Properties of Elastomeric Calcium Phosphate Cement-Chitosan Composites
Shozo Takagi, Laurence C. Chow, S Hirayama, F Eichmiller
Self-hardening calcium phosphate cements (CPC) have been shown to be efficacious in a number of clinical applications for which other currently available materials do not work well. However, for some applications, for example in filling periodontal defects, it is desirable to have a highly osteoconductive material such as CPC in a non-rigid resorbable elastomeric matrix. In the present study, chitosan was evaluated as the matrix for preparing non-rigid CPC materials. Solutions containing mass fractions of 5 % and 15 % of chitosan (5CHT and 15CHT, respectively), 15 % of chitosan-malate (CHTM) and chitosan-lactate (CHTL) were prepared. The CPC powder was an equimolar mixture of tetracalcium phosphate and dicalcium phosphate anhydrous. Cement specimens were prepared by mixing CPC powder with a chitosan solution at a powder/liquid ratio of 2 to 2.5. The CPC-chitosan composites thus prepared were more stable in water than conventional CPC and did not disintegrate even after being placed in water immediately after mixing. The increase in pH induced by the CPC setting reaction drastically reduced the solubility of chitosan, leading to an initial hardening of the CPC-chitosan paste within about 10 min in all cases. Flexural modulus was measured on CPC-chitosan samples (n = 5) at 1 d or 7 d in a saliva-like solution. The 1-d flexural modulus (GPa) for CPC, 5CHT, 15CHT, CHTM and CHTL were 4.52 0.13; 1.19 0.25; 1.20 0.22; 1.38 0.36; and 2.38 0.54, respectively, and no decrease in this quantity was found in the 7-d samples. In addition, the compressive strength and flexural tensile strength were also found to be constant during this time period except for the 5CHT and CHTL samples. Powder x-ray diffraction analysis demonstrated that chitosan did not interfere the conversion of the CPC in these samples to hydroxyapatite. This experiment demonstrates that CPC-chitosan composites are flexible, stable in a wet environment and have reasonable physical strength.