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A photocrosslinkable chitosan to which both azide and lactose moieties were introduced (Az-CH-LA) was prepared as a biological adhesive for soft tissues and its effectiveness was compared with that of fibrin glue. Introduction of the lactose moieties resulted in a much more water-soluble chitosan at neutral pH. Application of ultraviolet light (UV) irradiation to photocrosslinkable Az-CH-LA produced an insoluble hydrogel within 60 s. This hydrogel firmly adhered two pieces of sliced ham with each other, depending upon the Az-CH-LA concentration. The binding strength of the chitosan hydrogel prepared from 30-50 mg/mL of Az-CH-LA was similar to that of fibrin glue. Compared to the fibrin glue, the chitosan hydrogel more effectively sealed air leakage from pinholes on isolated small intestine and aorta and from incisions on isolated trachea. Neither Az-CH-LA nor its hydrogel showed any cytotoxicity in cell culture tests of human skin fibroblasts, coronary endothelial cells, and smooth muscle cells. Furthermore, all mice studied survived for at least 1 month after implantation of 200 microL of photocrosslinked chitosan gel and intraperitoneal administration of up to 1 mL of 30 mg/mL of Az-CH-LA solution. These results suggest that the photocrosslinkable chitosan developed here has the potential of serving as a new tissue adhesive in medical use.

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Silver nanoparticle (Ag NP)/chitosan (Ch) composites with antiviral activity against H1N1 influenza A virus were prepared. The Ag NP/Ch composites were obtained as yellow or brown floc-like powders following reaction at room temperature in aqueous medium. Ag NPs (3.5, 6.5, and 12.9 nm average diameters) were embedded into the chitosan matrix without aggregation or size alternation. The antiviral activity of the Ag NP/Ch composites was evaluated by comparing the TCID50 ratio of viral suspensions treated with the composites to untreated suspensions. For all sizes of Ag NPs tested, antiviral activity against H1N1 influenza A virus increased as the concentration of Ag NPs increased; chitosan alone exhibited no antiviral activity. Size dependence of the Ag NPs on antiviral activity was also observed: antiviral activity was generally stronger with smaller Ag NPs in the composites. These results indicate that Ag NP/Ch composites interacting with viruses exhibit antiviral activity.