Naturally Derived Maleic Chitosan/Thiolated Sodium Hyaluronate Hydrogels as Potential 3D Printing Tissue Engineering Materials

3D printing is an attractive method to accurately construct artificial organs or alternative materials with complicated structures and functional performance. Naturally derived hydrogels have emerged as promising materials for the preparation of biomimetic 3D organization or scaffolds by 3D printing due to their good biocompatibility, high water content, and fascinating 3D network. However, the poor printing properties and weak structural stability of naturally derived hydrogels limit their applications. In this study, photopolymerizable hydrogels are designed based on maleic chitosan (MCS) and thiolated sodium hyaluronate (SHHA). The Michael addition between MCS and SHHA improves the viscosity of the mixed solution. Moreover, it benefits the 3D printing process, followed by photopolymerization (acrylate-thiol step-chain polymerization and acrylate–acrylate chain polymerization) to form a stable covalent network rapidly. The rheological property, swelling behaviors, microstructure, and in vitro degradation are tuned by adjusting the molar ratio of the thiol group and acrylate group. In addition, MCS/SHHA hydrogel scaffolds with good accuracy and enhanced structural stability are prepared using extrusion-based 3D printing and photopolymerization technology. The hydrogels display excellent cytocompatibility and can support adherence of L929 cells, which can be used as prospective materials for tissue engineering applications.     

Transparent alumina ceramics fabricated by 3D printing and vacuum sintering

Transparent alumina ceramics were fabricated using an extrusion-based 3D printer and post-processing steps including debinding, vacuum sintering, and polishing. Printable slurry recipes and 3D printing parameters were optimized to fabricate quality green bodies of varying shapes and sizes. Two-step vacuum sintering profiles were found to increase density while reducing grain size and thus improving the transparency of the sintered alumina ceramics over single-step sintering profiles. The 3D printed and two-step vacuum sintered alumina ceramics achieved greater than 99 % relative density and total transmittance values of about 70 % at 800 nm and above, which was comparable to that of conventional CIP processed alumina ceramics. This demonstrates the capability of 3D printing to compete with conventional transparent ceramic forming methods along with the additional benefit of freedom of design and production of complex shapes.     

Natural Polysaccharides as Multifunctional Components for One-Step 3D Printing Tough Hydrogels

Natural polysaccharides (NPS) are regarded as biomolecular and structural components for preparing high-performance tough hydrogels. But the one-step fabrication of NPS-containing hydrogels in seconds and the template-free design of complicated high-resolution structures are still significant challenges in this field. To meet these requirements, various NPS-containing tough hydrogels are fabricated and processed into 2D/3D structures via the combination of Ru(bpy)₃²⁺-mediated photochemistry and extrusion 3D printing technique. The whole fabrication process is one-step, completed in tens of seconds under visible light irradiation. It is found that the used NPS plays a key role in achieving the fabrication of high-performance structured tough hydrogels. The high reactivity of functional groups in the used NPS can shorten their gelation times. Long rigid chains of the used NPS, their hierarchical assemblies, and contrasting multinetworks benefit from the efficient dissipation of mechanical energy and enhancement of its operational stability. Strong supramolecular interactions enable hydrogel precursors to have high viscosities, therefore providing good controllability to design high-resolution and complicated tough hydrogel structures via extrusion 3D printing. It is anticipated that this straightforward fabrication strategy and findings will open new horizons for NPS-containing materials.     

Linking fresh paste microstructure,rheology and extrusion characteristics of cementitious binders for 3D printing

Cementitious binders amenable to extrusion-based 3D printing are formulated by tailoring the fresh microstructure through the use of fine limestone powder or a combination of limestone powder and microsilica or metakaolin. Mixtures are proportioned with and without a superplasticizer to enable different particle packings at similar printability levels. A simple microstructural parameter, which implicitly accounts for the solid volume and inverse square dependence of particle size on yield stress can be used to select preliminary material combinations for printable binders. The influence of composition/microstructure on the response of pastes to extension or squeezing are also brought out. Extrusion rheology is used in conjunction with a phenomenological model to better understand the properties of significance in extrusion-based printing of cementitious materials. The extrusion yield stress and die wall slip shear stress extracted from the model enables an understanding of their relationships with the fresh paste microstructure, which are crucial in selecting binders, extrusion geometry, and processing parameters for 3D printing.     

