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Silk Fibroin Materials
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Silk Fibroin Materials

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

Deadline for manuscript submissions: closed (30 September 2020) | Viewed by 78457

Special Issue Editor

Dr. Yasumoto Nakazawa

E-Mail Website
Guest Editor
Department of Biotechnology and Life Scinece, Tokyo University of Agriculture and Technology, Koganei, Tokyo, Japan
Interests: silk materials; bio-based materials; tissue engineering
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Silk produced by most insects, such as Lepidoptera (silkworms), Araneae (spiders), and Hhymenoptera (ants, bees and hornets), is a natural fiber having excellent mechanical properties and structural characteristics. Such properties are attributed to the higher-order structure and primary structure. The primary structure of silk is a very simple repetitive domain structure, and this repetitive structure is common to various silks, such as spider pull yarn and wild species, in addition to silk fibroin, produced by B. mori. Further, spectroscopic studies, such as X-ray and NMR, have clearly indicated that a very strong hydrogen bond network formed from these primary structures constitutes a crystalline region of the silk.

Furthermore, the nature of silk has been dramatically expanded by technological innovations, such as processing and modification by various genetic recombinations, including genome editing. This way, the utility of silk has grown beyond the limits of conventional fiber, also dispersing to new fields such as a pharmaceutical/medical devices, cosmetics, etc.

Based on the progress of these technologies, this Special Issue calls for papers on structural analysis of various types of silk materials, novel processing methods, and applications in many fields. Topics of particular interest include but are not limited to:

  • Structural analysis of various silks in liquid and solid state;
  • Study on self-aggregation and structure control of silk;
  • Research on new use of silk (medical, environment, chemistry, food, etc);
  • Research on new processing methods of silks;
  • Research on genetically modified silks;
  • Creation of bioinspired materials based on silks.

Dr. Yasumoto Nakazawa
Guest Editor

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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

  • Silk fIbroin
  • Bioinspired materials of silks
  • Tissue engineering based on silks
  • Recombinant silk
  • Silk processing

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Published Papers (17 papers)

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12 pages, 10181 KiB  
Article
Click Decoration of Bombyx mori Silk Fibroin for Cell Adhesion Control
by Hidetoshi Teramoto, Minori Shirakawa and Yasushi Tamada
Molecules 2020, 25(18), 4106; https://doi.org/10.3390/molecules25184106 - 08 Sep 2020
Cited by 5 | Viewed by 2620
Abstract
Silk fibroin produced by the domesticated silkworm, Bombyx mori, has been studied widely as a substrate for tissue engineering applications because of its mechanical robustness and biocompatibility. However, it is often difficult to precisely tune silk fibroin’s biological properties due to the [...] Read more.
Silk fibroin produced by the domesticated silkworm, Bombyx mori, has been studied widely as a substrate for tissue engineering applications because of its mechanical robustness and biocompatibility. However, it is often difficult to precisely tune silk fibroin’s biological properties due to the lack of easy, reliable, and versatile methodologies for decorating it with functional molecules such as those of drugs, polymers, peptides, and enzymes necessary for specific applications. In this study we applied an azido-functionalized silk fibroin, AzidoSilk, produced by a state-of-the-art biotechnology, genetic code expansion, to produce silk fibroin decorated with cell-repellent polyethylene glycol (PEG) chains for controlling the cell adhesion property of silk fibroin film. Azido groups can act as selective handles for chemical reactions such as a strain-promoted azido-alkyne cycloaddition (SPAAC), known as a click chemistry reaction. We found that azido groups in AzidoSilk film were selectively decorated with PEG chains using SPAAC. The PEG-decorated film demonstrated decreased cell adhesion depending on the lengths of the PEG chains. Azido groups in AzidoSilk can be decomposed by UV irradiation. By partially decomposing azido groups in AzidoSilk film in a spatially controlled manner using photomasks, cells could be spatially arranged on the film. These results indicated that SPAAC could be an easy, reliable, and versatile methodology to produce silk fibroin substrates having adequate biological properties. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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11 pages, 1535 KiB  
Article
Oral Bioavailability Evaluation of Celastrol-Encapsulated Silk Fibroin Nanoparticles Using an Optimized LC-MS/MS Method
by Shuyu Zhan, Amy Paik, Felicia Onyeabor, Baoyue Ding, Sunil Prabhu and Jeffrey Wang
Molecules 2020, 25(15), 3422; https://doi.org/10.3390/molecules25153422 - 28 Jul 2020
Cited by 7 | Viewed by 2477
Abstract
Celastrol (CL), a compound isolated from Tripterygium wilfordii, possesses various bioactivities such as antitumor, anti-inflammatory and anti-obesity effects. In previous studies, we developed CL-encapsulated silk fibroin nanoparticles (CL-SFNP) with satisfactory formulation properties and in vitro cancer cytotoxicity effect. For further in vivo [...] Read more.
