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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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Review

42 pages, 12062 KiB  
Review
FDM-Based 3D Printing of Polymer and Associated Composite: A Review on Mechanical Properties, Defects and Treatments
by Sachini Wickramasinghe, Truong Do and Phuong Tran
Polymers 2020, 12(7), 1529; https://doi.org/10.3390/polym12071529 - 10 Jul 2020
Cited by 565 | Viewed by 36599
Abstract
Fused deposition modelling (FDM) is one of the fastest-growing additive manufacturing methods used in printing fibre-reinforced composites (FRC). The performances of the resulting printed parts are limited compared to those by other manufacturing methods due to their inherent defects. Hence, the effort to [...] Read more.
Fused deposition modelling (FDM) is one of the fastest-growing additive manufacturing methods used in printing fibre-reinforced composites (FRC). The performances of the resulting printed parts are limited compared to those by other manufacturing methods due to their inherent defects. Hence, the effort to develop treatment methods to overcome these drawbacks has accelerated during the past few years. The main focus of this study is to review the impact of those defects on the mechanical performance of FRC and therefore to discuss the available treatment methods to eliminate or minimize them in order to enhance the functional properties of the printed parts. As FRC is a combination of polymer matrix material and continuous or short reinforcing fibres, this review will thoroughly discuss both thermoplastic polymers and FRCs printed via FDM technology, including the effect of printing parameters such as layer thickness, infill pattern, raster angle and fibre orientation. The most common defects on printed parts, in particular, the void formation, surface roughness and poor bonding between fibre and matrix, are explored. An inclusive discussion on the effectiveness of chemical, laser, heat and ultrasound treatments to minimize these drawbacks is provided by this review. Full article
(This article belongs to the Section Polymer Processing and Engineering)
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18 pages, 3146 KiB  
Review
Present Status in Polymeric Mouthguards. A Future Area for Additive Manufacturing?
by Ana M. Sousa, Ana C. Pinho, Ana Messias and Ana P. Piedade
Polymers 2020, 12(7), 1490; https://doi.org/10.3390/polym12071490 - 3 Jul 2020
Cited by 26 | Viewed by 9676
Abstract
Athletes from contact sports are more prone to orofacial injuries because of the exposure to possible shocks and collisions derived from physical proximity. The use of protector polymeric mouthguards proved to be useful in the prevention of the described injuries. There are different [...] Read more.
Athletes from contact sports are more prone to orofacial injuries because of the exposure to possible shocks and collisions derived from physical proximity. The use of protector polymeric mouthguards proved to be useful in the prevention of the described injuries. There are different types of mouthguards with varying ranges of protection and prices, but they are all made from polymers and share the same propose: to absorb and dissipate the impact energy resulting from the shocks. As they are used inside the mouth, they should not impair breathing and speaking nor compromise the comfort of the athlete. However, the ideal mouthguard is yet to be created. The choice of the most appropriate polymeric material and the standard required properties have not yet been reported. Regardless of the numerous studies in this field, normalized control parameters for both material characterization and mouthguard fabrication are absent. This paper aims to present a review of the current types of available mouthguards and their properties/characteristics. Moreover, a detailed description of the most common polymers for the fabrication of mouthguards, together with the manufacturing techniques, are discussed. Full article
(This article belongs to the Special Issue Polymer Connect: Polymer Science and Composite Materials)
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45 pages, 3261 KiB  
Review
Stimuli-Responsive Polymeric Nanocarriers for Drug Delivery, Imaging, and Theragnosis
by Sabya Sachi Das, Priyanshu Bharadwaj, Muhammad Bilal, Mahmood Barani, Abbas Rahdar, Pablo Taboada, Simona Bungau and George Z. Kyzas
Polymers 2020, 12(6), 1397; https://doi.org/10.3390/polym12061397 - 22 Jun 2020
Cited by 327 | Viewed by 16579
Abstract
In the past few decades, polymeric nanocarriers have been recognized as promising tools and have gained attention from researchers for their potential to efficiently deliver bioactive compounds, including drugs, proteins, genes, nucleic acids, etc., in pharmaceutical and biomedical applications. Remarkably, these polymeric nanocarriers [...] Read more.
In the past few decades, polymeric nanocarriers have been recognized as promising tools and have gained attention from researchers for their potential to efficiently deliver bioactive compounds, including drugs, proteins, genes, nucleic acids, etc., in pharmaceutical and biomedical applications. Remarkably, these polymeric nanocarriers could be further modified as stimuli-responsive systems based on the mechanism of triggered release, i.e., response to a specific stimulus, either endogenous (pH, enzymes, temperature, redox values, hypoxia, glucose levels) or exogenous (light, magnetism, ultrasound, electrical pulses) for the effective biodistribution and controlled release of drugs or genes at specific sites. Various nanoparticles (NPs) have been functionalized and used as templates for imaging systems in the form of metallic NPs, dendrimers, polymeric NPs, quantum dots, and liposomes. The use of polymeric nanocarriers for imaging and to deliver active compounds has attracted considerable interest in various cancer therapy fields. So-called smart nanopolymer systems are built to respond to certain stimuli such as temperature, pH, light intensity and wavelength, and electrical, magnetic and ultrasonic fields. Many imaging techniques have been explored including optical imaging, magnetic resonance imaging (MRI), nuclear imaging, ultrasound, photoacoustic imaging (PAI), single photon emission computed tomography (SPECT), and positron emission tomography (PET). This review reports on the most recent developments in imaging methods by analyzing examples of smart nanopolymers that can be imaged using one or more imaging techniques. Unique features, including nontoxicity, water solubility, biocompatibility, and the presence of multiple functional groups, designate polymeric nanocues as attractive nanomedicine candidates. In this context, we summarize various classes of multifunctional, polymeric, nano-sized formulations such as liposomes, micelles, nanogels, and dendrimers. Full article
(This article belongs to the Special Issue Polymeric Materials for Drug Delivery Application)
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22 pages, 4131 KiB  
Review
Solar Cells for Indoor Applications: Progress and Development
by Swarup Biswas and Hyeok Kim
Polymers 2020, 12(6), 1338; https://doi.org/10.3390/polym12061338 - 12 Jun 2020
Cited by 82 | Viewed by 8712
Abstract
The Internet of things (IoT) has been rapidly growing in the past few years. IoT connects numerous devices, such as wireless sensors, actuators, and wearable devices, to optimize and monitor daily activities. Most of these devices require power in the microwatt range and [...] Read more.
The Internet of things (IoT) has been rapidly growing in the past few years. IoT connects numerous devices, such as wireless sensors, actuators, and wearable devices, to optimize and monitor daily activities. Most of these devices require power in the microwatt range and operate indoors. To this end, a self-sustainable power source, such as a photovoltaic (PV) cell, which can harvest low-intensity indoor light, is appropriate. Recently, the development of highly efficient PV cells for indoor applications has attracted tremendous attention. Therefore, different types of PV materials, such as inorganic, dye-sensitized, organic, and perovskite materials, have been employed for harvesting low-intensity indoor light energy. Although considerable efforts have been made by researchers to develop low-cost, stable, and efficient PV cells for indoor applications, Extensive investigation is necessary to resolve some critical issues concerning PV cells, such as environmental stability, lifetime, large-area fabrication, mechanical flexibility, and production cost. To address these issues, a systematic review of these aspects will be highly useful to the research community. This study discusses the current status of the development of indoor PV cells based on previous reports. First, we have provided relevant background information. Then, we have described the different indoor light sources, and subsequently critically reviewed previous reports regarding indoor solar cells based on different active materials such as inorganic, dye-sensitized, organic, and perovskite. Finally, we have placed an attempt to provide insight into factors needed to further improve the feasibility of PV technology for indoor applications. Full article
(This article belongs to the Special Issue Photovoltaic Semiconductor Materials)
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14 pages, 1439 KiB  
Review
The Modelling of Extrusion Processes for Polymers—A Review
by Marko Hyvärinen, Rowshni Jabeen and Timo Kärki
Polymers 2020, 12(6), 1306; https://doi.org/10.3390/polym12061306 - 8 Jun 2020
Cited by 79 | Viewed by 19865
Abstract
Extrusion processes are widely used in industries that aim to produce advanced solutions for increasingly sophisticated demands in the plastic, food, and pharmaceutical sectors. Though the process has been in use since the 1930s, limited information is available on the analytical computation of [...] Read more.
Extrusion processes are widely used in industries that aim to produce advanced solutions for increasingly sophisticated demands in the plastic, food, and pharmaceutical sectors. Though the process has been in use since the 1930s, limited information is available on the analytical computation of extrusion. Generally, production has been carried out based on empirical experience and trial-and-error approaches. The development of industrial operations is, however, best addressed by modelling the processes involved, and the flow of polymer melts and fibers in extruders has been subjected to some previous studies. Also included an overview of design of a die as well as challenges in sheet/film production. This article systematically and critically reviews the literature related to the process design, machine design, process parameters, flow models, and flow analysis of extrusion with a focus on modelling the extrusion of composite materials. Full article
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24 pages, 3183 KiB  
Review
Chitosan-Based Drug Delivery System: Applications in Fish Biotechnology
by Yuanbing Wu, Ania Rashidpour, María Pilar Almajano and Isidoro Metón
Polymers 2020, 12(5), 1177; https://doi.org/10.3390/polym12051177 - 21 May 2020
Cited by 70 | Viewed by 8372
Abstract
Chitosan is increasingly used for safe nucleic acid delivery in gene therapy studies, due to well-known properties such as bioadhesion, low toxicity, biodegradability and biocompatibility. Furthermore, chitosan derivatization can be easily performed to improve the solubility and stability of chitosan–nucleic acid polyplexes, and [...] Read more.
Chitosan is increasingly used for safe nucleic acid delivery in gene therapy studies, due to well-known properties such as bioadhesion, low toxicity, biodegradability and biocompatibility. Furthermore, chitosan derivatization can be easily performed to improve the solubility and stability of chitosan–nucleic acid polyplexes, and enhance efficient target cell drug delivery, cell uptake, intracellular endosomal escape, unpacking and nuclear import of expression plasmids. As in other fields, chitosan is a promising drug delivery vector with great potential for the fish farming industry. This review highlights state-of-the-art assays using chitosan-based methodologies for delivering nucleic acids into cells, and focuses attention on recent advances in chitosan-mediated gene delivery for fish biotechnology applications. The efficiency of chitosan for gene therapy studies in fish biotechnology is discussed in fields such as fish vaccination against bacterial and viral infection, control of gonadal development and gene overexpression and silencing for overcoming metabolic limitations, such as dependence on protein-rich diets and the low glucose tolerance of farmed fish. Finally, challenges and perspectives on the future developments of chitosan-based gene delivery in fish are also discussed. Full article
(This article belongs to the Special Issue Functional Chitosan-Based Composites)
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10 pages, 648 KiB  
Review
Lignin as a UV Light Blocker—A Review
by Hasan Sadeghifar and Arthur Ragauskas
Polymers 2020, 12(5), 1134; https://doi.org/10.3390/polym12051134 - 15 May 2020
Cited by 230 | Viewed by 13450
Abstract
Lignin is the by-product of pulp and paper industries and bio-refining operations. It is available as the leading natural phenolic biopolymer in the market. It has chromophore functional groups and can absorb a broad spectrum of UV light in range of 250–400 nm. [...] Read more.
