Swelling Behavior Of Amino Acid Ester Modified Poly(NVP-co-MMA) Hydrogels

Equilibrium swelling degree of the ionic N-Vinyl pyrrolidone-methylmethacrylate copolymer hydrogel was reached within48hours, which was notcommensurate with the rate of growth and development of children’s eyes, resulted inthe multiplethe surgeries for the evisceration or enucleation. The overall objective ofthis project was to provide a kind of ophthalmic tissue filler hydrogel and itspreparation method, which can be able to swell very slowly in the environment ofhuman body fluids. And the release rate of the swelling ability can be regulated.N-vinyl pyrrolidone (NVP) was copolymerized with methyl methacrylate (MMA)with allyMA and EGDM as crosslinking agents and AIBN as the initiator throughbulk polymerization. After polymerization, the neutral copolymer hydrogel wastransformed into an ionized hydrogel by converting–COOCH3groups into COOH.Furthermore, with water-soluble EDC as the catalyst, the carboxyl groups wereconverted partially into amido bonds through the amidation reaction with amino acidesters. Amino acid esters were hydrolyzed very slowly in pHysiological environment,which can achieve a long-term swelling behavior of the NVP-MMA copolymerhydrogels. The efficiency of the amidation reaction was greatly depended on theconcentration of the EDC/NHS and amino acid esters, amidation time andtemperature. The volume swelling degree of the hydrogels was increased more rapidlyin alkaline than in neutral solution because of the accelerated hydrolysis of theintroduced amino acid esters.The vivo experimental results showed that the long-term swelling behavior wasdepended on the tissue fluid in the orbital and periorbital tissue extrusion. Theequilibrium swelling degree of the hydrogel sample in vivo was slightly less than thatin vitro. Different ester copolymer hydrogel possessed the different initial swellingbalancing, which had nothing with the long-term swelling behavior, remained parallelrelationship. The smaller ester-substitution degree was, the more easily the finalequilibrium swelling degree can be reached; the greater ester-substitution degree was,the more difficult the final equilibrium swelling degree can be reached. So we cancontrol copolymer hydrogels long-term swelling time through increasingester-substitution efficiency, to meet the requirements for the children patients withorbital growth and development.