Biodegradation-Dependent Trace Element Accumulation: A Study on Calcium Phosphate Ceramics and Polymers

Summary

Röntgen microanalysis revealed the accumulation of trace elements such as silicon, titanium, aluminum, iron, and chromium in electron-dense inclusion bodies in the cytoplasm of phagocytes associated with the implantation of a tricalcium phosphate ceramic, Estane^R polyether urethane, HPOE/PBT copolymer or polypropylene oxide into the rat middle ear. The constituent element magnesium was found as well. In only one case did hydroxyapatite implanted in the human middle ear give rise to the presence of these elements in phagocyte cytoplasm, and trace element accumulation at the implantation site was not found for Silastic^R implants.

To find out whether a wound reaction, foreign body reaction or implant biodegradation, was responsible for this accumulation, we injected biodegradable tricalcium phosphate and the almost impervious inflammatory agent crocidolite asbestos into the mouse peritoneal cavity. This implantation technique strongly reduced the wound reaction. Tricalcium phosphate induced the accumulation of trace elements whereas asbestos did not. This finding points strongly to biodegradation as a cause of trace element accumulation, which was confirmed by the finding of trace element accumulation in cultured mouse peritoneal macrophages incubated with tricalcium phosphate but not in those exposed to asbestos.

Since all of the elements in question accounted for 0.2% or less of the materials under study, these results not only indicate that biodegradable biomaterial generally leads to trace element accumulation but also underscore the importance of using extremely pure biomaterials.