Water-Stable Silk Films with Reduced β-Sheet Content

Abstract

Silk fibers have outstanding mechanical properties. These fibers are insoluble in organic solvents and water, are biocompatible, and exhibit slow biodegradation in vitro and in vivo due to the hydrophobic nature of the protein and the presence of a high content of β‐sheet structure. Regenerated silk fibroin can be processed into a variety of materials normally stabilized by the induction of β‐sheet formation through the use of solvents or by physical stretching. To extend the biomaterial utility of silk proteins, options to form water‐stable silk‐based materials with reduced β‐sheet formation would be desirable. To address this need for more rapidly degradable silk biomaterials, we report the preparation of water‐stable films from regenerated silk fibroin solutions, with reduced β‐sheet content. The keys to this process are the preparation of concentrated (8 % by weight) aqueous solutions of fibroin and a subsequent water‐based annealing procedure. These new materials degrade more rapidly due to the reduced β‐sheet content, as determined in vitro via enzymatic hydrolysis, yet support human adult stem‐cell expansion in vitro in a similar or improved fashion to the crystallized proteins in film form. These new silk‐based materials extend the range of biomaterial properties that can be generated from this unique family of proteins.

Toward Biodegradable Mg–Air Bioelectric Batteries Composed of Silk Fibroin–Polypyrrole Film

“…They were consistent with the previously reported water-annealed silk films. [22,26] The PPy-modified side of SF-PPy film showed only PPy characteristic peaks due to its complete coverage on the silk substrate. It exhibited absorption peaks of C-N absorption at around 1293 cm -1 , PPy ring breathing at 1150 cm -1 and C-H in plane bending modes at about 1025 cm -1 .…”

Biocompatible silk fibroin scaffold prepared by reactive inkjet printing

“…Similarly, the degradation rate of RSF can be controlled by varying the processing route [1,2]. For instance, water-annealed films are more flexible and have a faster degradation rate than that of methanol treated films [1]. Silk degrades into non-harmful peptides and free amino acids that can be easily removed by the body [10], which is superior to materials such as polyesters that degrade into acidic by-products, leading to increased levels of inflammation around the implant site.…”

“…By increasing the b-sheet content using approaches such as controlled drying and alcohol immersion, the mechanical properties of RSF films can be improved. Similarly, the degradation rate of RSF can be controlled by varying the processing route [1,2]. For instance, water-annealed films are more flexible and have a faster degradation rate than that of methanol treated films [1].…”

“…3c. As discussed earlier, the ability to selectively induce regions of different crystallinity could be used to control degradation rate, since the degradation of RSF structures is related to their b-sheet content [1,2]. Inkjet printing offers greater flexibility in controlling the crystallinity of the RSF structure due to its selectively patterning nature.…”

“…Silk is a versatile, natural material favoured for its mechanical strength, excellent biocompatibility, adaptable biodegradability [1,2], easy processing [3] and flexible structural modification [4]. Silk has a long history of use [5]; recently, regenerated silk fibroin (RSF) has been used as a building block for the fabrication of biomedical devices [3].…”