POEGMA hydrogel cross-linked by starch-based microspheres: synthesis and characterization

Abstract

Hydrogels with high mechanical strength and controllable stimuli responses are highly desirable in the biomedical field. Herein, starch-based microspheres were used as macrosized cross-linkers to synthesize a series of extremely tough and thermosensitive poly[2-(2-methoxyethoxy) ethyl methacrylate-co-oligo (ethylene glycol) methyl ether methacrylate] (POEGMA) hydrogels. Scanning electron microscopy and confocal laser scanning microscopy showed that the starch-based microspheres were uniformly distributed in the hydrogel network. Compression test results indicated that the POEGMA hydrogel exhibits strength of 3.0 MPa, which is ten times greater than that of conventional hydrogels cross-linked using small molecules. This improvement in mechanical strength is attributable to the even distribution of the cross-linking points in the hydrogel, because of which the length of the flexible polymer chains between the microspheres was similar. As a result, the polymer network can readily dissipate stress. Moreover, the mechanical strength of the POEGMA hydrogel can be regulated efficiently by varying the amount of microspheres used. In addition, the POEGMA hydrogel exhibited a lower critical solution temperature (LCST) of 37°C when the 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA)/oligo(ethylene glycol) methyl ether methacrylate (OEGMA300) mass ratio was 70/30. Further, the LCST of the POEGMA hydrogel can also be adjusted by adding salt or ethanol. The LCST decreased in the presence of sodium chloride but increased in the presence of ethanol.