Preparation And Properties Research Of Different Types Of Chitosan Composite Hydrogel

In the research,different molecular weight and deacetylation degree of chitosan(CS), nano hydroxyapatite(n-HA), and polyvinyl alcohol(PVA) were used to prepare porous n-HA/PVA/CS composite hydrogel by physical crosslinking method and particle hole drilling method, and their properties were tested. Besides, the antibacterial activity and the related properties of n-HA/PVA/CS composite hydrogel in the simulated body fluid were deeply studied, and the artificial cornea scaffold materials with good antibacterial ability and stability were designed.Artificial cornea can be used to the treatment of corneal blindness.At present,the artificial cornea has become a hot research topic due to the severely shortage of donor cornea. The current design of artificial cornea mainly consist of porous skirt bracket and the optical center. The skirt bracket is the part that connected with host corneal directly. Most artificial cornea failed because of poor biocompatibility between heterogeneous materials and host tissue. And after implantation, their eyes often appear corneal prolapse, inflammation and other complications. So,seeking for materials with good biocompatibility is acted as a breakthrough in the development of artificial cornea.Chitosan is widely used in a variety of biological materials aspects for its unique biological sources and good biocompatibility. It inhibits the growth of microorganisms and also promotes the growth of epithelial cells which is conducive to the remodeling and construction of new structural organization. This function is suitable to artificial cornea scaffold. Porous n-HA/PVA/CS composite hydrogel has good flexibility and can reduce the mechanical stimulation of peripheral cells and tissues.Its three-dimensional network structure and good biocompatibility are conducive to the growth of fibroblast and collagen deposition. Moreover, the porous hydrogels own a new property—antibacterial activity. Based on the above properties,porous n-HA/PVA/CS composite hydrogel is available for keratoprosthesis skirt scaffold.The research includes are as follow:1. The chitosan with different molecular weight and different degree of acetylation were selected by the control variate method.Porous n-HA/PVA/CS composite hydrogel materials were prepared by physical crosslinking method and dissolved salt method. The effects of chitosan on the moisture content, mechanical properties and swelling properties of the composite were investigated. The structure of n-HA/PVA/CS composite hydrogel material were investigated by XRD and TG-DTA. The results showed that the pores in porous n-HA/PVA/CS composite hydrogel were penetrating and distributed evenly. The water content of chitosan composite hydrogel decreased with the increase of the molecular weight and the deacetylation of chitosan,. But it was generally between 70% and 80%.The tensile strength of chitosan composite hydrogel increased along with the deacetylation and molecular weight of chitosan.The tensile strength is 0.2 ~ 0.55 MPa. The swelling properties increased along with the deacetylation of chitosan and decreased with the increase of the molecular weight of chitosan.2. Antibacterial property and the minimum bacteriostasis concentration of different molecular weight and degrees of acetylation of chitosan and n-HA/PVA/CS composite hydrogel were studied by turbidimetric method and tablet method.At the same time, the antibacterial mechanism of chitosan was concluded by the results of the antibacterial activity. The results showed that minimal inhibitory concentrations(MIC) of n-HA/PVA/CS composite hydrogel of the S.aureus and E.coli were both 0.5g/L. When the composite hydrogel concentration was 2.0 g/L, the antibacterial effect is the best with 84% of S.aureus and 99% of E.coli. When molecular weight of chitosan was 2×105, the inhibitory trend of S.aureus and E.coli generally are increased with the degree of deacetylation of chitosan. At 91.1% deacetylation degree,the chitosan had the best antibacterial. It was because the higher the degree of acetylation of chitosan, the more free amino groups. The combination of chitosan and carbohydrate or phosphate wall acidon on the sbacterial wall also increased, which made the breeding of bacteria blocked, displaying an inhibitory effect. When deacetylation degree of chitosan was 80.9%, the inhibitory trend of S.aureus andE.coli generally increased with the increase of molecular weight. But when it reached a certain molecular weight, the inhibitory effect decreased with the increase of molecular weight. The reason for this trend was that chitosan could inhibit bacteria from two ways. When the molecular weight was very small, it absorbed cytoplasmic anion and flocculated by entering cells to inhibit bacterial growth. When the molecular weight was gradually increasing, it could make effect not only by the way above, but also by another way. It formed a layer of polymer film at the cell surface and destroyed the structure of cell wall and cell membrane. In this way, the materials acted as bacteriostasic activity by changing cell membrane permselectivity and disrupting normal cell physiological activities, or absorbed negatively charged bacteria and interfered with the synthesis of cell wall to dissolve the bacterial cell wall and let it death. When the molecular weight reached a certain value, the first antibacterial mechanism was no longer applicable, then the antibacterial properties of chitosan would decrease.3. Different types of n-HA/PVA/CS hydrogels properties were studied in simulated body fluid. The changes of simulated body fluids pH, chitosan sustained release quantity in simulation of fluid, material weight loss rate, mechanical properties and morphology were mainly considered. The results showed that the pH value was stable between 7.2-7.3, weight loss rate was around 15% and the tensile strength decreased, ranging from 15% to 25%. Chitosan sustained release amount was different with the types of chitosan. When the molecular weight was 2400, the chitosan sustained release quantity of chitosan hydrogel was the highest, which could be up to 0.8 g/L after 16 days of immersion. When the molecular weight were 2×105and 8×105~106 respectively, chitosan hydrogel release amount were both about 0.5g/L. The morphology of the material was not much changing, but the pores slightly increased. Overall, the stability of the chitosan composite hydrogel was well. It was suitable for long-term implantation of the human eye, and the sustained release of chitosan helped to provide growth space for cell and fiber cells embedded in porous scaffold materials.