Preparation And Biological Activity Of Chitosan-Zinc Oxide Composite Antibacterial Dressings

Skin is the barrier between human body and external environment. It can protect body tissues and organs from physical, mechanical, chemical damages and pathogenic microorganism’s invasion. If the wound can’t recover in time, it should be covered with dressing immediately. Most traditional dressings in clinical application can only provide basic physical protection. Hence the development of new wound dressing has attracted more and more attention in recent years. Chitosan is a natural biopolymer with good biocompatibility, biodegradability and moisture retention. Furthermore it has the properties of acceleration of blood clotting and wound healing, shortening wound healing time, and decreasement scar formation. Inorganic antibacterial agents such as zinc oxide and silver have outstanding antibacterial ability, furthermore these inorganic agents are unlikely to induce microbes to acquired resistance. Therefore, compositing zinc oxide or silver into chitosan to formation of composite dressing can prevent wound from infection caused by pathogenic microorganisms, and it can meet the requirements of an ideal dressing. In this thesis, chitosan-zinc oxide composite dressing and chitosan-Ag/zinc oxide composite dressing were prepared. And the basic physical properties, in vitro biological activity such as antimicrobial resistance and cytotoxicity, procoagulant property of the composite dressing were measured. Furthermore, the effects of the dressings on the healing process in vivo were evaluated systematically. The main works were summarized as follows:1. Chitosan-zinc oxide composite antibacterial dressing were prepared in three methods of in-situ synthesis, microwave-ultrasonund and immersion method. The immersion method was determined as the optimum method. The basic physical properties of the as-prepared dressing such as porosity, water absorption and moisture retention were measured and the results showed that the dressing has good flexibility, about 80% increase in porosity, a 20~25-fold water absorption rate, and at least 16 hours moisture retention time, which can provide continuous moist environment for wound healing. Antibacterial activities against common pathogenic bacteria and drug resistant bacteria, cytotoxicity on normal human cells and procoagulant properties were also measured, and the results showed that the dressing has antibacterial activity, much higher blood clotting ability and low toxicity to normal human cells.2. To further enhance the antibacterial properties of composite dressings, Ag/ZnO was synthesized via deposition- precipitation method and chitosan-Ag loaded zinc oxide composite dressing was made successfully. In this study, we determined basic physical properties of dressing such as porosity, water absorption and moisture retention,antibacterial activities against common pathogenic bacteria and their drug resistant bacteria, cytotoxicity on normal human cells and procoagulant properties. The results showed that the dressing has high porosity, swelling ratio, water absorption and moisture retention, as well as effective blood clotting ability. Moreover, the chitosan-Ag loaded zinc oxide composite dressing has enhanced antibacterial effect on common wound bacteria, including the drug-resistant bacteria, and it has no obvious toxicity to normal human cells. These results clearly reveal that this composite dressing has a great potential application in preventing wound infections caused by bacteria.3. Wound healing effects of chitosan-zinc oxide, chitosan-Ag/zinc oxide composite dressings on mice wound were evaluated, including using chitosan dressings and zinc oxide ointment gauze as a compared group. The results showed that the chitosan dressings we prepared have better effects on promoting wound healing than that of zinc oxide ointment gauze. It can shorten healing time of wounds and promote wound granulation tissue proliferation, reduce aggregation of inflammatory cells and reduce the formation of scar tissue in the wound. During the period of wound healing, the mice were growing in good conditions. With the introduction of inorganic antibacterial agents such as zinc oxide into chitosan dressings can make wound smoothing. Thus, the prepared composite dressings have excellent ability to repair tissue, antibacterial ability and anti-inflammatory ability. It can fit the moist healing theoretical model well. In conclusion, it is a kind of safe, reliable and novel multifunctional dressing.