Preparation And Characterization Of Thermo-sensitivehydrogel For Nerve Regeneration

In terms of no cure for the damaged central nerve cell, the thesis is going to prepare a novel temperature-sensitive hydrogel with unique grid structure. The respond range of the novel hydrogel locates around 37?. Further more, the gel was given bioactive by grafting polypeptide to its surface carboxyl group, which makes it a novel material for nerve regeneration.Firstly, low-molecular chain transfer agent,4-cyanopentanoic acid dithiobenzoate(CADB), was synthesized from sulfur, benzyl chloride, 4-cyanopentanoic acid dithiobenzoate. Then it was used to initiate RAFT polymerization of NIPAM to prepare well-defined and low-dispersity PNIPAMs with terminal chain transfer agent group. ?-carboxy, ?-acrylate PEG(Ac-PEG-COOH) and ?-acrylate, ?-acrylate PEG(Ac-PEG-Ac) were synthesized successfully from ethyl bromoacetate and acryloyl chloride. The PNIPAM-b-PEG-COOH precursor and the PNIPAM-b-PEG-g-IKVAV precursor were synthesized successfully by grafting Ac-PEG-COOH and Ac-PEG-g-IKVAV to PNIPAM, respectively.In the end, the hydrogels grafted with PNIPAM/PNIPAM-b-PEG-COOH/PNIPAM-bPEG-g-IKVAV were synthesized successfully from PNIPAM/ PNIPAM-b-PEG-COOH/PNIPAM- b-PEG-g-IKVAV precursors.The results from the analysis of gelation mechanism was concluded that the gelation process includes two steps. The first step, the PNIPAM/PNIPAM-b-PEGCOOH/PNIPAM-b-PEG-g-IKVAV precursor cross-linked with each other by the terminal vinyl group, which formed multi-arm star polymers. The second step, multi-arm star polymers were connected by Ac-PEG-Ac crosslinker to form mutual cross-linked network. BISAM was mainly consumed at interior cross-linking of multi-arm star polymers.It has been discussed that the effects of composition, structure and feed ratios on the swelling properties of hydrogel grafted PNIPAM/PNIPAM-b-PEG-COOH. It was concluded that the swelling properties of gels was controlled together by the interior structure, the cross-linking density, the hydrophily of grafting chain and the composition.It can be know from analysing the curve of the swelling ratio as a function of the temperature that the hydrogels is sensitive to environmental temperature and the hydrogels disappears the noncontinuous phase transition with temperature increasing. The temperature of phase transition locates between 35 ?ant 40?. The result of deswelling dynamics from 20 to 40 shows that the hydrogels have the capability ? ?of rapid-deswelling. The gel lost a large number of water and shrunk rapidly within the first 20 min. Then, the deswelling process slow down until the phase transition was done. The result of swelling dynamics curve of dry hydrogels at 20 ?shows that the hydrogels have the capability of rapid-swelling and gels could complete 85% of saturated swelling at 5min. The SEM result shows that the majority of internal porous exists inside the gel. And the porous structure could be controlled by cross-linking density and swelling temperature.The hydrogel grafted PNIPAM-b-PEG-g-IKVAV shows rapid response, rapid swelling and rapid deswelling properties...