Mechanical evaluation of polymeric filaments and their corresponding 3D printed samples

3D printing technologies permits to produce functional parts with complex geometries, optimized topologies or enhanced internal structures. The relationship between mechanical performance and manufacturing parameters should be exhaustively analyzed to warrant the long term success of printed products. In this work, the mechanical performance of filaments based on acrylonitrile butadiene styrene (ABS), polylactic acid (PLA) and polylactic acid/polyhydroxyalkanoate (PLA/PHA) was investigated and also compared with their corresponding 3D printed samples. In general, the specimen dimensional deviations were found to be within the tolerances defined by the standard testing protocols. Density values revealed a high level of filament fusion promoting a nearly solid internal structure. The filaments exhibited improved tensile performance with respect to their corresponding printed samples. Tensile and bending performance looked quite independent of the raster angle. Izod impact behavior was increased, for ABS systems printed with the ±45° raster orientation. Quasi-static fracture tests displayed improved crack initiation resistance with the 0°/90° raster angle. The crack propagation observed for the ±45° specimens, through the bonding of the inter-layers, suggests weak entanglements.     

Extrusion 3D printing of conjugated polymers

Conjugated polymers combine electronic charge transport properties with the ability to transport ions, enabling transduction between ionic and electronic currents. Many applications of conjugated polymers, such as biointerfaces, actuators, and energy storage, benefit from 3D structures. Among different methods for 3D fabrication, extrusion-based 3D printing is a versatile approach that is compatible with multimaterial fabrication processes. This review summarizes progress in the emerging field of 3D printed conjugated polymers using three extrusion printing processes: direct ink write, meniscus-guided printing, and electrohydrodynamic printing. Ink designs for direct in write are described in depth, including strategies for modifying the rheology and conductivity of the inks.     

Biofunctional rapid prototyping for tissue-engineering applications: 3D bioplotting versus 3D printing

Two important rapid-prototyping technologies (3D Printing and 3D Bioplotting) were compared with respect to the computer-aided design and free-form fabrication of biodegradable polyurethane scaffolds meeting the demands of tissue-engineering applications. Aliphatic polyurethanes were based on lysine ethyl ester diisocyanate and isophorone diisocyanate. Layer-by-layer construction of the scaffolds was performed by 3D Printing, that is, bonding together starch particles followed by infiltration and partial crosslinking of starch with lysine ethyl ester diisocyanate. Alternatively, the 3D Bioplotting process permitted three-dimensional dispensing and reactive processing of oligoetherurethanes derived from isophorone diisocyanate, oligoethylene oxide, and glycerol. The scaffolds were characterized with X-ray microtomography, scanning electron microscopy, and mechanical testing. Osteoblast-like cells were seeded on such scaffolds to demonstrate their potential in tissue engineering. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 624–638, 2004     

Recent Advances in 3D Printing of Photocurable Polymers: Types,Mechanism, and Tissue Engineering Application

The conversion of liquid resin into solid structures upon exposure to light of a specific wavelength is known as photopolymerization. In recent years, photopolymerization-based 3D printing has gained enormous attention for constructing complex tissue-specific constructs. Due to the economic and environmental benefits of the biopolymers employed, photo-curable 3D printing is considered an alternative method for replacing damaged tissues. However, the lack of suitable bio-based photopolymers, their characterization, effective crosslinking strategies, and optimal printing conditions are hindering the extensive application of 3D printed materials in the global market. This review highlights the present status of various photopolymers, their synthesis, and their optimization parameters for biomedical applications. Moreover, a glimpse of various photopolymerization techniques currently employed for 3D printing is also discussed. Furthermore, various naturally derived nanomaterials reinforced polymerization and their influence on printability and shape fidelity are also reviewed. Finally, the ultimate use of those photopolymerized hydrogel scaffolds in tissue engineering is also discussed. Taken together, it is believed that photopolymerized 3D printing has a great future, whereas conventional 3D printing requires considerable sophistication, and this review can provide readers with a comprehensive approach to developing light-mediated 3D printing for tissue-engineering applications.     

Polybenzimidazole-based thiol-ene photosensitive composition for DLP 3D printing

Aphotosensitive composition based on N-allylated poly[2,2'-(p-oxydiphenylene)-5,5'-dibenzimidazole] and pentaerythritol tetrakis(3-mercaptopropionate) has been developed. This photosensitive composition is capable of forming cross-linked 3D-structures due to UV-initiated thiol-ene polymerization. Using digital light processing 3D printing, 3D-objects with high resolution, mechanical strength and thermal resistance up to 397 °C are formed.     

