Synthesis Of Degradable Injectable Hydrogels And Applications In Drug Delivery And Cell Culture

As novel biomedical materials, injectable hydrogels show bright application perspective. Especially, degradable polysaccharide-based injectable hydrogels have been extensively studied due to their biodegradability and biocompatibility. However, several challenges still remain for clinical applications. For example, the polysaccharide derived from animal sources present the risk of batch-to-batch variations and the possibility of immune responses upon injection; critical gelation concentration at which gelation occurs is high; incorporating synthetic polymers into the backbone of polysaccharide may increase the cytotoxicity of the hydrogel when they are non-biodegradable and not readily cleared away from the body under physiological conditions; the physico-chemical properties of the drugs and drug-polymer interaction are not considered. In view of these problems, we synthesized a series of novel degradable polysaccharide-based injectable hydrogels and investigated their potential applications in drug delivery and cell culture.A series of degradable polysaccharide-based injectable hydrogels were developed, and were characterized by Fourier transform infrared (FTIR) spectroscopy and 1H NMR. Scanning electron microscopy (SEM) was employed to investigate the porous structure of the hydrogels. Hydrogel gelation time was measured by the vial inversion method and UV/vis spectroscopy. The swelling and degradation behavior of the hydrogels in PBS were determined by weighing method. Cytotoxicity evaluation of the hydrogels were performed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay. The potential applications of the injectable hydrogels in drug delivery and cell culture were inveatigated. The detailed research contents are as follows:1. Injectable hydrogels derived from oxidized carboxymethylcellulose (OCMC) and N-succinyl-chitosan (NSC) were prepared by Schiff base reaction. The gelation readily took place at physiological pH and temperature. Several parameters, such as matrix gelation time, equilibrium swelling ratio, matrix degradation rate and drug release profile, were investigated. The in vitro cytotoxicity studies showed that the OCMC/NSC hydrogels were non-cytotoxic. The controlled release profile of BSA was obtained. Importantly, activity of released BSA was retained. This newly described OCMC/NSC hydrogels formed without requiring additional initiators, crosslinkers or light sources, eliminating the toxicity associated with such agents. 2. Injectable and biodegradable hydrogels based on oxidized chondroitin sulfate (OChS) and N-succinyl-chitosan (NSC) were developed. We focused on the physical characteristics of the hydrogels (e.g. crosslinking density, molecular weight between crosslinks and mechanical strength) and the effects of physico-chemical properties of the drugs and drug-polymer interaction on drug release behaviors. The model drugs aminophylline, indomethacin and lysozyme were easily incorporated into the hydrogels by mixing with the gel precursors. Release studies showed that the physico-chemical properties of the drugs and drug-polymer interaction play an important role in drug release behaviors. The study provided necessary information for the design and development of novel drug delivery systems.3. CMC-g-PNIPAAm copolymers were developed by decorating the backbone of carboxymethylcellulose (CMC) with linear chains of poly(N-isopropylacrylamide) (PNIPAAm), with the ultimate aim of synthesizing a biodegradable and injectable hydrogel that also possesses a low gelation concentration. Their aqueous solutions were found to undergo a reversible subphysiological phase transition at the concentration of 2 wt%. The value is much lower than that reported for many PNIPAAm-based copolymers. The phase transition behavior, gelation time, injectability, viscosity, swelling, degradation and cytocompatibility were explored. Lysozyme was used as the model drug. In vitro release of lysozyme from the injectable hydrogel was studied. Secondary and tertiary structure analysis and biological assays of the released protein showed that encapsulation and release did not affect the protein conformation and functionality. These results indicate that this biocompatible and injectable hydrogel system may be useful as a potential vehicle for therapeutic proteins for sustained release applications.4. Biohybrid injectable hydrogels based on chondroitin sulfate (ChS) and poly(N-isopropylacrylamide) (PNIPAAm) were developed. PNIPAAm was synthesized at various molecular weights by RAFT polymerization. The molecular weight range suitable for renal clearance was an important factor in the experimental design. The phase transition temperature was between room temperature and 37℃and the gelation time was 70-90 s, indicating their possibility for further clinical application. Hydrogel degradation was determined in PBS with 100 U/ml of hyaluronidase at 37℃and the results revealed that the hydrogels lost above 40% of their weight after 4 weeks. In vitro two-dimensional (2-D) and three-dimensional (3-D) cell cultures were performed. Cells demonstrated excellent viability when cultured with the hydrogel. In addition, the arrangement of multiple cell layers in the hydrogel was achieved. These results indicate the injectable hydrogels may be expected to have wide potential applications as a vehicle for the delivery of therapeutic cells.