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Frontiers in Silk Science-How Silks/Biomimetic Polymers Solve Specific Challenges?

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Materials Chemistry".

Deadline for manuscript submissions: closed (15 March 2022) | Viewed by 31056

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Special Issue Editors

Dr. Sean Blamires

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Guest Editor

School of Biological, Earth & Environmental Sciences, Faculty of Science, University of New South Wales (UNSW) Australia, Sydney, Australia
Interests: silk; biomimetics; structures; properties; structure–function analysis

Dr. Ben Allardyce

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Guest Editor

Institute for Frontier Materials, Deakin University, Geelong, Australia
Interests: biomaterials; silk; silk fibroin materials; fibres

Special Issue Information

Dear Colleagues,

Most synthetic materials are petrochemical-based thermoplastic products that need filtration and management of their toxic byproducts. In the absence of any means of biodegradation, the environmental and other impacts of synthetic materials will only increase exponentially.

The functional capacities of modern materials are now at their usable limits. While a relatively good performance can be achieved by synthetic polymers, such as nylon, polyethylene, polyester, Kevlar, and epoxy, they are unable to adapt to changing demands across environments. Depending on the circumstances, these performance limitations might be considered inadequate.

Natural materials, such as silk, are manufactured using biochemical building blocks (peptides/proteins, carbohydrates, and salts) in water. Furthermore, animals can tune the functionality of these materials across environments by varying their biochemistry and/or biomolecular expression. We thus can learn a lot about materials manufacturing by examining the processes by which animals express, synthesize, and utilize functional materials.

This Special Issue of Molecules will compile research and review papers across pure and applied chemical sciences to examine the nature and processes of natural and/or biomimetic/bio-inspired materials, such as silks, glues, and other functional biomaterials . It will focus on environmental solutions but will incorporate other (e.g., medical, engineering) solutions.

Dr. Sean Blamires
Dr. Ben Allardyce
Guest Editors

Manuscript Submission Information

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

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

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

Keywords

Biomimicry
Fibres
Environmentally benign materials
Recombinant technologies
Spinning technologies
Pure research
Applied research

Published Papers (10 papers)

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Research

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12 pages, 1938 KiB

Open AccessCommunication

3D Printing of Monolithic Proteinaceous Cantilevers Using Regenerated Silk Fibroin

by Xuan Mu, Constancio Gonzalez-Obeso, Zhiyu Xia, Jugal Kishore Sahoo, Gang Li, Peggy Cebe, Yu Shrike Zhang and David L. Kaplan

Molecules 2022, 27(7), 2148; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27072148 - 26 Mar 2022

Cited by 7 | Viewed by 2514

Abstract

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

(This article belongs to the Special Issue Frontiers in Silk Science-How Silks/Biomimetic Polymers Solve Specific Challenges?)

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13 pages, 20543 KiB

Open AccessArticle

Processing-Structure-Properties Relationships of Glycerol-Plasticized Silk Films

by Hao Lyu, Ziyang Sun, Yang Liu, Xin Yu and Chengchen Guo

Molecules 2022, 27(4), 1339; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27041339 - 16 Feb 2022

Cited by 8 | Viewed by 2926

Abstract

Silk possesses excellent mechanical properties and biocompatibility due to its unique protein sequences and hierarchical structures. Thus, it has been widely used as a biomaterial in a broad spectrum of biomedical applications. In this study, an in-depth investigation of glycerol-plasticized silk films was carried out to understand the processing-structure-properties relationships. A series of glycerol-plasticized silk films with glycerol contents in the range of 0 to 30% (w/w) were prepared. The molecular structures and organizations of silk proteins and the interactions between glycerol and proteins were studied using FTIR, XRD, and DSC. At a low glycerol content (<12%), DSC revealed that the glass transition temperature and thermally induced crystallization temperature decreased as the glycerol content increased, implying that glycerol mainly interacts with silk proteins through hydrogen bonding. As the glycerol content further increased, the chain mobility of the silk proteins was promoted, leading to the formation of β-sheet structures, water insolubility, and increased crystallinity. In addition, the stretchability and toughness of the films were significantly enhanced. The role of glycerol as a plasticizer in regulating the silk protein structures and determining the properties of the films was thoroughly discussed. Full article

(This article belongs to the Special Issue Frontiers in Silk Science-How Silks/Biomimetic Polymers Solve Specific Challenges?)

