Controlled Synthesis Of UV-crosslinkable Chitosan Hydrogel And PH/Temperature Responsive Swelling Behavior

In recent years,regenerative medicine and other disciplines for minimally invasive treatment technologies have developed significantly,which are more acceptable to doctors and patients because they do not require too much surgery.Injectable in-situ forming hydrogels are a desirable choice.The UV-induced injectable in-situ forming hydrogels based on chitosan,a natural product,appear to have better performance.Therefore,it is very important to develop and synthesize novel UV-induced in-situ forming chitosan hydrogels.At the same time,traditional chitosan hydrogels can absorb excess water and swell in aqueous solution,so they cannot respond to external environmental stimulation.As minimally invasive implants,hydrogels are expected to have a small swelling degree to reduce the pressure on the surrounding tissues,while tissue filled hydrogels are expected to have a certain swelling degree.So,it is of great significance to study how to develop smart responsive chitosan hydrogels,and then regulate the swelling behavior of hydrogels.In this paper,UV light was used as the forming technology of crosslinking chitosan hydrogels,and the regulation of swelling behavior of chitosan hydrogels as the research purpose.On the one hand,starting from UV crosslinking,"thiol-ene/yne"clicking chemistry was applied to form chitosan hydrogel.On the other hand,the pH and temperature responsiveness of hydrogel were realized by introducing temperature responsive thiol-terminated polymer with the pH-responsive chitosan derivative.In addition,the application of chitosan hydrogel in drug controlled and sustained release and compatibility in vivo and in vitro were further studied.The research contents mainly include the following aspects:In order to realize the pH responsiveness of chitosan hydrogel under alkaline condition,the amino protection/deprotection strategy was used to introduce allyl group into the C₆ hydroxyl group of chitosan,and the pH responsiveness of original chitosan was preserved by retaining a large number of amino groups.The results showed that allyl chitosan hydrogels showed obvious swelling behavior in acidic environment and shrinking behavior in alkaline environment with the maximum swelling ratio up to 14.5 times.,showing obvious pH responsiveness.The pH responsive behavior of hydrogel was used to release small molecule DOX and macromolecule BSA,and the results showed that acidic condition promoted BSA release while alkaline condition promoted DOX release.By introducing the thermal-responsive PNIPAM into allyl chitosan,UV photo-initiated the"thiol-ene"click reaction between allyl chitosan and dithiol-functionalized PNIPAM,giving the hydrogel double pH and temperature responsiveness.The results showed that acidity and low temperature environment were beneficial to the swelling behavior of hydrogel,while alkalinity and high temperature environment significantly inhibited the swelling behavior of hydrogel,showing obvious double responsive effect of pH and temperature,with the maximum swelling ratio up to 22 times.At the same time,the survival rate of the cells was 100%after the hydrogel extract was co-cultured with the cells for 1 day,and the subcutaneous inflammation experiment also showed that the inflammation disappeared after 7 days,showing good biocompatibility in vitro and in vivo.In order to realize the difficulty in the release of water-soluble drugs in chitosan hydrogels,dithiol-functionalized PF127 components were introduced to improve the drug load of water-soluble drugs.The results showed that the hydrogel can be prepared rapidly by UV-triggered"thiol-yne"click chemical reaction between propargyl chitosan and dithiol-functionalized PF127.The swelling performance showed that the pH response was obvious when the PF127 content was low,while the pH response was obviously inhibited when the PF127 content was high.In drug release,the special structure of PF127 also significantly increased the drug loading capacity and delayed the release effect of DOX and ASP.In order to inhibit the swelling behavior of chitosan hydrogels,chitosan derivative with hydrophobic short chain-pentenyl groups were synthesized by acylation reaction between pentenyl anhydride and amino group in chitosan.The introduction of the pentenyl group can provide UV crosslinking properties and give the derivative water solubility for chitosan.According to the study,the swelling degree after reaching the equilibrium of the three different substituted hydrogels was 74%,64%and 57%at 37℃in pH=7.2 condition,respectively,indicating that all the pentenyl chitosan hydrogels were in contractive nonswelling state.The cell survival rate after 5 days of co-culture of pentenyl chitosan was over 90%,and the subcutaneous inflammation experiment proved that the inflammation disappeared after 7 days,showing good biocompatibility in vitro and in vivo.In summary,in this paper,the swelling degree of chitosan hydrogels can be controlled by changing pH and temperature by retaining the amino group of chitosan and introducing the thermo-sensitive polymer,and the"nonswelling"property of chitosan hydrogels the hydrophobicity of chitosan hydrogels could be enhanced after the introduction of hydrophobic short chain crosslinking.These new design methods provide new research ideas for the preparation of chitosan hydrogels and provide scientific basis for further research on the application of chitosan hydrogels as biomedical materials and drug release materials.