UCST-type phase transition driven by protein-derived polypeptide employing gelatin and chitosan

Here, we describe the thermosensitive reversible phase transition behaviors of polyelectrolyte complex composed of gelatin and chitosan (G/C complex). An aqueous dispersion of the G/C complexes showed a clear upper critical solution temperature (UCST) at around 30°C. The thermosensitive phase transition behavior showed excellent reversibility and large thermal hysteresis as a usual phenomenon based on the intra- and inter-molecular interaction change. A high correlation was observed between the UCST of the G/C complex and the helix-melting temperature of gelatin by circular dichroism, which suggested that the phase transition of the G/C complex corresponded to the secondary structure (helix-coil) transition of gelatin. Notably, the UCST of the G/C complex shifted to lower temperatures in the presence of urea, which is well known to destabilize gelatin, whereas the addition of salt led to the dissolution of the G/C complex. It is envisaged that the results of this study will have a significant impact on the fabrication of UCST-type thermosensitive materials, which can be utilized under aqueous physiological conditions using well-known biopolymers. This protein-derived functional material, which responds to the secondary structure transition, could also be used for the development of novel UCST-type thermosensitive biomaterials.