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14 pages, 2982 KiB

Open AccessArticle

Nanoscale Material Heterogeneity of Glowworm Capture Threads Revealed by AFM

by Dakota Piorkowski, Bo-Ching He, Sean J. Blamires, I-Min Tso and Deborah M. Kane

Molecules 2021, 26(12), 3500; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26123500 - 08 Jun 2021

Cited by 4 | Viewed by 2346

Abstract

Adhesive materials used by many arthropods for biological functions incorporate sticky substances and a supporting material that operate synergistically by exploiting substrate attachment and energy dissipation. While there has been much focus on the composition and properties of the sticky glues of these bio-composites, less attention has been given to the materials that support them. In particular, as these materials are primarily responsible for dissipation during adhesive pull-off, little is known of the structures that give rise to functionality, especially at the nano-scale. In this study we used tapping mode atomic force microscopy (TM-AFM) to analyze unstretched and stretched glowworm (Arachnocampa tasmaniensis) capture threads and revealed nano-scale features corresponding to variation in surface structure and elastic modulus near the surface of the silk. Phase images demonstrated a high resolution of viscoelastic variation and revealed mostly globular and elongated features in the material. Increased vertical orientation of 11–15 nm wide fibrillar features was observed in stretched threads. Fast Fourier transform analysis of phase images confirmed these results. Relative viscoelastic properties were also highly variable at inter- and intra-individual levels. Results of this study demonstrate the practical usefulness of TM-AFM, especially phase angle imaging, in investigating the nano-scale structures that give rise to macro-scale function of soft and highly heterogeneous materials of both natural and synthetic origins. Full article

(This article belongs to the Special Issue Frontiers in Silk Science-How Silks/Biomimetic Polymers Solve Specific Challenges?)

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17 pages, 1834 KiB

Open AccessArticle

Stretching of Bombyx mori Silk Protein in Flow

by Charley Schaefer, Peter R. Laity, Chris Holland and Tom C. B. McLeish

Molecules 2021, 26(6), 1663; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26061663 - 16 Mar 2021

Cited by 8 | Viewed by 2499

Abstract

The flow-induced self-assembly of entangled Bombyx mori silk proteins is hypothesised to be aided by the ‘registration’ of aligned protein chains using intermolecularly interacting ‘sticky’ patches. This suggests that upon chain alignment, a hierarchical network forms that collectively stretches and induces nucleation in a precisely controlled way. Through the lens of polymer physics, we argue that if all chains would stretch to a similar extent, a clear correlation length of the stickers in the direction of the flow emerges, which may indeed favour such a registration effect. Through simulations in both extensional flow and shear, we show that there is, on the other hand, a very broad distribution of protein–chain stretch, which suggests the registration of proteins is not directly coupled to the applied strain, but may be a slow statistical process. This qualitative prediction seems to be consistent with the large strains (i.e., at long time scales) required to induce gelation in our rheological measurements under constant shear. We discuss our perspective of how the flow-induced self-assembly of silk may be addressed by new experiments and model development. Full article

(This article belongs to the Special Issue Frontiers in Silk Science-How Silks/Biomimetic Polymers Solve Specific Challenges?)

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14 pages, 41112 KiB

Open AccessArticle

A Facile Strategy for Fabrication Lysozyme-Loaded Mesoporous Silica Nanotubes from Electrospun Silk Fibroin Nanofiber Templates

by Jingxin Zhu, Haijuan Wu, Ding Wang, Yanlong Ma and Lan Jia

Molecules 2021, 26(4), 1073; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26041073 - 18 Feb 2021

Cited by 7 | Viewed by 2065

Abstract

This paper presents a facile and low-cost strategy for fabrication lysozyme-loaded mesoporous silica nanotubes (MSNTs) by using silk fibroin (SF) nanofiber templates. The “top-down method” was adopted to dissolve degummed silk in CaCl₂/ formic acid (FA) solvent, and the solution containing SF nanofibrils was used for electrospinning to prepare SF nanofiber templates. As SF contains a large number of -OH, -NH₂ and -COOH groups, the silica layer could be easily formed on its surface by the Söber sol-gel method without adding any surfactant or coupling agent. After calcination, the MSNTs were obtained with inner diameters about 200 nm, the wall thickness ranges from 37 ± 2 nm to 66 ± 3 nm and the Brunauer–Emmett–Teller (BET) specific surface area was up to 200.48 m²/g, the pore volume was 1.109 cm³/g. By loading lysozyme, the MSNTs exhibited relatively high drug encapsulation efficiency up to 31.82% and an excellent long-term sustained release in 360 h (15 days). These results suggest that the MSNTs with the hierarchical structure of mesoporous and macroporous will be a promising carrier for applications in biomacromolecular drug delivery systems. Full article

(This article belongs to the Special Issue Frontiers in Silk Science-How Silks/Biomimetic Polymers Solve Specific Challenges?)

