Susceptibility of calcium-deficient hydroxyapatite-collagen composite to irradiation

A quality of a tooth and a bone, which are biomaterials, have an individual difference, and are thought to be affected by body fluid. Therefore, the addition dose method is usually applied to the dosimetry using a tooth and a bone. However, the irradiation of an addition dose can not carry out under the similar environment to original irradiation, that is, the addition dose can be only made on the biomaterial excised from body. This paper was studied on a susceptibility of calcium deficient hydroxyapatite-collagen composite (c-DAp), which is near bone and teeth, to X-ray irradiation by means of ESR spectroscopy. The c-DAp were prepared by the electrolytic deposition method using Ca(H2PO4)·H2O (MCP) electrolytic solutions added with various concentrations of collagen. The ESR spectrum of calcium deficient hydroxyapatite without collagen (DAp) has the peaks assigned to the hyperfine structure of H+ (hyperfine coupling constant=50.8 mT, I=1/2) due to HPO42- ion which captured the hole released by X-ray irradiation. This ESR peak intensity of c-DAp decreased in an increase in the amount of collagen added into MCP electrolytic solution, because dangling H+ of HPO42- binds to carboxyl group of collagen due to hydrogen bond. The ESR signal intensities at near g=2 in DAp, c=DAp and stoichiometric hydroxyapatite (HAp) after X-ray irradiation depended on the absorbed dose in the range from 6 to 380 Gy. Each ESR signal intensity in DAp, c-DAp, or HAp decreased on suspending the X-ray irradiated DAp, c-DAp or HAp in the simulated body fluid. Furthermore, the susceptibility of DAp and c-DAp to x-ray irradiation were about one tenth of that of HAp. (author)