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3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Processing and Engineering".

Deadline for manuscript submissions: closed (20 November 2020) | Viewed by 96985

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Special Issue Editors

Prof. Dr. Naba Dutta

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Guest Editor

School of Engineering, Chemical and Environmental Engineering, RMIT University, Melbourne 3000, Australia
Interests: polymer; biopolymer; biomimetic polymer; bioinspired functional materials; nanomaterials; organic-inorganic hybrids; energy materials; electrodes; fuel cell; electrocatalysis

Prof. Namita Roy Choudhury

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Guest Editor

Chemical and Environmental Engineering, School of Engineering, RMIT University, Melbourne, VIC 3000, Australia
Interests: polymer engineering and science; colloid and polymer science; interfacial engineering; surface coating; biomimetic protein polymer; graphene hybrids & ink; elastic gel; advanced polymer for energy and biomedical applications

Special Issue Information

Dear Colleagues,

This Special Issue is dedicated to recent advances and innovations in additive manufacturing (AM) and 3D/4D printing—terms that are used interchangeably—with polymers, polymer hydrogels, and adaptive soft materials. The intention is to capture advances in both materials and methods, technical challenges, and future perspectives. AM is a set of emerging technologies that enable fabrication of components using a simple layer-by-layer technique, which has continued to evolve through over 40 years of development. AM enables integration of computer-aided design and visualization of complex components and their efficient, reliable and flawless manufacturing. In general, AM embodies seven process categories namely, VAT photo-polymerisation, material jetting, binder jetting, material extrusion, powder bed fusion, sheet lamination, and directed energy deposition, and is considered to be one of the most versatile and promising technologies of this century. AM provides freedom of design, easy prototyping, customization, streamlined logistics, and opportunities to manufacture existing products in a new way and to create complex new products and shapes previously impossible using traditional fabrication methods.

The promising applications of 3D-printing are very broad across many industrial sectors including the aerospace, defense, automotive and construction industry. Moreover, AM is developing its capabilities at an accelerated pace in several medical fields including orthopedics, dentistry, hearing care, and surgery. With 3D scanning and printing techniques, patients can potentially have access to personalized prosthesis thoroughly tailored and customized to their exact body measurements. It is envisioned that the feasibility of four-dimensional (4D), a more recent and evolving AM technique, will potentially revolutionize biomedicine and customized prosthesis. 4D printing is a key enabler with a significant competitive advantage over 3D and involves 3D printing with smart materials that can respond to external stimuli and it also permits the creation of on-demand dynamically controllable shapes autonomously without human intervention. The key to 4D printing lies in the use of innovative adaptive materials. It has been predicted that AM market will reach ~$21 billion by 2020. Nevertheless, progression of AM is also facing significant challenges including product standardization, high cost of equipment and products, knowledge gap and complexity in intellectual property issues.

The goal of this Special Issue is to publish original research articles, as well as critical reviews and perspectives as well as communications and letters from leaders, in both academia and industry, on all aspects related to the recent advances in 3D/4D printing with polymers, polymer hydrogels, and adaptive soft materials.

Prof. Dr. Naba Dutta
Prof. Namita Roy Choudhury
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Additive manufacturing
3-D/4-D printing
Fused deposition modeling
Filament extrusion
Processing technologies
Process–property relationship
Engineering polymers
Thermoplastic elastomer material
Stimulus-responsive hydrogels
Responsive polymers
Adaptive materials
Soft materials
Composites

Published Papers (13 papers)

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Research

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14 pages, 2893 KiB

Open AccessArticle

Characterization of Polycaprolactone Nanohydroxyapatite Composites with Tunable Degradability Suitable for Indirect Printing

by Stephanie E. Doyle, Lauren Henry, Ellen McGennisken, Carmine Onofrillo, Claudia Di Bella, Serena Duchi, Cathal D. O'Connell and Elena Pirogova