Keto-coumarin scaffold for photoinitiators for 3D printing and photocomposites

The purposes of this paper are moving toward (a) the development of a new series of photoinitiators (PIs) which are based on the keto-coumarin (KC) core, (b) the introduction of light-emitting diodes (LEDs) as inexpensive and safe sources of irradiation, (c) the study of the photochemical mechanisms through which the new PIs react using different techniques such as Fourier transform infrared, UV–visible or fluorescence spectroscopy, and so on, (d) the use of such compounds (presenting good reactivity and excellent photopolymerization initiating abilities) for two specific and high added value applications: 3D printing (@405 nm) and preparation of thick glass fiber photocomposites with excellent depth of cure, and finally (e) the comparison of the performance of these KC derivatives versus other synthesized coumarin derivatives. In this study, six well-designed KC derivatives ( KC-C , KC-D , KC-E , KC-F , KC-G , and KC-H ) are examined as high-performance visible-light PIs for the cationic polymerization of epoxides as well as the free-radical polymerization of acrylates upon irradiation with LED@405 nm. Excellent polymerization rates are obtained using two different approaches: a photo-oxidation process in combination with an iodonium (Iod) salt and a photo-reduction process when associated with an amine (N-phenylglycine or ethyl 4-(dimethylamino)benzoate). High final reactive conversions were obtained. A full picture of the involved photochemical mechanisms is provided.     

3D printing for aqueous and non-aqueous redox flow batteries

Additive manufacturing technologies, generally grouped under the name of 3D printing, are experiencing an explosion of interest during the last few years. The possibility of fast prototyping enabled by 3D printing has been recognized as a crucial booster for device fabrication and general scientific advancements. In this review, attention is focused on the latest developments in the field of redox flow batteries which are, similar to other energy related devices, characterized by the recent adoption of 3D printing methods for the fabrication of key components. Whether simply to investigate flow phenomena, test new designs or fabricate final-product components with custom features, the use of 3D printing can critically drive this field of research towards better performing energy-storage systems. The latest and most representative examples of redox flow battery studies will be discussed, categorized in relation to the electrolyte used and whether the devices are employed in aqueous or non-aqueous applications.     

3D printing of conjugated polymers

Three‐dimensional (3D) printing brings exciting prospects to the realm of conjugated polymers (CPs) and organic electronics through vastly enhanced design flexibility, structural complexity, and environmental sustainability. However, the use of 3D printing for CPs is still in its infancy and remains full of challenges. In this review, we highlight recent studies that demonstrate proof‐of‐concept strategies to mitigate some of these problems. Two general additive manufacturing approaches are featured: direct ink writing and vat photopolymerization. We conclude with an outlook for this thriving field of research and draw attention to the new possibilities that 3D printing can bring to CPs. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1592–1605     

3D printed polylactic acid nanocomposite scaffolds for tissue engineering applications

In this study, biodegradable polylactic acid (PLA) and PLA nanocomposite scaffolds reinforced with magnetic and conductive fillers, were processed via fused filament fabrication additive manufacturing and their bioactivity and biodegradation characteristics were examined. Porous 3D architectures with 50% bulk porosity were 3D printed, and their physicochemical properties were evaluated. Thermal analysis confirmed the presence of ~18 wt% of carbon nanostructures (CNF and GNP; nowonwards CNF) and ~37 wt% of magnetic iron oxide (Fe₂O₃) particles in the filaments. The in vitro degradation tests of scaffolds showed porous and fractured struts after 2 and 4 weeks of immersion in DMEM respectively, although a negligible weight loss is observed. Greater extent of degradation is observed in PLA with magnetic fillers followed by PLA with conductive fillers and neat PLA. In vitro bioactivity study of scaffolds indicate enhancement from ~2.9% (PLA) to ~5.32% (PLA/CNF) and ~ 3.12% (PLA/Fe₂O₃). Stiffness calculated from the compression tests showed decrease from ~680 MPa (PLA) to 533 MPa and 425 MPa for PLA/CNF and PLA/Fe₂O₃ respectively. Enhanced bioactivity and faster biodegradation response of PLA nanocomposites with conductive fillers make them a potential candidate for tissue engineering applications such as scaffold bone replacement and regeneration.     