Celastrol (CL), a compound isolated from Tripterygium wilfordii, possesses various bioactivities such as antitumor, anti-inflammatory and anti-obesity effects. In previous studies, we developed CL-encapsulated silk fibroin nanoparticles (CL-SFNP) with satisfactory formulation properties and in vitro cancer cytotoxicity effect. For further in vivo oral bioavailability evaluation, in this study, a simple and reliable LC-MS/MS method was optimized and validated to determine CL concentration in rat plasma. The separation of CL was performed on a C18 column (150 by 2 mm, 5 µm) following sample preparation using liquid–liquid extraction with the optimized extraction solvent of tert-butyl methylether. The assay exhibited a good linearity in the concentration range of 0.5–500 ng/mL with the lower limit of quantification (LLOQ) of 0.5 ng/mL. The method was validated to meet the requirements for bioassay with accuracy of 91.1–110.0%, precision (RSD%) less than 9.1%, extraction recovery of 63.5–74.7% and matrix effect of 87.3–101.2%. The developed method was successfully applied to the oral bioavailability evaluation of CL-SFNP. The pharmacokinetic results indicated the AUC0-∞ values of CL were both significantly (p < 0.05) higher than those for pure CL after intravenous (IV) or oral (PO) administration of equivalent CL in rats. The oral absolute bioavailability (F, %) of CL significantly (p < 0.05) increased from 3.14% for pure CL to 7.56% for CL-SFNP after dosage normalization. This study provides valuable information for future CL product development. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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11 pages, 1902 KiB  
Article
Silk Fibroin Promotes the Regeneration of Pancreatic β-Cells in the C57BL/KsJ-Leprdb/db Mouse
by So-young Park, Boyoung Kim, Yun Kyung Lee, Sueun Lee, Jin Mi Chun, Jun-Gyo Suh and Jun Hong Park
Molecules 2020, 25(14), 3259; https://doi.org/10.3390/molecules25143259 - 17 Jul 2020
Cited by 6 | Viewed by 2575
Abstract
Diabetes mellitus is a chronic metabolic disease, and its progression leads to serious complications. Although various novel therapeutic approaches for diabetes mellitus have developed in the last three decades, its prevalence has been rising more rapidly worldwide. Silk-related materials have been used as [...] Read more.
Diabetes mellitus is a chronic metabolic disease, and its progression leads to serious complications. Although various novel therapeutic approaches for diabetes mellitus have developed in the last three decades, its prevalence has been rising more rapidly worldwide. Silk-related materials have been used as anti-diabetic remedies in Oriental medicine and many studies have shown the effects of silk fibroin (SF) in both in vitro and in vivo models. In our previous works, we reported that hydrolyzed SF improved the survival of HIT-T15 cells under high glucose conditions and ameliorated diabetic dyslipidemia in a mouse model. However, we could not provide a precise molecular mechanism. To further evaluate the functions of hydrolyzed SF on the pancreatic β-cell, we investigated the effects of hydrolyzed SF on the pancreatic β-cell proliferation and regeneration in the mouse model. Hydrolyzed SF induced the expression of the proliferating cell nuclear antigen (PCNA) and reduced the apoptotic cell population in the pancreatic islets. Hydrolyzed SF treatment not only induced the expression of transcription factors involved in the pancreatic β-cell regeneration in RT-PCR results but also increased neurogenin3 and Neuro D protein levels in the pancreas of those in the group treated with hydrolyzed SF. In line with this, hydrolyzed SF treatment generated insulin mRNA expressing small cell colonies in the pancreas. Therefore, our results suggest that the administration of hydrolyzed SF increases the pancreatic β-cell proliferation and regeneration in C57BL/KsJ-Leprdb/db mice. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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12 pages, 2426 KiB  
Article
Properties of Biomimetic Artificial Spider Silk Fibers Tuned by PostSpin Bath Incubation
by Gabriele Greco, Juanita Francis, Tina Arndt, Benjamin Schmuck, Fredrik G. Bäcklund, Andreas Barth, Jan Johansson, Nicola M. Pugno and Anna Rising
Molecules 2020, 25(14), 3248; https://doi.org/10.3390/molecules25143248 - 16 Jul 2020
Cited by 23 | Viewed by 4216
Abstract
Efficient production of artificial spider silk fibers with properties that match its natural counterpart has still not been achieved. Recently, a biomimetic process for spinning recombinant spider silk proteins (spidroins) was presented, in which important molecular mechanisms involved in native spider silk spinning [...] Read more.