Polymers 2021, 13(2), 295; https://doi.org/10.3390/polym13020295 - 18 Jan 2021

Cited by 21 | Viewed by 3096

Abstract

Degradable bone implants are designed to foster the complete regeneration of natural tissue after large-scale loss trauma. Polycaprolactone (PCL) and hydroxyapatite (HA) composites are promising scaffold materials with superior mechanical and osteoinductive properties compared to the single materials. However, producing three-dimensional (3D) structures with high HA content as well as tuneable degradability remains a challenge. To address this issue and create homogeneously distributed PCL-nanoHA (nHA) scaffolds with tuneable degradation rates through both PCL molecular weight and nHA concentration, we conducted a detailed characterisation and comparison of a range of PCL-nHA composites across three molecular weight PCLs (14, 45, and 80 kDa) and with nHA content up to 30% w/w. In general, the addition of nHA results in an increase of viscosity for the PCL-nHA composites but has little effect on their compressive modulus. Importantly, we observe that the addition of nHA increases the rate of degradation compared to PCL alone. We show that the 45 and 80 kDa PCL-nHA groups can be fabricated via indirect 3D printing and have homogenously distributed nHA even after fabrication. Finally, the cytocompatibility of the composite materials is evaluated for the 45 and 80 kDa groups, with the results showing no significant change in cell number compared to the control. In conclusion, our analyses unveil several features that are crucial for processing the composite material into a tissue engineered implant. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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19 pages, 9842 KiB

Open AccessArticle

Photocurable Methacrylate Derivatives of Polylactide: A Two-Stage Synthesis in Supercritical Carbon Dioxide and 3D Laser Structuring

by Vladislav S. Kaplin, Nikolay N. Glagolev, Valentina T. Shashkova, Irina A. Matveeva, Ilya V. Shershnev, Tatyana S. Zarkhina, Nikita V. Minaev, Nadezhda A. Aksenova, Boris S. Shavkuta, Evgeny A. Bezrukov, Aleksandr S. Kopylov, Daria S. Kuznetsova, Anastasiia I. Shpichka, Peter S. Timashev and Anna B. Solovieva

Polymers 2020, 12(11), 2525; https://doi.org/10.3390/polym12112525 - 29 Oct 2020

Cited by 3 | Viewed by 2130

Abstract

A two-stage polylactide modification was performed in the supercritical carbon dioxide medium using the urethane formation reaction. The modification resulted in the synthesis of polymerizable methacrylate derivatives of polylactide for application in the spatial 3D structuring by laser stereolithography. The use of the supercritical carbon dioxide medium allowed us to obtain for the first time polymerizable oligomer-polymer systems in the form of dry powders convenient for further application in the preparation of polymer compositions for photocuring. The photocuring of the modified polymers was performed by laser stereolithography and two-photon crosslinking. Using nanoindentation, we found that Young’s modulus of the cured compositions corresponded to the standard characteristics of implants applied in regenerative medicine. As shown by thermogravimetric analysis, the degree of crosslinking and, hence, the local stiffness of scaffolds were determined by the amount of the crosslinking agent and the photocuring regime. No cytotoxicity was observed for the structures. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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19 pages, 24030 KiB

Open AccessArticle

Research of TPU Materials for 3D Printing Aiming at Non-Pneumatic Tires by FDM Method

by Jun Wang, Bin Yang, Xiang Lin, Lei Gao, Tao Liu, Yonglai Lu and Runguo Wang

Polymers 2020, 12(11), 2492; https://doi.org/10.3390/polym12112492 - 27 Oct 2020

Cited by 50 | Viewed by 6773

Abstract

3D printing technology has been widely used in various fields, such as biomedicine, clothing design, and aerospace, due to its personalized customization, rapid prototyping of complex structures, and low cost. However, the application of 3D printing technology in the field of non-pneumatic tires has not been systematically studied. In this study, we evaluated the application of potential thermoplastic polyurethanes (TPU) materials based on FDM technology in the field of non-pneumatic tires. First, the printing process of TPU material based on fused deposition modeling (FDM) technology was studied through tensile testing and SEM observation. The results show that the optimal 3D printing temperature of the selected TPU material is 210 °C. FDM technology was successfully applied to 3D printed non-pneumatic tires based on TPU material. The study showed that the three-dimensional stiffness of 3D printed non-pneumatic tires is basically 50% of that obtained by simulation. To guarantee the prediction of the performance of 3D printed non-pneumatic tires, we suggest that the performance of these materials should be moderately reduced during the structural design for performance simulation. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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19 pages, 6661 KiB

Open AccessArticle

3D Printed Silicone Meniscus Implants: Influence of the 3D Printing Process on Properties of Silicone Implants

by Eric Luis, Houwen Matthew Pan, Anil Kumar Bastola, Ram Bajpai, Swee Leong Sing, Juha Song and Wai Yee Yeong

