Synthesis And Characterization Of Chitosan-g-PEG Conjugate

Chitosan (beta-(1,4)-2-Amino-2-deoxy-D-glucose), a glycosaminoglycan which is derived from the partial or complete N-deacetylation of chitin, is naturally abundant in the world. It has excellent properties such as biocompatibility, biodegradability, non-toxicity, etc. Chitosan has been applied in researches on control release of drugs, anticancer drugs as well as biomaterials. However, as the amino group of chitosan has a pKa range of5.5to6.5, chitosan can not dissolve in solutions with a pH value above6.5, which limits the application of chitosan in medical area.Polyethylene glycol (PEG) is a polymer prepared by anion ring-opening polymerization of ethylene oxide, which has properties of hydrophilicity, non-toxicity and immunogenicity. PEG has already been approved by FDA for application in injections. PEGylation, attaching PEG to any drug peptide, polymer or chemical moiety, is believed to increase water solubility, control permeability through biological barriers, overcome tumor resistance, improve bioactivity and reduce protein immunogenicity. It is promising in medical and pharmaceutical areas.In this study, PEG derivative with an active carboxyl terminal was synthesized based on anionic ring-opening polymerization; the PEG derivative was utilized to graft to chitosan through amido bond formed by reaction of the carboxyl group of the PEG derivative and free amino group of chitosan. The biocompatibility of chitosan-g-PEG was investigated. The details are as follows:(1) PEG carboxylic ester (PEG-COOCH2CH3) was synthesized by anionic ring-opening polymerization with EO as monomer, ethyl glycolate as initiator, potassium hydroxide (KOH) and18-crown-6as catalysts in a stainless steel autoclave. After hydrolysis of the ester, carboxyl PEG derivative (PEG-COOH) was achieved. By feeding EG and EO with different ratios of1.04:20,1.04:40, and1.04:60, three batches of PEG-COOCH2CH3were prepared together with their corresponding PEG-COOH. FTIR,1H-NMR and GPC were utilized to characterize the prepared polymers. FTIR spectra of the polymers synthesized indicated the formation of new carbonyl bond.1H-NMR suggested the polymers were designed ones by assigning every proton signal correctly. Data of the molecular weight as well as PDI of the polymers given by GPC suggested that the polymers synthesized in this approach were narrowly distributed and could meet the needs in the aspects of molecular weights.(2) EDC-NHS coupling system was employed to graft carboxyl PEG derivative to chitosan through amido bond, achieving chitosan-grafted-PEG; FTIR,1H-NMR arid XRD were used to characterize the prepared polymers. FTIR spectra of the polymers synthesized indicated the formation of new amido bond.1H-NMR confirmed that chitosan-g-PEG was successfully prepared by assigning every proton signal correctly. XRD analysis showed that the crystalline property of chitosan-g-PEG was similar to that of carboxyl PEG derivative.(3) Films of chitosan and chitosan-g-PEG were prepared; meanwhile, the hydrophilicity, protein adsorption and cell compatibility of them were investigated. The results showed that compared to chitosan, films consisted of chitosan-g-PEG had better hydrophilicity and less protein adsorption. Cell prolification of L929on each film measured by MTT test on day1,3,5after cell seeding showed non-significant difference, indicating the films made by chitosan and chitosan-g-PEG did not harm the living cells when exposed directly and chitosan-g-PEG and chitosan have good biocompatibility.