Efficient production of artificial spider silk fibers with properties that match its natural counterpart has still not been achieved. Recently, a biomimetic process for spinning recombinant spider silk proteins (spidroins) was presented, in which important molecular mechanisms involved in native spider silk spinning were recapitulated. However, drawbacks of these fibers included inferior mechanical properties and problems with low resistance to aqueous environments. In this work, we show that ≥5 h incubation of the fibers, in a collection bath of 500 mM NaAc and 200 mM NaCl, at pH 5 results in fibers that do not dissolve in water or phosphate buffered saline, which implies that the fibers can be used for applications that involve wet/humid conditions. Furthermore, incubation in the collection bath improved the strain at break and was associated with increased β-sheet content, but did not affect the fiber morphology. In summary, we present a simple way to improve artificial spider silk fiber strain at break and resistance to aqueous solvents. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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15 pages, 3375 KiB  
Article
Structural Characterization of Black Widow Spider Dragline Silk Proteins CRP1 and CRP4
by Mikayla Shanafelt, Taylor Rabara, Danielle MacArt, Caroline Williams, Ryan Hekman, Hyun Joo, Jerry Tsai and Craig Vierra
Molecules 2020, 25(14), 3212; https://doi.org/10.3390/molecules25143212 - 14 Jul 2020
Cited by 1 | Viewed by 2668
Abstract
Spider dragline silk represents a biomaterial with outstanding mechanical properties, possessing high-tensile strength and toughness. In black widows at least eight different proteins have been identified as constituents of dragline silk. These represent major ampullate spidroins MaSp1, MaSp2, MaSp’, and several low-molecular weight [...] Read more.
Spider dragline silk represents a biomaterial with outstanding mechanical properties, possessing high-tensile strength and toughness. In black widows at least eight different proteins have been identified as constituents of dragline silk. These represent major ampullate spidroins MaSp1, MaSp2, MaSp’, and several low-molecular weight cysteine-rich protein (CRP) family members, including CRP1, CRP2, and CRP4. Molecular modeling predicts that CRPs contain a cystine slipknot motif, but experimental evidence to support this assertion remains to be reported. To advance scientific knowledge regarding CRP function, we recombinantly expressed and purified CRP1 and CRP4 from bacteria and investigated their secondary structure using circular dichroism (CD) under different chemical and physical conditions. We demonstrate by far-UV CD spectroscopy that these proteins contain similar secondary structure, having substantial amounts of random coil conformation, followed by lower levels of beta sheet, alpha helical and beta turn structures. CRPs are thermally and pH stable; however, treatment with reagents that disrupt disulfide bonds impact their structural conformations. Cross-linking mass spectrometry (XL-MS) data also support computational models of CRP1. Taken together, the chemical and thermal stability of CRPs, the cross-linking data, coupled with the structural sensitivity to reducing agents, are experimentally consistent with the supposition CRPs are cystine slipknot proteins. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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12 pages, 1077 KiB  
Article
Mechanical Properties and Weibull Scaling Laws of Unknown Spider Silks
by Gabriele Greco and Nicola M. Pugno
Molecules 2020, 25(12), 2938; https://doi.org/10.3390/molecules25122938 - 26 Jun 2020
Cited by 14 | Viewed by 2831
Abstract
Spider silks present extraordinary mechanical properties, which have attracted the attention of material scientists in recent decades. In particular, the strength and the toughness of these protein-based materials outperform the ones of many man-made fibers. Unfortunately, despite the huge interest, there is an [...] Read more.
