The Preparation And Properties Of Crosslinked Hydrogels Based On Natural Polysaccharides

In recent years, cellulose, chitosan and their derivatives have been widely used toprepare hydrogels for their low-cost, large availability, renewability, biocompabilityand biodegradability. In this thesis, sodium carboxymethylcellulose (CMC),hydroxyethylcellulose (HEC), and carboxymethylchitosan (CMCS) were used toprepare different crosslinked hydrogels which show potential application in drugdelivery, cell-culturing scaffold and dye adsorbents.CMC and HEC were used to prepare novel crosslinked hydrogels usingammonium persulfate (APS) as an initiator and methylenebisacrylamide (MBA) as acrosslinking agent. The hydrogel structure was confirmed using fourier transforminfrared spectoscopy (FT-IR), thermal analysis (TG/DTG), X-ray diffraction (XRD),and scanning electron microscopy (SEM). The results showed that the crosslinkingreaction has carried out successfully. The swelling properties of the CMC/HECcrosslinked hydrogels were measured in various solutions with pH values rangingfrom1.2to8.8. The maximum swelling capacity was achieved at pH5.0. The pH-and ionic strength-sensitivity and reversibility of the CMC/HEC crosslinkedhydrogels were also investigated. The on-off switching behavior was confirmed,which indicated the potential for drug delivery. The release of bovine serum albumin(BSA) from drug-loaded hydrogels was examined at pH7.4and1.2. The total releaseof the loaded BSA was18%at pH1.2and85%at pH7.4, respectively. Thesignificant difference of BSA release between the low and high pH implied thepotentially controlled release of oral medication and the desirable protection instomach.To avoid introducing toxic reagents, CMCS and CMC were used to preparehydrogel film by ionical and covalent crosslinking with CaSO4and genipin,respectively. FT-IR comfirmed the covalent crosslinking. TG/DTG showed that thethermal ability of hydrogel film was slightly changed. SEM observation showed thethree-dimentional network sturcture. The swelling ratio of the crosslinked CMCS/CMC hydrogel films was investigated at different pH solutions (1.0-9.0), andthe results indicated that the crosslinked hydrogels had the swelling-deswellingproperties with two primary peaks of swelling ratio at pH3.0and7.0. The surfacemorphologies of the crosslinked hydrogels at different pH values provided evidencesof the swelling-deswelling properties. The mechanical properties of the hydrogelfilms were also examined. The ionical and covalent crosslinking were found to have asignificant difference (p<0.05) on the toughness and max load, respectively, of thecrosslinked hydrogels. Furthermore, genipin concentration and Ca2+concentration hada significant effect on max load and toughness, respectively. The3T3cellscomparatively cultured on the crosslinked hydrogels and the negative and positivecontrols suggested the biocompatibility of the crosslinked CMCS/CMC films.Another hydrogels were prepared from CMCS with genipin as crosslinker andCMC as strengthening reagent. The effects of dye initial concentration, genipinconcentration and pH on the adsorption of Methyl Orange (MO)and Methylene Blue(MB) onto the crosslinked hydrogel was investigated. The results showed that themaximum adsorption amount of MO and MB reached39.38mg/g and60.86mg/g,respectively, when the initial concentration was kept at250mg/L. Holding the genipinconcentration at2.5mM, the maximum adsorption ratio of MO and MB was43%and71%, respectively.