometric complexity, hindering their potential applications. Additive manufacturing, or 3D printing, has emerged as a transformative solution, enabling the fabrication of intricate geometries, unparalleled design flexibility, dematerialization and enhanced material properties. This mini‐review explores recent advancements in additive manufacturing techniques applied to polyurethanes, focusing on three prominent 3D printing modalities: vat photopolymerization, direct ink write and fused filament fabrication. Examining the successful integration of polyurethanes with these cutting‐edge 3D printing methods illuminates the remarkable progress achieved in tailoring part design, expanding the range of applications and unlocking novel material−object functionalities. This mini‐review aims to provide valuable insight into the latest trends and development in 3D printing polyurethanes, paving the way for their future utilization in diverse industries. © 2023 Society of Chemical Industry.
Water‐soluble polymers (WSPs) represent a diverse class of macromolecules, and this diversity arises from the breadth of functionality derived from both natural and synthetic sources. Nature provides abundant WSPs through biosynthetic pathways in plants, animals, and fungi, and biological processes yield precisely controlled and well‐defined structures. Polymer chemists strive to develop synthetic methods that mimic the precision of natural processes. Monomers that are derived from petroleum feedstocks together with naturally sourced monomers provide a rich catalog of WSP precursors. Monomer structure, reactivity, concentration, sequence control, and reaction conditions influence polymeric microstructures, solubility, and aqueous solution structure. This article provides an overview of WSP fundamentals and highlights recent advancements in natural, nonionic, ionic, associative, and high‐performance WSPs. Recent advances in the design and performance of WSPs have critically improved the technological impact of filtration processes, water purification, drilling efficiency, and pharmaceutical applications. From modulating the rheological and filtration properties to establishing novel drug delivery systems through controllable self‐assembly, WSPs represent a critical enabling field for many emerging and diverse applications. WSPs will help to address many of the emerging challenges of our times, from energy generation and storage to water availability and next‐generation life‐saving medical technologies. This article will point to the potential impacts based on fundamental structure‐property‐processing relationships.
Vat photopolymerization (VP) Additive Manufacturing (AM), in which UV light is selectively applied to cure photo‐active polymers into complex geometries with micron‐scale resolution, has a limited selection of aliphatic thermoset materials that exhibit relatively poor thermal performance. Ring‐opening dianhydrides with acrylate‐containing nucleophiles yielded diacrylate ester‐dicarboxylic acids that enabled photo‐active polyimide (PI) precursors, termed polysalts, upon neutralization with an aromatic diamine in solution. In situ FTIR spectroscopy coupled with a solution and photo‐rheological measurements revealed a previously unknown time‐dependent instability of 4,4′‐oxydianiline (ODA) polysalts due to an aza‐Michael addition. Replacement of the electron‐donating ether‐containing diamine with an electron withdrawing sulfone‐containing monomer, e.g., 4,4′‐diaminodiphenyl sulfone (DDS), prohibited the aza‐Michael addition of the aromatic amine to the activated acrylate double bond. Novel DDS polysalt photocurable solutions are similarly analyzed and validated long‐term stability, which enabled reproducible printing of polyimide organogel intermediates. Subsequent VP AM afforded 3‐dimensional (3D) structures of intricate complexity and excellent surface finish, as demonstrated with scanning electron microscopy. In addition, the novel PMDA‐HEA/DDS solution enabled the production of the first beam latticed architecture comprised of all‐aromatic polyimide. The versatility of a polysalt platform for multi‐material printing is further demonstrated by printing parts with alternating polysalt compositions.
Vat photopolymerization (VP) and direct ink write (DIW) additive manufacturing (AM) provide complex geometries with precise spatial control employing a vast array of photo‐reactive polymeric systems. Although VP is recognized for superior resolution and surface finish, DIW provides versatility for higher viscosity systems. However, each AM platform presents specific rheological requirements that are essential for successful 3D printing. First, viscosity requirements constrain VP polymeric materials to viscosities below 10 Pa s. Thus, this requirement presents a challenging paradox that must be overcome to attain the physical performance of high molecular weight polymers while maintaining suitable viscosities for VP polymeric materials. Second, the necessary rheological complexity that is required for DIW pastes requires additional rheological measurements to ensure desirable thixotropic behavior. This manuscript describes the importance of rheological measurements when designing polymeric latexes for AM. Latexes effectively decouple the dependency of viscosity on molecular weight, thus enabling high molecular weight polymers with low viscosities. Photo‐crosslinking of water‐soluble monomers and telechelic oligomeric diacrylates in the presence of the latex enables the fabrication of a scaffold, which is restricted to the continuous aqueous phase and effectively surrounds the latex nanoparticles enabling the printing of otherwise inaccessible high molecular weight polymers. Rheological testing, including both steady and oscillatory shear experiments, provides insights into system properties and provides predictability for successful printing. This perspective article aims to provide an understanding of both chemical functionality (photo‐ and thermal‐reactivity) and rheological response and their importance for the successful design and evaluation of VP and DIW processable latex formulations.
