Low Temperature Sythesized α-TCP Bone Cement - A Possibility to Improve Physicochemical Properties and Cell Response
DEMIR O. 1
1 Riga Technical University , Riga, Latvia
Öznur Demir1,2, Athanasia Pylostomou1,2, Dagnija Loca1,2 1Rudolfs Cimdins Riga Biomaterials Innovations and Development Centre of RTU, Institute of General Chemical Engineering, Faculty of Materials Science and Applied Chemistry, Riga Technical University, Pulka St 3, Riga, LV-1007, Latvia 2Baltic Biomaterials Centre of Excellence, Headquarters at Riga Technical University, Riga, Latvia
The interest in bone substitute biomaterials is still unanimously recognized. Specifically, calcium phosphate cements (CPCs) are clinically applied for orthopedic and maxilla facial surgery. One of the most common reactants for CPC is α-tricalcium phosphate (α-TCP), which has the ability to hydrolyze to calcium-deficient hydroxyapatite (CDHAp) upon contact with an aqueous solution. α-TCP is a much more efficient reactant for CPC owing to its lower density, the higher free energy of formation, and more reactivity and solubility. In this study, low-temperature α-TCP (LT- α-TCP) powder was obtained by thermally treated amorphous calcium phosphate with significantly high specific surface area (SSA) (>60 m2/g) at 650 - 750 οC. Afterward, produced α-TCP powder was used as a powder phase to form an injectable, self-setting bone cement by mixing sodium-hydrogen phosphate buffers as a setting solution. Having said that, changes in the pH of the liquid phase utterly influence the formation of the final crystalline phase. Thus, the setting mechanism of bone cement can be altered. This study aimed to assess the effect of liquid phase pH on the setting reaction of LT- α-TCP powder, as well as conversion of the hardened cement paste to the hydroxyapatite (HAp) phase and as a final step to assess the in vitro cellular effect. During the injection period, all cement pastes were able to be injected before the maximum force reached 300N, indicating that all prepared cement formulations were injectable. Although the setting time of the cement pastes increased almost six times when the pH value of the liquid phase was elevated from 6.0 to 7.4, it was found to be in the range of clinically acceptable limits (15 min). The compressive strength of the hardened cements was significantly improved by using the physiological pH value of the liquid phase. The setting reaction of α-TCP powder with the liquid phase having pH 6.0 and 7.4 resulted in the transformation of α-TCP to the heterogeneous nucleation of HAp. As the hydrolysis process does not always end with the same phase, different degrees of HAp phases exist, like in autologous bone, which positively influences bone-forming cells. In the preliminary study, the cellular response of cements prepared using liquid phase with pH 7.4 showed significantly higher viability of MC3T3-E1 cells than other cement formulations. Since the present study was designed to produce an injectable bone cement having a clinically suitable setting time, injectability, and mechanical properties, a liquid phase with pH of 7.4 was found to be beneficial for the local treatment of bone defects, especially in the non-load bearing sites.
Acknowledgement: The authors acknowledge financial support from the European Union’s Horizon 2020 research and innovation programme under the grant agreement No. 857287 (BBCE – Baltic Biomaterials Centre of Excellence).