Assessment of the release of nickel from biomaterials in vivo and in vitro: enhancement by lipopolysaccharide

Abstract

Biodevices are implanted for long periods of time, so the release of metal ions from alloys should be tested in tissues to assess the risk of inducing metal allergies. However there is little evidence that the release of metal ions from alloys in vivo is similar to that in vitro. We implanted metal wires in mice and determined the concentration of metal ions in tissue to analyze the mechanisms responsible for metal allergies. The release of ions from the Ni wire was detected within 8 h and attained a plateau 72 h after the implantation. Furthermore, it was significantly increased by an injection of LPS. The results indicated that the release of Ni was apparently enhanced by inflammatory responses. We also established an in vitro assay system using the murine macrophage cell line RAW 264. The addition of LPS apparently increased the amount of Ni released into the medium, indicating the activation of the cells to have enhanced the elution of ions from the Ni plate. Our in vitro model using LPS-stimulated RAW264 cells might reflect the elution of Ni in inflamed tissue.