Lignin is the by-product of pulp and paper industries and bio-refining operations. It is available as the leading natural phenolic biopolymer in the market. It has chromophore functional groups and can absorb a broad spectrum of UV light in range of 250–400 nm. Using lignin as a natural ingredient in sunscreen cream, transparent film, paints, varnishes and microorganism protection has been actively investigated. Both in non-modified and modified forms, lignin provides enhancing UV protection of commercial products with less than a 10% blend with other material. In mixtures with other synthetic UV blockers, lignin indicated synergic effects and increased final UV blocking potential in compare with using only synthetic UV blocker or lignin. However, using lignin as a UV blocker is also challenging due to its complex structure, polydispersity in molecular weight, brownish color and some impurities that require more research in order to make it an ideal bio-based UV blocker. Full article
(This article belongs to the Special Issue Progress in Lignin Value-Added Polymers)
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22 pages, 2905 KiB  
Review
Production of Sustainable and Biodegradable Polymers from Agricultural Waste
by Chrysanthos Maraveas
Polymers 2020, 12(5), 1127; https://doi.org/10.3390/polym12051127 - 14 May 2020
Cited by 210 | Viewed by 27207
Abstract
Agro-wastes are derived from diverse sources including grape pomace, tomato pomace, pineapple, orange, and lemon peels, sugarcane bagasse, rice husks, wheat straw, and palm oil fibers, among other affordable and commonly available materials. The carbon-rich precursors are used in the production bio-based polymers [...] Read more.
Agro-wastes are derived from diverse sources including grape pomace, tomato pomace, pineapple, orange, and lemon peels, sugarcane bagasse, rice husks, wheat straw, and palm oil fibers, among other affordable and commonly available materials. The carbon-rich precursors are used in the production bio-based polymers through microbial, biopolymer blending, and chemical methods. The Food and Agriculture Organization (FAO) estimates that 20–30% of fruits and vegetables are discarded as waste during post-harvest handling. The development of bio-based polymers is essential, considering the scale of global environmental pollution that is directly linked to the production of synthetic plastics such as polypropylene (PP) and polyethylene (PET). Globally, 400 million tons of synthetic plastics are produced each year, and less than 9% are recycled. The optical, mechanical, and chemical properties such as ultraviolet (UV) absorbance, tensile strength, and water permeability are influenced by the synthetic route. The production of bio-based polymers from renewable sources and microbial synthesis are scalable, facile, and pose a minimal impact on the environment compared to chemical synthesis methods that rely on alkali and acid treatment or co-polymer blending. Despite the development of advanced synthetic methods and the application of biofilms in smart/intelligent food packaging, construction, exclusion nets, and medicine, commercial production is limited by cost, the economics of production, useful life, and biodegradation concerns, and the availability of adequate agro-wastes. New and cost-effective production techniques are critical to facilitate the commercial production of bio-based polymers and the replacement of synthetic polymers. Full article
(This article belongs to the Special Issue Biodegradable and Sustainable Polymers)
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28 pages, 3967 KiB  
Review
A Review on Barrier Properties of Poly(Lactic Acid)/Clay Nanocomposites
by Shuvra Singha and Mikael S. Hedenqvist
Polymers 2020, 12(5), 1095; https://doi.org/10.3390/polym12051095 - 11 May 2020
Cited by 70 | Viewed by 7431
Abstract
Poly(lactic acid) (PLA) is considered to be among the best biopolymer substitutes for the existing petroleum-based polymers in the field of food packaging owing to its renewability, biodegradability, non-toxicity and mechanical properties. However, PLA displays only moderate barrier properties to gases, vapors and [...] Read more.
Poly(lactic acid) (PLA) is considered to be among the best biopolymer substitutes for the existing petroleum-based polymers in the field of food packaging owing to its renewability, biodegradability, non-toxicity and mechanical properties. However, PLA displays only moderate barrier properties to gases, vapors and organic compounds, which can limit its application as a packaging material. Hence, it becomes essential to understand the mass transport properties of PLA and address the transport challenges. Significant improvements in the barrier properties can be achieved by incorporating two-dimensional clay nanofillers, the planes of which create tortuosity to the diffusing molecules, thereby increasing the effective length of the diffusion path. This article reviews the literature on barrier properties of PLA/clay nanocomposites. The important PLA/clay nanocomposite preparation techniques, such as solution intercalation, melt processing and in situ polymerization, are outlined followed by an extensive account of barrier performance of nanocomposites drawn from the literature. Fundamentals of mass transport phenomena and the factors affecting mass transport are also presented. Furthermore, mathematical models that have been proposed/used to predict the permeability in polymer/clay nanocomposites are reviewed and the extent to which the models are validated in PLA/clay composites is discussed. Full article
(This article belongs to the Special Issue Performance and Application of Novel Biocomposites)
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20 pages, 2506 KiB  
Review
Functional Micro- and Nanofibers Obtained by Nonwoven Post-Modification
by Tomasz Kowalczyk
Polymers 2020, 12(5), 1087; https://doi.org/10.3390/polym12051087 - 10 May 2020
Cited by 23 | Viewed by 3978
Abstract
Micro- and nanofibers are historically-known materials that are continuously reinvented due to their valuable properties. They display promise for applications in many fields, from tissue engineering to catalysis or sensors. In the first application, micro- and nanofibers are mainly produced from a limited [...] Read more.
Micro- and nanofibers are historically-known materials that are continuously reinvented due to their valuable properties. They display promise for applications in many fields, from tissue engineering to catalysis or sensors. In the first application, micro- and nanofibers are mainly produced from a limited library of biomaterials with properties that need alteration before use. Post-modification is a very effective method for attaining on-demand features and functions of nonwovens. This review summarizes and presents methods of functionalization of nonwovens produced by electrostatic means. The reviewed modifications are grouped into physical methods, chemical modification, and mixed methods. Full article
(This article belongs to the Special Issue Functional Electrospun Nanofibers)
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23 pages, 2446 KiB  
Review
Activation Energies and Temperature Dependencies of the Rates of Crystallization and Melting of Polymers
by Sergey Vyazovkin
Polymers 2020, 12(5), 1070; https://doi.org/10.3390/polym12051070 - 7 May 2020
Cited by 66 | Viewed by 8663
Abstract
The objective of this review paper is to survey the phase transition kinetics with a focus on the temperature dependence of the rates of crystallization and melting, as well as on the activation energies of these processes obtained via the Arrhenius kinetic treatment, [...] Read more.
The objective of this review paper is to survey the phase transition kinetics with a focus on the temperature dependence of the rates of crystallization and melting, as well as on the activation energies of these processes obtained via the Arrhenius kinetic treatment, including the treatment by isoconversional methods. The literature is analyzed to track the development of the basic models and their underlying concepts. The review presents both theoretical and practical considerations regarding the kinetic analysis of crystallization and melting. Both processes are demonstrated to be kinetically complex, and this is revealed in the form of nonlinear Arrhenius plots and/or the variation of the activation energy with temperature. Principles which aid one to understand and interpret such results are discussed. An emphasis is also put on identifying proper computational methods and experimental data that can lead to meaningful kinetic interpretation. Full article
(This article belongs to the Special Issue Recent Developments on Calorimetry and Thermal Analysis of Polymers and Nanocomposites)
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30 pages, 7109 KiB  
Review
Water-Soluble Photoinitiators in Biomedical Applications
by Wiktoria Tomal and Joanna Ortyl
Polymers 2020, 12(5), 1073; https://doi.org/10.3390/polym12051073 - 7 May 2020
Cited by 166 | Viewed by 26521
Abstract
Light-initiated polymerization processes are currently an important tool in various industrial fields. The advancement of technology has resulted in the use of photopolymerization in various biomedical applications, such as the production of 3D hydrogel structures, the encapsulation of cells, and in drug delivery [...] Read more.
Light-initiated polymerization processes are currently an important tool in various industrial fields. The advancement of technology has resulted in the use of photopolymerization in various biomedical applications, such as the production of 3D hydrogel structures, the encapsulation of cells, and in drug delivery systems. The use of photopolymerization processes requires an appropriate initiating system that, in biomedical applications, must meet additional criteria such as high water solubility, non-toxicity to cells, and compatibility with visible low-power light sources. This article is a literature review on those compounds that act as photoinitiators of photopolymerization processes in biomedical applications. The division of initiators according to the method of photoinitiation was described and the related mechanisms were discussed. Examples from each group of photoinitiators are presented, and their benefits, limitations, and applications are outlined. Full article
(This article belongs to the Special Issue Biomedical Polymer Materials II)
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25 pages, 4090 KiB  
Review
Potential Natural Fiber Polymeric Nanobiocomposites: A Review
by K. M. Faridul Hasan, Péter György Horváth and Tibor Alpár
Polymers 2020, 12(5), 1072; https://doi.org/10.3390/polym12051072 - 7 May 2020
Cited by 172 | Viewed by 16583
Abstract
Composite materials reinforced with biofibers and nanomaterials are becoming considerably popular, especially for their light weight, strength, exceptional stiffness, flexural rigidity, damping property, longevity, corrosion, biodegradability, antibacterial, and fire-resistant properties. Beside the traditional thermoplastic and thermosetting polymers, nanoparticles are also receiving attention in [...] Read more.
