Strength of Calcium Phosphate Cements
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0975-DD10-04
Strength of Calcium Phosphate Cements Alexander Veresov1, Alexander Stepuk1, Alexander Kuznetsov1, Valery Putlayev2, and Vladimir Kuznetsov3 1 Materials Science, Moscow State University, Leninskie Gory, Moscow, 119992, Russian Federation 2 Chemistry, Moscow State University, Leninskie Gory, Moscow, 119992, Russian Federation 3 Institute of Mechanics, Moscow State University, Leninskie Gory, Moscow, 119992, Russian Federation
ABSTRACT Calcium phosphate materials are widely used to treat bone defects. HA bioceramics traditionally used in medicine have a serious disadvantage: their limited resorbability. Calcium phosphate cements seem to be promising compounds to replace conventional ceramics; however, high macroporosity of the hardened materials leads to low mechanical strength. The main objective of the present work was the development of new chemically bonded materials based on αtricalcium phosphate (α-TCP) and hydroxylapatite phase. The main idea was to combine the benefit of ceramics technology to improve the materialís strength (compacting of powders to reduce the starting macroporosity), with the advantages of a cement product (small resorbable calcium phosphate particles). α-Ca3(PO4)2-based biocements were synthesized with an initial composition of HA, α- and β-TCP, containing 80% wt. of TCP phase. The rate of α-TCP transformation to apatite phase during the setting reaction was about 20% wt. in the case of cylindrical samples (8mm x 8 mm) at 60oC for 50 hours. The fabricated TCP ñ bio-composites demonstrated high mechanical strength and stiffness. The most efficient results (σc = 120 MPa) were achieved with samples containing chitosan biopolymer. INTRODUCTION Calcium phosphate materials are widely used to treat bone defects. It is believed that hydroxylapatite (HA) compound Ca10(PO4)6(OH)2 is almost an ideal biomaterial, due to its chemical similarity with bone mineral phase. HA bioceramics traditionally used in medicine have a serious disadvantage: the solubility constant of pure stoichiometric HA is very low (Ksp = 10-117M18), so dense apatite ceramics with large grains are not resorbable and the material could not be replaced by growing bone tissue for many years after implantation. Calcium phosphate cements (mixtures of cement powder and water hardened to form bulk material) seem to be promising compounds to replace conventional ceramics [1]. The cement body consists of submicron sized disordered particles, which closely resemble the shape and morphology of bone mineral (plates 40x20x5 nm). The final cement product is microporous; it is possible to load it with drugs to treat the initial inflammation process. But the high macroporosity of the hardened materials (as a result of the high initial water content; the typical water-to-powder weight ratio is around 0.5) leads to low mechanical strength (σс = 5-30 MPa). The compressive strength should reach a value of 100 MPa to be comparable with ceramics and bone [2].
The principal objective of the present work was a development of new chemicall
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