基于浆料形态的陶瓷3D打印技术的浆料体系研究进展

3D打印技术因其操作简单便捷、成型快速灵活、可制备复杂结构的器件等优点,在精密陶瓷零件制造方面具有广泛应用。本文根据3D打印陶瓷的材料形态综述不同3D打印技术在陶瓷制备方面的特点,重点介绍了陶瓷3D打印成型技术中直写式3D打印、光固化3D打印、喷墨3D打印等技术所涉及的粘结剂、分散剂等组分的应用及作用机理,并对水基和非水基两种类型的添加剂组分进行总结和探讨,以期为3D打印技术制备高性能陶瓷样件提供参考。     

High temperature strength of an ultra high temperature ceramic produced by additive manufacturing

In this study hafnium diboride was fabricated using the additive manufacturing technique robocasting. Parts have been successfully produced with complex shapes and internal structures not possible via conventional manufacturing techniques. Following pressureless sintering, the monolithic parts reach densities of 94–97% theoretical. These parts exhibit bending strength of 364 ± 31 MPa at room temperature, and maintain strengths of 196 ± 5 MPa up to 1950 °C, which is comparable to UHTC parts produced by traditional means. These are the highest temperature mechanical tests that a 3D printed part has ever undergone. The successful printing of the high density HfB₂ demonstrates the versatile range materials that can be produced via robocasting using Pluronic pastes.     

Alumina-based filters made via binder jet 3D printing of alumina powder,colloidal silica infiltration,and sintering

Alumina-based, porous filter media was made via a binder jet 3D printing process consisting of an alumina powder printing step with subsequent heating, colloidal silica infiltration, drying, and sintering to consolidate particles yet retain a net open porous microstructure. The composites made were alumina-silica or alumina-mullite, where the silica sintering aid was used to densify and join the alumina particles. The resulting composite structures had open porosities in the 25–31 vol% range as measured by Archimedes density. Pressure drops were measured across the filter media at constant flow rates to compare disc shapes and complex, 3D printed filters based on the N95 design requirements. Complex, 3D-printed alumina composites were produced with acceptable pressure drops for N95 implementation.     

基于3D打印技术制造柔性传感器研究进展

与传统的涂覆、沉积等加工手段相比,使用3D打印技术可制造复杂立体功能结构的传感器,将3D打印与柔性传感技术结合可以促进未来生物医疗、人工智能等领域的发展。本文介绍了国内外基于3D打印技术制造柔性传感器的最新进展,其中包括聚酰亚胺等多种基底材料、纳米金属等多种打印传感材料;按照熔融沉积、黏弹性墨水沉积、粉末烧结熔化、还原光聚合和材料喷射的制造原理分别阐述了多种传感器的材料选择、成型特点,并对制造方法进行总结分析。虽然3D打印制造柔性传感器件存在着缺乏行业标准及多种类打印材料等问题,但经过不断创新与发展,3D打印将成为柔性传感领域极佳的制造手段。     

3D-printed polymer packing structures: Uniformity of morphology and mechanical properties via microprocessing conditions

Three-dimensional (3D) printing is an attractive approach to fabricate highly porous extremely lightweight structures for architecture antivibrational packaging. We report 3D printing processing of model packaging structures using biodegradable poly(lactic acid) (PLA) as a source material, with acrylonitrile butadiene styrene (ABS) utilized as a common 3D printing source material as a traditional benchmarked material. The effects of printing temperature, speed, and layer morphology on the layer-by-layer 3D-printed structures and their mechanical properties were considered. Three different characteristic morphologies were identified based on printing temperature; the microscopic surface roughness was dependent on the printing speed and layer height. We demonstrate that the mechanical performances and surface properties of 3D-printed PLA structures could be improved by optimization of printing conditions. Specifically, we evaluate that these PLA-based 3D structures printed exhibited better surface qualities and enhanced mechanical performance than traditional ABS-based structures. Results showed that the PLA-based 3D structures possessed the favorable mechanical performance with 34% higher Young's modulus and 23% higher tensile strength in comparison to the ABS-based 3D structures. This study provides guidelines for achieving high-quality 3D-printed lightweight structures, including smooth surfaces and durable mechanical properties, and serves as a framework to create biodegradable 3D-printed parts for human use.     

Modified commercial UV curable elastomers for passive 4D printing

ABSTRACT

Conventional 4D printing technologies are realized by combining 3D printing with soft active materials such as shape memory polymers (SMPs) and hydrogels. However, the intrinsic material property limitations make the SMP or hydrogel-based 4D printing unsuitable to fabricate the actuators that need to exhibit fast-response, reversible actuations. Instead, pneumatic actuations have been widely adopted by the soft robotics community to achieve fast-response, reversible actuations, and many efforts have been made to apply the pneumatic actuation to 3D printed structures to realize passive 4D printing with fast-response, reversible actuation. However, the 3D printing of soft actuators/robots heavily relies on the commercially available UV curable elastomers the break strains of which are not suf?cient for certain applications which require larger elastic deformation. In this paper, we present two simple approaches to tune the mechanical properties such as stretchability, stiffness, and durability of the commercially available UV curable elastomers by adding: (i) mono-acrylate based linear chain builder; (ii) urethane diacrylate-based crosslinker. Material property characterizations have been performed to investigate the effects of adding the two additives on the stretchability, stiffness, mechanical repeatability as well as viscosity. Demonstrations of fully printed robotic finger, grippers, and highly deformable 3D lattice structure are also presented.     

