A gentamicin-loaded hydroxyapatite/collagen bone-like nanocomposite (GNT-HAp/Col) was fabricated and evaluated for its absorption–desorption properties, antibacterial efficacy, and cytotoxicity. The hydroxyapatite/collagen bone-like nanocomposite (HAp/Col) powder was mixed with gentamicin sulfate (GNT) in phosphate-buffered saline (PBS) at room temperature. After 6 h mixing, the GNT adsorption in all conditions reached plateau by Langmuir’s isotherm, and maximum GNT adsorption amount was 34 ± 7 μg in 250 μg/mL GNT solution. Saturated GNT-loaded HAp/Col powder of 100 mg was soaked in 10 mL of PBS at 37 °C and released all GNT in 3 days. A shaking culture method for a GNT extraction from the GNT-HAp/Col and an inhibition zone assay for the GNT-HAp/Col compact showed antibacterial efficacy to Escherichia coli (E. coli) at least for 2 days. From the release profile of the GNT from the GNT-HAp/Col powder, antibacterial efficacy would affect E. coli at least for 3 days. Further, no cytotoxicities were observed on MG-63 cells. Thus, the GNT-HAp/Col is a good candidate of bioresorbable anti-infection bone void fillers by prevention initial infections, which is the primary cause of implant-associated infection even for rapid bioresorbable materials.

Osteosarcoma has a poor survival rate due to relapse and metastasis. Zoledronic acid (ZOL), an anti-resorptive and anti-tumor agent, is used for treating osteosarcoma. Delivery of ZOL to the target region is difficult due to its high binding affinity to bone minerals. This study developed a novel treatment for osteosarcoma by delivering ZOL to the target region locally and sustainably. In this study, we fabricated a novel bone substitute by loading ZOL on β-tricalcium phosphate (β-TCP). The ZOL-loaded β-TCP (ZOL/β-TCP) would be expected to express the inhibitory effects via both bound-ZOL (bound to β-TCP) and free-ZOL (release from ZOL/β-TCP). To explore the ability to release ZOL from the ZOL/β-TCP, the amount of released ZOL was measured. The released profile indicates that a small amount of ZOL was released, and most of it remained on the β-TCP. Our data showed that ZOL/β-TCP could successfully express the effects of ZOL via both bound-ZOL and free-ZOL. In addition, we examined the biological effects of bound/free-ZOL using osteosarcoma and osteoclasts (target cells). The results showed that two states of ZOL (bound/free) inhibit target cell activities. As a result, ZOL/β-TCP is a promising candidate for application as a novel bone substitute.

The anti-washout property, viscosity, and cytocompatibility to an osteoblastic cell line, MG-63, of anti-washout pastes were investigated. Mixing a hydroxyapatite/collagen bone-like nanocomposite (HAp/Col), an aqueous solution of sodium alginate (Na-Alg), which is a paste hardening and lubricant agent, and supplementation of calcium carbonate or calcium citrate (Ca-Cit) as a calcium resource for the hardening reaction realized an injectable bone paste. Adding Ca-Cit at a concentration greater than eight times the Ca ion concentration to Na-Alg improved the anti-washout property. Although the viscosity test indicated a gradual increase in the paste viscosity as the calcium compounds increased, pastes with excess supplementation of calcium compounds exhibited injectability through a syringe with a 1.8 mm inner diameter, realizing an injectable bone filler. Furthermore, the anti-washout pastes with Ca-Cit had almost the same cell proliferation rate as that of the HAp/Col dense body. Therefore, HAp/Col injectable anti-washout pastes composed of the HAp/Col, Na-Alg, and Ca-Cit are potential candidates for bioresorbable bone filler pastes.

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 100212¯m. The HAp/Col powder and that treated with 100 mM CaCl 2 (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 100 mM 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 , CaSO 4 ·0.5H 2 O and calcium citrate. The prepared paste was set by direct injection to 100 mM CaCl 2 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.