Compositional Influence of Cross-linked Polyion Hydrogels from Poly(L-Lysine) and Poly(L-Glutamic Acid) on Their Properties for Potential Skin Applications

Chemically cross-linked hydrogels are synthesized from a set of protected L-lysine and L-glutamic acid containing homo and copolypetides. Cross-linking of the linear copolypeptides is achieved through the incorporation of L-tryptophan and its reaction with hexamethylene bis(triazolinodione). Upon deprotection, hydrogels with oppositely charged polypeptides of different L-lysine and L-glutamic acid composition form pH-dependent polyion complexes through electrostatic interaction. The obtained networks show distinct pH-dependent differences in their water swelling and rheological properties. Hydrogels at pH 4 display higher strengths compared to pH 8 and their rheological properties scale with L-lysine/L-glutamic acid ratio. At pH 8 results suggests that ionic interactions and presumably secondary structure effects have a significant impact on the hydrogel properties. This is further evident from the influence of the copolypetide structures, random versus block copolypeptides, used in the cross-linked hydrogel. None of the hydrogel shows any significant cytotoxicity against skin cell lines. Cross-linked hydrogels from different lysine and glutamic acid copolypeptides and polypeptide blends show structure and pH dependent properties. The hydrogels are compatible with skin cells rendering them suitable for skin and wound care applications. image