Self-Assembly and Hydrogelation of Coil-Sheet Poly(l -lysine)- block-poly(l -threonine) Block Copolypeptides

This study reports the self-assembly and hydrogelation of coil-sheet poly(l-lysine)-block-poly(l-threonine) (PLL-b-PLT) block copolypeptides. Our experiments showed that the PLL-b-PLT block copolypeptides with degrees of polymerization (DPs) between 30 and 60 can self-assemble to form fibrils due to the packing of sheetlike PLT at low polymer concentrations; moreover, further increasing the polymer concentration can result in the formation of transparent hydrogels due to fibril entanglements. The hydrogelation was determined by the orientation and packing of the fibril assemblies, which aremainly dictated by the balance between the intermolecular hydrogen bonding interactions and charge repulsion exerted respectively by sheetlike PLT and positively charged, coil PLL segments. The noncovalent interactions can be manipulated by varying the polypeptide chain length and composition, which would result in these block copolypeptides exhibiting different critical gelation concentrations (CGCs), gel molecular assemblies, and mechanical properties.