The influence of grafted cellulose nanofibers and postextrusion annealing treatment on selected properties of poly(lactic acid) filaments for 3D printing

l ‐lactide monomers were grafted onto cellulose nanofibers (CNFs) via ring‐opening polymerization, forming poly(lactic acid) grafted cellulose nanofibers (PLA‐g‐CNFs). PLA‐g‐CNFs and pristine PLA were then blended in chloroform and dried to prepare a master batch. PLA‐g‐CNFs/PLA composite filaments targeted for 3D printing were produced by compounding the master batch in PLA matrix and melt extrusion. The as‐extruded composite filaments were subsequently thermal annealed in a conventional oven, and their morphological, thermal, and mechanical properties were evaluated. PLA was successfully grafted on the surface of CNFs as demonstrated by elemental analysis, and the concentration of grafted PLA was estimated to be 33 wt %. The grafted PLA were highly crystallized, contributing to the growth of crystalline regions of PLA matrix. The incorporation of PLA‐g‐CNFs improved storage modulus of the composite filaments in both low temperature glassy state and high temperature rubbery state. Postextrusion annealing treatment led to 28 and 63% increases for tensile modulus and strength of the filaments, respectively. Simulated Young's moduli from the Halpin‐Tsai and Krenchel models were found comparable with the experimental values. The formed composite filaments are suitable for use in 3D printing. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 847–855     

3D printed biodegradable composites: An insight into mechanical properties of PLA/chitosan scaffold

Three-dimensional (3D) printing is a frontier manufacturing approach with great potential to benefit biomedical and patient care sectors. In the last decades, different types of biomedical materials were investigated in purpose of developing medical tools and devices. The present study attempts to assess mechanical performances (namely: tensile, compression, and flexural) of the newly developed chitosan-reinforced poly-lactic-acid (PLA) scaffolds by using fused filament fabrication (FFF) based 3D printing technology. Specifically, the effects of chitosan loading, infill density and annealing temperature on mechanical behavior of PLA composite scaffolds are investigated via design of experiments. Moreover, fracture behavior under various load types is studied with the help of selective electron microscopy. It is found that the strength of the produced composite samples depends significantly on the loading of chitosan and infill density, while annealing temperature does not affect mechanical response. Overall, the developed PLA composite scaffolds are mechanically efficient and they appear suitable for clinical purposes.     

3D Printing of Monolithic Proteinaceous Cantilevers Using Regenerated Silk Fibroin

Silk fibroin, regenerated from Bombyx mori, has shown considerable promise as a printable, aqueous-based ink using a bioinspired salt-bath system in our previous work. Here, we further developed and characterized silk fibroin inks that exhibit concentration-dependent fluorescence spectra at the molecular level. These insights supported extrusion-based 3D printing using concentrated silk fibroin solutions as printing inks. 3D monolithic proteinaceous structures with high aspect ratios were successfully printed using these approaches, including cantilevers only supported at one end. This work provides further insight and broadens the utility of 3D printing with silk fibroin inks for the microfabrication of proteinaceous structures.     

Miniaturized free-flow electrophoresis: production,optimization, and application using 3D printing technology

The increasing resolution of three-dimensional (3D) printing offers simplified access to, and development of, microfluidic devices with complex 3D structures. Therefore, this technology is increasingly used for rapid prototyping in laboratories and industry. Microfluidic free flow electrophoresis (μFFE) is a versatile tool to separate and concentrate different samples (such as DNA, proteins, and cells) to different outlets in a time range measured in mere tens of seconds and offers great potential for use in downstream processing, for example. However, the production of μFFE devices is usually rather elaborate. Many designs are based on chemical pretreatment or manual alignment for the setup. Especially for the separation chamber of a μFFE device, this is a crucial step which should be automatized. We have developed a smart 3D design of a μFFE to pave the way for a simpler production. This study presents (1) a robust and reproducible way to build up critical parts of a μFFE device based on high-resolution MultiJet 3D printing; (2) a simplified insertion of commercial polycarbonate membranes to segregate separation and electrode chambers; and (3) integrated, 3D-printed wells that enable a defined sample fractionation (chip-to-world interface). In proof of concept experiments both a mixture of fluorescence dyes and a mixture of amino acids were successfully separated in our 3D-printed μFFE device.     

