SURFACE INSTABILITY OF CALCIUM-PHOSPHATE CERAMICS IN TISSUE-CULTURE MEDIUM AND THE EFFECT ON ADHESION AND GROWTH OF ANCHORAGE-DEPENDENT ANIMAL-CELLS

The surface of biocompatible ceramics made of synthesized hydroxyapati te (HAP) and p-tricalcium phosphate (TCP) was found to be extremely ac tive in tissue culture medium. Using mixed ceramics of HAP and TCP whi ch had been prepared with different Ca/P molar ratios adjusted in step wise fashion to values of 1.50, 1.55, 1.60, 1.64 and 1.67, the charact eristics of the surface were investigated. The time-dependent variatio n of zeta potential of the TCP-HAP ceramics immersed in distilled wate r and in culture medium with and without addition of fetal bovine seru m showed that the surface was unstable with significant changes in the charge being observed. Dry TCP powder had a zeta potential of -19 mV, which shifted to -7 mV after soaking in water and to -26 mV in cultur e medium. In contrast, HAP had a zeta potential of -11 mV in a dry sta te, -9 mV in water and -29 mV in culture medium. Concentrations of cal cium and phosphate dissolved in distilled water showed the solubility was higher for TCP than for HAP. In comparison, it was found that diss olved calcium and phosphate in the medium were removed from the soluti on by deposition on immersed TCP-HAP ceramics. These results suggested that the stability of the surface was closely related to both reactio ns of association and dissociation of calcium and phosphate in tissue culture medium. The zeta potential analysis also suggested that Ca-def icient HAP, which has a similar crystal structure to HAP with a Ca/P r atio less than 1.67, was generated by degradation and reforming of the surface layer. The most stable structure which was the most suitable for adhesion of L-929 cells was obtained by the mixture of 20% TCP and 80% HAP ceramics. In conclusion, the stability of the surface structu re was considered to be the dominant factor for the enhancement of the adhesiveness of cells on TCP-HAP ceramics. (C) 1997 John Wiley & Sons , Inc.