Masae Sumita

Metal ion release from titanium with active oxygen species generated by rat macrophages in vitro

The release of metal ions due to active oxygen species generated by macrophages (Mphi) phagocytosing high-density polyethylene (HDPE) particles was studied in vitro to investigate the mechanism behind the release of metal ions from titanium implants into nearby tissues in the absence of wear and fretting in vivo. To determine the effects of Mphis on metal ion release, titanium disks were immersed in different solutions and the titanium ions released from the titanium disks into each solution were quantified. The results revealed that active oxygen species generated by Mphis induced the metal ion release. In particular, the ion release was accelerated with HDPE because the Mphis that phagocytosed HDPE generated more active oxygen species than Mphis that did not phagocytose any HDPE. Metal ions were also released by organic species in the absence of Mphis. These are some of the causes for metal ion release from titanium implants in the absence of wear and fretting in vivo.

Quantitative evaluation of cell attachment to glass, polystyrene, and fibronectin- or collagen-coated polystyrene by measurement of cell adhesive shear force and cell detachment energy.

Quantitative evaluation of a materials affinity for cells is essential to understanding cell-material interaction inside a body and it is also necessary for the development of new biomaterials with superior biocompatibility. In the present study, the shear force and the total energy necessary to detach a single murine fibroblast L929 adhering to glass, polystyrene, and fibronectin- or collagen-coated polystyrene were measured directly by applying a lateral force, using a cantilever, to the cell. The projected area of the cell was also measured, and then cell adhesive shear strength and cell detachment surface energy were determined by dividing the shear force and the total energy by the area. Among these four materials, the cells on collagen-coated polystyrene have the highest cell adhesive shear strength and cell detachment surface energy (1500 Pa and 29 pJ on average, respectively), followed by the cells on fibronectin-coated polystyrene (1000 Pa and 16 pJ, respectively). The cells on glass and polystyrene had almost the same cell adhesive shear strength and cell detachment surface energy (420-670 Pa and 7-11 pJ, respectively). These observations suggest that cell adhesive shear strength and cell detachment surface energy depend on the number of the bindings between the cell and a materials surface rather than on the strength of each binding.

Generic tendency of metal salt cytotoxicity for six cell lines

Systematic cytotoxicity evaluation of various metallic elements may contribute to the development of new metallic biomaterials with superior biocompatibility. It is generally reported that the cytotoxicity of a chemical differs with cell lines. However, our previous study revealed a high correlation in the cytotoxicity of 43 metal salts between two murine cell lines. If there is any generic tendency toward metal salt cytotoxicity for many kinds of cells, that information is helpful for the determination of the chemical composition of new metallic biomaterials that are expected to have lower cytotoxicity. In this study, the cytotoxicity of 12 metal salts was evaluated using four cell lines, and the results were compared, including those for two other cell lines obtained in our previous study. A metal salt concentration that reduced cell viability to 50% of that without any metal salt (IC(50)) was used as an index to compare the metal salt cytotoxicity between cell lines. The correlation was statistically proved by the IC(50)s of 12 metal salts among these cell lines (p < 0.01), suggesting the existence of a generic tendency to metal salt cytotoxicity beyond cell lines. The metal salt order of toxicity from the highest was K(2)Cr(2)O(7), AgNO(3), VCl(3), SbCl(3), CuCl(2), CoCl(2), NiCl(2), ZnCl(2), Cr(NO(3))(3), FeCl(3), TiCl(4), and Al(NO(3))(3). The sensitivity for metal salt cytotoxicity differed with cell lines; IMR-32 had the highest sensitivity among the six cell lines.