Injectable Enzymatically Hardened Calcium Phosphate Biocement

Current injectable bone cements lack sufficient control over setting time and osteogenic potential. Prior research has shown that calcium phosphate cements can mimic cancellous bone properties but often lack bioactivity. This gap motivated the development of a new cement system that integrates enzymatic hardening with anionic polyelectrolytes. Established methods for cement characterization include compressive strength testing and in vitro bioactivity assessments. No prior work had resolved the challenge of balancing injectability with rapid hardening and enhanced osteogenicity. This paper introduces a composite cement system with a novel hardening mechanism. The study addresses the need for better control over setting time and improved osteogenic response in injectable cements. The research builds on prior knowledge of calcium phosphate systems but introduces a new enzymatic approach.

The aim of this study was to develop and evaluate a new injectable calcium phosphate cement system using enzymatic hardening. The specific problem targeted was the lack of controllable setting times and limited osteogenic potential in existing injectable cements. The motivation came from the need for a bone defect repair material that can be injected and rapidly hardened. The study focused on integrating phytic acid and phytase into the hardening liquid. It also aimed to assess how anionic polyelectrolytes affect cement properties. The research sought to determine if the new system could achieve mechanical properties similar to cancellous bone. The goal was to enhance osteogenic activity through controlled ion release and gene expression. The study aimed to verify the noncytotoxic nature and wash-out resistance of the cement.

Composite cements were prepared by combining a calcium phosphate powder mixture with a hardening liquid containing anionic polyelectrolytes. The hardening liquid included phytic acid and phytase, along with small amounts of polyacrylic acid and carboxymethyl cellulose. Phase and microstructural analysis was conducted to assess cement composition. Compressive strength testing was used to evaluate mechanical properties. Ion release was measured to determine the chemical behavior of the cements. In vitro testing was performed to assess bioactivity and cytotoxicity. The setting time was controlled by adjusting the P/L ratio or the reaction time of phytic acid and phytase. The effect of polyacrylic acid content on hydroxyapatite particle morphology was analyzed.

The setting time of the cements was successfully controlled between 7 and 28 minutes by altering the P/L ratio or the reaction time of phytic acid and phytase. The wet compressive strength reached up to 15 MPa, which is comparable to cancellous bone. Increasing the polyacrylic acid content to 1 wt% refined the morphology of hydroxyapatite particles. Cement pastes showed high resistance to wash-out immediately after mixing. Noncytotoxic properties were confirmed through extract testing. Phytic acid supported the formation of calcium deposits in vitro. The addition of polyacrylic acid and carboxymethyl cellulose enhanced alkaline phosphatase activity. Osteogenic gene expression, including osteopontin, osteocalcin, and IGF1, was strongly up-regulated in osteogenic αMEM 50% CXI extracts.

The fully injectable composite calcium phosphate cements with anionic polyelectrolyte addition demonstrated good mechanical and physicochemical properties. The study showed that the setting time could be controlled through adjustments in the P/L ratio or reaction time. Cement compressive strength was comparable to cancellous bone, indicating potential for bone defect repair. The addition of anionic polyelectrolytes refined hydroxyapatite particle morphology. The cements exhibited high resistance to wash-out and noncytotoxic properties. Phytic acid supported calcium deposit formation, and the combination of polyacrylic acid and carboxymethyl cellulose enhanced osteogenic activity. Strong up-regulation of osteogenic genes was observed in the extracts. The findings suggest that these cements are promising for applications in bone defect regeneration.