Spider silks present extraordinary mechanical properties, which have attracted the attention of material scientists in recent decades. In particular, the strength and the toughness of these protein-based materials outperform the ones of many man-made fibers. Unfortunately, despite the huge interest, there is an absence of statistical investigation on the mechanical properties of spider silks and their related size effects due to the length of the fibers. Moreover, several spider silks have never been mechanically tested. Accordingly, in this work, we measured the mechanical properties and computed the Weibull parameters for different spider silks, some of them unknown in the literature. We also measured the mechanical properties at different strain rates for the dragline of the species Cupiennius salei. For the same species, we measured the strength and Weibull parameters at different fiber lengths. In this way, we obtained the spider silk scaling laws directly and according to Weibull’s prediction. Both length and strain rates affect the mechanical properties of spider silk, as rationalized by Weibull’s statistics. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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10 pages, 3802 KiB  
Article
Higher Gene Expression Related to Wound Healing by Fibroblasts on Silk Fibroin Biomaterial than on Collagen
by Tomoko Hashimoto, Katsura Kojima and Yasushi Tamada
Molecules 2020, 25(8), 1939; https://doi.org/10.3390/molecules25081939 - 22 Apr 2020
Cited by 14 | Viewed by 3555
Abstract
Silk fibroin (SF), which offers the benefits of biosafety, biocompatibility, and mechanical strength, has potential for use as a good biomedical material, especially in the tissue engineering field. This study investigated the use of SF biomaterials as a wound dressing compared to commercially [...] Read more.
Silk fibroin (SF), which offers the benefits of biosafety, biocompatibility, and mechanical strength, has potential for use as a good biomedical material, especially in the tissue engineering field. This study investigated the use of SF biomaterials as a wound dressing compared to commercially available collagen materials. After human fibroblasts (WI-38) were cultured on both films and sponges, their cell motilities and gene expressions related to wound repair and tissue reconstruction were evaluated. Compared to the collagen film (Col film), the SF film induced higher cell motility; higher expressions of genes were observed on the SF film. Extracellular matrix production-related genes were up-regulated in WI-38 fibroblasts cultured on the SF sponges. These results suggest that SF-based biomaterials can accelerate wound healing and tissue reconstruction. They can be useful biomaterials for functional wound dressings. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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7 pages, 1413 KiB  
Communication
Hierarchically Porous Silk/Activated-Carbon Composite Fibres for Adsorption and Repellence of Volatile Organic Compounds
by Aled D. Roberts, Jet-Sing M. Lee, Adrián Magaz, Martin W. Smith, Michael Dennis, Nigel S. Scrutton and Jonny J. Blaker
Molecules 2020, 25(5), 1207; https://doi.org/10.3390/molecules25051207 - 07 Mar 2020
Cited by 4 | Viewed by 3884
Abstract
Fabrics comprised of porous fibres could provide effective passive protection against chemical and biological (CB) threats whilst maintaining high air permeability (breathability). Here, we fabricate hierarchically porous fibres consisting of regenerated silk fibroin (RSF) and activated-carbon (AC) prepared through two fibre spinning techniques [...] Read more.
Fabrics comprised of porous fibres could provide effective passive protection against chemical and biological (CB) threats whilst maintaining high air permeability (breathability). Here, we fabricate hierarchically porous fibres consisting of regenerated silk fibroin (RSF) and activated-carbon (AC) prepared through two fibre spinning techniques in combination with ice-templating—namely cryogenic solution blow spinning (Cryo-SBS) and cryogenic wet-spinning (Cryo-WS). The Cryo-WS RSF fibres had exceptionally small macropores (as low as 0.1 µm) and high specific surface areas (SSAs) of up to 79 m2·g−1. The incorporation of AC could further increase the SSA to 210 m2·g−1 (25 wt.% loading) whilst also increasing adsorption capacity for volatile organic compounds (VOCs). Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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19 pages, 3543 KiB  
Article
Silk Particle Production Based on Silk/PVA Phase Separation Using a Microfabricated Co-flow Device
by Natalia Vargas Montoya, Rachel Peterson, Kimberly J. Ornell, Dirk R. Albrecht and Jeannine M. Coburn
Molecules 2020, 25(4), 890; https://doi.org/10.3390/molecules25040890 - 17 Feb 2020
Cited by 15 | Viewed by 3808
Abstract
Polymeric particles are ideal drug delivery systems due to their cellular uptake-relevant size. Microparticles could be developed for direct injection of drug formulations into a diseased site, such as a tumor, allowing for drug retention and slow drug exposure over time through sustained [...] Read more.
