Study Of Quick Response Temperature Sensitive Hydrogels And Its Application On Immobilized Enzyme

Temperature sensitive hydrogels’swelling ratio can be changed significantly near the lower critical solution temperature, poly(N-isopropyl acrylamide) is the most widely used.It has a broad application prospect in drug controlled release、material separation and enzyme immobilization, etc.Used it for immobilizing enzymes can realize homogeneous catalysis and heterogeneous separation, and is good for separation、reuse and continuous production.In this paper, N-isopropyl acrylamide (NIPAm) as raw material, polyethylene glycol(PEG) as the pore-foaming agent, bring in linear poly(2-hydroxyethyl methacrylate)(PHEMA) or ethylenediamine modified poly (2-hydroxyethyl methacrylate)(PAEMA), a series of porous semi-interpenetrating network hydrogels were prepared by free radical polymerization method, the swelling properties were studied. The best PNIPAm/PHEMA②and PNIPAm/PAEMA Ⅳwere selected and characterized by FT-IR、SEM. DSC, etc. The result showed that these two hydrogels have porous structure and the aperture was more than5microns, phase transition temperature were34.2℃and34.4℃respectively, with fast temperature response rate. Maleic imide group was introduced by modified with maleic anhydride, these two hydrogels remained porous structure and fast temperature response performance, phase transition temperature were34.4℃and34.8℃respectively.NIPAm and HEMA as raw materials, temperature sensitive microsphere P(NIPAm-co-HEMA) was prepared by soap-free emulsion polymerization, characterized by FT-IR、SEM、DSC、sizer, etc. The result showed that hydrogel as a spherical particle, with the average size of22.4microns in the state of swelling under room temperature, and fast temperature response rate, phase transition temperature was36.2℃. Modified with maleic anhydride, the hydrogel remained spherical, with the average size reduced to13.0microns in the state of swelling under room temperature, because its hydrophilicity was reduced, it still had fast temperature response performance, and phase transition temperature was35.8℃.The enzymes were immobilized while the porous semi-interpenetrating network hydrogels and hydrogel microsphere as carriers, glutaraldehyde as crosslinking agent. The result showed that the performance of the immobilized enzyme was best with microgel P(NIPAm-co-HEMA) as the carrier and concentration of glutaraldehyde was2.5vol%. Meanwhile, the activity of immobilized lipase was0.25U/g, activity recovery was1.84%and the stability was of82%or more; the activity of immobilized glucoamylase was12.46U/mL, activity recovery was3.52%and the stability was of83%or more. The enzymes were immobilized by click reaction with maleic anhydride modified porous semi-interpenetrating hydrogels and hydrogel microsphere as the carriers. The result showed that the performance of the immobilized lipase was best with maleic anhydride modified PNIPAm/PAEMA Ⅳ as carrier, its activity was0.82U/g, activity recovery was6.03%and the stability was around90%; the performance of the immobilized glucoamylase was best with maleic anhydride modified hydrogel microsphere P(NIPAm-co-HEMA) as carrier, its activity was17.72U/mL, activity recovery was5.00%and the stability was of88%or more. The activity of immobilized enzyme by means of click reaction was2-5times that glutaraldehyde as the crosslinking agent with high stability. Finally, several influence factors were studied through the determination of immobilized enzyme activity under conditions of different concentration of substrate、temperature and pH.