Polyelectrolyte complexes (PECs), assemblies of oppositely charged polymers with powerful properties and wide‐ranging applications, are currently not melt‐processable via any conventional means and have been limited commercially to applications only as coatings. Herein, a unique strategy of pairing a polycation with an oppositely charged photopolymerizable monomer is employed. Vat photopolymerization of this mixture yields 3D spatial control over PECs for the first time. The properties of these 3D‐printed PECs are evaluated and are found to be similar to conventionally studied PEC materials. The water sensitivity of the PEC parts is adjustable through the incorporation of a small amount of a hydrophilic covalent crosslinker, highlighting potential future applications of these materials in 4D printing. Finally, the upcyclability of the additively manufactured PECs is demonstrated through the dissolution of a printed part and its incorporation into virgin resin to yield a part composed of partially recycled material. This chemistry has the potential to dramatically expand the application space of PEC materials and is a step towards a more circular economy for the field of additive manufacturing.
Chemical sensors worn on the body could make possible the continuous, noninvasive, and accurate monitoring of vital human signals, which is necessary for remote health monitoring and telemedicine. Attractive for creating high-performance, wearable chemical sensors are atomically thin materials with intriguing physical features, abundant chemistry, and high surface-to-volume ratios. These advantages allow for appropriate material-analyte interactions, resulting in a high level of sensitivity even at trace analyte concentrations. Previous review articles covered the material and device elements of 2D material-based wearable devices extensively. In contrast, little research has addressed the existing state, future outlook, and promise of 2D materials for wearable chemical sensors. We provide an overview of recent advances in 2D-material-based wearable chemical sensors to overcome this deficiency. The structure design, manufacturing techniques, and mechanisms of 2D material-based wearable chemical sensors will be evaluated, as well as their applicability in human health monitoring. Importantly, we present a thorough review of the current state of the art and the technological gaps that would enable the future design and nanomanufacturing of 2D materials and wearable chemical sensors. Finally, we explore the challenges and opportunities associated with designing and implementing 2D wearable chemical sensors.
Degradable poly(ethylene glycol) (PEG) hydrogels provide a versatile platform for drug delivery and tissue engineering, and acetal functionalization now enables photo-processible PEG oligomers with selective and facile degradation in acidic environments. Tailored morphologies within acetal-functionalized hydrogels provided fundamental understanding of the multiphase network degradation. End group modification of poly(ethylene glycol) (Mn = 2,000 g/mol) with 2-(vinyloxy)ethyl acrylate yielded polyether precursors with both pH-sensitive acetals and photo-curable acrylate end groups. UV-initiated binary thiol-acrylate crosslinking of the acetal-functionalized PEG diacrylate with varied amounts of a thiol-functionalized three-armed PEG provided pH-degradable networks. Controlled stoichiometric imbalance of thiol and acrylate functionalities ensured predictable plateau storage moduli from 2 × 105 to 8 × 105 Pa. Small-angle X-ray scattering (SAXS) and dynamic mechanical analysis (DMA) confirmed that the thiol/acrylate molar ratio provided hydrogels with varying network architectures and crosslink densities. Spectroscopic monitoring of an imbedded mobile dye (Direct Red-81) quantified hydrogel degradation rates. Degradable hydrogels exhibited bulk degradation in acidic solution. Gels with the lowest crosslink density fully degraded in aqueous solutions at pH 3.4 within 60 h, while the highly crosslinked gels fully degraded over 3 weeks. All hydrogels displayed long-term stability in phosphate-buffered saline (pH 7.4) beyond 3 mo, suggesting stable hydrogels for selective degradation and cargo release in low pH environments.
We introduce a novel experimental method that uses an ultraviolet (UV) photorheometer to enable accurate and repeatable measurements of cure depth for a wide range of photopolymers. When exposed to UV irradiation within the rheometer, the cured thickness of the photoresin is measured by lowering the upper plate while monitoring the commensurate axial force. The encoder-measured distance is correlated with axial force to measure cure depth under different UV curing conditions. This technique enables precise measurements of photocured films thinner than 50 µm, which can then be used to establish working curve equations for photopolymerization-based additive manufacturing (AM) processes. This process is validated through the evaluation of three unique photoresins, including a commercially available VP stiff photoresin, a highly-viscous photoresin that cures into a “soft” gel, and a highly solids-loaded photoresin with particles that greatly limit maximum cure depth. In addition, the technique is employed to explore the impact of UV irradiance on curing behavior of photoresins.
