Comparison of Crosslinker Types and Initiation Systems of Thermoresponsive PNIPAM Hydrogels

Thermoresponsivehydrogels are three-dimensional polymer networks which undergo conformationalchanges in aqueous media depending on the external temperature. As the lowercritical temperature (LCST) is close to the body temperature,poly(N-isopropylacrylamide) (PNIPAM) is the main thermoresponsive hydrogel usedfor biomedical applications. Below LCST, PNIPAM hydrogels swell in aqueousmedia, above LCST they become insoluble and shrink. This behavior makes itpossible to design drug release systems controlled by external temperature.Swelling/shrinking response of PNIPAM hydrogel depends on several factors suchas crosslinker type, crosslinking density, hydrophobic/hydrophilic balance andinitiator type. In this study, the effects of the initiation system and thecrosslinker type on different thermoresponsive hydrogels were compared. Forthis purpose, thermoresponsive hydrogels were synthesized by using ethyleneglycol dimethylacrylate (EGDMA) and N,N′-ethylene bisacrylamide (EBAM) ascrosslinkers via photo and thermal initiation systems. The hydrogels werecharacterized by FTIR spectroscopy and scanning electron microscope (SEM).Effects of the initiation system and the crosslinker type on the release,swelling behavior, morphology and the biocompatibility behavior of thehydrogels were investigated. The hydrogels synthesized with EBAM demonstrated morepromising results compared to the one synthesized EGDMA. It was concluded thatpoly(EBAM-co-NIPAM)-P has the highest swelling ratio and poly(EBAM-co-NIPAM)-Tis the most biocompatible hydrogel. In terms of release characteristics, there wasnot a significant difference between the hydrogels, even though their swellingcharacteristics differ.
Thermoresponsivehydrogels are three-dimensional polymer networks which undergo conformationalchanges in aqueous media depending on the external temperature. As the lowercritical temperature (LCST) is close to the body temperature,poly(N-isopropylacrylamide) (PNIPAM) is the main thermoresponsive hydrogel usedfor biomedical applications. Below LCST, PNIPAM hydrogels swell in aqueousmedia, above LCST they become insoluble and shrink. This behavior makes itpossible to design drug release systems controlled by external temperature.Swelling/shrinking response of PNIPAM hydrogel depends on several factors suchas crosslinker type, crosslinking density, hydrophobic/hydrophilic balance andinitiator type. In this study, the effects of the initiation system and thecrosslinker type on different thermoresponsive hydrogels were compared. Forthis purpose, thermoresponsive hydrogels were synthesized by using ethyleneglycol dimethylacrylate (EGDMA) and N,N′-ethylene bisacrylamide (EBAM) ascrosslinkers via photo and thermal initiation systems. The hydrogels werecharacterized by scanning electron microscope (SEM) and FTIR spectroscopy. Effectsof the initiation system and the crosslinker type on the release, swellingbehavior, morphology and the biocompatibility behavior of the hydrogels wereinvestigated. The hydrogels synthesized with EBAM demonstrated more promisingresults compared to the one synthesized EGDMA. It was concluded that poly(EBAM-co-NIPAM)-Phas the highest swelling ratio and poly(EBAM-co-NIPAM)-T is the mostbiocompatible hydrogel. In terms of release characteristics, there was not asignificant difference between the hydrogels, even though their swellingcharacteristics differ.