Composite materials reinforced with biofibers and nanomaterials are becoming considerably popular, especially for their light weight, strength, exceptional stiffness, flexural rigidity, damping property, longevity, corrosion, biodegradability, antibacterial, and fire-resistant properties. Beside the traditional thermoplastic and thermosetting polymers, nanoparticles are also receiving attention in terms of their potential to improve the functionality and mechanical performances of biocomposites. These remarkable characteristics have made nanobiocomposite materials convenient to apply in aerospace, mechanical, construction, automotive, marine, medical, packaging, and furniture industries, through providing environmental sustainability. Nanoparticles (TiO2, carbon nanotube, rGO, ZnO, and SiO2) are easily compatible with other ingredients (matrix polymer and biofibers) and can thus form nanobiocomposites. Nanobiocomposites are exhibiting a higher market volume with the expansion of new technology and green approaches for utilizing biofibers. The performances of nanobiocomposites depend on the manufacturing processes, types of biofibers used, and the matrix polymer (resin). An overview of different natural fibers (vegetable/plants), nanomaterials, biocomposites, nanobiocomposites, and manufacturing methods are discussed in the context of potential application in this review. Full article
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22 pages, 2274 KiB  
Review
Recent Advances in Tissue Adhesives for Clinical Medicine
by Liangpeng Ge and Shixuan Chen
Polymers 2020, 12(4), 939; https://doi.org/10.3390/polym12040939 - 18 Apr 2020
Cited by 101 | Viewed by 13334
Abstract
Tissue adhesives have attracted more attention to the applications of non-invasive wound closure. The purpose of this review article is to summarize the recent progress of developing tissue adhesives, which may inspire researchers to develop more outstanding tissue adhesives. It begins with a [...] Read more.
Tissue adhesives have attracted more attention to the applications of non-invasive wound closure. The purpose of this review article is to summarize the recent progress of developing tissue adhesives, which may inspire researchers to develop more outstanding tissue adhesives. It begins with a brief introduction to the emerging potential use of tissue adhesives in the clinic. Next, several critical mechanisms for adhesion are discussed, including van der Waals forces, capillary forces, hydrogen bonding, static electric forces, and chemical bonds. This article further details the measurement methods of adhesion and highlights the different types of adhesive, including natural or biological, synthetic and semisynthetic, and biomimetic adhesives. Finally, this review article concludes with remarks on the challenges and future directions for design, fabrication, and application of tissue adhesives in the clinic. This review article has promising potential to provide novel creative design principles for the generation of future tissue adhesives. Full article
(This article belongs to the Special Issue Advanced Polymeric Biomaterials for Tissue Engineering)
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38 pages, 2947 KiB  
Review
Recent Advances in Bioplastics: Application and Biodegradation
by Tanja Narancic, Federico Cerrone, Niall Beagan and Kevin E. O’Connor
Polymers 2020, 12(4), 920; https://doi.org/10.3390/polym12040920 - 15 Apr 2020
Cited by 219 | Viewed by 30347
Abstract
The success of oil-based plastics and the continued growth of production and utilisation can be attributed to their cost, durability, strength to weight ratio, and eight contributions to the ease of everyday life. However, their mainly single use, durability and recalcitrant nature have [...] Read more.
The success of oil-based plastics and the continued growth of production and utilisation can be attributed to their cost, durability, strength to weight ratio, and eight contributions to the ease of everyday life. However, their mainly single use, durability and recalcitrant nature have led to a substantial increase of plastics as a fraction of municipal solid waste. The need to substitute single use products that are not easy to collect has inspired a lot of research towards finding sustainable replacements for oil-based plastics. In addition, specific physicochemical, biological, and degradation properties of biodegradable polymers have made them attractive materials for biomedical applications. This review summarises the advances in drug delivery systems, specifically design of nanoparticles based on the biodegradable polymers. We also discuss the research performed in the area of biophotonics and challenges and opportunities brought by the design and application of biodegradable polymers in tissue engineering. We then discuss state-of-the-art research in the design and application of biodegradable polymers in packaging and emphasise the advances in smart packaging development. Finally, we provide an overview of the biodegradation of these polymers and composites in managed and unmanaged environments. Full article
(This article belongs to the Special Issue Recent Advances in Bioplastics II)
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38 pages, 2616 KiB  
Review
Proteins and Peptides as Important Modifiers of the Polymer Scaffolds for Tissue Engineering Applications—A Review
by Katarzyna Klimek and Grazyna Ginalska
Polymers 2020, 12(4), 844; https://doi.org/10.3390/polym12040844 - 6 Apr 2020
Cited by 133 | Viewed by 9911
Abstract
Polymer scaffolds constitute a very interesting strategy for tissue engineering. Even though they are generally non-toxic, in some cases, they may not provide suitable support for cell adhesion, proliferation, and differentiation, which decelerates tissue regeneration. To improve biological properties, scaffolds are frequently enriched [...] Read more.
Polymer scaffolds constitute a very interesting strategy for tissue engineering. Even though they are generally non-toxic, in some cases, they may not provide suitable support for cell adhesion, proliferation, and differentiation, which decelerates tissue regeneration. To improve biological properties, scaffolds are frequently enriched with bioactive molecules, inter alia extracellular matrix proteins, adhesive peptides, growth factors, hormones, and cytokines. Although there are many papers describing synthesis and properties of polymer scaffolds enriched with proteins or peptides, few reviews comprehensively summarize these bioactive molecules. Thus, this review presents the current knowledge about the most important proteins and peptides used for modification of polymer scaffolds for tissue engineering. This paper also describes the influence of addition of proteins and peptides on physicochemical, mechanical, and biological properties of polymer scaffolds. Moreover, this article sums up the major applications of some biodegradable natural and synthetic polymer scaffolds modified with proteins and peptides, which have been developed within the past five years. Full article
(This article belongs to the Special Issue Biodegradable Polymer Scaffolds for Tissue Engineering)
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59 pages, 21028 KiB  
Review
Application of the Finite Element Method in the Analysis of Composite Materials: A Review
by Sarah David Müzel, Eduardo Pires Bonhin, Nara Miranda Guimarães and Erick Siqueira Guidi
Polymers 2020, 12(4), 818; https://doi.org/10.3390/polym12040818 - 4 Apr 2020
Cited by 126 | Viewed by 21163
Abstract
The use of composite materials in several sectors, such as aeronautics and automotive, has been gaining distinction in recent years. However, due to their high costs, as well as unique characteristics, consequences of their heterogeneity, they present challenging gaps to be studied. As [...] Read more.
The use of composite materials in several sectors, such as aeronautics and automotive, has been gaining distinction in recent years. However, due to their high costs, as well as unique characteristics, consequences of their heterogeneity, they present challenging gaps to be studied. As a result, the finite element method has been used as a way to analyze composite materials subjected to the most distinctive situations. Therefore, this work aims to approach the modeling of composite materials, focusing on material properties, failure criteria, types of elements and main application sectors. From the modeling point of view, different levels of modeling—micro, meso and macro, are presented. Regarding properties, different mechanical characteristics, theories and constitutive relationships involved to model these materials are presented. The text also discusses the types of elements most commonly used to simulate composites, which are solids, peel, plate and cohesive, as well as the various failure criteria developed and used for the simulation of these materials. In addition, the present article lists the main industrial sectors in which composite material simulation is used, and their gains from it, including aeronautics, aerospace, automotive, naval, energy, civil, sports, manufacturing and even electronics. Full article
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20 pages, 4647 KiB  
Review
A Mini-Review on Anion Exchange and Chelating Polymers for Applications in Hydrometallurgy, Environmental Protection, and Biomedicine
by Piotr Cyganowski and Anna Dzimitrowicz
Polymers 2020, 12(4), 784; https://doi.org/10.3390/polym12040784 - 2 Apr 2020
Cited by 15 | Viewed by 4129
Abstract
The rapidly increasing demand for technologies aiming to resolve challenges of separations and environmental protection causes a sharp increase in the demand for ion exchange (IX) and chelating polymers. These unique materials can offer target-selective adsorption properties vital for the removal or recovery [...] Read more.
The rapidly increasing demand for technologies aiming to resolve challenges of separations and environmental protection causes a sharp increase in the demand for ion exchange (IX) and chelating polymers. These unique materials can offer target-selective adsorption properties vital for the removal or recovery of harmful and precious materials, where trace concentrations thereof make other techniques insufficient. Hence, recent achievements in syntheses of IX and chelating resins designed and developed in our research group are discussed within this mini-review. The aim of the present work is to reveal that, due to the diversified and unique physiochemical characteristics of the proposed materials, they are not limited to traditional separation techniques and could be used in multifunctional areas of applications, including catalysis, heat management, and biomedicine. Full article
(This article belongs to the Special Issue Colloid and Interface)
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26 pages, 7328 KiB  
Review
Thermal Welding by the Third Phase Between Polymers: A Review for Ultrasonic Weld Technology Developments
by Jianhui Qiu, Guohong Zhang, Eiichi Sakai, Wendi Liu and Limin Zang
Polymers 2020, 12(4), 759; https://doi.org/10.3390/polym12040759 - 31 Mar 2020
Cited by 28 | Viewed by 6678
Abstract
Ultrasonic welding (USW) is a promising method for the welds between dissimilar materials. Ultrasonic thermal welding by the third phase (TWTP) method was proposed in combination with the formation of a third phase, which was confirmed as an effective technology for polymer welding [...] Read more.
Ultrasonic welding (USW) is a promising method for the welds between dissimilar materials. Ultrasonic thermal welding by the third phase (TWTP) method was proposed in combination with the formation of a third phase, which was confirmed as an effective technology for polymer welding between the two dissimilar materials compared with the traditional USW. This review focused on the advances of applying the ultrasonic TWTP for thermoplastic materials. The research development on the ultrasonic TWTP of polycarbonate (PC) and polymethyl methacrylate (PMMA), polylactic acid (PLA) and polyformaldehyde (POM), and PLA and PMMA are summarized according to the preparation of the third phase, welded strength, morphologies of rupture surfaces, thermal stability, and others. The review aimed at providing guidance for using ultrasonic TWTP in polymers and a basic understanding of the welding mechanism, i.e., interdiffusion and molecular motion mechanisms between the phases. Full article
(This article belongs to the Special Issue Processing and Molding of Polymers)
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25 pages, 3195 KiB  
Review
Influence of Nanoparticles on Thermal and Electrical Conductivity of Composites
by Divan Coetzee, Mohanapriya Venkataraman, Jiri Militky and Michal Petru
Polymers 2020, 12(4), 742; https://doi.org/10.3390/polym12040742 - 27 Mar 2020
Cited by 104 | Viewed by 8579
Abstract
This review analyzes thermal and electrically conductive properties of composites and how they can be influenced by the addition of special nanoparticles. Composite functional characteristics—such as thermal and electrical conductivity, phase changes, dimensional stability, magnetization, and modulus increase—are tuned by selecting suitable nanoparticle [...] Read more.