Polymers 2020, 12(9), 2136; https://doi.org/10.3390/polym12092136 - 18 Sep 2020

Cited by 34 | Viewed by 5586

Abstract

Osteoarthritis of the knee with meniscal pathologies is a severe meniscal pathology suffered by the aging population worldwide. However, conventional meniscal substitutes are not 3D-printable and lack the customizability of 3D printed implants and are not mechanically robust enough for human implantation. Similarly, 3D printed hydrogel scaffolds suffer from drawbacks of being mechanically weak and as a result patients are unable to execute immediate post-surgical weight-bearing ambulation and rehabilitation. To solve this problem, we have developed a 3D silicone meniscus implant which is (1) cytocompatible, (2) resistant to cyclic loading and mechanically similar to native meniscus, and (3) directly 3D printable. The main focus of this study is to determine whether the purity, composition, structure, dimensions and mechanical properties of silicone implants are affected by the use of a custom-made in-house 3D-printer. We have used the phosphate buffer saline (PBS) absorption test, Fourier transform infrared (FTIR) spectroscopy, surface profilometry, thermo-gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) to effectively assess and compare material properties between molded and 3D printed silicone samples. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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11 pages, 7505 KiB

Open AccessArticle

Effect of Absorbent Foam Filling on Mechanical Behaviors of 3D-Printed Honeycombs

by Leilei Yan, Keyu Zhu, Yunwei Zhang, Chun Zhang and Xitao Zheng

Polymers 2020, 12(9), 2059; https://doi.org/10.3390/polym12092059 - 10 Sep 2020

Cited by 17 | Viewed by 3629

Abstract

Polylactic acid (PLA) hexagonal honeycomb structures were fabricated by using 3D-printing technology. By filling with absorbent polymethacrylimide (PMI) foam, a novel absorbent-foam-filled 3D-printed honeycomb was obtained. The in-plane (L- and W-direction) and out-of-plane (T-direction) compressive performances were studied experimentally and numerically. Due to absorbent PMI foam filling, the elastic modulus, compressive strength, energy absorption per unit volume, and energy absorption per unit mass of absorbent-foam-filled honeycomb under L-direction were increased by 296.34%, 168.75%, 505.57%, and 244.22%, respectively. Moreover, the elastic modulus, compressive strength, energy absorption per unit volume, and energy absorption per unit mass, under W-direction, also have increments of 211.65%, 179.85, 799.45%, and 413.02%, respectively. However, for out-of-plane compression, the compressive strength and energy absorption per unit volume were enhanced, but the density has also been increased; thus, it is not competitive in energy absorption per unit mass. Failure mechanism and dimension effects of absorbent-foam-filled honeycomb were also considered. The approach of absorbent foam filling made the 3D-printed honeycomb structure more competitive in electromagnetic wave stealth applications, while acting simultaneously as load-carrying structures. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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19 pages, 11646 KiB

Open AccessArticle

Mechanical Performances of Lightweight Sandwich Structures Produced by Material Extrusion-Based Additive Manufacturing

by Sebastian Marian Zaharia, Larisa Anamaria Enescu and Mihai Alin Pop

Polymers 2020, 12(8), 1740; https://doi.org/10.3390/polym12081740 - 04 Aug 2020

Cited by 53 | Viewed by 9989

Abstract

Material Extrusion-Based Additive Manufacturing Process (ME-AMP) via Fused Filament Fabrication (FFF) offers a higher geometric flexibility than conventional technologies to fabricate thermoplastic lightweight sandwich structures. This study used polylactic acid/polyhydroxyalkanoate (PLA/PHA) biodegradable material and a 3D printer to manufacture lightweight sandwich structures with honeycomb, diamond-celled and corrugated core shapes as a single part. In this paper, compression, three-point bending and tensile tests were performed to evaluate the performance of lightweight sandwich structures with different core topologies. In addition, the main failure modes of the sandwich structures subjected to mechanical tests were evaluated. The main failure modes that were observed from mechanical tests of the sandwich structure were the following: face yielding, face wrinkling, core/skin debonding. Elasto-plastic finite element analysis allowed predicting the global behavior of the structure and stressing distribution in the elements of lightweight sandwich structures. The comparison between the results of bending experiments and finite element analyses indicated acceptable similarity in terms of failure behavior and force reactions. Finally, the three honeycomb, diamond-celled and corrugated core typologies were used in the leading edge of the wing and were impact tested and the results created favorable premises for using such structures on aircraft models and helicopter blade structures. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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21 pages, 5828 KiB