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12 pages, 6044 KiB

Open AccessArticle

Roll-to-Roll Production of Spider Silk Nanofiber Nonwoven Meshes Using Centrifugal Electrospinning for Filtration Applications

by Fabian Müller, Shakir Zainuddin and Thomas Scheibel

Molecules 2020, 25(23), 5540; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25235540 - 26 Nov 2020

Cited by 26 | Viewed by 3469

Abstract

Filtration systems used in technical and medical applications require components for fine particle deep filtration to be highly efficient and at the same time air permeable. In high efficiency filters, nonwoven meshes, which show increased performance based on small fiber diameters (e.g., using nanofibers), can be used as fine particle filter layers. Nanofiber nonwoven meshes made by electrospinning of spider silk proteins have been recently shown to exhibit required filter properties. Needle-based electrospinning, however, is limited regarding its productivity and scalability. Centrifugal electrospinning, in contrast, has been shown to allow manufacturing of ultrathin polymer nonwoven meshes in an efficient and scalable manner. Here, continuous roll-to-roll production of nonwoven meshes made of recombinant spider silk proteins is established using centrifugal electrospinning. The produced spider silk nanofiber meshes show high filter efficiency in the case of fine particulate matter below 2.5 µm (PM2.5) and a low pressure drop, resulting in excellent filter quality. Full article

(This article belongs to the Special Issue Frontiers in Silk Science-How Silks/Biomimetic Polymers Solve Specific Challenges?)

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20 pages, 2846 KiB

Open AccessArticle

Sericin-Induced Melanogenesis in Cultured Retinal Pigment Epithelial Cells Is Associated with Elevated Levels of Hydrogen Peroxide and Inflammatory Proteins

by Ayyad Zartasht Khan, Catherine Joan Jackson, Tor Paaske Utheim, Sjur Reppe, Dipak Sapkota, Ole Kristoffer Olstad, Bernd Thiede and Jon Roger Eidet

Molecules 2020, 25(19), 4395; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25194395 - 24 Sep 2020

Cited by 1 | Viewed by 1934

Abstract

We previously demonstrated that the silk protein sericin promotes pigmentation of retinal pigment epithelium (RPE) by activating the NF-κB pathway. Among numerous agents, NF-κB can be activated by hydrogen peroxide. In the present study, we explored possible associations between reactive oxygen species and sericin-induced melanogenesis in RPE. The proteome of human fetal RPE cultured for seven days with or without 1% sericin was analyzed using ingenuity pathway analysis (IPA). The proteomic data was verified by immunofluorescence and immunoblotting. Light microscopy and scanning electron microscopy were used to assess morphology. Dihydroethidium (DHE) and dihydrorhodamine (DHR) assays were used to measure superoxide and hydrogen peroxide species. Expression levels of proteins related to inflammation, differentiation, cell survival and cell adhesion were higher in cells cultured in Dulbecco’s Modified Eagle Medium (DMEM) with 1% sericin, whereas cells cultured in DMEM alone showed higher expression levels of proteins associated with Bruch’s membrane and cytoskeleton. Despite upregulation of inflammatory proteins, sericin co-cultured RPE yielded significantly higher cell viability compared to cells cultured without sericin. Addition of sericin to culture media significantly increased hydrogen peroxide-levels without significantly affecting superoxide-levels. We suggest that sericin-induced melanogenesis in cultured RPE is associated with elevated levels of superoxide dismutase, hydrogen peroxide and inflammatory proteins. Full article

(This article belongs to the Special Issue Frontiers in Silk Science-How Silks/Biomimetic Polymers Solve Specific Challenges?)