This technique enables measurement of AM process-relevant cure depths with process-relevant irradiance and wavelengths and has applications in advanced material development for a range of AM and traditional UV processing technologies. This technique meets identified gaps in current cure depth characterization techniques, including the need for automated instrumental approaches to reduce human error in measurements, the need to directly measure cure depths less than 150 µm, and the need to measure curing behavior at different UV irradiances/wavelengths. Due to the non-linear cure depth versus exposure behavior of some photoresins, it is important to directly measure cure depths at AM process-relevant sizes (<150 µm), as a working curve made from measurements of thicker films leads to more inaccurate predictions than those made from measuring thinner films.
Vat photopolymerization (VP) is an advanced additive manufacturing (AM) platform that enables production of intricate three‐dimensional (3D) monoliths that are unattainable with conventional manufacturing methods. In this work, modification of amorphous poly(arylene ether sulfone)s (PSU) allowed for VP printing. Post‐polymerization telechelic functionalization with acrylate functionality yielded photo‐crosslinkable PSUs across a molecular weight range. 1H NMR spectroscopy confirmed chemical composition and quantitative acrylate functionalization. Addition of diphenyl‐(2,4,6‐trimethylbenzoyl)phosphine oxide (TPO) photo‐initiator to 30 wt. % PSU solutions in NMP provided a photo‐curable composition. However, subsequent photo‐rheological studies elucidated rapid photo‐degradation of the polysulfone main chain, which was especially apparent in high Mn (15 kg·mol−1) PSU formulations. UV‐light intensity and wavelength range were altered to reduce degradation while allowing for efficient crosslinking. The addition of 0.5 wt. % of avobenzone photo‐blocker produced an ill‐defined structure with 6 kg·mol−1 PSU. For higher molecular weights (>12 kg·mol−1), solutions with a low molar mass reactive diluent, i.e., trimethylolpropane triacrylate, enabled the printing of an organogel with a storage modulus (>105 Pa) sufficient for vat photopolymerization. Employing multicomponent solutions provided well‐defined parts with complex geometries through vat photopolymerization. This article is protected by copyright. All rights reserved
This paper presents a towards support-free design method for 3D printing (3DP) of thin-walled composite based on stratified manufacturability reinforcement (SMR). The thickness classification is carried out on manifold structure to describe probability distribution via probabilistic statistical approaches. The fundamentals of composite materials for functional requirements are introduced for hereafter transient thermal structure coupling calculation. Afterwards, to accomplish 3DP electromechanical servo motion, a mechanical equipment, namely dexterous robot with multi-axis degrees of freedom (DOFs) platform is schematically implemented. Thereout, the towards support-free design model is established likewise at different stratifications, by increasing the DOFs and reachable posture space, for the sake of support diminution. The lightweight ribbed specimens are taken as numerical examples to minimize the support quantitatively of each stratified layer, by investigating the effect of density and accessible workspace on external support amount. The temperature, deformation of both noncomposite and composite during 3DP are compared so as to confirm the manufacturability using Finite element analysis (FEA). The physical experiment is conducted with emphasis on infrared temperature distribution, tensile strength and non-contact optical profilometer where the external support can be evaluated quantitatively by electronic weighing balance. The test results proved that the proposed SMR method can improve the overall manufacturability, by virtue of towards support-free design, owing to considering both composite material properties and machine multi-axis dexterity, even under stringent multiple constraints of high strength and high precision.
Additive manufacturing (AM), also known as 3D printing, is a promising technology to produce complex shapes with little waste material in a distributed fashion. AM can be implemented with various materials, but metal and polymer are dominant feedstocks. During the deposition process for polymeric AM, the polymer may encounter repetitive softening or melting, applied shear flow including multiple constrictions, cooling and solidification, solvent evaporation, polymerization and crosslinking, or coalescence across interfaces. This leads to the need to invoke polymer science principles to rationally predict the response of the polymeric feedstock to the shear fields, thermal gradients, and reaction fronts that they will encounter in the complex 3D printing process. Elucidating the fate of the macromolecules as they experience the 3D printing process provides a foundation to design new materials that are formulated to bias the formation of robust structures and interfaces. As such, polymers in AM offer a unique opportunity to apply polymer science principles to address shortcomings, offer potential solutions, and advance the technology. This article provides a focused discussion of how polymer science principles drive the growth of three common polymeric AM techniques, fused filament fabrication, direct‐ink write, and vat polymerization.