Polymeric particles are ideal drug delivery systems due to their cellular uptake-relevant size. Microparticles could be developed for direct injection of drug formulations into a diseased site, such as a tumor, allowing for drug retention and slow drug exposure over time through sustained release mechanisms. Bombyx mori silk fibroin has shown promise as a biocompatible biomaterial both in research and the clinic. Silk has been previously used to make particles using an emulsion-based method with poly(vinyl alcohol) (PVA). In this study, polydimethylsiloxane-based microfluidic devices were designed, fabricated, and characterized to produce silk particles through self-association of silk when exposed to PVA. Three main variables resulted in differences in particle size and size distribution, or polydispersity index (PDI). Utilizing a co-flow microfluidic device decreased the PDI of the silk particles as compared to an emulsion-based method (0.13 versus 0.65, respectively). With a flow-focusing microfluidics device, lowering the silk flow rate from 0.80 to 0.06 mL/h resulted in a decrease in the median particle size from 6.8 to 3.0 μm and the PDI from 0.12 to 0.05, respectively. Lastly, decreasing the silk concentration from 12% to 2% resulted in a decrease in the median particle size from 5.6 to 2.8 μm and the PDI from 0.81 to 0.25, respectively. Binding and release of doxorubicin, a cytotoxic drug commonly used for cancer treatment, with the fabricated silk particles was evaluated. Doxorubicin loading in the silk particles was approximately 41 µg/mg; sustained doxorubicin release occurred over 23 days. When the cytotoxicity of the released doxorubicin was tested on KELLY neuroblastoma cells, significant cell death was observed. To demonstrate the potential for internalization of the silk particles, both KELLY and THP-1-derived macrophages were exposed to fluorescently labelled silk particles for up to 24 h. With the macrophages, internalization of the silk particles was observed. Additionally, THP-1 derived macrophages exposure to silk particles increased TNF-α secretion. Overall, this microfluidics-based approach for fabricating silk particles utilizing PVA as a means to induce phase separation and silk self-assembly is a promising approach to control particle size and size distribution. These silk particles may be utilized for a variety of biomedical applications including drug delivery to multiple cell types within a tumor microenvironment. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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12 pages, 3002 KiB  
Article
Direct Recovery of the Rare Earth Elements Using a Silk Displaying a Metal-Recognizing Peptide
by Nobuhiro Ishida, Takaaki Hatanaka, Yoichi Hosokawa, Katsura Kojima, Tetsuya Iizuka, Hidetoshi Teramoto, Hideki Sezutsu and Tsunenori Kameda
Molecules 2020, 25(3), 761; https://doi.org/10.3390/molecules25030761 - 10 Feb 2020
Cited by 2 | Viewed by 3767
Abstract
Rare earth elements (RE) are indispensable metallic resources in the production of advanced materials; hence, a cost- and energy-effective recovery process is required to meet the rapidly increasing RE demand. Here, we propose an artificial RE recovery approach that uses a functional silk [...] Read more.
Rare earth elements (RE) are indispensable metallic resources in the production of advanced materials; hence, a cost- and energy-effective recovery process is required to meet the rapidly increasing RE demand. Here, we propose an artificial RE recovery approach that uses a functional silk displaying a RE-recognizing peptide. Using the piggyBac system, we constructed a transgenic silkworm in which one or two copies of the gene coding for the RE-recognizing peptide (Lamp1) was fused with that of the fibroin L (FibL) protein. The purified FibL-Lamp1 fusion protein from the transgenic silkworm was able to recognize dysprosium (Dy3+), a RE, under physiological conditions. This method can also be used with silk from which sericin has been removed. Furthermore, the Dy-recovery ability of this silk was significantly improved by crushing the silk. Our simple approach is expected to facilitate the direct recovery of RE from an actual mixed solution of metal ions, such as seawater and industrial wastewater, under mild conditions without additional energy input. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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18 pages, 6272 KiB  
Article
Silk/Natural Rubber (NR) and 3,4-Dihydroxyphenylalanine (DOPA)-Modified Silk/NR Composites: Synthesis, Secondary Structure, and Mechanical Properties
by Hiromitsu Sogawa, Treratanakulwongs Korawit, Hiroyasu Masunaga and Keiji Numata
Molecules 2020, 25(1), 235; https://doi.org/10.3390/molecules25010235 - 06 Jan 2020
Cited by 8 | Viewed by 4599
Abstract
Silk composites with natural rubber (NR) were prepared by mixing degummed silk and NR latex solutions. A significant enhancement of the mechanical properties was confirmed for silk/NR composites compared to a NR-only product, indicating that silk can be applied as an effective reinforcement [...] Read more.
