Preparation of injectable hydroxyapatite/collagen paste using sodium alginate and influence of additives

Preparation of injectable hydroxyapatite/collagen bone-like nanocomposite (HAp/Col) paste utilizing sodium alginate (Na-Alg) and influence of additives on the paste properties were investigated. The HAp/Col at the HAp and collagen mass ratio of 80:20 synthesized by a simultaneous titration method was pelletized to 100-212 μm. The HAp/Col powder and that treated with 100mM CaCl₂ (Ca-HAp/Col) were used as starting powders. A paste was prepared by mixing of the starting powder and Na-Alg solution at one of several powder/liquid ratios. The paste was directly injected into 100mM CaCl ₂ solution to confirm setting capability, and examined a viscosity, hardening behavior, compressive strength and decay property. In addition, the paste supplemented with an organic acid or a calcium compound as an additive was also prepared to examine influences of the additive on paste properties. The organic acid was chosen from citric, succinic, malic, lactic and glycolic acids, and the calcium compound was chosen from Ca(OH)₂, Ca(CO) ₃, CaSO₄·0.5H₂O and calcium citrate. The prepared paste was set by direct injection to 100mM CaCl₂ solution. The suitable mixing conditions of the paste were a P/L ratio of 0.6 at the 90:10 mass ratio of Ca-HAp/Col and solution of low viscous Na-Alg. All additives increased the paste viscosity; however, the mechanisms were different between organic acids and calcium compounds. Organic acids rapidly decreased pH to form Alg gel by deposition of Alg. Contrarily, calcium compounds supplied Ca ²⁺ ions to form egg-box structure for gelation of Alg, and the reaction depended on solubility of compound. Additives also increased decaying time but could not realize anti-decay in the present conditions. The results suggested that the HAp/Col injectable paste can be utilized in rapid prototyping materials and might be good candidate for injectable artificial bone with further improvement in anti-decay property.