Synthesis Of Thermoresponsive Hydrogels Cross-Linked With Acryloyloxyethylamino-Polysuccinimide

The hydrogels have been extensively applied as materials useful for tissueengineering and biomedicine because of their high water content, flexibility intailoring physiochemical properties and closely resemble natural living tissue.Environment-activity hydrogels have been studied most in the hydrogels. One of themost representative example is poly(N-isopropylacrylamide) (PNIPAAm). PNIPAAmexhibits a unique phase transition at lower critical solution temperature (LCST) in thevicinity of 32℃, which is close to physiological temperature. In this process,hydrogels undergo a reversible, discontinuous volume change.In this paper, biodegradable polysuccinimide (PSI) was obtained bymicrowave irradiation using maleic anhydride as materials. The PSI was convertedinto hydroxyethylamino-polysuccinimide (HEA-PSI) by partial ring-opening reactionwith ethanolamine. HEA-PSI was then acrylated by acryloyl chloride to obtain theacryloyloxethylamino-polysuccinimide (AEA-PSI) cross-linker with acryl groups.With AEA-PSI cross-linker, a series of biodegradable temperature-sensitiveP(N-isopropylacrylamide-co-acrylic acid) P(NIPAAm-co-AAc) hydrogels wereprepared by radical polymerization in phosphate buffer solution (PBS, pH=7.4).This work evaluated the water contents, lower critical solution temperature(LCST), the thermodynamics, the morphology and the biodegradable behaviors ofP(NIPAAm-co-AAc) hydrogels. The water contents of AEA-PSI-cross-linkedP(NIPAAm-co-AAc) hydrogels was more than 90% even at 37℃, which was controlled by the monomer molar ratio of NIPAAm/AAc, swelling media and thecross-linking density. The water content was higher in distilled water than in PBS(pH=7.4) solution. Hydrogels were pliable and transparent at room temperature butwhile above the LCST, hydrogels became stiff and opaque. The LCST ofAEA-PSI-cross-linked P(NIPAAm-co-AAc) hydrogels was significantly influencedby monomer ratio of the NIPAAm/AAc. The LCST increased with increase AAcmolar ratio. The thermodynamics stability was also characterized bythermogravimetry. By the thermal analysis, the thermal degradation of the hydrogelsappeared at a low temperature indicating that the hydrogels was possible to bedegraded. The morphological characteristics of hydrogels after exposure to distilledwater or PBS solution, and subsequently freeze-drying had been examined by scanelectron microscopy (SEM). The hydrogels exposed to PBS solution were corroded,indicating that the hydrogels were degradable in PBS. In enzymatic degradationstudies, breakdown of the AEA-PSI-cross-linked P(NIPAAm-co-AAc) hydrogels wasdependent on the cross-linking density and the concentration of the trypsin. Themacromolecule hydrophilic drug bovine serum albumin (BSA) was loaded into theAEA-PSI-cross-linked P(NIPAAm-co-AAc) hydrogels, and the loaded efficiencycould reach 98%. The BSA release behavior depended on the cross-linking densityand the NIPAAm/AAc molar ratio of the AEA-PSI-cross-linked P(NIPAAm-co-AAc)hydrogels.