pH and ion-selective swelling behaviour of keratin and keratose 3D hydrogels

Abstract

The oxidation of keratin hydrogels was optimized aiming to obtain keratose hydrogels while maintaining the original 3D structure and pH-responsive behaviour. In addition, we present a comparative study of their dual-stimuli responsive behaviour regarding the pH-responsiveness and their previously non-described ion selective responsiveness. Keratose and keratin hydrogels showed similar swellings when contracted at low pH, and the former showed steeper expansion and higher swelling than the latter at high pH. In addition, both hydrogels showed selective responsiveness toward Ca2+ ions when expanded, and toward Cu2+ ions when contracted. IR, Raman, ss-NMR, HRMAS NMR, SAXS, and thermal characterization demonstrated that oxidation does not interfere with the stimuli-responsive mechanisms related to protein conformation. The higher swelling of keratose hydrogels would be originated in the increase of the mobility of the chains after oxidation coupled to the hydration of sulfonic acid groups.