An experimental confirmation of thermal transitions in native and regenerated spider silks.

Biological structures such as spider silks are formed by proteins. The physical properties of such proteins are determined by environmental conditions such as temperature and humidity. In this paper, we confirm the thermal transitions that take place in spider silks using differential scanning calorimetry and study how the interaction of spider silk proteins with water affects the onset temperatures for these thermal processes. Native fibres and regenerated films of dragline silk and egg sac silk from Argiope argentata spiders were used to study thermal transitions of protein based structures. For the first time, differential scanning calorimetry (DSC) tests were carried out with spider silk samples of relatively large mass (10mg). Previous attempts of DSC tests applied to spider silk samples failed to detect thermal transitions in a conclusive way. The tests reported here, however, show thermal transitions on both natural and regenerated samples that are in agreement with results from dynamic mechanical analysis (DMA) tests reported in the literature. The water content on spider silks seems to lower the temperatures at which such thermal transitions take place. The results also confirm that the amorphous regions of native and regenerated spider silk and silk worm silk give rise to similar thermal transitions.