Impact of initial solvent on thermal stability and mechanical properties of recombinant spider silk films

Abstract

Spider silk fibers are one of the most remarkable biopolymers displaying a unique combination of mechanical properties, biocompatibility and biodegradability. The recombinant production of spider silk proteins now allows the processing of silk proteins into novel materials with the aim of future applications. Here, we analyzed films made of a recombinantly produced, engineered spider silk protein with a sequence derived from the dragline silk protein ADF4 of the European garden spider Araneus diadematus. An influence of different initial solvents (aqueous buffer, hexafluoro-2-propanol and formic acid) on certain film properties was identified in as cast as well as methanol post-treated films: while no significant effects on the films' thermal stability were observed, a significant influence on their mechanical properties could be shown. Interestingly, solvent-induced effects were sustained after methanol post-treatment and could be correlated with the presence and arrangement of secondary structure elements. Insights into molecular orientation of individual structural elements within the films upon applied load were revealed by combined polarized IR spectroscopy and mechanical measurements.