This review analyzes thermal and electrically conductive properties of composites and how they can be influenced by the addition of special nanoparticles. Composite functional characteristics—such as thermal and electrical conductivity, phase changes, dimensional stability, magnetization, and modulus increase—are tuned by selecting suitable nanoparticle filler material. The conductivity of composites can be related to the formation of conductive pathways as nanofiller materials form connections in the bulk of a composite matrix. With increasing use of nanomaterial containing composites and relatively little understanding of the toxicological effects thereof, adequate disposal and recyclability have become an increasing environmental concern. Full article
(This article belongs to the Special Issue Damage Mechanics of Polymer Composites)
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29 pages, 2039 KiB  
Review
Recent Progress on Luminescent Metal-Organic Framework-Involved Hybrid Materials for Rapid Determination of Contaminants in Environment and Food
by Chi-Xuan Yao, Ning Zhao, Ji-Chao Liu, Li-Jun Chen, Jing-Min Liu, Guo-Zhen Fang and Shuo Wang
Polymers 2020, 12(3), 691; https://doi.org/10.3390/polym12030691 - 20 Mar 2020
Cited by 50 | Viewed by 7421
Abstract
The high speed of contaminants growth needs the burgeoning of new analytical techniques to keep up with the continuous demand for monitoring and legislation on food safety and environmental pollution control. Metal-organic frameworks (MOFs) are a kind of advanced crystal porous materials with [...] Read more.
The high speed of contaminants growth needs the burgeoning of new analytical techniques to keep up with the continuous demand for monitoring and legislation on food safety and environmental pollution control. Metal-organic frameworks (MOFs) are a kind of advanced crystal porous materials with controllable apertures, which are self-assembled by organic ligands and inorganic metal nodes. They have the merits of large specific surface areas, high porosity and the diversity of structures and functions. Latterly, the utilization of metal-organic frameworks has attracted much attention in environmental protection and the food industry. MOFs have exhibited great value as sensing materials for many targets. Among many sensing methods, fluorometric sensing is one of the widely studied methods in the detection of harmful substances in food and environmental samples. Fluorometric detection based on MOFs and its functional materials is currently one of the most key research subjects in the food and environmental fields. It has gradually become a hot research direction to construct the highly sensitive rapid sensors to detect harmful substances in the food matrix based on metal-organic frameworks. In this paper, we introduced the synthesis and detection application characteristics (absorption, fluorescence, etc.) of metal-organic frameworks. We summarized their applications in the MOFs-based fluorometric detection of harmful substances in food and water over the past few years. The harmful substances mainly include heavy metals, organic pollutants and other small molecules, etc. On this basis, the future development and possible application of the MOFs have prospected in this review paper. Full article
(This article belongs to the Special Issue Polymers in Agriculture and Food Science)
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33 pages, 7363 KiB  
Review
Hybrid Sol–gel Coatings for Corrosion Mitigation: A Critical Review
by Rita B. Figueira
Polymers 2020, 12(3), 689; https://doi.org/10.3390/polym12030689 - 19 Mar 2020
Cited by 80 | Viewed by 9536
Abstract
The corrosion process is a major source of metallic material degradation, particularly in aggressive environments, such as marine ones. Corrosion progression affects the service life of a given metallic structure, which may end in structural failure, leakage, product loss and environmental pollution linked [...] Read more.
The corrosion process is a major source of metallic material degradation, particularly in aggressive environments, such as marine ones. Corrosion progression affects the service life of a given metallic structure, which may end in structural failure, leakage, product loss and environmental pollution linked to large financial costs. According to NACE, the annual cost of corrosion worldwide was estimated, in 2016, to be around 3%–4% of the world’s gross domestic product. Therefore, the use of methodologies for corrosion mitigation are extremely important. The approaches used can be passive or active. A passive approach is preventive and may be achieved by emplacing a barrier layer, such as a coating that hinders the contact of the metallic substrate with the aggressive environment. An active approach is generally employed when the corrosion is set in. That seeks to reduce the corrosion rate when the protective barrier is already damaged and the aggressive species (i.e., corrosive agents) are in contact with the metallic substrate. In this case, this is more a remediation methodology than a preventive action, such as the use of coatings. The sol-gel synthesis process, over the past few decades, gained remarkable importance in diverse areas of application. Sol–gel allows the combination of inorganic and organic materials in a single-phase and has led to the development of organic–inorganic hybrid (OIH) coatings for several applications, including for corrosion mitigation. This manuscript succinctly reviews the fundamentals of sol–gel concepts and the parameters that influence the processing techniques. The state-of-the-art of the OIH sol–gel coatings reported in the last few years for corrosion protection, are also assessed. Lastly, a brief perspective on the limitations, standing challenges and future perspectives of the field are critically discussed. Full article
(This article belongs to the Special Issue Sol-Gel Chemistry in Polymers Research)
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26 pages, 4263 KiB  
Review
Coumarins into Polyurethanes for Smart and Functional Materials
by José María Cuevas, Rubén Seoane-Rivero, Rodrigo Navarro and Ángel Marcos-Fernández
Polymers 2020, 12(3), 630; https://doi.org/10.3390/polym12030630 - 10 Mar 2020
Cited by 26 | Viewed by 6418
Abstract
Polyurethanes are of undoubted interest for the scientific community and the industry. Their outstanding versatility from tailor-made structures turns them into major polymers for use in a wide range of different applications. As with other polymers, new, emerging molecules and monomers with specific [...] Read more.
Polyurethanes are of undoubted interest for the scientific community and the industry. Their outstanding versatility from tailor-made structures turns them into major polymers for use in a wide range of different applications. As with other polymers, new, emerging molecules and monomers with specific attributes can provide new functions and capabilities to polyurethanes. Natural and synthetic coumarin and its derivatives are characterised by interesting biological, photophysical and photochemical properties. Then, the polyurethanes can exploit those features of many coumarins which are present in their composition to achieve new functions and performances. This article reviews the developments in the proper use of the special properties of coumarins in polyurethanes to produce functional and smart materials that can be suitable for new specific applications. Full article
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18 pages, 3193 KiB  
Review
Hydrogel-Based Colloidal Photonic Crystal Devices for Glucose Sensing
by Wenwei Tang and Cheng Chen
Polymers 2020, 12(3), 625; https://doi.org/10.3390/polym12030625 - 9 Mar 2020
Cited by 56 | Viewed by 8913
Abstract
Diabetes, a common epidemic disease, is increasingly hazardous to human health. Monitoring body glucose concentrations for the prevention and therapy of diabetes has become very important. Hydrogel-based responsive photonic crystal (PC) materials are noninvasive options for glucose detection. This article reviews glucose-sensing materials/devices [...] Read more.
Diabetes, a common epidemic disease, is increasingly hazardous to human health. Monitoring body glucose concentrations for the prevention and therapy of diabetes has become very important. Hydrogel-based responsive photonic crystal (PC) materials are noninvasive options for glucose detection. This article reviews glucose-sensing materials/devices composed of hydrogels and colloidal photonic crystals (CPCs), including the construction of 2D/3D CPCs and 2D/3D hydrogel-based CPCs (HCPCs). The development and mechanisms of glucose-responsive hydrogels and the achieved technologies of HCPC glucose sensors were also concluded. This review concludes by showing a perspective for the future design of CPC glucose biosensors with functional hydrogels. Full article
(This article belongs to the Special Issue Biodegradable Polymers for Biomedical Application)
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30 pages, 4737 KiB  
Review
Polymer- and Hybrid-Based Biomaterials for Interstitial, Connective, Vascular, Nerve, Visceral and Musculoskeletal Tissue Engineering
by Anatolii Abalymov, Bogdan Parakhonskiy and Andre G. Skirtach
Polymers 2020, 12(3), 620; https://doi.org/10.3390/polym12030620 - 9 Mar 2020
Cited by 68 | Viewed by 7294
Abstract
In this review, materials based on polymers and hybrids possessing both organic and inorganic contents for repairing or facilitating cell growth in tissue engineering are discussed. Pure polymer based biomaterials are predominantly used to target soft tissues. Stipulated by possibilities of tuning the [...] Read more.
In this review, materials based on polymers and hybrids possessing both organic and inorganic contents for repairing or facilitating cell growth in tissue engineering are discussed. Pure polymer based biomaterials are predominantly used to target soft tissues. Stipulated by possibilities of tuning the composition and concentration of their inorganic content, hybrid materials allow to mimic properties of various types of harder tissues. That leads to the concept of “one-matches-all” referring to materials possessing the same polymeric base, but different inorganic content to enable tissue growth and repair, proliferation of cells, and the formation of the ECM (extra cellular matrix). Furthermore, adding drug delivery carriers to coatings and scaffolds designed with such materials brings additional functionality by encapsulating active molecules, antibacterial agents, and growth factors. We discuss here materials and methods of their assembly from a general perspective together with their applications in various tissue engineering sub-areas: interstitial, connective, vascular, nervous, visceral and musculoskeletal tissues. The overall aims of this review are two-fold: (a) to describe the needs and opportunities in the field of bio-medicine, which should be useful for material scientists, and (b) to present capabilities and resources available in the area of materials, which should be of interest for biologists and medical doctors. Full article
(This article belongs to the Special Issue Bioactive Polymer Scaffolds and Thin Films for Biomedical Applications: State-of-the-Art and Challenges)
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32 pages, 1301 KiB  
Review
Progress in Polymeric Nano-Medicines for Theranostic Cancer Treatment
by Imran Ali, Mosa Alsehli, Luciana Scotti, Marcus Tullius Scotti, Shang-Ting Tsai, Ruei-Siang Yu, Ming Fa Hsieh and Jung-Chih Chen
Polymers 2020, 12(3), 598; https://doi.org/10.3390/polym12030598 - 6 Mar 2020
Cited by 86 | Viewed by 8394
Abstract
Cancer is a life-threatening disease killing millions of people globally. Among various medical treatments, nano-medicines are gaining importance continuously. Many nanocarriers have been developed for treatment, but polymerically-based ones are acquiring importance due to their targeting capabilities, biodegradability, biocompatibility, capacity for drug loading [...] Read more.
Cancer is a life-threatening disease killing millions of people globally. Among various medical treatments, nano-medicines are gaining importance continuously. Many nanocarriers have been developed for treatment, but polymerically-based ones are acquiring importance due to their targeting capabilities, biodegradability, biocompatibility, capacity for drug loading and long blood circulation time. The present article describes progress in polymeric nano-medicines for theranostic cancer treatment, which includes cancer diagnosis and treatment in a single dosage form. The article covers the applications of natural and synthetic polymers in cancer diagnosis and treatment. Efforts were also made to discuss the merits and demerits of such polymers; the status of approved nano-medicines; and future perspectives. Full article
(This article belongs to the Special Issue Polymeric Colloidal Materials for Biomedical Applications)
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22 pages, 2296 KiB  
Review
Poly(N-isopropylacrylamide)-Based Thermoresponsive Composite Hydrogels for Biomedical Applications
by Xiaomin Xu, Yang Liu, Wenbo Fu, Mingyu Yao, Zhen Ding, Jiaming Xuan, Dongxiang Li, Shengjie Wang, Yongqing Xia and Meiwen Cao
Polymers 2020, 12(3), 580; https://doi.org/10.3390/polym12030580 - 5 Mar 2020
Cited by 250 | Viewed by 19798
Abstract
Poly(N-isopropylacrylamide) (PNIPAM)-based thermosensitive hydrogels demonstrate great potential in biomedical applications. However, they have inherent drawbacks such as low mechanical strength, limited drug loading capacity and low biodegradability. Formulating PNIPAM with other functional components to form composited hydrogels is an effective strategy to make [...] Read more.
