The influence of inhibitors containing various functional groups (i. e., phosphonate, hydroxyl, and carboxyl) on the kinetics of crystal growth of hydroxyapatite (HAP) has been studied at pH=7.40, 37°C and at low supersaturations. It has been found that the crystal growth of HAP is significantly retarded in the presence of micromolar concentrations of hydroxy phosphonoacetic acid (HPA) and 2-phosphono butane 1, 2, 4- tricarboxylic acid (PBTC), with PBTC being a more potent inhibitor than HPA. Three other inhibitors, α-hydroxy carboxylic acids (i. e., glycolic acid, GLA; malic acid, MLA; mandelic acid, MDA), dicarboxylic acid (malonic acid, MNA), and poly (acrylic acid), PAA, all exhibit inhibitory activity but to a varying degree. Among these inhibitors the overall effectiveness, in terms of decreasing power, is PAA>MLA>MNA>GLA>MDA. The retarding effect of these inhibitors is discussed in relation to the calcium-inhibitor complex formation on the HAP seed crystals and the structural features of the inhibitor molecules. The fit of the experimental data to the Langmuir adsorption isotherm supports a mechanism of inhibition through molecular adsorption of the inhibitor ions on the surface of the growing crystals.

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The potentiality of titanium coating by polyphosphate bioglasses may present an interest for the bioactivity of prosthesis. Nevertheless, it is necessary, to control their mechanical properties evolution in presence of body fluids. In this paper, we present our first results obtained by Vickers indentation method. The adhesion of glass on titanium substrate does not depend on its partial dissolution in human fluid body.

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Applicability of polyphosphate coacervate to coating processes was examined systematically. The physical properties such as density, viscosity, surface tension and wettability, of coacervate of Na₂O-CaO-P₂O₅ are strongly dependent on the Ca/Na ratio.

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Porous ceramics of β-tricalcium phosphate (β-Ca₃(PO₄)₂; β-TCP) with different micro-structure were prepared by sintering. They have almost the same porosity of about 60% and almost the same macro-pores of 150-400μm in size. One of them had micro-pores of O.1-0.5μm in size, another one had few micro-pores. These porous, β-TCP were implanted into the femoral condyle of adult rabbits, then their bio-resorption was analized. The, β-TCP with micropores showed obviously bio-degradation in comparison with the, β-TCP without micro-pores.

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More than 30 modifications of apatites and orthophosphates of the required composition have been synthesized by the mechanochemical method. The localization of ions and atoms into the positions of apatite structure has been revealed, which could not be done with the help of other methods. The synthesized phosphates can be used as the material for bioceramics and other purposes.

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The effect of additives such as polyvinylalcohol, polyacrylamide, acrylamide and acrylic acid on the mechanical properties of calcium phosphate cement was investigated, measuring the diametral tensile strength of the hardened cement made by pressing the cement paste. Of the additives tested, the combined use of acrylamide monomer and acrylic acid was effective to improve the mechanical properties of the hardened cement. For the cements made by pressing at various pressures (72.8-291MPa), the addition of acrylamide and acrylic acid resulted in an about 30% increase of the diametral tensile strength and an about 7% increase of the bulk density compared to the control (no additives). The hardened cement with acrylamide and acrylic acid exhibited a diametral tensile strength of 15.4 MPa as the largest values obtained.

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The induction time for the transformation of amorphous calcium phosphate (ACP) to hydroxyapatite (HAP) was monitored at pH7.40, 37°C, and calcium=phosphate=3.20mM, in the presence of polymeric and nonpolymeric inhibitors containing various functional groups. The polymeric inhibitors evaluated include: poly (acrylic acid), molecular weight 850 to 20000; poly (acrylamide), PAm; poly (diallyldimethylammonium chloride), PDa; copolymers of acrylic acid: hydroxylpropyl acrylate, AA: HPA; acrylic acid: 2-acrylamido-2-methylpropane sulfonic acid, AA: SA; acrylic acid: vinyl acetate, AA: VAc; acrylic acid: vinyl alcohol, AA: VOH. The non-polymeric inhibitors investigated include: pyrophosphate, PYP; 1-hydroxyethylidine-1, 1-diphosphonic acid, HEDP; and 2-phosphonobutane-1, 2, 4-tricarboxylic acid, PBTC. It was found that PAc and acrylic acid-based copolymers were effective in delaying ACP transformation reaction. The inhibitors effectiveness was greatly affected by polymer M_w and ionic charge. For homopolymers the order in terms of decreasing effectiveness is: PAc >> PAm> PDa=control (no inhibitor). Among copolymers, a AA: SA copolymer showed the best overall performance in terms of delaying the ACP phase transformation. For non-polymeric inhibitors, it was observed that both polyphosphate and phosphonates are potent inhibitors with HEDP more effective than PYP, as expected. The combination of PAc and PYP or HEDP or PBTC leads to a synergistic delay in the onset of the phase transformation. Reaction solutions containing 30 ppm PAc-2 (M_w 2100) and 17 ppm HEDP resulted in a>400% increase in induction time over what would be anticipated from an additive effect from these inhibitors.

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