Wearable multimodal sensors could enable the continuous, non-invasive, precise monitoring of vital human signals critical for remote health monitoring and telemedicine. Atomically thin materials with intriguing physical characteristics, rich chemistry, and extreme sensitivity to external stimuli are attractive for implementing high-performance wearable sensors. Despite the increased interest and efforts in 2D materials-based wearable sensors, reducing the manufacturing and integration costs while improving the product performance remains challenging. Previous review articles provided good coverage discussing the material and device aspects of 2D materials-based wearable devices. However, few reviews discussed the status quo, prospects, and opportunities for the scalable nanomanufacturing of 2D materials wearable sensors for health monitoring. To fill this gap, we have reviewed the recent advances in 2D materials-based wearable health sensors. We discussed the structure design, fabrication processing, the mechanisms of 2D materials-based wearable health sensors, and their applications for human health monitoring. More significantly, we have provided a systematic discussion of the state-of-the-art and technological gaps for enabling future design and nanomanufacturing of 2D materials wearable health sensors. Finally, we discussed the challenges and opportunities associated with the scalable nanomanufacturing of 2D wearable health sensors.
This article is protected by copyright. All rights reserved.
Poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) is functionalized via radical grafting with 4-vinyl-1-cyclohexene 1,2-epoxide (VCHO) initiated using 2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane. The existence of the epoxide group on the SEBS backbone is evidenced by ¹H nuclear magnetic resonance. A size exclusion chromatography (SEC) study reveals some chain coupling, and this phenomenon is limited by controlling the quantities of peroxide and monomer reagents used during the radical grafting. Photo-crosslinking of SEBS-g-VCHO under ultraviolet irradiation in the presence of a cationic initiator is then successfully performed with resultant gel contents higher than 85%. Mechanical properties of SEBS and crosslinked materials are measured by tensile tests on thin films. On the one hand, those tests reveal a significant increase of Young's modulus of the crosslinked materials. On the other hand, the diminution of elongation at break is much more limited; crosslinked materials retain their elastomeric properties with an elongation at break greater than 200%. Finally, the photosensitive SEBS-g-VCHO is used to show the adhesion performance of the photo-crosslinking coating as well as a resin for the stereolithography process.
Nanocolloidal gels are emerging as a promising class of materials with applications as inks in 2D and 3D printing. Polymer nanoparticles (NPs) offer many advantages as potential building blocks of nanocolloidal gels, due to the ability to control NP dimensions, charge, surface chemistry, and functionality; however, their applications as inks in printing are yet to be explored. Here, functional nanocolloidal hydrogels formed by percolating oppositely charged latex NPs with different dimensions and charge densities are reported. The shear‐thinning and self‐healing properties of the nanocolloidal gels and the mechanical properties of the resulting printed films are examined. NP functionality is achieved by covalently labeling them with different fluorescent dyes that emit at two distinct wavelengths. Using these NPs, a facile route for 3D printing of multicolored fluorescence patterns is shown, with each color being visualized under a specific, well‐defined excitation wavelength. Nanocolloidal inks based on oppositely charged latex nanoparticles (NPs) are developed for 2D and 3D extrusion‐based printing. The inks exhibit shear‐thinning and self‐healing properties dependent on NP size and charge density. Inks formed by NPs labeled with distinct fluorescent dyes are used to print multicolor patterns.
Spinodal decomposition and phase transitions have emerged as viable methods to generate a variety of bicontinuous materials. Here, we show that when arrested phase separation is coupled to the time scales involved in three-dimensional (3D) printing processes, hydrogels with multiple length scales spanning nanometers to millimeters can be printed with high fidelity. We use an oil-in-water nanoemulsion-based ink with rheological and photoreactive properties that satisfy the requirements of stereolithographic 3D printing. This ink is thermoresponsive and consists of poly(dimethyl siloxane) droplets suspended in an aqueous phase containing the surfactant sodium dodecyl sulfate and the cross-linker poly(ethylene glycol) dimethacrylate. Control of the hydrogel microstructure can be achieved in the printing process due to the rapid structural recovery of the nanoemulsions after large strain-rate yielding, as well as the shear thinning behavior that allows the ink to conform to the build platform of the printer. Wiper operations are used to ensure even spreading of the yield stress ink on the optical window between successive print steps. Post-processing of the printed samples is used to generate mesoporous hydrogels that serve as size-selective membranes. Our work demonstrates that nanoemulsions, which belong to a class of solution-based materials with flexible functionalities, can be printed into prototypes with complex shapes using a commercially available 3D printer with a few modifications.
Ceramic stereolithography and related additive manufacturing methods involving photopolymerization of ceramic powder suspensions are reviewed in terms of the capabilities of current devices. The practical fundamentals of the cure depth, cure width, and cure profile are related to the optical properties of the monomer, ceramic, and photo-active components. Postpolymerization steps, including harvesting and cleaning the objects, binder burnout, and sintering, are discussed and compared with conventional methods. The prospects for practical manufacturing are discussed.