Silk composites with natural rubber (NR) were prepared by mixing degummed silk and NR latex solutions. A significant enhancement of the mechanical properties was confirmed for silk/NR composites compared to a NR-only product, indicating that silk can be applied as an effective reinforcement for rubber materials. Attenuated total reflection Fourier transform infrared (ATR-FTIR) and wide-angle X-ray diffraction (WAXD) analysis revealed that a β-sheet structure was formed in the NR matrix by increasing the silk content above 20 wt%. Then, 3,4-dihydroxyphenylalanine (DOPA)-modified silk was also blended with NR to give a DOPA-silk/NR composite, which showed superior mechanical properties to those of the unmodified silk-based composite. Not only the chemical structure but also the dominant secondary structure of silk in the composite was changed after DOPA modification. It was concluded that both the efficient adhesion property of DOPA residue and the secondary structure change improved the compatibility of silk and NR, resulting in the enhanced mechanical properties of the formed composite. The knowledge obtained herein should contribute to the development of the fabrication of novel silk-based elastic materials. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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18 pages, 4947 KiB  
Article
Grafting versus Crosslinking of Silk Fibroin-g-PNIPAM via Tyrosine-NIPAM Bridges
by Ionut-Cristian Radu, Iuliana-Elena Biru, Celina-Maria Damian, Andreea-Cristina Ion, Horia Iovu, Eugenia Tanasa, Catalin Zaharia and Bianca Galateanu
Molecules 2019, 24(22), 4096; https://doi.org/10.3390/molecules24224096 - 13 Nov 2019
Cited by 21 | Viewed by 4093
Abstract
This paper reports the synthesis and complex characterization of novel polymeric networks based on the crosslinking of Bombyx mori silk fibroin via poly(N-isopropylacrylamide) bridges generated by an ammonium cerium nitrate redox system. The research study gives an understanding of the polymerization [...] Read more.
This paper reports the synthesis and complex characterization of novel polymeric networks based on the crosslinking of Bombyx mori silk fibroin via poly(N-isopropylacrylamide) bridges generated by an ammonium cerium nitrate redox system. The research study gives an understanding of the polymerization mechanism in terms of the generation of radical sites, radical growth and termination reaction, as well as the involvement of modifications on silk fibroin structure and properties. The physico-chemical characterization was carried out by FTIR-ATR, X-ray photoelectron spectroscopy and RAMAN spectroscopy with unravelling the chemical modification. The structural characterization and spatial arrangement by secondary structure were carried out by X-ray diffraction and circular dichroism. The thermal behavior and thermal stability were evaluated by differential scanning calorimetry and thermogravimetric analysis. The novel complex polymer network is intended to be used in the field of smart drug delivery systems. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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16 pages, 3129 KiB  
Article
Structure Water-Solubility Relationship in α-Helix-Rich Films Cast from Aqueous and 1,1,1,3,3,3-Hexafluoro-2-Propanol Solutions of S. c. ricini Silk Fibroin
by Kelvin O. Moseti, Taiyo Yoshioka, Tsunenori Kameda and Yasumoto Nakazawa
Molecules 2019, 24(21), 3945; https://doi.org/10.3390/molecules24213945 - 31 Oct 2019
Cited by 8 | Viewed by 3253
Abstract
Silk fibroin (SF) produced by the domesticated wild silkworm, Samia cynthia ricini (S. c. ricini) is attracting increasing interest owing to its unique mechanical properties, biocompatibility, and abundance in nature. However, its utilization is limited, largely due to lack of appropriate [...] Read more.
