Controlled Radical Polymerization And Biocompatibility Evaluation Of Thermoresponsive Cellulose Nanowhisker

Bacterial cellulose（BC） produced by Acetobacter xylinum is a kind of natural polymer cellulose, whose 3D network is composed of nanofibers. Cellulose polymer chains derived from D-glucose units（β-（1,4）-glycosidic bonds） have a great number of hydroxyl groups on the surface, which are easy to be modified by kinds of chemical reactions leading to functionalizations such as polymer grafting（grafting onto and grafting from）, cationization, and other covalent and non-covalent modifications. BC owns unique properties including good biocompatibility, high crystallinity and good mechanical property, and has a wide range of applications including chemical engineering materials and biomedical materials.BC could have more applications in the field of biomaterial. In this study, bacterial cellulose nanowhisker（BCNW） was prepared from BC film, and modified by thermoresponsive polymer. The potential application of the new copolymers as emblization material was studied.The comparision of two methods for BCNW preparation by acid hydrolysis and refeigeration-rubbing showed the BCNW was only got by acid hydrolysis. The tests of the properties for BC showed that BC is hydrophilic, high water content（97 %） and good biocompatibility.Thermoresponsive copolymer was generated by grafting poly（Nisopropylacrylamide）（PNIPAM） side chains from bacterial cellulose whiskers with Atom Transfer Radical Polymerization（ATRP）. Chemical evidences for the success of the polymerization were provided by Fourier transform infrared spectroscopy and 1HNMR data. The different nano structures were showed by transmission electron microscopy images within the context of temperature change. A sol-gel transition and the thermoresponsive property of the BCNW-g-PNIPAM were tested by differential scanning calorimetry.The lower critical solution temperature（LCST） is below the body temperature. Good biocompatibility of these nanocopolymers for using as embolic materials was demonstrated by cytotoxicity examination in human umbilical vein endothelial cells.In addition, another more excellent thermoresponsive polymer named poly（2-（2′- methoxyethoxy）ethyl methacrylate）（PMEO₂MA） was used to form copolymer together with BCNW by ATRP. Chemical evidences for the success of the polymerization were provided by Fourier transform infrared spectroscopy and 1HNMR data. The LCST of BCNW-g-PMEO₂ MA is 28.5 ℃, which is below the body temperature. And new copolymer was obtained by the adding of oligo（ethyleneglycol） methacrylate（OEGMA）, OEGMA and MEO₂ MA were copolymerized on the surface of BCNW. And the LCST of BCNW-g-P（OEGMA-co-MEO₂MA） is 31.5℃. The excellent biocompatibility of the materials was showed by cell cytotoxity tests. They exhibit the potential to be used as emblic materials.