Presence of β-Turn Structure in Recombinant Spider Silk Dissolved in Formic Acid Revealed with NMR

Spider dragline silk is a biopolymer with excellent mechanical properties. The development of recombinant spider silk protein (RSP)-based materials with these properties is desirable. Formic acid (FA) is a spinning solvent for regenerated Bombyx mori silk fiber with excellent mechanical properties. To use FA as a spinning solvent for RSP with the sequence of major ampullate spider silk protein from Araneus diadematus, we determined the conformation of RSP in FA using solution NMR to determine the role of FA as a spinning solvent. We assigned 1H, 13C, and 15N chemical shifts to 32-residue repetitive sequences, including polyAla and Gly-rich regions of RSP. Chemical shift evaluation revealed that RSP is in mainly random coil conformation with partially type II β-turn structure in the Gly-Pro-Gly-X motifs of the Gly-rich region in FA, which was confirmed by the 15N NOE data. In addition, formylation at the Ser OH groups occurred in FA. Furthermore, we evaluated the conformation of the as-cast film of RSP dissolved in FA using solid-state NMR and found that β-sheet structure was predominantly formed.

Silk Protein Composite Bioinks and Their 3D Scaffolds and In Vitro Characterization

This paper describes the use of silk protein, including fibroin and sericin, from an alkaline solution of Ca(OH)2 for the clean degumming of silk, which is neutralized by sulfuric acid to create calcium salt precipitation. The whole sericin (WS) can not only be recycled, but completely degummed silk fibroin (SF) is also obtained in this process. The inner layers of sericin (ILS) were also prepared from the degummed silk in boiling water by 120 °C water treatment. When the three silk proteins (SPs) were individually grafted with glycidyl methacrylate (GMA), three grafted silk proteins (G-SF, G-WS, G-ILS) were obtained. After adding I2959 (a photoinitiator), the SP bioinks were prepared with phosphate buffer (PBS) and subsequently bioprinted into various SP scaffolds with a 3D network structure. The compressive strength of the SF/ILS (20%) scaffold added to G-ILS was 45% higher than that of the SF scaffold alone. The thermal decomposition temperatures of the SF/WS (10%) and SF/ILS (20%) scaffolds, mainly composed of a β-sheet structures, were 3 °C and 2 °C higher than that of the SF scaffold alone, respectively. The swelling properties and resistance to protease hydrolysis of the SP scaffolds containing sericin were improved. The bovine insulin release rates reached 61% and 56% after 5 days. The L929 cells adhered, stretched, and proliferated well on the SP composite scaffold. Thus, the SP bioinks obtained could be used to print different types of SP composite scaffolds adapted to a variety of applications, including cells, drugs, tissues, etc. The techniques described here provide potential new applications for the recycling and utilization of sericin, which is a waste product of silk processing.

Silk Microlens Array

Optics that are capable of merging with biomaterials create a variety of opportunities for sensing disease, for therapeutics, and for augmenting brain-machine interface. The FDA has approved silk devices for sutures and reconstructive surgery. Recently, a silk product made from regenerated silk protein is FDA approved for orthopedic application, as the understanding of structure and processing technologies of silk fibroin has been improved. Here, we report a facile fabrication process to construct silk microlens array. The process includes preparation of regenerated silk solution and casting on a micropatterned poly(dimethylsiloxane) (PDMS) master. Due to the identical surface area of a unit patterned regime, the silk solution exhibits a partial wetting state in the vicinity of the silk solution–PDMS–vapor interface with same contact angle, and after drying, produces consistent radius of curvature within the microlens array. This in turn provides highly uniform focal length, focal spot diameter, and imaging performance of individual lens. Our results provide the foundation for biophotonic microlens adding new capabilities for implantable and degradable devices from regenerated silk protein.

Challenges and Opportunities of Silk Protein Hydrogels in Biomedical Applications

In the context of this era of complementary interdisciplinary advances, the design and preparation of hydrogel materials has been a hot avenue of research for a variety of applications. Silk...

Fabrication of flexible conductive silk fibroin/polythiophene membrane and its properties

Silk fibroin (SF) film is an insulating material, which can be combined with polythiophene derivatives with electrical conductivity to obtain a flexible conductive material. In this work, poly(3,4-ethylenedioxythiophene) (PEDOT) was used to graft a silk protein film. The hydroxyl radical is formed by activation and oxidation of the silk protein film polymerized with the PEDOT radical formed by oxidation of 3,4-ethylenedioxythiophene to obtain a conductive silk film. The SF/PEDOT film, when tested, showed excellent electrical conductivity with resistance up to 63 Ω·cm−2, good flexibility, mechanical properties, fastness, and biocompatibility.