Study of mixed Ca-Zn hydroxyapatite surface modified by lactic acid

The new hybrid inorganic-organic composites, Ca(10−x)Znx(PO4)6(OH)2-lactic acid, at different amounts of zinc and lactic acid were prepared by dissolution of the organic compound in an hydroxyapatite suspension. They were characterized by XRD, IR, MAS NMR (13C and 1H) and chemical analysis. The crystallinity was slightly affected by the presence of organic fragments. IR and (13C and 1H) MAS NMR measurements indicate that the carboxylic groups of the acid interact with calcium and zinc ions of hydroxyapatite surface. Chemical analysis displays that zinc promotes the acid grafting. A mechanism of surface modification is proposed based on the obtained results.

► New hybrid compounds Ca(10−x)ZnxHAp-(Lacid)n with 0 ≤ x ≤ 2; n = 5, 10, 20 or 40 were prepared. ► For treated Ca8Zn2HAp, DRX and 13C MAS NMR confirm the appearance of new crystalline phase; zinc phosphate (ZnP2O7). ► These obtained results display that the presence of some amount of zinc exalts the reactivity of the apatitic surface.