Silk fibroin (SF) produced by the domesticated wild silkworm, Samia cynthia ricini (S. c. ricini) is attracting increasing interest owing to its unique mechanical properties, biocompatibility, and abundance in nature. However, its utilization is limited, largely due to lack of appropriate processing strategies. Various strategies have been assessed to regenerate cocoon SF, as well as the use of aqueous liquid fibroin (LFaq) prepared by dissolution of silk dope obtained from the silk glands of mature silkworm larvae in water. However, films cast from these fibroin solutions in water or organic solvents are often water-soluble and require post-treatment to render them water-stable. Here, we present a strategy for fabrication of water-stable films from S. c. ricini silk gland fibroin (SGF) without post-treatment. Aqueous ethanol induced gelation of fibroin in the posterior silk glands (PSG), enabling its separation from the rest of the silk gland. When dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), the SGF-gel gave a solution from which a transparent, flexible, and water-insoluble film (SGFHFIP) was cast. Detailed structural characterization of the SGFHFIP as-cast film was carried out and compared to a conventional, water-soluble film cast from LFaq. FTIR and 13C solid-state NMR analyses revealed both cast films to be α-helix-rich. However, gelation of SGF induced by the 40%-EtOH-treatment resulted in an imperfect β-sheet structure. As a result, the SGF-gel was soluble in HFIP, but some β-sheet structural memory remains, and the SGFHFIP as-cast film obtained has some β-sheet content which renders it water-resistant. These results reveal a structure water-solubility relationship in S. c. ricini SF films that may offer useful insights towards tunable fabrication of novel biomaterials. A plausible model of the mechanism that leads to the difference in water resistance of the two kinds of α-helix-rich films is proposed. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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14 pages, 2261 KiB  
Article
Aggregation State of Residual α-Helices and Their Influence on Physical Properties of S. c. ricini Native Fiber
by Kelvin O. Moseti, Taiyo Yoshioka, Tsunenori Kameda and Yasumoto Nakazawa
Molecules 2019, 24(20), 3741; https://doi.org/10.3390/molecules24203741 - 17 Oct 2019
Cited by 5 | Viewed by 2492
Abstract
Formation of the α-helical conformation in the poly-l-alanine (PA) sequence regions, subsequent structural transition to β-sheet during natural spinning, and presence of residual α-helices in Samia cynthia ricini (S. c. ricini) native silk fiber have been [...] Read more.
Formation of the α-helical conformation in the poly-l-alanine (PA) sequence regions, subsequent structural transition to β-sheet during natural spinning, and presence of residual α-helices in Samia cynthia ricini (S. c. ricini) native silk fiber have been experimentally proven. However, the aggregation state of the residual α-helices, and their influence on the mechanical deformation behavior in native fiber remain unclear. Here we show that the α-helices form an ordered aggregation state with a hexagonal packing in the aqueous solution, some of which remain during natural spinning. X-ray scattering and differential scanning calorimetry (DSC) analyses revealed occurrence of a structural transition of the residual α-helices to the β-sheet structure, accompanied by disappearance of the plateau region in the force-strain curve, due to heat-treatment at ~220 °C. On the basis of X-ray scattering before and after tensile stretching of S. c. ricini native silk, a direct connection between the plateau region and the α-helix to β-sheet structural transition was confirmed. Our findings demonstrate the importance of the PA sequence regions in fiber structure formation and their influence on the tensile deformation behavior of S. c. ricini silk, features believed to be essentially similar in other saturniid silks. We strongly believe the residual ordered α-helices to be strategically and systematically designed by S. c. ricini silkworms to impart flexibility in native silk fiber. We anticipate that these knowledge forms a basis for fruitful strategies in the design and development of amino acid sequences for artificial silks with desired mechanical properties. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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Review

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41 pages, 14779 KiB  
Review
Silk Fibroin-Based Materials for Catalyst Immobilization
by Shanshan Lv
Molecules 2020, 25(21), 4929; https://doi.org/10.3390/molecules25214929 - 24 Oct 2020
Cited by 21 | Viewed by 5302
Abstract
Silk fibroin is a widely and commercially available natural protein derived from silkworm cocoons. Thanks to its unique amino acid composition and structure, which lead to localized nanoscale pockets with limited but sufficient hydration for protein interaction and stabilization, silk fibroin has been [...] Read more.