Open AccessArticle

Flame-Retardant Polyamide Powder for Laser Sintering: Powder Characterization, Processing Behavior and Component Properties

by Kevin Schneider, Katrin Wudy and Dietmar Drummer

Polymers 2020, 12(8), 1697; https://doi.org/10.3390/polym12081697 - 29 Jul 2020

Cited by 11 | Viewed by 3277

Abstract

Up to now, laser-sintered components have been barely used by industries such as aerospace and transport industry due to high flammability. By the use of flame retardants, the flammability of laser-sintered parts should be reduced to extend their range of possible applications. This paper aims to investigate the influence of halogen-free phosphinate-based flame retardants on process-relevant characteristics and process behavior, as well as mechanical and physical properties. Most importantly, the flammability of the material should be reduced. Two different types of phosphinate-based fillers were used in a concentration between 10 and 25 wt % in combination with the matrix material polyamide 12 (PA12). Thermal, optical, and powder properties of the mixtures were analytically investigated. Furthermore, the mechanical characterization of the sintered specimen was carried out. The addition of filler in laser sintering changes the process behavior and properties of the component. With this investigation, the correlation among flame retardants, process-relevant characteristics, process behavior, and resulting part properties was derived for the first time. Finally, a mixture of 15–20 wt % of flame retardant leads to the best trade-off between flame retardancy and mechanical properties. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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13 pages, 6396 KiB

Open AccessArticle

The Photoinitiator Lithium Phenyl (2,4,6-Trimethylbenzoyl) Phosphinate with Exposure to 405 nm Light Is Cytotoxic to Mammalian Cells but Not Mutagenic in Bacterial Reverse Mutation Assays

by Alexander K. Nguyen, Peter L. Goering, Rosalie K. Elespuru, Srilekha Sarkar Das and Roger J. Narayan

Polymers 2020, 12(7), 1489; https://doi.org/10.3390/polym12071489 - 03 Jul 2020

Cited by 31 | Viewed by 6146

Abstract

Lithium phenyl (2,4,6-trimethylbenzoyl) phosphinate (LAP) is a free radical photo-initiator used to initiate free radical chain polymerization upon light exposure, and is combined with gelatin methacryloyl (GelMA) to produce a photopolymer used in bioprinting. The free radicals produced under bioprinting conditions are potentially cytotoxic and mutagenic. Since these photo-generated free radicals are highly-reactive but short-lived, toxicity assessments should be conducted with light exposure. In this study, photorheology determined that 10 min exposure to 9.6 mW/cm² 405 nm light from an LED light source fully crosslinked 10 wt % GelMA with >3.4 mmol/L LAP, conditions that were used for subsequent cytotoxicity and mutagenicity assessments. These conditions were cytotoxic to M-1 mouse kidney collecting duct cells, a cell type susceptible to lithium toxicity. Exposure to ≤17 mmol/L (0.5 wt %) LAP without light was not cytotoxic; however, concurrent exposure to ≥3.4 mmol/L LAP and light was cytotoxic. No condition of LAP and/or light exposure evaluated was mutagenic in bacterial reverse mutation assays using S. typhimurium strains TA98, TA100 and E. coli WP2 uvrA. These data indicate that the combination of LAP and free radicals generated from photo-excited LAP is cytotoxic, but mutagenicity was not observed in bacteria under typical bioprinting conditions. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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11 pages, 6348 KiB

Open AccessEditor’s ChoiceArticle

A Simplified 2D Numerical Simulation of Photopolymerization Kinetics and Oxygen Diffusion–Reaction for the Continuous Liquid Interface Production (CLIP) System

by Kentaro Taki

Polymers 2020, 12(4), 875; https://doi.org/10.3390/polym12040875 - 10 Apr 2020

Cited by 13 | Viewed by 3163

Abstract

Additive manufacturing is a versatile technology for producing customized 3D products. In 2015, the Continuous Liquid Interface Production (CLIP) system was developed as a part of projection-type, UV-curable resin 3D printers. The CLIP system utilized the dead zone where oxygen inhibition occurs and prevents the UV-cured product from adhering to the UV illumination window. The CLIP system successfully produced complex shapes in a short time. This study investigated how the relationship between the photopolymerization rate, oxygen inhibition rate, and oxygen diffusion rate affects the shape of the product by means of a numerical simulation of the photopolymerization kinetics with oxygen diffusion and reaction. The results indicate that the vertical production speed and transmittance of UV light are crucial to controlling the conversion and shape precision of products. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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Review

