Evaluation of apatite-forming ability and antibacterial activity of raw silk fabrics doped with metal ions

Raw silk can be doped with metal elements such as calcium and zinc due to the high affinity of sericin, which forms its outer layer. Raw silk doped in this manner is expected to possess various favourable properties as biomaterials. In this study, we investigated metal-doped raw silk fabric’s apatite-forming ability in simulated body fluid (SBF), as well as its antibacterial activity against Escherichia coli. The samples were prepared by soaking the fabric in aqueous solutions containing calcium, copper, or zinc ions. Both Cu-doped and Zn-doped raw silk fabric showed antibacterial activity, suggesting that antibacterial agents released from the samples killed the bacteria. Additionally, Ca-doped raw silk fabric showed both apatite-forming ability and antibacterial activity. The apatite formation on fabric might be because calcium ions released from the sample increased the degree of supersaturation of SBF with respect to apatite, and accelerated apatite formation. Additionally, the release of calcium ions caused local pH increases, resulting in bacterial hardly survival at the sample surface. Therefore, Ca-doped, Cu-doped, and Zn-doped raw silk fabrics may have applications as antibacterial biomaterials. Furthermore, Ca-doped raw silk fabric has the potential to bind to living bone.