Protein Paper from Exfoliated Eri Silk Nanofibers

The exfoliation of silk fiber is an attractive method to produce silk micro- and nanofibers that retain the secondary structure of native silk. However, most fibrillation methods used to date require the use of toxic and/or expensive solvents and the use of high energy. This study describes a low cost, scalable method to produce microfibrillated silk nanofibers without the use of toxic chemicals by controlling the application of shear using commercially scalable milling and homogenization equipment. Manipulation of the degumming conditions (alkaline concentration and degumming temperature) and the shear in milling and/or homogenization enabled control over the degree of fibrillation. The microfibrillated silk was then characterized to determine structural change during processing and the stability of the resulting suspensions at different pH. Silk nanofibers obtained from milling degummed silk were characterized using atomic force microscopy. Nanofibers obtained both with and without high-pressure homogenization were then used to produce silk "protein paper" through casting. Silk degumming conditions played a critical role in determining the degree of microfibrillation and the properties of the cast silk papers. The silk papers produced from homogenized nanofibers showed excellent mechanical properties, high water absorption, and wicking properties. The silk papers were excellent for supporting the attachment and growth of human skin keratinocytes, demonstrating application possibilities in healthcare such as wound healing.