Industries such as orthodontics and athletic apparel are adopting vat photopolymerization (VP) to manufacture customized products with performance tailored through geometry. However, vat photopolymerization is limited by low manufacturing speeds and the trade-off between manufacturable part size and feature resolution. Current VP platforms and their optical sub-systems allow for simultaneous maximization of only two of three critical manufacturing metrics: layer fabrication time, fabrication area, and printed feature resolution. The Scanning Mask Projection Vat Photopolymerization (S-MPVP¹) system was developed to address this shortcoming. However, models developed to determine S-MPVP process parameters are accurate only for systems with an intensity distribution that can be approximated with a first order Gaussian distribution. Limitations of optical elements and the use of heterogeneous photopolymers result in non-analytic intensity distributions. Modeling the effect of non-analytic intensity distribution on the resultant cure profile is necessary for accurate manufacturing of multiscale products. In this work, a model to predict the shape of cured features using analytic and non-analytic intensity distribution is presented. First, existing modeling techniques developed for laser and mask projection VP processes were leveraged to create a numerical model to relate the process parameters (i.e. scan speed, mask pattern irradiance) of the S-MPVP system with the resulting cure profile. Then, by extracting the actual intensity distribution from the resin surface, we demonstrate the model's ability to use non-analytic intensity distribution for computing the irradiance for any projected pattern. Using a custom S-MPVP system, process parameters required to fabricate test specimens were experimentally determined. These parameters were then input into the S-MPVP model and the resulting cure profiles were simulated. Comparison between the simulated and printed specimens dimensions demonstrates the model’s effectiveness in predicting the dimensions of the cured shape with an error of 2.9%.
In recent years, 3D printing has led to a disruptive manufacturing revolution that allows complex architected materials and structures to be created by directly joining sequential layers into designed 3D components. However, customized feedstocks for specific 3D printing techniques and applications are limited or nonexistent, which greatly impedes the production of desired structural or functional materials. Colloids, with their stable biphasic nature, have tremendous potential to satisfy the requirements of various 3D printing methods owing to their tunable electrical, optical, mechanical, and rheological properties. This enables materials delivery and assembly across the multiple length scales required for multifunctionality. Here, a state-of-the-art review on advanced colloidal processing strategies for 3D printing of organic, ceramic, metallic, and carbonaceous materials is provided. It is believed that the concomitant innovations in colloid design and 3D printing will provide numerous possibilities for the fabrication of new constructs unobtainable using traditional methods, which will significantly broaden their applications.
Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering Volume 10 is June 7, 2019. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Additive manufacturing enables the creation of novel structures and geometries previously unattainable through traditional processing techniques. In particular, vat photopolymerization provides unprecedented resolution through the tailored delivery of light with photo-crosslinkable or photo-polymerizable materials. Traditionally, chemical crosslinks generate a permanent network, which exhibits swelling but not dissolution. In this work, photopolymerization of photo-reactive monomers with acrylate, acrylamide, and vinyl polymerizable sites enabled the formation of water-soluble 3D printed parts using vat photopolymerization. A library of monomers with varied ionic and hydrogen bonding sites provided photopolymerized films with tensile properties approaching 1200 % elongation at break and 0.47 MPa stress at 100 % elongation. The rate of polymerization and the subsequent mechanical properties revealed a dependence on the type of supramolecular interactions and functionality on the resulting hydrogel. The diverse functionality of the monomers enabled aqueous dissolution times ranging from 27 to 41 min. Vat photopolymerization of a trimethylammonium ethyl acrylate chloride solution and with 30 wt% N-vinyl pyrrolidone provided 3D parts with fine structural resolution. This method of creating soluble, water-swollen structures through vat photopolymerization provides future research with a larger library of monomers for diverse applications including soluble support scaffolds.
This work describes the first example of a hydrogenated polybutadiene elastomer photopolymer that addresses the process constraints of vat photopolymerization (VP) additive manufacturing. A synthetic method, which involves simultaneous thiol-ene step growth chain extension and acrylate crosslinking, addresses traditional challenges associated with this leading 3D printing platform. This facile, one-pot strategy combines the processing advantages of low molecular weight oligomers with the tunable thermomechanical and mechanical performance of higher molecular weight polymeric networks directly during printing, without requiring a post-processing step. The addition of photo-initiator to mixtures of liquid polybutadiene oligomer and miscible dithiols enabled selective photocuring under UV exposure to form high-strain, elastic parts in comparison to neat diacrylate systems. Photolithographic printing of these photopolymers enabled the fabrication of three-dimensional, hydrocarbon elastomer objects. Photorheology elucidated curing behavior as a function of composition and UV intensity, while optical imaging and SEM revealed quality and resolution.
