Long-term observation of subcutaneous tissue reaction to synthetic auditory ossicle (Bioceram) in rats

To evaluate biocompatibility to tissue in long-term implantation, Bioceram discs made of aluminum oxide (Al2O3) were implanted subcutaneously within the interscapular region of 64 rats for six to 20 months. Histological sections stained with haematoxylin and eosin (H&E) and the surface of the implant material were observed using light microscopy. Different cell types and the thickness of fibrous capsules surrounding the implants were examined quantitatively by light microscopy. Small numbers of macrophages (2.8 +/- 0.7%) and lymphocytes (2.7 +/- 0.9%) were observed at six months after implantation, gradually decreasing to zero at 16, 18 and 20 months. Neither neutrophils nor foreign body giant cells were seen in any specimens. The thickness of fibrous capsules surrounding the implants was closely related to the shape of the implant, but there was no significant change between six and 20 months after implantation. No change in Bioceram surfaces were observed under stereoscopic microscopy from six to 20 months after implantation. The study results indicate that Bioceram is a satisfactory biocompatible material for reconstructive surgery from the viewpoint of long-term tissue response. Present results of experiments with Bioceram are also compared to previous results with Apaceram and different tissue responses of the two materials are discussed.