Poly(N-isopropylacrylamide) (PNIPAM)-based thermosensitive hydrogels demonstrate great potential in biomedical applications. However, they have inherent drawbacks such as low mechanical strength, limited drug loading capacity and low biodegradability. Formulating PNIPAM with other functional components to form composited hydrogels is an effective strategy to make up for these deficiencies, which can greatly benefit their practical applications. This review seeks to provide a comprehensive observation about the PNIPAM-based composite hydrogels for biomedical applications so as to guide related research. It covers the general principles from the materials choice to the hybridization strategies as well as the performance improvement by focusing on several application areas including drug delivery, tissue engineering and wound dressing. The most effective strategies include incorporation of functional inorganic nanoparticles or self-assembled structures to give composite hydrogels and linking PNIPAM with other polymer blocks of unique properties to produce copolymeric hydrogels, which can improve the properties of the hydrogels by enhancing the mechanical strength, giving higher biocompatibility and biodegradability, introducing multi-stimuli responsibility, enabling higher drug loading capacity as well as controlled release. These aspects will be of great help for promoting the development of PNIPAM-based composite materials for biomedical applications. Full article
(This article belongs to the Special Issue Stimuli-Sensitive Amphiphilic Polymers and Their Biomedical Applications)
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20 pages, 5993 KiB  
Review
Solvent-Free Approaches for the Processing of Scaffolds in Regenerative Medicine
by Víctor Santos-Rosales, Ana Iglesias-Mejuto and Carlos A. García-González
Polymers 2020, 12(3), 533; https://doi.org/10.3390/polym12030533 - 2 Mar 2020
Cited by 37 | Viewed by 5527
Abstract
The regenerative medicine field is seeking novel strategies for the production of synthetic scaffolds that are able to promote the in vivo regeneration of a fully functional tissue. The choices of the scaffold formulation and the manufacturing method are crucial to determine the [...] Read more.
The regenerative medicine field is seeking novel strategies for the production of synthetic scaffolds that are able to promote the in vivo regeneration of a fully functional tissue. The choices of the scaffold formulation and the manufacturing method are crucial to determine the rate of success of the graft for the intended tissue regeneration process. On one hand, the incorporation of bioactive compounds such as growth factors and drugs in the scaffolds can efficiently guide and promote the spreading, differentiation, growth, and proliferation of cells as well as alleviate post-surgical complications such as foreign body responses and infections. On the other hand, the manufacturing method will determine the feasible morphological properties of the scaffolds and, in certain cases, it can compromise their biocompatibility. In the case of medicated scaffolds, the manufacturing method has also a key effect in the incorporation yield and retained activity of the loaded bioactive agents. In this work, solvent-free methods for scaffolds production, i.e., technological approaches leading to the processing of the porous material with no use of solvents, are presented as advantageous solutions for the processing of medicated scaffolds in terms of efficiency and versatility. The principles of these solvent-free technologies (melt molding, 3D printing by fused deposition modeling, sintering of solid microspheres, gas foaming, and compressed CO2 and supercritical CO2-assisted foaming), a critical discussion of advantages and limitations, as well as selected examples for regenerative medicine purposes are herein presented. Full article
(This article belongs to the Special Issue Bioactive Polymer Scaffolds and Thin Films for Biomedical Applications: State-of-the-Art and Challenges)
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17 pages, 535 KiB  
Review
Studies of Cellulose and Starch Utilization and the Regulatory Mechanisms of Related Enzymes in Fungi
by Bao-Teng Wang, Shuang Hu, Xing-Ye Yu, Long Jin, Yun-Jia Zhu and Feng-Jie Jin
Polymers 2020, 12(3), 530; https://doi.org/10.3390/polym12030530 - 2 Mar 2020
Cited by 74 | Viewed by 6968
Abstract
Polysaccharides are biopolymers made up of a large number of monosaccharides joined together by glycosidic bonds. Polysaccharides are widely distributed in nature: Some, such as peptidoglycan and cellulose, are the components that make up the cell walls of bacteria and plants, and some, [...] Read more.
Polysaccharides are biopolymers made up of a large number of monosaccharides joined together by glycosidic bonds. Polysaccharides are widely distributed in nature: Some, such as peptidoglycan and cellulose, are the components that make up the cell walls of bacteria and plants, and some, such as starch and glycogen, are used as carbohydrate storage in plants and animals. Fungi exist in a variety of natural environments and can exploit a wide range of carbon sources. They play a crucial role in the global carbon cycle because of their ability to break down plant biomass, which is composed primarily of cell wall polysaccharides, including cellulose, hemicellulose, and pectin. Fungi produce a variety of enzymes that in combination degrade cell wall polysaccharides into different monosaccharides. Starch, the main component of grain, is also a polysaccharide that can be broken down into monosaccharides by fungi. These monosaccharides can be used for energy or as precursors for the biosynthesis of biomolecules through a series of enzymatic reactions. Industrial fermentation by microbes has been widely used to produce traditional foods, beverages, and biofuels from starch and to a lesser extent plant biomass. This review focuses on the degradation and utilization of plant homopolysaccharides, cellulose and starch; summarizes the activities of the enzymes involved and the regulation of the induction of the enzymes in well-studied filamentous fungi. Full article
(This article belongs to the Special Issue Main Applications of Plant, Fungal and Algal Polysaccharides: Current Vision and Future Horizon)
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34 pages, 9037 KiB  
Review
Microscopic Techniques for the Analysis of Micro and Nanostructures of Biopolymers and Their Derivatives
by Abhilash Venkateshaiah, Vinod V.T. Padil, Malladi Nagalakshmaiah, Stanisław Waclawek, Miroslav Černík and Rajender S. Varma
Polymers 2020, 12(3), 512; https://doi.org/10.3390/polym12030512 - 27 Feb 2020
Cited by 73 | Viewed by 13221
Abstract
Natural biopolymers, a class of materials extracted from renewable sources, is garnering interest due to growing concerns over environmental safety; biopolymers have the advantage of biocompatibility and biodegradability, an imperative requirement. The synthesis of nanoparticles and nanofibers from biopolymers provides a green platform [...] Read more.
Natural biopolymers, a class of materials extracted from renewable sources, is garnering interest due to growing concerns over environmental safety; biopolymers have the advantage of biocompatibility and biodegradability, an imperative requirement. The synthesis of nanoparticles and nanofibers from biopolymers provides a green platform relative to the conventional methods that use hazardous chemicals. However, it is challenging to characterize these nanoparticles and fibers due to the variation in size, shape, and morphology. In order to evaluate these properties, microscopic techniques such as optical microscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM) are essential. With the advent of new biopolymer systems, it is necessary to obtain insights into the fundamental structures of these systems to determine their structural, physical, and morphological properties, which play a vital role in defining their performance and applications. Microscopic techniques perform a decisive role in revealing intricate details, which assists in the appraisal of microstructure, surface morphology, chemical composition, and interfacial properties. This review highlights the significance of various microscopic techniques incorporating the literature details that help characterize biopolymers and their derivatives. Full article
(This article belongs to the Special Issue Polymer Materials in Environmental Chemistry)
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30 pages, 10316 KiB  
Review
Carbon-Based Polymer Nanocomposite for High-Performance Energy Storage Applications
by Samarjeet Singh Siwal, Qibo Zhang, Nishu Devi and Vijay Kumar Thakur
Polymers 2020, 12(3), 505; https://doi.org/10.3390/polym12030505 - 26 Feb 2020
Cited by 162 | Viewed by 14803
Abstract
In recent years, numerous discoveries and investigations have been remarked for the development of carbon-based polymer nanocomposites. Carbon-based materials and their composites hold encouraging employment in a broad array of fields, for example, energy storage devices, fuel cells, membranes sensors, actuators, and electromagnetic [...] Read more.
In recent years, numerous discoveries and investigations have been remarked for the development of carbon-based polymer nanocomposites. Carbon-based materials and their composites hold encouraging employment in a broad array of fields, for example, energy storage devices, fuel cells, membranes sensors, actuators, and electromagnetic shielding. Carbon and its derivatives exhibit some remarkable features such as high conductivity, high surface area, excellent chemical endurance, and good mechanical durability. On the other hand, characteristics such as docility, lower price, and high environmental resistance are some of the unique properties of conducting polymers (CPs). To enhance the properties and performance, polymeric electrode materials can be modified suitably by metal oxides and carbon materials resulting in a composite that helps in the collection and accumulation of charges due to large surface area. The carbon-polymer nanocomposites assist in overcoming the difficulties arising in achieving the high performance of polymeric compounds and deliver high-performance composites that can be used in electrochemical energy storage devices. Carbon-based polymer nanocomposites have both advantages and disadvantages, so in this review, attempts are made to understand their synergistic behavior and resulting performance. The three electrochemical energy storage systems and the type of electrode materials used for them have been studied here in this article and some aspects for example morphology, exterior area, temperature, and approaches have been observed to influence the activity of electrochemical methods. This review article evaluates and compiles reported data to present a significant and extensive summary of the state of the art. Full article
(This article belongs to the Special Issue Carbon-Based Polymer Nanocomposites for High-Performance Applications)
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20 pages, 2446 KiB  
Review
Emerging Developments in the Use of Electrospun Fibers and Membranes for Protective Clothing Applications
by Avinash Baji, Komal Agarwal and Sruthi Venugopal Oopath
Polymers 2020, 12(2), 492; https://doi.org/10.3390/polym12020492 - 24 Feb 2020
Cited by 85 | Viewed by 9806
Abstract
There has been increased interest to develop protective fabrics and clothing for protecting the wearer from hazards such as chemical, biological, heat, UV, pollutants etc. Protective fabrics have been conventionally developed using a wide variety of techniques. However, these conventional protective fabrics lack [...] Read more.