Using methacrylated poly(trimethylene carbonate) oligomers unimodal (prepared from one macromer) and bimodal (prepared from two macromers with different molecular weights) photo‐crosslinked networks and structures are prepared by stereolithography. The obtained biodegradable networks are flexible and elastic. Compared to the corresponding unimodal networks, the tensile properties of bimodal poly(trimethylene carbonate) (PTMC) network films are significantly enhanced. Resilient materials with increased toughness and suture retention strengths are obtained. The mechanical properties of the bimodal networks compare favorably with those of unimodal networks prepared previously from PTMC macromers with much higher molecular weights. Tough porous PTMC structures with designed diamond pore network architectures can also be readily prepared by stereolithography. Upon swelling of these PTMC structures in a solvent, the pore sizes and pore size distribution increases while the porosity decreases. Bimodal networks and network structures are prepared using poly(trimethylene carbonate) macromers of different molecular weights. Bimodal networks with mechanical properties equal to those of unimodal networks prepared from macromers with much higher molecular weights can be prepared. Bimodal network structures can be prepared by stereolithography. The analyses of these bimodal networks and structures is described in detail.
Photopatterning of reactive sites in gels enables arbitrary patterning of nanoparticles
Shrinking problems in 3D printing
Although a range of materials can now be fabricated using additive manufacturing techniques, these usually involve assembly of a series of stacked layers, which restricts three-dimensional (3D) geometry. Oran et al. developed a method to print a range of materials, including metals and semiconductors, inside a gel scaffold (see the Perspective by Long and Williams). When the hydrogels were dehydrated, they shrunk 10-fold, which pushed the feature sizes down to the nanoscale.
Science , this issue p. 1281 ; see also p. 1244
A novel, poly(dimethyl siloxane)-based photopolymer that exhibits simultaneous linear chain extension and crosslinking was suitable for vat photopolymerization additive manufacturing. Photopolymer compositions consisted of dithiol and diacrylate functional poly(dimethyl siloxane) oligomers, where simultaneous thiol-ene coupling and free radical polymerization provided for linear chain extension and crosslinking, respectively. Compositions possessed low viscosity before printing and the modulus and tensile strain at break of a photocured, higher molecular weight precursor after printing. Photorheology and soxhlet extraction demonstrated highly efficient photocuring, revealing a calculated molecular weight between crosslinks of 12,600 g/mol and gel fractions in excess of 90% while employing significantly lower molecular weight precursors (i.e. < 5300 g/mol). These photocured objects demonstrated a 2× increase in tensile strain at break as compared to a photocured 5300 g/mol PDMS diacrylamide alone. These results are broadly applicable to the advanced manufacturing of objects requiring high elongation at break.
A series of photoresins suitable for production of elastomeric objects via digital light processing additive manufacturing are reported. Notably, the printing procedure is readily accessible using only entry-level equipment under ambient conditions using visible light projection. The photoresin formulations were found to be modular in nature and straightforward adjustments to the resin components enabled access to a range of compositions and mechanical properties. Collectively, the series includes silicones, hydrogels, and hybrids thereof. Printed test specimens displayed maximum elongations of up to 472% under tensile load, tunable swelling behavior in water, and Shore A hardness values from 13.7 to 33.3. A combination of the resins was used to print a functional multi-material three-armed pneumatic gripper. These photoresins could be transformative to advanced prototyping applications such as simulated human tissues, stimuli-responsive materials, wearable devices, and soft robotics.
High-performance, all-aromatic, insoluble, engineering thermoplastic polyimides, such as pyromellitic dianhydride and 4,4'-oxydianiline (PMDA-ODA) (Kapton), exhibit exceptional thermal stability (up to ≈600 °C) and mechanical properties (Young's modulus exceeding 2 GPa). However, their thermal resistance, which is a consequence of the all-aromatic molecular structure, prohibits processing using conventional techniques. Previous reports describe an energy-intensive sintering technique as an alternative technique for processing polyimides with limited resolution and part fidelity. This study demonstrates the unprecedented 3D printing of PMDA-ODA using mask-projection stereolithography, and the preparation of high-resolution 3D structures without sacrificing bulk material properties. Synthesis of a soluble precursor polymer containing photo-crosslinkable acrylate groups enables light-induced, chemical crosslinking for spatial control in the gel state. Postprinting thermal treatment transforms the crosslinked precursor polymer to PMDA-ODA. The dimensional shrinkage is isotropic, and postprocessing preserves geometric integrity. Furthermore, large-area mask-projection scanning stereolithography demonstrates the scalability of 3D structures. These unique high-performance 3D structures offer potential in fields ranging from water filtration and gas separation to automotive and aerospace technologies.
Stretchable UV curable (SUV) elastomers can be stretched by up to 1100% and are suitable for digital light processing (DLP) based 3D printing technology. DLP printing of these SUV elastomers enables the direct creation of highly deformable complex 3D hollow structures such as balloons, soft actuators, grippers, and Bucky ball electronical switches.
