Surface modification of alpha-tricalcium phosphate with inositol phosphate for cement fabrication

摘要

Introduction: Calcium phosphate bioceramics have been used for bone grafting due to their biocompatibility and osteoconductivity. Among them, calcium phosphate cement has an advantage in that the users can form desired shapes during surgical operation and has therefore received much attention. We have previously developed novel a-tricalcium phosphate (α-TCP) cement with biodegradabilrty and osteoconductivity, set by chelating capability of inositol phosphate (IP6). The cement powder was prepared by surface modification in IP6 solution. However, the adsorption behavior of IP6 on the α-TCP powder is not studied in detail. In the present study, the adsorption behavior of IP6 on the α-TCP powder was circumstantially examined to optimize the IP6 concentration for surface modification of α-TCP powder. Materials and Methods: The starting α-TCP powder was ground for 120 min using zirconia balls (10 mm in diameter). The obtained α-TCP slurry was filtrated and freeze-dried for 24 h. The as-prepared α-TCP powder was surface-modified in IP6 solution (0,500,1000,3000 ppm, pH7.3) up to 24 h. The slurry was centrifuged to collect supernatant solution and deposition. Amount of IP6 adsorbed on α-TCP powder was measured with an inductively coupled plasma atomic emission spectrometer (ICP-AES). Raman spectrometer was used to clarify IP6 adsorption on α-TCP powder. The release of Ca~(2+) and PO_4~(3-) ions from the IP6 surface modified α-TCP powders was examined in acetic acid-sodium acetate (Ac-AcNa, pH 5.5) and 2-[4-(2-hydroxyethyl)-1-piperazinyrjethanesulfonic acid (HEPES, pH 7.0) buffers. The change of crystal phase before and after the elusion test was examined using X-ray diffractometer (XRD). Results and Discussion: Amount of IP6 adsorbed on α-TCP powder increased with IP6 concentration and reached a plateau within 12 h. The XRD patterns of IP6-α-TCP powders after adsorption test (500-, 1000- and 3000-IP6-α-TCP) showed α-TCP single phase. The result indicates that the IP6 adsorption inhibited the phase transition of α-TCP to HAp. Raman spectroscopic study showed that the peaks corresponding to IP6 molecule were detected only in 3000-IP6-α-TCP spectra because of low IP6 concentration for surface modification of α-TCP in 500- and 1000-IP6-α-TCP powders. The release of Ca~(2+) and PO_4~(3-) ions from the IP6 surface modified powders in Ac-AcNa and HEPES was constant value till 7 days. The crystal phase of 500-, 1000- and 3000-IP6-α-TCP powders after release test was α-TCP single phase; however, the 0-IP6-α-TCP powder was converted to HAp single phase. These results show that the IP6-α-TCP powders were more stable in Ac-AcNa and HEPES buffers than 0-IP6-α-TCP powder without IP6 surface modification. Conclusion: It was found that the IP6 could adsorb on the α-TCP powder in 500,1000, and 3000 ppm IP6 solution and amount of IP6 adsorbed on α-TCP powder reached a plateau within 12 h. The prepared 500-, 1000- and 3000-IP6-α-TCP powders were stable in Ac-AcNa and HEPES buffers. Thus, surface modification of α-TCP powder in 500, 1000, and 3000 ppm IP6 solution would be suitable for preparation of stable cement powder.