There has been increased interest to develop protective fabrics and clothing for protecting the wearer from hazards such as chemical, biological, heat, UV, pollutants etc. Protective fabrics have been conventionally developed using a wide variety of techniques. However, these conventional protective fabrics lack breathability. For example, conventional protective fabrics offer good protection against water but have limited ability in removing the water vapor and moisture. Fibers and membranes fabricated using electrospinning have demonstrated tremendous potential to develop protective fabrics and clothing. These fabrics based on electrospun fibers and membranes have the potential to provide thermal comfort to the wearer and protect the wearer from wide variety of environmental hazards. This review highlights the emerging applications of electrospinning for developing such breathable and protective fabrics. Full article
(This article belongs to the Special Issue Electrospun Nanofibers: Theory and Its Applications)
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28 pages, 2602 KiB  
Review
Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) as a Promising Polymer Material for Biomedical Applications: A Concise Review
by Muzamil Hussain, Rizwan Ali Naqvi, Naseem Abbas, Shahzad Masood Khan, Saad Nawaz, Arif Hussain, Nida Zahra and Muhammad Waqas Khalid
Polymers 2020, 12(2), 323; https://doi.org/10.3390/polym12020323 - 4 Feb 2020
Cited by 126 | Viewed by 22604
Abstract
Ultra-High Molecular Weight Polyethylene (UHMWPE) is used in biomedical applications due to its high wear-resistance, ductility, and biocompatibility. A great deal of research in recent decades has focused on further improving its mechanical and tribological performances in order to provide durable implants in [...] Read more.
Ultra-High Molecular Weight Polyethylene (UHMWPE) is used in biomedical applications due to its high wear-resistance, ductility, and biocompatibility. A great deal of research in recent decades has focused on further improving its mechanical and tribological performances in order to provide durable implants in patients. Several methods, including irradiation, surface modifications, and reinforcements have been employed to improve the tribological and mechanical performance of UHMWPE. The effect of these modifications on tribological and mechanical performance was discussed in this review. Full article
(This article belongs to the Special Issue Biopolymers for Biomedical Applications)
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21 pages, 4046 KiB  
Review
The Importance of Poly(ethylene glycol) Alternatives for Overcoming PEG Immunogenicity in Drug Delivery and Bioconjugation
by Thai Thanh Hoang Thi, Emily H. Pilkington, Dai Hai Nguyen, Jung Seok Lee, Ki Dong Park and Nghia P. Truong
Polymers 2020, 12(2), 298; https://doi.org/10.3390/polym12020298 - 2 Feb 2020
Cited by 420 | Viewed by 34530
Abstract
Poly(ethylene glycol) (PEG) is widely used as a gold standard in bioconjugation and nanomedicine to prolong blood circulation time and improve drug efficacy. The conjugation of PEG to proteins, peptides, oligonucleotides (DNA, small interfering RNA (siRNA), microRNA (miRNA)) and nanoparticles is a well-established [...] Read more.
Poly(ethylene glycol) (PEG) is widely used as a gold standard in bioconjugation and nanomedicine to prolong blood circulation time and improve drug efficacy. The conjugation of PEG to proteins, peptides, oligonucleotides (DNA, small interfering RNA (siRNA), microRNA (miRNA)) and nanoparticles is a well-established technique known as PEGylation, with PEGylated products have been using in clinics for the last few decades. However, it is increasingly recognized that treating patients with PEGylated drugs can lead to the formation of antibodies that specifically recognize and bind to PEG (i.e., anti-PEG antibodies). Anti-PEG antibodies are also found in patients who have never been treated with PEGylated drugs but have consumed products containing PEG. Consequently, treating patients who have acquired anti-PEG antibodies with PEGylated drugs results in accelerated blood clearance, low drug efficacy, hypersensitivity, and, in some cases, life-threatening side effects. In this succinct review, we collate recent literature to draw the attention of polymer chemists to the issue of PEG immunogenicity in drug delivery and bioconjugation, thereby highlighting the importance of developing alternative polymers to replace PEG. Several promising yet imperfect alternatives to PEG are also discussed. To achieve asatisfactory alternative, further joint efforts of polymer chemists and scientists in related fields are urgently needed to design, synthesize and evaluate new alternatives to PEG. Full article
(This article belongs to the Special Issue Biopolymers for Medical Applications)
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29 pages, 1252 KiB  
Review
A Review on the Partial and Complete Dissolution and Fractionation of Wood and Lignocelluloses Using Imidazolium Ionic Liquids
by Hatem Abushammala and Jia Mao
Polymers 2020, 12(1), 195; https://doi.org/10.3390/polym12010195 - 11 Jan 2020
Cited by 91 | Viewed by 6972
Abstract
Ionic liquids have shown great potential in the last two decades as solvents, catalysts, reaction media, additives, lubricants, and in many applications such as electrochemical systems, hydrometallurgy, chromatography, CO2 capture, etc. As solvents, the unlimited combinations of cations and anions have given [...] Read more.
Ionic liquids have shown great potential in the last two decades as solvents, catalysts, reaction media, additives, lubricants, and in many applications such as electrochemical systems, hydrometallurgy, chromatography, CO2 capture, etc. As solvents, the unlimited combinations of cations and anions have given ionic liquids a remarkably wide range of solvation power covering a variety of organic and inorganic materials. Ionic liquids are also considered “green” solvents due to their negligible vapor pressure, which means no emission of volatile organic compounds. Due to these interesting properties, ionic liquids have been explored as promising solvents for the dissolution and fractionation of wood and cellulose for biofuel production, pulping, extraction of nanocellulose, and for processing all-wood and all-cellulose composites. This review describes, at first, the potential of ionic liquids and the impact of the cation/anion combination on their physiochemical properties and on their solvation power and selectivity to wood polymers. It also elaborates on how the dissolution conditions influence these parameters. It then discusses the different approaches, which are followed for the homogeneous and heterogeneous dissolution and fractionation of wood and cellulose using ionic liquids and categorize them based on the target application. It finally highlights the challenges of using ionic liquids for wood and cellulose dissolution and processing, including side reactions, viscosity, recyclability, and price. Full article
(This article belongs to the Special Issue Bio-Based Polymers for Engineered Green Materials)
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38 pages, 4008 KiB  
Review
Recent Advances in Natural Gum-Based Biomaterials for Tissue Engineering and Regenerative Medicine: A Review
by Reza Mohammadinejad, Anuj Kumar, Marziyeh Ranjbar-Mohammadi, Milad Ashrafizadeh, Sung Soo Han, Gilson Khang and Ziba Roveimiab
Polymers 2020, 12(1), 176; https://doi.org/10.3390/polym12010176 - 9 Jan 2020
Cited by 142 | Viewed by 14094
Abstract
The engineering of tissues under a three-dimensional (3D) microenvironment is a great challenge and needs a suitable supporting biomaterial-based scaffold that may facilitate cell attachment, spreading, proliferation, migration, and differentiation for proper tissue regeneration or organ reconstruction. Polysaccharides as natural polymers promise great [...] Read more.
The engineering of tissues under a three-dimensional (3D) microenvironment is a great challenge and needs a suitable supporting biomaterial-based scaffold that may facilitate cell attachment, spreading, proliferation, migration, and differentiation for proper tissue regeneration or organ reconstruction. Polysaccharides as natural polymers promise great potential in the preparation of a three-dimensional artificial extracellular matrix (ECM) (i.e., hydrogel) via various processing methods and conditions. Natural polymers, especially gums, based upon hydrogel systems, provide similarities largely with the native ECM and excellent biological response. Here, we review the origin and physico-chemical characteristics of potentially used natural gums. In addition, various forms of scaffolds (e.g., nanofibrous, 3D printed-constructs) based on gums and their efficacy in 3D cell culture and various tissue regenerations such as bone, osteoarthritis and cartilage, skin/wound, retinal, neural, and other tissues are discussed. Finally, the advantages and limitations of natural gums are precisely described for future perspectives in tissue engineering and regenerative medicine in the concluding remarks. Full article
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45 pages, 23366 KiB  
Review
Machine-Learning-Assisted De Novo Design of Organic Molecules and Polymers: Opportunities and Challenges
by Guang Chen, Zhiqiang Shen, Akshay Iyer, Umar Farooq Ghumman, Shan Tang, Jinbo Bi, Wei Chen and Ying Li
Polymers 2020, 12(1), 163; https://doi.org/10.3390/polym12010163 - 8 Jan 2020
Cited by 112 | Viewed by 20728
Abstract
Organic molecules and polymers have a broad range of applications in biomedical, chemical, and materials science fields. Traditional design approaches for organic molecules and polymers are mainly experimentally-driven, guided by experience, intuition, and conceptual insights. Though they have been successfully applied to discover [...] Read more.
Organic molecules and polymers have a broad range of applications in biomedical, chemical, and materials science fields. Traditional design approaches for organic molecules and polymers are mainly experimentally-driven, guided by experience, intuition, and conceptual insights. Though they have been successfully applied to discover many important materials, these methods are facing significant challenges due to the tremendous demand of new materials and vast design space of organic molecules and polymers. Accelerated and inverse materials design is an ideal solution to these challenges. With advancements in high-throughput computation, artificial intelligence (especially machining learning, ML), and the growth of materials databases, ML-assisted materials design is emerging as a promising tool to flourish breakthroughs in many areas of materials science and engineering. To date, using ML-assisted approaches, the quantitative structure property/activity relation for material property prediction can be established more accurately and efficiently. In addition, materials design can be revolutionized and accelerated much faster than ever, through ML-enabled molecular generation and inverse molecular design. In this perspective, we review the recent progresses in ML-guided design of organic molecules and polymers, highlight several successful examples, and examine future opportunities in biomedical, chemical, and materials science fields. We further discuss the relevant challenges to solve in order to fully realize the potential of ML-assisted materials design for organic molecules and polymers. In particular, this study summarizes publicly available materials databases, feature representations for organic molecules, open-source tools for feature generation, methods for molecular generation, and ML models for prediction of material properties, which serve as a tutorial for researchers who have little experience with ML before and want to apply ML for various applications. Last but not least, it draws insights into the current limitations of ML-guided design of organic molecules and polymers. We anticipate that ML-assisted materials design for organic molecules and polymers will be the driving force in the near future, to meet the tremendous demand of new materials with tailored properties in different fields. Full article
(This article belongs to the Special Issue Artificial Intelligence in Polymer Science and Chemistry)
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25 pages, 2958 KiB  
Review
Piezoelectric Scaffolds as Smart Materials for Neural Tissue Engineering
by Angelika Zaszczynska, Paweł Sajkiewicz and Arkadiusz Gradys
Polymers 2020, 12(1), 161; https://doi.org/10.3390/polym12010161 - 8 Jan 2020
Cited by 100 | Viewed by 9994
Abstract
Injury to the central or peripheral nervous systems leads to the loss of cognitive and/or sensorimotor capabilities, which still lacks an effective treatment. Tissue engineering in the post-injury brain represents a promising option for cellular replacement and rescue, providing a cell scaffold for [...] Read more.