3D printing dielectric elastomers for advanced functional structures: A mini-review

Three-dimensional (3D) printed bionic products play an important role in intelligent robotics, microelectronics, and polymers. The printing and manufacturing process of 3D printers is conducive to obtaining soft structures that meet specific requirements, and saves time and cost. Soft intelligent robotics, an emerging research field, has always been developed based on soft materials and actuators with their biological properties. This article reviews the current understanding of 3D bioprinting technologies for dielectric elastomers (DEs), DE actuators (DEAs) and soft robots, such as inkjet, extrusion, laser-induced and stereolithography bioprinting. 3D printers for fabricating soft materials are presented and classified. The approaches to exploit 3D bioprinters for DEs/DEAs are as follows: (1) 3D printing DEAs utilize ionic hydrogel–elastomer hybrids that are analogous to human muscles, and the DEAs usually have flexible structures and large deformations with multiple functionalities. (2) An electrohydrodynamic (EHD) 3D printer confers high printing resolution and high production efficiency, which offers advantages such as full automation and flexible design. The optimal printing conditions are mainly determined by the effects of printing voltages and ink properties, which are related to the formation of the liquid cone and the printed line width. Furthermore, the advantages of 3D bioprinting technologies have accelerated their development and applications.     

Additive Manufacturing of Polymer-Based Lubrication

The fast growth of 3D printing technology gives designers many ways to make structures that are hard to see. 3D printing lets you customize complex structures in any way you want and make rapid prototypes of materials. It enables you to simulate things more effectively. So far, experiments with polymer-based lubrication have been done on atomically smooth surfaces, under dynamic conditions, and on the nano- or micro-scale. Polymer-based lubrication in 3D printing has been studied in depth, which has made it possible to make significant, multifunctional 3D structures with microscale accuracy. It is a crucial way to approach lubrication and has sparked much scientific interest. A thorough literature review is done to keep track of the latest advances in 3D printing for structural polymer-based lubrication simulation. The design and lubrication performance quality of bio-inspired, different-sized simulation structures is given much attention. The material requirements, skills, and representative applications of various 3D printing technologies are summarized. The efficient directions for future research in designing and making 3D-printed lubrication structures are also pointed out.     

Effect of the slurry composition on the piezoelectric properties of PZT ceramics fabricated via materials extrusion 3D printing

Herein, the effect of the binder content in lead zirconate titanate (PZT) slurry has been systematically studied to improve the piezoelectric properties of PZT ceramics prepared via material extrusion 3D printing. For smooth printing, a slurry with a binder concentration ranging from 6 to 12 wt% was proposed. The porosity of the green body first decreased and then increased with an increase in the binder concentration, and the minimum porosity was obtained when the binder concentration reached 10 wt%. Samples with increased density were obtained after debinding and lead-rich atmosphere sintering. PZT piezoceramics fabricated using a binder content of 10 wt% exhibit the maximum relative density (96.9%), largest piezoelectric constant (342.6 pC/N) and dielectric constant (1621). Based on the above process, the wood pile structure and helical twentytetrahedral structural components were successfully fabricated using the material extrusion process. This research lays the foundation for the engineering application of 3D printing to fabricate high-performance piezoceramics with complex shapes.     

Photocurable pentaerythritol triacrylate/lithium phenyl-2,4,6-trimethylbenzoylphosphinate-based ink for extrusion-based 3D printing of magneto-responsive materials

Recent advances in additive manufacturing made it feasible to fabricate products with desired shapes and features. Herein, a new, photocurable 3D printer ink mainly based on pentaerythritol triacrylate (PETA) is reported. To achieve rapid curing needed for 3D printing process, high performance water-soluble photoinitiator, lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), was emulsified in PETA monomers and this suspension was evaluated for its polymerization kinetics by exposing to 395 nm UV-light. The distinct influences of LAP and triethanolamine (TEA) concentrations on photo-polymerization and printability were examined and an optimum concentration for extrusion-based 3D printing was found to be 10 mM and 1.62 M for LAP and TEA, respectively. Synthesized PETA-based 3D printer ink was functionalized by dispersing magnetic particles/flakes into the mixture, and consequently, a magneto responsive ink was obtained to be used in specialized applications. A ring-shaped structure embedded with micron sized iron flakes was printed as a prototype. This study presents a versatile photo-curable polymer formulation with possible translation to high performance 3D printing of customizable shapes that can be utilized in a wide range of areas such as micro-robotics and medical science.     

