Antibacterial materials are widely used to prevent hospital-acquired infections. In our previous report, metal (calcium, copper or zinc)-doped raw silk fabrics were shown to possess strong antibacterial activities against Escherichia coli. However, antibacterial materials may occasionally be harmful to the human body; thus, in this study, we investigated the cytotoxicities of extracts from metal-doped raw silk fabrics with respect to fibroblasts and osteoblasts indirectly. Calcium-doped raw silk fabric demonstrated cytocompatibility with fibroblasts. Contrarily, copper- and zinc-doped raw silk fabrics remarkably decreased the cell densities of fibroblasts, indicating their cytotoxic effects. This observation could be attributed to the high concentrations of the released copper or zinc ions. However, calcium-, copper- and zinc-doped raw silk fabrics did not demonstrate any cytotoxic effects on osteoblasts because a high concentration of the serum alleviated the effects of these metal ions released from the fabrics. Thus, calcium-doped raw silk fabric is a promising antibacterial material that does not induce strong cytotoxicity. This study will facilitate the design of materials that are both antibacterial and safe.
Raw silk can be doped with metal element such as Ca and Zn due to high affinity of sericin, outer layer of the raw silk. Thus, raw silk doped with metal element is expected to show various functions favorable as biomaterials. In this study, we investigated to apatite-forming ability in simulated body fluid (SBF) and antibacterial activity against Escherichia coli of metal-doped raw silk fabric. The samples were prepared by soaking in the aqueous solution containing Ca, Cu or Zn ion. Cu-doped and Zn-doped raw silk fabric showed antibacterial activity, suggesting antibacterial agents of Cu and Zn released from the samples killed the bacteria. On the other hand, Ca-doped raw silk fabric showed both apatite-forming ability and antibacterial activity. The apatite formation on fabric is might be because Ca ion released from the sample increased a degree of supersaturation of SBF to respect with apatite and accelerate the apatite formation. Also, it is considered that release of Ca ion causes pH increase locally and the bacteria hardly survive at the sample surface. Therefore, Ca-doped, Cu-doped and Zn-doped raw silk fabric are useful as antibacterial biomaterials. Further, Ca-doped raw silk fabric has potential to bond to living bone.
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.
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