Redefining injectable PMMA bone cement: Beta-tricalcium phosphate integration for bioactive and osteoconductive performance for minimally invasive applications

Background: Poly(methyl methacrylate) (PMMA) is commonly used as injectable bone cement; however, its exothermic polymerization, excessive stiffness, and bioinertness limit its clinical performance. To address these drawbacks, various types of PMMA-based bone cements modified with ceramic components have been developed. Objective: We refined a PMMA-based bone cement with a high substitution of beta-tricalcium phosphate (β-TCP) for minimally invasive applications. Methods: Composite cements with various weight ratios of β-TCP were in vitro characterized for the injectability, curing profile, radiopacity, weight change, compressive strength, and cytocompatibility. Osteoblast-like MG-63 cells were utilized for the biological assessments. For the in vivo evaluation, the composites were injected into the distal femora of rabbits, followed by micro-computed tomography (μ-CT) and histological analyses conducted after 24 weeks. Results: Incorporation of β-TCP significantly lowered the maximum curing temperature and extended the setting time, while good injectability was still maintained. As the β-TCP content increased, both radiopacity and compressive strength increased proportionally with minor weight changes after immersion in simulated body fluid. Cytocompatibility assays demonstrated a reduction in lactate dehydrogenase release with β-TCP substitution, accompanied by improved cell viability. In vivo studies using μ-CT and histology demonstrated improved bone-cement adaptation, direct contact with host bone, and deposition of new bone matrix without the formation of fibrous tissue. Conclusion: β-TCP substitution enhanced the handling, radiological, mechanical, and biological properties of PMMA cement, enabling partial osteointegration at the bone-cement interface. The findings suggest that this injectable PMMA/β-TCP composite can be delivered through a biopsy needle and holds promise for minimally invasive applications such as vertebroplasty, kyphoplasty, and defect filling.