We demonstrate a series of materials compatible on Carbon’s light-based CLIP technology that exhibit a range of useful properties for final manufactured parts in a variety of applications.
The textbook seeks to bring readers with no prior knowledge or experience in interfacial phenomena, colloid science or nanoscience to the point where they can comfortably enter the current scientific and technical literature in the area. Designed as a pedagogical tool, this book recognizes the cross-disciplinary nature of the subject. To facilitate learning, the topics are developed from the beginning with ample cross-referencing. The understanding of concepts is enhanced by clear descriptions of experiments and provisions of figures and illustrations. © 2010 by World Scientific Publishing Co. Pte. Ltd. All rights reserved.
This book covers in detail the various aspects of joining materials to form parts. A conceptual overview of rapid prototyping and layered manufacturing is given, beginning with the fundamentals so that readers can get up to speed quickly. Unusual and emerging applications such as micro-scale manufacturing, medical applications, aerospace, and rapid manufacturing are also discussed. This book provides a comprehensive overview of rapid prototyping technologies as well as support technologies such as software systems, vacuum casting, investment casting, plating, infiltration and other systems. This book also: Reflects recent developments and trends and adheres to the ASTM, SI, and other standards Includes chapters on automotive technology, aerospace technology and low-cost AM technologies Provides a broad range of technical questions to ensure comprehensive understanding of the concepts covered.
This chapter explores the unifying concepts in intermolecular and interparticle forces. The chapter explains the association of like molecules or particles in a medium. It shows that independently of the type of interaction force involved, certain semiquantitative relations, known as combining relations, that describe molecular forces are applicable quite generally to all systems, that is, to the interactions of molecules, particles, surfaces, and even complex multicomponent systems. The chapter discusses specific interactions as well as complementary (lock-and-key) interactions, and presents examples to show how such specific interactions can result from the complementary shapes of molecules, in which like molecules cannot fit together, whereas unlike molecules can. The examples also show that specific interactions can be the result of an inherently specific interatomic bond, such as the hydrogen bond. The chapter explains the concepts of surface and interfacial energy, and the association of unlike molecules, particles, or surfaces in a third medium. The chapter also discusses about particle–surface and particle–interface interactions as well as the concepts of engulfing and ejections.
Natural rubber latex as a raw material for industry is relatively young. Although solid rubber has been known ever since the days Christopher Columbus and his men marvelled at the natives of Haiti playing with a ball made from the gum of a tree—which was in 1496—latex received little attention until the third decade of the twentieth century. By that time the rubber plantation industry had developed to such an extent that it appeared feasible to collect, preserve and transport latex on a large scale. Malaya was the first to export latex in commercial quantities in 1922, followed by Indonesia in 1926 and by Liberia in 1935. At the outbreak of World War II annual world production of latex had reached 44,000 tons but it was not until 1948 that production was back at the same level again. The last ten years have shown a rapid increase with world production reaching 168,000 tons in 1957. This would not have been possible without the application to manufacturing of scientific methods which in turn were ...
Transparent Interpenetrating Polymer Networks (IPNs) with poly(methyl methacrylate) (PMMA) as the stiff phase and polyurethane (PU) as the ductile phase with varying PMMA:PU ratios in the range of 90:10 to 70:30 were formulated. Static tensile and fracture tests indicate significant failure strain and crack initiation toughness enhancements with a loss of stiffness relative to PMMA. Dynamic fracture tests were conducted using a long-bar impact loading apparatus in conjunction with an optical method and high-speed photography. Low-velocity impact tests were also performed using a drop-tower. Dynamic fracture and low-velocity impact responses show that an optimum range of PMMA:PU ratios in the IPNs can produce enhanced fracture toughness and impact energy absorption capability when compared to PMMA. Fractographic examination supports macro-measurements by showing a distinct change in surface morphology associated with improved macroscale fracture toughness.
A variety of simultaneous and sequential interpenetrating polymer networks (IPNs) based on a polyurethane (PU) network and poly(methyl methacrylate) (PMMA) in linear and network forms were evaluated in terms of dynamic and static mechanical behaviour. IPNs of mid-range composition produced broad tan δ peaks with significant intensities at room temperature to influence elongation to failure. Unusually high elongations at failure were recorded in the simultaneous IPNs due to improved homogeneity in the distribution of the component polymers. The patterns of behaviour of the elastic modulus, hardness and glass transition temperature suggest the occurrence of phase inversion in the simultaneous IPNs and dual-phase continuity in the sequential IPNs. Synergism was experienced in various IPN properties with maximum improvements occurring in the PU/PMMA composition range to .
