Noriaki Masuda

Preparation of Antibacterial Silver-Doped Silica Glass Microspheres by Sol-Gel Method

Various kinds of inorganic substances doped with silver ion have been developed as antibacterial materials, and some of them are already commercialized. Colorless and more chemically durable materials which slowly release the silver ion are, however, still desired to be developed. If they take a form of microsphere less than 1 μm in diameter, they are easily mixed with organic polymers and can be formed into a thin film, fine fibers, etc. In the present study, preparation of silver-doped silica glass microsphere less than 1 μm in diameter was attempted by using sol-gel method. Tetraethoxysilane was first partially pre-hydrolyzed by water in ethanol, then aluminium triisopropoxide was added to the solution to form Si-O-Al bond, and finally, ammonia solution containing silver nitrate was added to the solution to form silica microspheres doped with silver ion together with aluminium ion. As a result, monodispersed microspheres 0.4–0.6 μm in diameter with the nominal compositions Si/Al/Ag=1/0.01–0.03/0.003–0.03, where Al/Ag=1–3.3, in molar ratio were obtained. They were colorless, highly chemically durable, and slowly released the silver ion into water at 37 oC. The microspheres with the composition Si/Al/Ag=1/0.01/0.01 showed excellent antibacterial activity against Escherichia coli. The minimum inhibitory concentration (MIC) of the microspheres was 400, which is less than that (800) of commercialized antibacterial materials. Introduction Silver-containing materials show antibacterial property and the silver is non-toxic. Various kinds of antibacterial silver-containing materials have been developed and some of them have already been in commercial use. Antibacterial materials are required to be colorless, highly chemically durable and to release silver ion slowly for a long period, when they are used by being mixed with organic polymers. If they take a form of monodispersed microsphere less than 1 μm in diameter, they are more desirable, since fine fibers or thin films of polymers containing the antibacterial particles homogeneously can be easily prepared and exposed surface area of the antibacterial particles is increased. The present authors previously showed that when silica glasses doped with silver ion together with aluminium ion are prepared by a sol-gel method, the resultant products are colorless, highly chemically durable and release the silver ion slowly into water for a long period [1]. In order to obtain fine powder, however, they must be crushed mechanically. The resultant grains are irregular in shape and most of them are larger than 1 μm in size. In the present study, monodispersed microspheres less than 1 μm in diameter of silica glass doped with silver and aluminium ions was attempted to be prepared by a sol-gel method. The structure and properties of the resultant products were examined. Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 229-232 doi:10.4028/www.scientific.net/KEM.240-242.229