Synthesis and hydrogelation of star-shaped poly(l-lysine) polypeptides modified with different functional groups

Abstract

We report the synthesis and hydrogelation of star-shaped poly(l-lysine) modified with indole or phenyl group (s-PLL-g-Indo or s-PLL-g-Phenyl). The star-shaped graft copolypeptides were synthesized using readily available alcohols as the initiators to perform ring-opening polymerization (ROP) promoted by 1,1,3,3-tetramethylguanidine (TMG), followed by deprotection and side chain modification. The introduction of non-covalent interactions including hydrophobic and hydrogen bonding interactions by side chain modification promoted the spontaneous hydrogelation of these star-shaped graft copolypeptides and the gelation concentration can be as low as 0.75 wt% upon increasing the polypeptide arm number and arm length. The gel mechanical properties and molecular structures were found to dependent on the polypeptide arm number, arm length, and grafting moiety. The versatility of the star-shaped architecture allows for direct modification of the side chain, which can be an additional approach to modulate the gel mechanical properties to meet the requirement for specific applications.