dl-Polyalanine as a PEG-Free Thermogel.

Thermogelling behavior of aqueous polymer solutions comes from the delicate balance between hydrophilic and hydrophobic moieties of the polymer. Typically, poly(ethylene glycol) (PEG) has been used as a hydrophilic block in most thermogels reported to date. However, recent papers have suggested the potential immunogenicity of PEG-conjugated compounds. Here, we report that aqueous solutions of dl-polyalanine (DL-PA) with a specific molecular weight can exhibit thermogelling behavior. In particular, DL-PA with a molecular weight (Mn) of 6690 Da, DL-PA67, exhibited sol-to-gel transition at the physiologically important temperature range of 30-40 °C. 1H NMR and FTIR data indicated that the mechanism of thermogelation is related to dehydration and conformational changes of DL-PA67 from random coil to β-sheet structures. Subcutaneous injection of an aqueous DL-PA67 solution into rats confirmed the gel formation and its histocompatibility with mild tissue irritation.