Effects of hydroxylapatite coating crystallinity on biosolubility, cell attachment efficiency and proliferation in vitro

A hydroxylapatite (HA) coating with similar to 97% crystalline HA content ( MP-1 treated HA coating, MP-HA) was tested in vitro for its biosolubility a nd cellular biocompatibility. The MP-HA coating was compared with a standar d HA coating with similar to 63% crystallinity (SHA) and an amorphous HA co ating with similar to 25% crystallinity (AHA), as well as a titanium (Ti) s urface without HA coating as a control. The topographic study with scanning electron microscopy indicated that MP-HA appeared more coarse, with projec ted nodules which altered the shape of cells attached to the substrate. Bio solubility study indicated that MP-HA had the least effect on the culture m edium pH, while AHA (P < 0.01) and SHA (P < 0.05) significantly raised the medium pH up to 8.2 and 7.75, respectively. X-ray diffraction (XRD) analysi s showed essentially unchanged levels of the total soluble phases of all co atings after incubation with culture medium, except that the CaO phase was rapidly dissolved from AHA coatings and completely eliminated from SHA coat ings. Cultures of human gingival fibroblasts on these HA coatings showed th at MP-HA and SHA had about the same cell attachment efficiency which was re latively lower than that of AHA coatings. MP-HA generated significant highe r cell proliferation rate relative to AHA (P < 0.01) and SHA (P < 0.05). Th is study indicated that surface chemistry and topography of lower crystalli nity might be favorable to cell attachment, but that elevated medium pH mig ht result in a cytotoxic effect that inhibits the proliferation of attached cells on coating surfaces. (C) 1999 Elsevier Science Ltd. All rights reser ved.