Characterization of the Degradation and Conversion of Bone Cement and Borate Bioactive Glass Composites

Abstract

Periprosthetic infections are a devastating complication of orthopedic procedures, costing time and money as well as the quality of life of affected patients. 13-93B3 is a boron-based bioactive glass that degrades and converts into hydroxyapatite when immersed in a physiological fluid. Its ability to break down and dissolve quickly would be useful for drug delivery when combined with bone cement because this glass can create passages in the cement that would increase the elution of incorporated antibiotics. The conversion of this bioactive glass into calcium phosphate products could also attract surrounding bone growth, further integrating implants with tissue and removing space on the cement surfaces where biofilms can form. While bioactive glasses have previously been added to bone cement, the incorporation of 13-93B3 into commercial bone cement has not yet been reported in literature. The focus of this study was to characterize composites of these materials by measuring its degradation rate and the identity of its resulting precipitate while monitoring for adverse reductions of mechanical strength. Particles of 13-93B3 with diameters of 5 μm, 33 μm, and 100 μm were mixed into a PMMA-based commercial bone cement, DePuy SmartSet MV, to create composites with 20%, 30%, and 40% glass loadings. The composites were formed into pellets and paired with bone cement control groups. These samples were soaked in phosphate-buffered saline (PBS). The compressive strength, Young’s modulus, water uptake, and weight loss of the pellets over time were recorded. The pH and boron concentrations of the solutions were measured at various soak durations. Results showed that smaller glass particles degraded faster in composites than larger particles, and that a higher amount of glass incorporation increased the amount of degradation that occurred. Composites with smaller glass diameters had higher compressive strengths than composites with larger glass particles, though the compressive strengths of all composites were found to be consistently above ASTM F451 and ISO 5833 standards. The conversion of 13-93B3 in the composites was studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy – attenuated total reflection (FTIR-ATR), and micro-Raman spectroscopy. The solid precipitate that accumulated on the surfaces was determined to be hydroxyapatite incorporated with magnesium ions from the dissolved glass. The presence of this magnesium in the hydroxyapatite layer could improve the adhesion of the bone cement to living bone. Results from these tests suggest that composites made of 13-93B3 and bone cement may have a promising future in helping to prevent periprosthetic infections and would benefit from further investigation.