ИСТИНА

The growing demands of regenerative medicine and orthopedic surgery require new bioactive materials for bone implants. Particular attention is paid to composite materials containing bioresorbable phase. Being the active source of necessary elements for inorganic part of bone resorbable materials are replaced by native growing bone tissue in the organism. Calcium-deficient or carbonate-containing hydroxyapatite Ca10 (PO4)6(OH)2, amorphous calcium phosphate, tricalcium phosphate (TCP) Ca3(PO4)2, phosphate glass, calcium pyrophosphate (CPP) Ca2P2O7, calcium polyphosphates, renanite NaCaPO4 can be regarded as such phase. The aim of this work is to obtain porous resorbable ceramic material based on calcium pyrophosphate Ca2P2O7 and polyphosphates. First, initial samples for ceramics were prepared by forming from cement mass. Then they were annealed at temperature range 600-1000°C. Brushite cements were synthetized from β-TCP and orthophosphoric acid by reaction (1): Ca3(PO4)2 + H3PO4 + 6H2O = 3CaHPO4*2H2O (1), In order to control the setting time of cement mass sodium pyrophosphate Na4P2O7, sodium hexametaphosphate (NaPO3)6 and citric acid were added to the liquid before mixing with TCP powder. During the heat treatment brushite converts to CPP by reaction (2): CaHPO4*2Н2О→ СаНРО4→Ca2P2O7 (2), System of sodium salts (NaPO3)6 and Na4P2O7 has a relatively low melting point. The presence of the melt promotes liquid sintering at rather low temperatures and improves the mechanical characteristics of ceramic materials. Porous structure (about 70% porosity with pore diameter ≈100 μm) is promoted by gas release during heat treatment of the cements. According to XRD-analysis, final ceramic material is based on CPP and contains 5-10% of double polyphosphates of sodium and calcium. In vitro and in vivo tests demonstrated that our material is nontoxic, bioactive and resorbable. Thus, in this study bioactive ceramic material based on CPP and polyphosphates with high rate of resorption and porous structure was obtained.