一种用于FDM型3D打印的改性PBT

以对苯二甲酸(PTA)、间苯二甲酸(PIA)、癸二酸(SA)和1,4-丁二醇(BDO)为原料,通过直接酯化和减压缩聚的方法制备了一种适合熔融沉积打印(FDM)型3D打印的改性聚对苯二甲酸丁二醇酯(PBT)——聚对苯二甲酸间苯二甲酸癸二酸丁二醇酯(PBTIS)。采用核磁共振氢谱(1 H-NMR)、凝胶渗透色谱法(GPC)、差示扫描量热法(DSC)、黏度计和熔体仪、万能电子拉力机和冲击试验机分别研究了其热性能、流变性能和力学性能。研究表明:当n(PTA)∶n(PIA)=7∶3,SA的物质的量分数为3%~5%时,PBTIS具有合适的熔点、良好的拉伸强度和弯曲强度及悬梁缺口冲击强度等力学性能。用桌面拉丝挤出机将PBTIS样品制成卷材并用3D打印机打印,结果表明其可以流畅地打印出所设计的三维物件。     

FDM 3D printing of combustible structures: First results

For the first time, complex geometry combustible structures of an ammonium perchlorate–polylactic acid composite have been successfully printed using fused deposition modeling (FDM). The structural and energetic capabilities of the printed structures are demonstrated. Combined with the ability to be produced by FDM printing, these combustible elements could afford many practical applications.     

Functionalized acrylic polyhydroxy urethanes as molecular tool box for photocurable thermosets and 3D printing

Liquid urethane (meth)acrylates represent attractive components of photocurable thermosets for applications ranging from coatings and adhesives to 3D printing. Herein we tailor liquid polyfunctional urethane methacrylates (UMA) derived from acrylic polyhydroxy urethanes. Cyclic carbonate methacrylates react with diamines to form dihydroxy-functional urethane dimethacrylates. In an “one-pot” process the hydroxy groups are functionalized either by reaction with 2-isocyanatoethyl methacrylate (IEMA) or by esterification with methacrylic anhydride (MAA) and acetic anhydride (AA). The hydroxy group esterification substantially lowers the resin viscosity (26–156 Pa•s). Hydroxy functionalization with IEMA and MAA affords tetrafunctional methacrylates. The corresponding photo-cured thermosets exhibit higher crosslinking density and improved stiffness as reflected by increasing the Young's modulus from 2900 to 3700 MPa combined with increasing the glass temperature from 135 to 204°C. Hence, this facile molecular UMA design enables to control functionality and thermoset properties over a wide range and meets the demands of 3D printing applications.     

Electrospun aligned nanofibers: A review

Electrospinning (e-spinning) is famous for the construction and production of ultrafine and continuous micro-/nanofibers. Then, the alignment of electrospun (e-spun) nanofibers becomes one of the most valuable research topics. Because aligned fibers have more advantages over random fibers, such as better mechanical properties, faster charge transport, more regular spatial structure, etc. This review summarizes various electrospinning techniques of fabricating aligned e-spun nanofibers, such as early conventional methods, near-field e-spinning, and three-dimensional (3D) printing e-spinning. Among them, four auxiliary preparation methods (e.g., auxiliary solid template, auxiliary liquid, auxiliary electromagnetic field and auxiliary airflow), two collection modes (static and dynamic collection), and the controllability of near-field e-spinning and 3D printing e-spinning are highlighted. The representative applications depending on aligned nanofibers are classified and briefly introduced, emphasizing in the fields of 1D applications (e.g., field-effect transistor, nanochannel and guidance carrier), 2D applications (e.g., platform for gas detection, filter, and electrode materials storage), and 3D applications (e.g., bioengineering, supercapacitor, and nanogenerator). At last, the challenges and prospects are addressed.     

3D打印生物医用材料研究进展

3D打印(亦称增材制造)技术因其独特的材料成型优势,在组织工程、航空航天、汽车制造、以及电子工业等众多领域显示出巨大的应用潜力。然而,在实际生物医学应用中,3D打印生物器件和组织器官除了要求具有复杂的结构和优异的生物学性能外,其打印结构的表面性质也需满足某些特定的要求,如3D打印组织骨架和器官必须具有生物相容性、抗菌性及细胞粘附性等。因此,将3D打印与传统表面修饰技术相结合,在不改变材料三维结构的基础上调控其表面生物化学性质,从而赋予3D打印生物骨架器官多功能化,可实现更为广泛的应用。本文以3D打印生物骨架及器官的表面修饰为主要内容对就近年来3D打印生物医用材料的最新研究进展进行了综述。