Optimization of thermoresponsive hydrogels based on oligomers with lower critical solution temperature (LCST) far below/above physiological temperatures for biomedical applications

Abstract

Hydrogels with oligo(ethylene glycol) (OEG), oligo(propylene glycol) (OPG), and for the first time with combined OEG/OPG pendant chains within the methacrylate (MA) network, were synthesized and the swelling behavior, thermal properties, microstructure, and genotoxicity were investigated. Prior to hydrogel fabrication, an optimized method was developed for oligo(propylene glycol) methacrylate (OPGMA), i.e., oligomer with an LCST below a temperature at which synthesis occurs, indicating that proper preparation and tuning of reaction conditions were required. PEG6MA and PPG5MA homopolymers, as well as P(EG6/PG5)MA copolymer hydrogel, were produced by gamma radiation-induced polymerization and crosslinking of OEG and OPG monomers from the monomer-solvent mixture by using different water/ethanol composition as a solvent and by exposing the reaction mixture to various radiation doses. The combination of OEG and OPG pendant chains within the same network was advantageous in that it allowed an easy tuning of the phase transition temperature. Thus, the volume phase transition (VPT) at temperatures above 70 °C observed in the case of PEG6MA, and in the case of PPG5MA at temperatures below 15 °C, could easily be tuned close to physiological temperatures for P(EG6/PG5)MA hydrogel. Finally, all obtained thermoresponsive hydrogels showed non-genotoxic and non-cytotoxic properties, which indicate promising potential for biomedical applications.