Chemical changes in hydroxyapatite biomaterial underin vivo andin vitro biological conditions

Abstract

The introduction of a synthetic calcium phosphate into a biological environment is likely to result in surface-mediated chemical events. On the basis of such an assessment, we studied the chemical changes occurring in the mineral after exposure of a synthetic hydroxyapatite ceramic to both in vivo (implantation in human) and in vitro (cell culture) conditions. A small amount of the material was phagocytized but the major remaining part behaved as a secondary nucleator as evidenced by the appearance of a newly formed mineral. Morphologically, the newly formed mineral appeared as tiny crystals precipitated and grown from the surface of the initial synthetic crystals. The density of the additional mineral increased from the periphery to the core of each biomaterial aggregate. Chemically, it was identified by IR spectroscopy as a carbonated apatitic mineral. We propose that the adsorption of biomolecules could inhibit precipitation, accounting for the increasing amount of precipitate from the periphery to the core of the aggregates.

Medical Application of Calcium Orthophosphate Bioceramics

“…Currently, it is agreed that the newly formed bone bonds directly to biomaterials through a carbonated CDHA layer precipitating at the bone/biomaterial interface. Strange enough but a careful seeking in the literature resulted in just a few publications [459,538,635,636], where the bioactivity mechanism of calcium orthophosphates was briefly described. For example, the chemical changes occurring after exposure of a synthetic HA bioceramics to both in vivo (implantation in human) and in vitro (cell culture) conditions were studied.…”

“…For example, the chemical changes occurring after exposure of a synthetic HA bioceramics to both in vivo (implantation in human) and in vitro (cell culture) conditions were studied. A small amount of HA was phagocytozed but the major remaining part behaved as a secondary nucleator as evidenced by the appearance of a newly formed mineral [635]. In vivo, a cellular activity (e.g., of macrophages or osteoclasts) associated with an acidic environment were found to result in partial dissolution of calcium orthophosphates, causing liberation of calcium and orthophosphate ions to the microenvironment.…”

Development of New Titanium Coating Material (CaTiO3-aC) with Modified Thermal Decomposition Method

“…On the other hand, hydroxyapatite (HA) has excellent bone conductivity with osteogenic tissue, and thus has been widely used as a filling material [2][3][4] . Thus HA is generally used as a coating material to improve bone conductivity of metal materials such as titanium and its alloys, stainless steel, and CoCr-Mo alloys 1,5,6) .…”

Formation of apatitic calcium phosphates in a Na-K-phosphate solution of pH 7.4

“…Synthetic, crystalline and stoichiometric hydroxyapatite (HA: Ca 10 (PO 4 ) 6 (OH) 2 ) with a Ca/P molar ratio in the vicinity of 1.67, and highly crystalline beta-tricalcium phosphate (TCP: Ca 3 (PO 4 ) 2 ) are commonly [1][2][3][4][5][6][7][8][9][10] conceived or used implant materials which are nevertheless not perfectly similar to the host bones. While the former of these bioceramics does not have a significant in vivo resorbability to take part in the remodeling of the natural bone unless the ceramic is porous enough, the latter simply undergoes quite a rapid (passive) dissolution at the low pH value (i.e., 4.2 to 4.3) of the osteoclastic environment [11].…”

“…In the course of developing simpler and robust manufacturing processes for the wet-chemical synthesis of nanosize, poorly crystalline calcium-deficient hydroxyapatite (with a nominal formula of Ca 9 (HPO 4 )(PO 4 ) 5 OH) bioceramics, we have found that the use of a simple Na-K-phosphate reference solution, as the synthesis medium, may simultaneously serve three purposes; namely, (1) to provide a neutral pH medium during synthesis, (2) [16] of the two), mainly depending on the Ca/P molar ratio adjustment (from 1.8 to 1.5, respectively) in the synthesis reactors. In this study, we report the use of a simple Na-K-phosphate solution in preparing Na-and K-doped, carbonated apatitic calcium phosphates in different forms, including apatitic powders, self-setting cements and coating layers on natural marble.…”