3D打印在微反应器制造中的应用

3D打印技术具有自由设计、生产时间短、节约材料、无需模具、易于制造复杂结构等优点,使其在微反应器设计和制造方面能够发挥巨大作用。本文对比了几种常用微反应器的制造工艺,重点综述了3D打印技术在微反应器制造中的应用进展。     

Developments in 4D-printing: a review on current smart materials,technologies, and applications

ABSTRACT

Recent advances in additive manufacturing (AM), commonly known as three-dimensional (3D)-printing, have allowed researchers to create complex shapes previously impossible using traditional fabrication methods. A research branch that originated from 3D-printing called four-dimensional (4D)-printing involves printing with smart materials that can respond to external stimuli. 4D-printing permits the creation of on-demand dynamically controllable shapes by integrating the dimension of time. Recent achievements in synthetic smart materials, novel printers, deformation mechanism, and mathematical modeling have greatly expanded the feasibility of 4D-printing. In this paper, progress in the 4D-printing field is reviewed with a focus on its practical applications. We discuss smart materials developed using 4D-printing with explanations of their morphing mechanisms. Additionally, case studies are presented on self-constructing structures, medical devices, and soft robotics. We conclude with challenges and future opportunities in the field of 4D-printing.     

Highly stretchable hydrogels for sensitive pressure sensor and programmable surface patterning by thermal bubble inkjet technology

Hydrogels with tough strength, programmable deformation are crucial for their practical applications. In this work, we reported the preparation and the programmable shape deformations of highly stretchable hydrogel. The graphene oxide/polyacrylamide/sodium alginate composite hydrogel was prepared, its microstructure and mechanical properties were studied. An aqueous calcium solution was selectively printed onto the hydrogel surfaces using an inkjet printer, resulting in programmable deformation of the composite hydrogel by creating regions of swelling/deswelling when subjected to external stimulations. Next, we fabricated a pressure-capacitance hydrogel sensor to demonstrate its application. Furthermore, the deformation rate and extent of the hydrogels can be controlled by adjusting the printing pattern position, number, length, and calcium solution concentration. Finally, several complex 2D and 3D shapes were fabricated by printing appropriate patterns on one or both surfaces of the hydrogel sheets.     

Improved 3D Printing and Cell Biology Characterization of Inorganic-Filler Containing Alginate-Based Composites for Bone Regeneration: Particle Shape and Effective Surface Area Are the Dominant Factors for Printing Performance

The use of organic–inorganic 3D printed composites with enhanced properties in biomedical applications continues to increase. The present study focuses on the development of 3D printed alginate-based composites incorporating inorganic fillers with different shapes (angular and round), for bone regeneration. Reactive fillers (bioactive glass 13–93 and hydroxyapatite) and non-reactive fillers (inert soda–lime glass) were investigated. Rheological studies and the characterization of various extrusion-based parameters, including material throughput, printability, shape fidelity and filament fusion, were carried out to identify the parameters dominating the printing process. It was shown that the effective surface area of the filler particle has the highest impact on the printing behavior, while the filler reactivity presents a side aspect. Composites with angular particle morphologies showed the same high resolution during the printing process, almost independent from their reactivity, while composites with comparable amounts of round filler particles lacked stackability after printing. Further, it could be shown that a higher effective surface area of the particles can circumvent the need for a higher filler content for obtaining convincing printing results. In addition, it was proven that, by changing the particle shape, the critical filler content for the obtained adequate printability can be altered. Preliminary in vitro biocompatibility investigations were carried out with the bioactive glass containing ink. The 3D printed ink, forming an interconnected porous scaffold, was analyzed regarding its biocompatibility in direct or indirect contact with the pre-osteoblast cell line MC3T3-E1. Both kinds of cell tests showed increased viability and a high rate of proliferation, with complete coverage of the 3D scaffolds’ surface already after 7 d post cell-seeding.     

Manufacturing of polymer/metal composites by fused deposition modeling process with polyethylene

In this study, production of metal/polymer composites using polyethylene as the matrix with various contents of metal powder was investigated. Fused deposition modeling (FDM) process is one of the most popular and conventional additive manufacturing methods to produce three-dimensional (3D) specimens from computer-aided design data with complex geometry and lower prices in comparison with the alternative methods. Given the advantages of this process, it seems inevitable for the development of new materials. Utilizing semicrystalline plastics impose challenges for producing parts due to printing issues such as distortion and warpage. In this experimental work, a compounding production line was implemented to produce composite filaments with 25, 50, and 75 wt % of copper powder suitable for the FDM process. After dealing with printing issues, flexural, electrical conductivity, and bulk density tests were done. The micrographs of the specimens were examined via scanning electron microscopy to reveal the distribution of the copper particles. It is believed that the metal/polymer filament could be used to print new 3D parts. The material could be utilized in electromagnetic structures for some specific applications, such as shielding, with new properties. Also, by solving printing problems for a semicrystalline polymer, it can be encouraging to examine printing process for other rarely used thermoplastics. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48717.