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Review

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24 pages, 7069 KiB

Open AccessReview

Silk Fibroin-Based Biomaterials for Tissue Engineering Applications

by Guangfei Li and Shan Sun

Molecules 2022, 27(9), 2757; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27092757 - 25 Apr 2022

Cited by 39 | Viewed by 4932

Abstract

Tissue engineering (TE) involves the combination of cells with scaffolding materials and appropriate growth factors in order to regenerate or replace damaged and degenerated tissues and organs. The scaffold materials serve as templates for tissue formation and play a vital role in TE. Among scaffold materials, silk fibroin (SF), a naturally occurring protein, has attracted great attention in TE applications due to its excellent mechanical properties, biodegradability, biocompatibility, and bio-absorbability. SF is usually dissolved in an aqueous solution and can be easily reconstituted into different forms, including films, mats, hydrogels, and sponges, through various fabrication techniques, including spin coating, electrospinning, freeze drying, and supercritical CO₂-assisted drying. Furthermore, to facilitate the fabrication of more complex SF-based scaffolds, high-precision techniques such as micro-patterning and bio-printing have been explored in recent years. These processes contribute to the diversity of surface area, mean pore size, porosity, and mechanical properties of different silk fibroin scaffolds and can be used in various TE applications to provide appropriate morphological and mechanical properties. This review introduces the physicochemical and mechanical properties of SF and looks into a range of SF-based scaffolds that have recently been developed. The typical applications of SF-based scaffolds for TE of bone, cartilage, teeth and mandible tissue, cartilage, skeletal muscle, and vascular tissue are highlighted and discussed followed by a discussion of issues to be addressed in future studies. Full article

(This article belongs to the Special Issue Frontiers in Silk Science-How Silks/Biomimetic Polymers Solve Specific Challenges?)

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15 pages, 1328 KiB

Open AccessReview

Advances in Skin Wound and Scar Repair by Polymer Scaffolds

by Shuiqing Zhou, Qiusheng Wang, Ao Huang, Hongdou Fan, Shuqin Yan and Qiang Zhang

Molecules 2021, 26(20), 6110; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26206110 - 10 Oct 2021

Cited by 20 | Viewed by 3999

Abstract

Scars, as the result of abnormal wound-healing response after skin injury, may lead to loss of aesthetics and physical dysfunction. Current clinical strategies, such as surgical excision, laser treatment, and drug application, provide late remedies for scarring, yet it is difficult to eliminate scars. In this review, the functions, roles of multiple polymer scaffolds in wound healing and scar inhibition are explored. Polysaccharide and protein scaffolds, an analog of extracellular matrix, act as templates for cell adhesion and migration, differentiation to facilitate wound reconstruction and limit scarring. Stem cell-seeded scaffolds and growth factors-loaded scaffolds offer significant bioactive substances to improve the wound healing process. Special emphasis is placed on scaffolds that continuously release oxygen, which greatly accelerates the vascularization process and ensures graft survival, providing convincing theoretical support and great promise for scarless healing. Full article

(This article belongs to the Special Issue Frontiers in Silk Science-How Silks/Biomimetic Polymers Solve Specific Challenges?)

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14 pages, 2385 KiB

Open AccessReview

Basic Principles in the Design of Spider Silk Fibers

by José Pérez-Rigueiro, Manuel Elices, Gustavo R. Plaza and Gustavo V. Guinea

Molecules 2021, 26(6), 1794; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26061794 - 23 Mar 2021

Cited by 18 | Viewed by 3171

Abstract

The prominence of spider silk as a hallmark in biomimetics relies not only on its unrivalled mechanical properties, but also on how these properties are the result of a set of original design principles. In this sense, the study of spider silk summarizes most of the main topics relevant to the field and, consequently, offers a nice example on how these topics could be considered in other biomimetic systems. This review is intended to present a selection of some of the essential design principles that underlie the singular microstructure of major ampullate gland silk, as well as to show how the interplay between them leads to the outstanding tensile behavior of spider silk. Following this rationale, the mechanical behavior of the material is analyzed in detail and connected with its main microstructural features, specifically with those derived from the semicrystalline organization of the fibers. Establishing the relationship between mechanical properties and microstructure in spider silk not only offers a vivid image of the paths explored by nature in the search for high performance materials, but is also a valuable guide for the development of new artificial fibers inspired in their natural counterparts. Full article

(This article belongs to the Special Issue Frontiers in Silk Science-How Silks/Biomimetic Polymers Solve Specific Challenges?)

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