Silk fibroin is a widely and commercially available natural protein derived from silkworm cocoons. Thanks to its unique amino acid composition and structure, which lead to localized nanoscale pockets with limited but sufficient hydration for protein interaction and stabilization, silk fibroin has been studied in the field of enzyme immobilization. Results of these studies have demonstrated that silk fibroin offers an important platform for covalent and noncovalent immobilization of enzymes through serving as a stabilization matrix/support with high retention of the biological activity of the enzymes of interest. In the hope of providing suggestions for potential future research directions, this review has been written to briefly introduce and summarize key advances in silk fibroin-based materials for immobilization of both enzymes/biocatalysts (including alkaline phosphatase, β-glucosidase, glucose oxidase, lipase, urease, uricase, horseradish peroxidase, catalase, xanthine oxidase, tyrosinase, acetylcholinesterase, neutral protease, α-chymotrypsin, amylase, organophosphorus hydrolase, β-galactosidase, carbonic anhydrase, laccase, zymolyase, phenylalanine ammonia-lyase, thymidine kinase, and several others) and non-enzymatic catalysts (such as Au, Pd, Fe, α-Fe2O3, Fe3O4, TiO2, Pt, ZnO, CuO, Cu2O, Mn3O4, and MnO2). Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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22 pages, 7439 KiB  
Review
Structure and Dynamics of Spider Silk Studied with Solid-State Nuclear Magnetic Resonance and Molecular Dynamics Simulation
by Tetsuo Asakura
Molecules 2020, 25(11), 2634; https://doi.org/10.3390/molecules25112634 - 05 Jun 2020
Cited by 19 | Viewed by 6701
Abstract
This review will introduce very recent studies using solid-state nuclear magnetic resonance (NMR) and molecular dynamics (MD) simulation on the structure and dynamics of spider dragline silks conducted by the author’s research group. Spider dragline silks possess extraordinary mechanical properties by combining high [...] Read more.
This review will introduce very recent studies using solid-state nuclear magnetic resonance (NMR) and molecular dynamics (MD) simulation on the structure and dynamics of spider dragline silks conducted by the author’s research group. Spider dragline silks possess extraordinary mechanical properties by combining high tensile strength with outstanding elongation before breaking, and therefore continue to attract attention of researchers in biology, biochemistry, biophysics, analytical chemistry, polymer technology, textile technology, and tissue engineering. However, the inherently non-crystalline structure means that X-ray diffraction and electron diffraction methods provide only limited information because it is difficult to study the molecular structure of the amorphous region. The most detailed picture of the structure and dynamics of the silks in the solid state experimentally have come from solid-state NMR measurements coupled with stable isotope labeling of the silks and the related silk peptides. In addition, combination of solid-state NMR and MD simulation was very powerful analytical tools to understand the local conformation and dynamics of the spider dragline silk in atomic resolution. In this review, the author will emphasize how solid-state NMR and MD simulation have contributed to a better understanding of the structure and dynamics in the spider dragline silks. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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20 pages, 4197 KiB  
Review
Spider Silk for Tissue Engineering Applications
by Sahar Salehi, Kim Koeck and Thomas Scheibel
Molecules 2020, 25(3), 737; https://doi.org/10.3390/molecules25030737 - 08 Feb 2020
Cited by 118 | Viewed by 18403
Abstract
Due to its properties, such as biodegradability, low density, excellent biocompatibility and unique mechanics, spider silk has been used as a natural biomaterial for a myriad of applications. First clinical applications of spider silk as suture material go back to the 18th century. [...] Read more.
Due to its properties, such as biodegradability, low density, excellent biocompatibility and unique mechanics, spider silk has been used as a natural biomaterial for a myriad of applications. First clinical applications of spider silk as suture material go back to the 18th century. Nowadays, since natural production using spiders is limited due to problems with farming spiders, recombinant production of spider silk proteins seems to be the best way to produce material in sufficient quantities. The availability of recombinantly produced spider silk proteins, as well as their good processability has opened the path towards modern biomedical applications. Here, we highlight the research on spider silk-based materials in the field of tissue engineering and summarize various two-dimensional (2D) and three-dimensional (3D) scaffolds made of spider silk. Finally, different applications of spider silk-based materials are reviewed in the field of tissue engineering in vitro and in vivo. Full article
(This article belongs to the Special Issue Silk Fibroin Materials)
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