Long-term performance of a low-modulus acrylic cement in a simulated physiological environment

A vertebroplasty bone cement, designed to exhibit mechanical properties closer to those of the vertebral bone, was investigated. Indeed, adjacent fractures are attributed to an excessive difference in elastic modulus between the vertebrae and the bone cement implying another operation to repair the newly damaged vertebra. The proposed solution to lower the mechanical properties is the introduction of gelatine in the powder of the cement. This low modulus bone cement was studied by quasi-static compression, dynamic mechanical analysis and fatigue tests. Compression testing showed a significant decrease of the elastic modulus of 33 % after 6 months of immersion in a PBS solution at 37 °C, confirmed by the dynamic mechanical analysis. This analysis also showed that immersion and the introduction of gelatine in the cement influence the relaxations of the PMMA matrix. Fatigue performance was also studied with and without gelatine and showed that it presents a characteristic life of at least 24,600 cycles for a load of 7 MPa. While compression testing indicates a reduction in mechanical performance, all others tests demonstrated that gelatine does not significantly impair the overall properties of acrylic bone cement that still possess sufficient properties to achieve its main goal to stabilise damaged vertebrae.