Injury to the central or peripheral nervous systems leads to the loss of cognitive and/or sensorimotor capabilities, which still lacks an effective treatment. Tissue engineering in the post-injury brain represents a promising option for cellular replacement and rescue, providing a cell scaffold for either transplanted or resident cells. Tissue engineering relies on scaffolds for supporting cell differentiation and growth with recent emphasis on stimuli responsive scaffolds, sometimes called smart scaffolds. One of the representatives of this material group is piezoelectric scaffolds, being able to generate electrical charges under mechanical stimulation, which creates a real prospect for using such scaffolds in non-invasive therapy of neural tissue. This paper summarizes the recent knowledge on piezoelectric materials used for tissue engineering, especially neural tissue engineering. The most used materials for tissue engineering strategies are reported together with the main achievements, challenges, and future needs for research and actual therapies. This review provides thus a compilation of the most relevant results and strategies and serves as a starting point for novel research pathways in the most relevant and challenging open questions. Full article
(This article belongs to the Special Issue Biodegradable Polymer Scaffolds for Tissue Engineering)
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19 pages, 2424 KiB  
Review
Research Progress on Polymer Solar Cells Based on PEDOT:PSS Electrodes
by Lin Hu, Jiaxing Song, Xinxing Yin, Zhen Su and Zaifang Li
Polymers 2020, 12(1), 145; https://doi.org/10.3390/polym12010145 - 7 Jan 2020
Cited by 93 | Viewed by 14178
Abstract
Solution-processed polymer solar cells (PSCs) have attracted dramatically increasing attention over the past few decades owing to their advantages of low cost, solution processability, light weight, and excellent flexibility. Recent progress in materials synthesis and devices engineering has boosted the power conversion efficiency [...] Read more.
Solution-processed polymer solar cells (PSCs) have attracted dramatically increasing attention over the past few decades owing to their advantages of low cost, solution processability, light weight, and excellent flexibility. Recent progress in materials synthesis and devices engineering has boosted the power conversion efficiency (PCE) of single-junction PSCs over 17%. As an emerging technology, it is still a challenge to prepare solution-processed flexible electrodes for attractive flexible PSCs. Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is one of the most promising candidates for electrodes due to its high conductivity (>4000 S/cm), excellent transmittance (>90%), intrinsically high work function (WF > 5.0 eV), and aqueous solution processability. To date, a great number of single-junction PSCs based on PEDOT:PSS electrodes have realized a PCE over 12%. In this review, we introduce the current research on the conductive complex PEDOT:PSS as well as trace the development of PEDOT:PSS used in electrodes for high performance PSCs and perovskite solar cells. We also discuss and comment on the aspects of conductivity, transmittance, work-function adjustment, film preparing methods, and device fabrications. A perspective on the challenges and future directions in this field is be offered finally. Full article
(This article belongs to the Special Issue Polymer-Based Solar Cells)
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27 pages, 2707 KiB  
Review
A Comprehensive Review on Water Diffusion in Polymers Focusing on the Polymer–Metal Interface Combination
by Chao Yang, Xiao Xing, Zili Li and Shouxin Zhang
Polymers 2020, 12(1), 138; https://doi.org/10.3390/polym12010138 - 6 Jan 2020
Cited by 80 | Viewed by 9236
Abstract
Water diffusion in polymers is relevant to a broad range of physicochemical phenomena and technological processes. Although many fields contributed to rapid progress in the fundamental knowledge of water–polymer interactions, detailed understandings come mainly from interpreting numerous experiments. These studies showed that a [...] Read more.
Water diffusion in polymers is relevant to a broad range of physicochemical phenomena and technological processes. Although many fields contributed to rapid progress in the fundamental knowledge of water–polymer interactions, detailed understandings come mainly from interpreting numerous experiments. These studies showed that a remarkably rich variety of diffusion forms between water and even seemingly simple polymers. In this review, focusing on the gravimetric and capacitance method, we discuss contradictions and problems existing for water diffusion in polymers in detail from perspectives of experiments and models, focusing on the analysis of error derived from widely used methods, especially for the Brasher–Kingsbury equation. We also provide a perspective on outstanding problems, challenges, and open questions, including water clusters, relaxation, and electrochemical reactions at the metal/polymer interface, as well as expanding the theoretical prospective. Full article
(This article belongs to the Special Issue Polymer Structures in Solution)
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18 pages, 2061 KiB  
Review
Degradation of Plastics under Anaerobic Conditions: A Short Review
by Xochitl Quecholac-Piña, María del Consuelo Hernández-Berriel, María del Consuelo Mañón-Salas, Rosa María Espinosa-Valdemar and Alethia Vázquez-Morillas
Polymers 2020, 12(1), 109; https://doi.org/10.3390/polym12010109 - 5 Jan 2020
Cited by 84 | Viewed by 18517
Abstract
Plastic waste is an issue of global concern because of the environmental impact of its accumulation in waste management systems and ecosystems. Biodegradability was proposed as a solution to overcome this problem; however, most biodegradable plastics were designed to degrade under aerobic conditions, [...] Read more.
Plastic waste is an issue of global concern because of the environmental impact of its accumulation in waste management systems and ecosystems. Biodegradability was proposed as a solution to overcome this problem; however, most biodegradable plastics were designed to degrade under aerobic conditions, ideally fulfilled in a composting plant. These new plastics could arrive to anaerobic environments, purposely or frequently, because of their mismanagement at the end of their useful life. This review analyzes the behavior of biodegradable and conventional plastics under anaerobic conditions, specifically in anaerobic digestion systems and landfills. A review was performed in order to identify: (a) the environmental conditions found in anaerobic digestion processes and landfills, as well as the mechanisms for degradation in those environments; (b) the experimental methods used for the assessment of biodegradation in anaerobic conditions; and (c) the extent of the biodegradation process for different plastics. Results show a remarkable variability of the biodegradation rate depending on the type of plastic and experimental conditions, with clearly better performance in anaerobic digestion systems, where temperature, water content, and inoculum are strictly controlled. The majority of the studied plastics showed that thermophilic conditions increase degradation. It should not be assumed that plastics designed to be degraded aerobically will biodegrade under anaerobic conditions, and an exact match must be done between the specific plastics and the end of life options that they will face. Full article
(This article belongs to the Special Issue Recent Advances in Bioplastics II)
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24 pages, 2136 KiB  
Review
Challenges with Verifying Microbial Degradation of Polyethylene
by Zahra Montazer, Mohammad B. Habibi Najafi and David B. Levin
Polymers 2020, 12(1), 123; https://doi.org/10.3390/polym12010123 - 5 Jan 2020
Cited by 203 | Viewed by 22942
Abstract
Polyethylene (PE) is the most abundant synthetic, petroleum-based plastic materials produced globally, and one of the most resistant to biodegradation, resulting in massive accumulation in the environment. Although the microbial degradation of polyethylene has been reported, complete biodegradation of polyethylene has not been [...] Read more.
Polyethylene (PE) is the most abundant synthetic, petroleum-based plastic materials produced globally, and one of the most resistant to biodegradation, resulting in massive accumulation in the environment. Although the microbial degradation of polyethylene has been reported, complete biodegradation of polyethylene has not been achieved, and rapid degradation of polyethylene under ambient conditions in the environment is still not feasible. Experiments reported in the literature suffer from a number of limitations, and conclusive evidence for the complete biodegradation of polyethylene by microorganisms has been elusive. These limitations include the lack of a working definition for the biodegradation of polyethylene that can lead to testable hypotheses, a non-uniform description of experimental conditions used, and variations in the type(s) of polyethylene used, leading to a profound limitation in our understanding of the processes and mechanisms involved in the microbial degradation of polyethylene. The objective of this review is to outline the challenges in polyethylene degradation experiments and clarify the parameters required to achieve polyethylene biodegradation. This review emphasizes the necessity of developing a biochemically-based definition for the biodegradation of polyethylene (and other synthetic plastics) to simplify the comparison of results of experiments focused for the microbial degradation of polyethylene. Full article
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23 pages, 4287 KiB  
Review
Lignin-Based Hydrogels: Synthesis and Applications
by Diana Rico-García, Leire Ruiz-Rubio, Leyre Pérez-Alvarez, Saira L. Hernández-Olmos, Guillermo L. Guerrero-Ramírez and José Luis Vilas-Vilela
Polymers 2020, 12(1), 81; https://doi.org/10.3390/polym12010081 - 3 Jan 2020
Cited by 139 | Viewed by 16732
Abstract
Polymers obtained from biomass are an interesting alternative to petro-based polymers due to their low cost of production, biocompatibility, and biodegradability. This is the case of lignin, which is the second most abundant biopolymer in plants. As a consequence, the exploitation of lignin [...] Read more.
Polymers obtained from biomass are an interesting alternative to petro-based polymers due to their low cost of production, biocompatibility, and biodegradability. This is the case of lignin, which is the second most abundant biopolymer in plants. As a consequence, the exploitation of lignin for the production of new materials with improved properties is currently considered as one of the main challenging issues, especially for the paper industry. Regarding its chemical structure, lignin is a crosslinked polymer that contains many functional hydrophilic and active groups, such as hydroxyls, carbonyls and methoxyls, which provides a great potential to be employed in the synthesis of biodegradable hydrogels, materials that are recognized for their interesting applicability in biomedicine, soil and water treatment, and agriculture, among others. This work describes the main methods for the preparation of lignin-based hydrogels reported in the last years, based on the chemical and/or physical interaction with polymers widely used in hydrogels formulations. Furthermore, herein are also reviewed the current applications of lignin hydrogels as stimuli-responsive materials, flexible supercapacitors, and wearable electronics for biomedical and water remediation applications. Full article
(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)
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32 pages, 1569 KiB  
Review
Application of Protein-Based Films and Coatings for Food Packaging: A Review
by Hongbo Chen, Jingjing Wang, Yaohua Cheng, Chuansheng Wang, Haichao Liu, Huiguang Bian, Yiren Pan, Jingyao Sun and Wenwen Han
Polymers 2019, 11(12), 2039; https://doi.org/10.3390/polym11122039 - 9 Dec 2019
Cited by 283 | Viewed by 17511
Abstract
As the IV generation of packaging, biopolymers, with the advantages of biodegradability, process ability, combination possibilities and no pollution to food, have become the leading food packaging materials. Biopolymers can be directly extracted from biomass, synthesized from bioderived monomers and produced directly by [...] Read more.
