Tuning the Degradation Rate of Poly(2-hydroxypropyl methacrylamide)-<i>g</i><i>raft</i>-oligo(lactic acid) Stereocomplex Hydrogels

Abstract

The degradation time of stereocomplex hydrogels based on poly(2-hydroxypropyl methacrylamide) (pHPMAm) with oligo(lactic acid) side chains of opposite chirality can be tailored from approximately 1 week to almost 3 months under physiological conditions by adjusting the grafting density and the side chain terminus. The polymers were prepared by free radical copolymerization of HPMAm−oligo(lactic acid) macromonomers and HPMAm. The viscoelasticity and degradation time of hydrogels formed by mixing aqueous solutions of two polymers containing side chains of opposite chirality increased with increasing grafting density. Gels based on polymers with side chains having acetyl chain ends degraded slower than those containing hydroxyl-terminating side chains, because of a change in the hydrolysis mechanism from slow random chain scission to more rapid chain end scission (backbiting), respectively. The ease of preparation and the possibility of tuning the degradation rate over a wide range make these pHPMAm-based hydrogels ideal materials for the controlled release of, e.g., therapeutic proteins.