Jump to: Research

39 pages, 1795 KiB

Open AccessReview

Additive Manufacturing of Polymer Materials: Progress, Promise and Challenges

by Saad Saleh Alghamdi, Sabu John, Namita Roy Choudhury and Naba K. Dutta

Polymers 2021, 13(5), 753; https://doi.org/10.3390/polym13050753 - 28 Feb 2021

Cited by 150 | Viewed by 22374

Abstract

The use of additive manufacturing (AM) has moved well beyond prototyping and has been established as a highly versatile manufacturing method with demonstrated potential to completely transform traditional manufacturing in the future. In this paper, a comprehensive review and critical analyses of the recent advances and achievements in the field of different AM processes for polymers, their composites and nanocomposites, elastomers and multi materials, shape memory polymers and thermo-responsive materials are presented. Moreover, their applications in different fields such as bio-medical, electronics, textiles, and aerospace industries are also discussed. We conclude the article with an account of further research needs and future perspectives of AM process with polymeric materials. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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24 pages, 4369 KiB

Open AccessReview

3D Printable Electrically Conductive Hydrogel Scaffolds for Biomedical Applications: A Review

by Sandya Shiranthi Athukorala, Tuan Sang Tran, Rajkamal Balu, Vi Khanh Truong, James Chapman, Naba Kumar Dutta and Namita Roy Choudhury

Polymers 2021, 13(3), 474; https://doi.org/10.3390/polym13030474 - 02 Feb 2021

Cited by 71 | Viewed by 10180

Abstract

Electrically conductive hydrogels (ECHs), an emerging class of biomaterials, have garnered tremendous attention due to their potential for a wide variety of biomedical applications, from tissue-engineered scaffolds to smart bioelectronics. Along with the development of new hydrogel systems, 3D printing of such ECHs is one of the most advanced approaches towards rapid fabrication of future biomedical implants and devices with versatile designs and tuneable functionalities. In this review, an overview of the state-of-the-art 3D printed ECHs comprising conductive polymers (polythiophene, polyaniline and polypyrrole) and/or conductive fillers (graphene, MXenes and liquid metals) is provided, with an insight into mechanisms of electrical conductivity and design considerations for tuneable physiochemical properties and biocompatibility. Recent advances in the formulation of 3D printable bioinks and their practical applications are discussed; current challenges and limitations of 3D printing of ECHs are identified; new 3D printing-based hybrid methods for selective deposition and fabrication of controlled nanostructures are highlighted; and finally, future directions are proposed. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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18 pages, 2685 KiB

Open AccessEditor’s ChoiceReview

Photo-Crosslinked Silk Fibroin for 3D Printing

by Xuan Mu, Jugal Kishore Sahoo, Peggy Cebe and David L. Kaplan

Polymers 2020, 12(12), 2936; https://doi.org/10.3390/polym12122936 - 09 Dec 2020

Cited by 55 | Viewed by 8858

Abstract

Silk fibroin in material formats provides robust mechanical properties, and thus is a promising protein for 3D printing inks for a range of applications, including tissue engineering, bioelectronics, and bio-optics. Among the various crosslinking mechanisms, photo-crosslinking is particularly useful for 3D printing with silk fibroin inks due to the rapid kinetics, tunable crosslinking dynamics, light-assisted shape control, and the option to use visible light as a biocompatible processing condition. Multiple photo-crosslinking approaches have been applied to native or chemically modified silk fibroin, including photo-oxidation and free radical methacrylate polymerization. The molecular characteristics of silk fibroin, i.e., conformational polymorphism, provide a unique method for crosslinking and microfabrication via light. The molecular design features of silk fibroin inks and the exploitation of photo-crosslinking mechanisms suggest the exciting potential for meeting many biomedical needs in the future. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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33 pages, 1680 KiB

Open AccessReview

An Overview of Additive Manufacturing of Polymers and Associated Composites

by Shukantu Dev Nath and Sabrina Nilufar

Polymers 2020, 12(11), 2719; https://doi.org/10.3390/polym12112719 - 17 Nov 2020

Cited by 84 | Viewed by 10695

Abstract

Additive manufacturing is rapidly evolving and opening new possibilities for many industries. This article gives an overview of the current status of additive manufacturing with polymers and polymer composites. Various types of reinforcements in polymers and architectured cellular material printing including the auxetic metamaterials and the triply periodic minimal surface structures are discussed. Finally, applications, current challenges, and future directions are highlighted here. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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