As the IV generation of packaging, biopolymers, with the advantages of biodegradability, process ability, combination possibilities and no pollution to food, have become the leading food packaging materials. Biopolymers can be directly extracted from biomass, synthesized from bioderived monomers and produced directly by microorganisms which are all abundant and renewable. The raw materials used to produce biopolymers are low-cost, some even coming from agrion dustrial waste. This review summarized the advances in protein-based films and coatings for food packaging. The materials studied to develop protein-based packaging films and coatings can be divided into two classes: plant proteins and animal proteins. Parts of proteins are referred in this review, including plant proteins i.e., gluten, soy proteins and zein, and animal proteins i.e., casein, whey and gelatin. Films and coatings based on these proteins have excellent gas barrier properties and satisfactory mechanical properties. However, the hydrophilicity of proteins makes the protein-based films present poor water barrier characteristics. The application of plasticizers and the corresponding post-treatments can make the properties of the protein-based films and coatings improved. The addition of active compounds into protein-based films can effectively inhibit or delay the growth of microorganisms and the oxidation of lipids. The review also summarized the research about the storage requirements of various foods that can provide corresponding guidance for the preparation of food packaging materials. Numerous application examples of protein-based films and coatings in food packaging also confirm their important role in food packaging materials. Full article
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45 pages, 5672 KiB  
Review
Core–Shell Fibers: Design, Roles, and Controllable Release Strategies in Tissue Engineering and Drug Delivery
by Muhammad Faiq Abdullah, Tamrin Nuge, Andri Andriyana, Bee Chin Ang and Farina Muhamad
Polymers 2019, 11(12), 2008; https://doi.org/10.3390/polym11122008 - 4 Dec 2019
Cited by 81 | Viewed by 10460
Abstract
The key attributes of core–shell fibers are their ability to preserve bioactivity of incorporated-sensitive biomolecules (such as drug, protein, and growth factor) and subsequently control biomolecule release to the targeted microenvironments to achieve therapeutic effects. Such qualities are highly favorable for tissue engineering [...] Read more.
The key attributes of core–shell fibers are their ability to preserve bioactivity of incorporated-sensitive biomolecules (such as drug, protein, and growth factor) and subsequently control biomolecule release to the targeted microenvironments to achieve therapeutic effects. Such qualities are highly favorable for tissue engineering and drug delivery, and these features are not able to be offered by monolithic fibers. In this review, we begin with an overview on design requirement of core–shell fibers, followed by the summary of recent preparation methods of core–shell fibers, with focus on electrospinning-based techniques and other newly discovered fabrication approaches. We then highlight the importance and roles of core–shell fibers in tissue engineering and drug delivery, accompanied by thorough discussion on controllable release strategies of the incorporated bioactive molecules from the fibers. Ultimately, we touch on core–shell fibers-related challenges and offer perspectives on their future direction towards clinical applications. Full article
(This article belongs to the Special Issue Advances in Polymer Nanofibers)
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25 pages, 2076 KiB  
Review
Silk Fibroin-Based Biomaterials for Biomedical Applications: A Review
by Thang Phan Nguyen, Quang Vinh Nguyen, Van-Huy Nguyen, Thu-Ha Le, Vu Quynh Nga Huynh, Dai-Viet N. Vo, Quang Thang Trinh, Soo Young Kim and Quyet Van Le
Polymers 2019, 11(12), 1933; https://doi.org/10.3390/polym11121933 - 24 Nov 2019
Cited by 307 | Viewed by 21843
Abstract
Since it was first discovered, thousands of years ago, silkworm silk has been known to be an abundant biopolymer with a vast range of attractive properties. The utilization of silk fibroin (SF), the main protein of silkworm silk, has not been limited to [...] Read more.
Since it was first discovered, thousands of years ago, silkworm silk has been known to be an abundant biopolymer with a vast range of attractive properties. The utilization of silk fibroin (SF), the main protein of silkworm silk, has not been limited to the textile industry but has been further extended to various high-tech application areas, including biomaterials for drug delivery systems and tissue engineering. The outstanding mechanical properties of SF, including its facile processability, superior biocompatibility, controllable biodegradation, and versatile functionalization have allowed its use for innovative applications. In this review, we describe the structure, composition, general properties, and structure-properties relationship of SF. In addition, the methods used for the fabrication and modification of various materials are briefly addressed. Lastly, recent applications of SF-based materials for small molecule drug delivery, biological drug delivery, gene therapy, wound healing, and bone regeneration are reviewed and our perspectives on future development of these favorable materials are also shared. Full article
(This article belongs to the Section Biobased and Biodegradable Polymers)
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28 pages, 6414 KiB  
Review
Cellulose in Ionic Liquids and Alkaline Solutions: Advances in the Mechanisms of Biopolymer Dissolution and Regeneration
by Omar A. El Seoud, Marc Kostag, Kerstin Jedvert and Naved I. Malek
Polymers 2019, 11(12), 1917; https://doi.org/10.3390/polym11121917 - 21 Nov 2019
Cited by 45 | Viewed by 6915
Abstract
This review is focused on assessment of solvents for cellulose dissolution and the mechanism of regeneration of the dissolved biopolymer. The solvents of interest are imidazole-based ionic liquids, quaternary ammonium electrolytes, salts of super-bases, and their binary mixtures with molecular solvents. We briefly [...] Read more.
This review is focused on assessment of solvents for cellulose dissolution and the mechanism of regeneration of the dissolved biopolymer. The solvents of interest are imidazole-based ionic liquids, quaternary ammonium electrolytes, salts of super-bases, and their binary mixtures with molecular solvents. We briefly discuss the mechanism of cellulose dissolution and address the strategies for assessing solvent efficiency, as inferred from its physico-chemical properties. In addition to the favorable effect of lower cellulose solution rheology, microscopic solvent/solution properties, including empirical polarity, Lewis acidity, Lewis basicity, and dipolarity/polarizability are determinants of cellulose dissolution. We discuss how these microscopic properties are calculated from the UV-Vis spectra of solvatochromic probes, and their use to explain the observed solvent efficiency order. We dwell briefly on use of other techniques, in particular NMR and theoretical calculations for the same purpose. Once dissolved, cellulose is either regenerated in different physical shapes, or derivatized under homogeneous conditions. We discuss the mechanism of, and the steps involved in cellulose regeneration, via formation of mini-sheets, association into “mini-crystals”, and convergence into larger crystalline and amorphous regions. We discuss the use of different techniques, including FTIR, X-ray diffraction, and theoretical calculations to probe the forces involved in cellulose regeneration. Full article
(This article belongs to the Special Issue Cellulose and Renewable Materials)
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17 pages, 3380 KiB  
Review
Review of Polymeric Materials in 4D Printing Biomedical Applications
by Ming-You Shie, Yu-Fang Shen, Suryani Dyah Astuti, Alvin Kai-Xing Lee, Shu-Hsien Lin, Ni Luh Bella Dwijaksara and Yi-Wen Chen
Polymers 2019, 11(11), 1864; https://doi.org/10.3390/polym11111864 - 12 Nov 2019
Cited by 105 | Viewed by 10731
Abstract
The purpose of 4D printing is to embed a product design into a deformable smart material using a traditional 3D printer. The 3D printed object can be assembled or transformed into intended designs by applying certain conditions or forms of stimulation such as [...] Read more.
The purpose of 4D printing is to embed a product design into a deformable smart material using a traditional 3D printer. The 3D printed object can be assembled or transformed into intended designs by applying certain conditions or forms of stimulation such as temperature, pressure, humidity, pH, wind, or light. Simply put, 4D printing is a continuum of 3D printing technology that is now able to print objects which change over time. In previous studies, many smart materials were shown to have 4D printing characteristics. In this paper, we specifically review the current application, respective activation methods, characteristics, and future prospects of various polymeric materials in 4D printing, which are expected to contribute to the development of 4D printing polymeric materials and technology. Full article
(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)
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28 pages, 2209 KiB  
Review
The Use of Chitosan, Alginate, and Pectin in the Biomedical and Food Sector—Biocompatibility, Bioadhesiveness, and Biodegradability
by Gheorghe Adrian Martău, Mihaela Mihai and Dan Cristian Vodnar
Polymers 2019, 11(11), 1837; https://doi.org/10.3390/polym11111837 - 8 Nov 2019
Cited by 388 | Viewed by 17626
Abstract
Nowadays, biopolymers as intelligent and active biopolymer systems in the food and pharmaceutical industry are of considerable interest in their use. With this association in view, biopolymers such as chitosan, alginate, pectin, cellulose, agarose, guar gum, agar, carrageenan, gelatin, dextran, xanthan, and other [...] Read more.
Nowadays, biopolymers as intelligent and active biopolymer systems in the food and pharmaceutical industry are of considerable interest in their use. With this association in view, biopolymers such as chitosan, alginate, pectin, cellulose, agarose, guar gum, agar, carrageenan, gelatin, dextran, xanthan, and other polymers have received significant attention in recent years due to their abundance and natural availability. Furthermore, their versatile properties such as non-toxicity, biocompatibility, biodegradability, and flexibility offer significant functionalities with multifunctional applications. The purpose of this review is to summarize the most compatible biopolymers such as chitosan, alginate, and pectin, which are used for application in food, biotechnological processes, and biomedical applications. Therefore, chitosan, alginate, and pectin are biopolymers (used in the food industry as a stabilizing, thickening, capsular agent, and packaging) with great potential for future developments. Moreover, this review highlights their characteristics, with a particular focus on their potential for biocompatibility, biodegradability, bioadhesiveness, and their limitations on certain factors in the human gastrointestinal tract. Full article
(This article belongs to the Special Issue Polymeric Materials for Food Engineering)
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25 pages, 7247 KiB  
Review
Viologen-Based Electrochromic Materials: From Small Molecules, Polymers and Composites to Their Applications
by Kwok Wei Shah, Su-Xi Wang, Debbie Xiang Yun Soo and Jianwei Xu
Polymers 2019, 11(11), 1839; https://doi.org/10.3390/polym11111839 - 8 Nov 2019
Cited by 147 | Viewed by 15151
Abstract
Organic materials have gained considerable attention for electrochromic (EC) applications owing to improved EC performance and good processability. As a class of well-recognized organic EC materials, viologens have received persistent attention due to the structural versatility and property tunability, and are major active [...] Read more.
Organic materials have gained considerable attention for electrochromic (EC) applications owing to improved EC performance and good processability. As a class of well-recognized organic EC materials, viologens have received persistent attention due to the structural versatility and property tunability, and are major active EC components for most of the marketed EC devices. Over the past two decades, extensive efforts have been made to design and synthesize different types of viologen-based materials with enhanced EC properties. This review summarizes chemical structures, preparation and EC properties of various latest viologen-based electrochromes, including small viologen derivatives, main-chain viologen-based polymers, conjugated polymers with viologen side-chains and viologen-based organic/inorganic composites. The performance enhancement mechanisms are concisely discussed. The current marketed viologens-based electrochromic devices (ECDs) are briefly introduced and an outlook on the challenges and future exploration directions for viologen-based materials and their ECDs are also proposed. Full article
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