Preparation of silk resins by hot pressing Bombyx mori and Eri silk powders

Structural and mechanical comparison of Eri and Mulberry silk fibroin nanofibers films through advanced mechanical treatments for sustainable applications

Mulberry silk (Bombyx mori) and eri silk (Samia/Philosamia ricini) are widely used silks. Eri silk is a wild silk that contains an arginine-glycine-aspartic acid tripeptide sequence within its structure, making it a potential and sustainable biomaterial. However, its poor solubility using conventional methods has resulted in limited research compared with that of mulberry silk fibroin. This study investigated the differences between nanofibrillated fibroins from both silks to assess their biomedical potential, focusing on their structural, morphological, and mechanical properties, as well as their biodegradability. Both silks were degummed and processed into fibroin microfibers (FMF) and fibroin nanofibers (FNF) via high-pressure ultrasonication and grinding in an aqueous solution. Analyses were performed using fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), atomic force microscopy (AFM), scanning electron microscope (SEM), UV-visible spectrometry, and thermogravimetric analysis (TGA) techniques. The results showed that both silks were prepared by high-pressure ultrasonication and exhibited microfibers when treated with a grinder machine, which can produce fibroin nanofibers. In terms of the type of fibroin, when comparing the properties of both silks, it was found that they have similar chemical structures but differ in their physical properties. Moreover, eri fibroin films showed superior transparency, high thermal resistance, and high strength, but were more brittle than mulberry fibroin films, which was attributed to amino acid differences. Eri silk has unique features that are interesting for the development of new materials and can create new pathways for utilizing non-mulberry silk.

Porous Thermoplastic Molded Regenerated Silk Crosslinked by the Addition of Citric Acid

Thermoplastic molded regenerated silk fibroin was proposed as a structural material in tissue engineering applications, mainly for application in bone. The protocol allows us to obtain a compact non-porous material with a compression modulus in the order of a Giga Pascal in dry conditions (and in the order of tens of MPa in wet conditions). This material is produced by compressing a lyophilized silk fibroin powder or sponge into a mold temperature higher than the glass transition temperature. The main purpose of the produced resin was the osteofixation and other structural applications in which the lack of porosity was not an issue. In this work, we introduced the use of citric acid in the thermoplastic molding protocol of silk fibroin to obtain porosity inside the structural material. The citric acid powder during the compression acted as a template for the pore formation. The mean pore diameter achieved by the addition of the higher amount of citric acid was around 5 μm. In addition, citric acid could effectively crosslink the silk fibroin chain, improving its mechanical strength. This effect was proved both by evaluating the compression modulus (the highest value recorded was 77 MPa in wet conditions) and by studying the spectra obtained by Fourier transform infrared spectroscopy. This protocol may be applied in the near future to the production of structural bone scaffolds.

Use of Bombyx mori silk fibroin in tissue engineering: From cocoons to medical devices, challenges, and future perspectives

Silk fibroin has become a prominent material in tissue engineering (TE) over the last 20 years with almost 10,000 published works spanning in all the TE applications, from skeleton to neuronal regeneration. Fibroin is an extremely versatile biopolymer that, due to its ease of processing, has enabled the development of an entire plethora of materials whose properties and architectures can be tailored to suit target applications. Although the research and development of fibroin TE materials and devices is mature, apart from sutures, only a few medical products made of fibroin are used in the clinical routines. <40 clinical trials of Bombyx mori silk-related products have been reported by the FDA and few of them resulted in a commercialized device. In this review, after explaining the structure and properties of silk fibroin, we provide an overview of both fibroin constructs existing in the literature and fibroin devices used in clinic. Through the comparison of these two categories, we identified the burning issues faced by fibroin products during their translation to the market. Two main aspects will be considered. The first is the standardization of production processes, which leads both to the standardization of the characteristics of the issued device and the correct assessment of its failure. The second is the FDA regulations, which allow new devices to be marketed through the 510(k) clearance by demonstrating their equivalence to a commercialized medical product. The history of some fibroin medical devices will be taken as a case study. Finally, we will outline a roadmap outlining what actions we believe are needed to bring fibroin products to the market.

Emerging Silk Material Trends: Repurposing, Phase Separation and Solution-Based Designs

Silk continues to amaze. This review unravels the most recent progress in silk science, spanning from fundamental insights to medical silks. Key advances in silk flow are examined, with specific reference to the role of metal ions in switching silk from a storage to a spinning state. Orthogonal thermoplastic silk molding is described, as is the transfer of silk flow principles for the triggering of flow-induced crystallization in other non-silk polymers. Other exciting new developments include silk-inspired liquid-liquid phase separation for non-canonical fiber formation and the creation of "silk organelles" in live cells. This review closes by examining the role of silk fabrics in fashioning facemasks in response to the SARS-CoV-2 pandemic.

H. Mohammed A, Akioka S, Ngo Trinh T. Fabrication of Silk Resin with High Bending Properties by Hot-Pressing and Subsequent Hot-Rolling

This research reports the processability and mechanical properties of silk resins prepared by hot-pressing followed by hot-rolling and then analyzes their thermal and structural properties. The results show that regenerated silk (RS) resins are better suited for hot-rolling than Eri and Bombyx mori silk resins (untreated silk). When hot-rolling at 160 °C with a 50% of reduction ratio, maximum bending strength and Young’s modulus of RS resin reaches 192 MPa and 10.2 GPa, respectively, after pretreatment by immersion in 40 vol% ethanol, and 229 MPa and 12.5 GPa, respectively, after pretreatment by immersion in boiling water. Increased strength of the material is attributed to the increased content of aggregated strands and intramolecular linking of β sheets (attenuated total reflectance Fourier-transform infrared spectroscopy) and higher crystallinity (X-ray diffraction analysis). After hot-pressing and hot-rolling, RS resins have a stable decomposition temperature (297 °C).