Interpenetrating polymer network materials (IPN's) and semi-IPN's have been synthesized from styrene-butadiene copolymers (SBR) as polymer I and polystyrene (PS) as polymer II. Synthetic details, such as the degree of cross-linking of each component, composition, and chemical compatibility, have been varied and their effect on the two-phase morphology has been examined by electron microscopy. The cross-link levels of both polymer I and polymer II were varied from zero to moderately high values. The polymer synthesized first forms the more continuous phase and tends to control the morphology. The second polymer forms a cellular structure whose size is determined principally by the degree of cross-linking of polymer I, with an increase in cross-linking producing a finer structure.
The article contains sections titled:
1.
Introduction
2.
Rubber Extraction
3.
Composition of Natural Rubber Latex
4.
Biosynthesis of Natural Rubber
5.
Commercial Extraction of Natural Latex
6.
Production of Natural Rubber
6.1.
Extraction by Evaporation of Water (Evaporation, Spray Drying)
6.2.
Coagulation
7.
Classification
7.1.
Technically Classified (TC) Rubber
7.2.
Standard Malaysian Rubber (SMR)
7.3.
Standardized Indonesian Rubber (SIR)
8.
Physical and Technological Properties of Solid Rubber
9.
Uses
10.
Modification
10.1.
Hydrogenated Natural Rubber
10.2.
Chlorinated Natural Rubber
10.3.
Hydrohalogenated Natural Rubber
10.4.
Cyclized Natural Rubber
10.5.
Resin‐Modified Natural Rubber
10.6.
Poly(Methyl Methacrylate)‐Grafted Natural Rubber
10.7.
Superior‐Processing Natural Rubber
10.8.
N ‐Phenylcarbamoylazoformate‐Modified Natural Rubber
10.9.
Polystyrene‐Grafted Natural Rubber
10.10.
Epoxidized Natural Rubber (ENR)
10.11.
Degraded Natural Rubber
10.12.
Thermoplastic Natural Rubber
11.
Compounding
12.
Summary
The mechanical behavior of polyurethane-poly(methyl methacrylate) interpenetrating polymer networks (PUR/PAc IPN's) was investigated. Stress-strain and impact resistance measurements were made on IPN's with a variable PUR content. The effect of the degree of crosslinking of each network on the mechanical properties was also studied. It appears that only the ultimate elongation varies largely upon changing the crosslink degree. The results are interpreted in terms of the contribution of each network to the mechanical behavior, but also by the interpenetration of both components and by the phase continuity of the PAc network.
Emulsion poly-mers are "products by process" whose main properties are deter-mined during polymerization. In this scenario of margins reduction, increasing competition, and public sensitivity to environmental issues, the challenge is to achieve an effi-cient production of high-quality materials in a consistent, safe, and environmentally friendly way. This highlight reviews the investi-gations carried out at The Univer-sity of the Basque Country to de-velop a knowledge-based strategy to achieve these goals. First, the research in fundamental mecha-nisms is discussed. This includes studies in radical entry and exit, oil-soluble initiators, propagation-rate constants of acrylic mono-mers, processes involved in the formation of branched and crosslinked polymers, microstruc-ture modification by postreaction operations, the formation of parti-cle morphology, and reactive sur-factants. The advanced mathemat-ical models developed in the group are also reviewed. In the second part, the advances in process de-velopment (optimization, online monitoring and control, monomer removal, production of high-sol-ids, low-viscosity latices, and pro-cess intensification) are presented.
The technical details of high-resolution cryo-scanning electron microscopy (cryo-SEM) in studying latex formation are presented. This technique was used to visualize the microstructure development during drying of monodisperse and bimodal latex coatings. The glass transition temperature of the monodisperse latexes ranged from 100 to −11 °C. The film formation process of these latexes, after they were coated onto silicon substrates, was followed. The micrographs showed particle ordering, formation of consolidation fronts, air invasion during drying, particles deformation, film coalescence and skinning phenomena, illuminating important physics that govern the drying process of latex coatings. The bimodal systems consisted of latex blends of large, hard and small, soft particles. Cryo-SEM revealed how porous, permeable structures were created by drying these latex blends. The porous structures were modulated by drying rate, the volume ratio and size ratio of the two kinds of particles. Binder migration phenomenon was observed at higher drying rate. In addition to microstructure investigation, permeability and strength in tension of the porous films were separately measured, illustrating the basic trade-off between integrity and strength on one hand, porosity and permeability on the other.
- Klempner D.
Polyurethane Resins Having Multiple Mechanisms of Hardening for Use in Producing Three-Dimensional Objects
- J P Rolland
- K Chen
- J Poelma
- J Goodrich
- R Pinschmidt
- J M Desimone
- L M Robeson
Pressure-Sensitive Adhesives Based on Carboxylated SBR Emulsion
- S G Takemoto
- O J Morrison