Particulate reinforced bone cements: The potential antibacteric role of nitrides

In recent years, silicon nitride (Si₃N₄) ceramics have gained popularity as bioactive structural materials with the capability to stimulate cell proliferation and fight pathogens. Despite displaying bioactive properties and having an excellent mechanical strength, the number of possible applications for silicon nitride is somehow limited by its brittle nature and high production costs. In this work, particles of Si₃N₄ have been added to Poly(methyl metachylate) (PMMA) bone cements to verify how this reinforcement influences mechanical and antibacterial properties. 5, 10 and 15% weight fractions of powders with average mesh size 25, 50 and 300 μm were mixed together with PMMA and molded into testing samples. Results of the in vitro testing with Escherichia coli and Staphylococcus epidermidis showed that the antibacterial effects of Si₃N₄ correlate positively with the fraction of ceramic used and are negatively correlated with the mesh size of the powders. Moreover, the smaller particles at the lowest concentration acted as a mechanical reinforcement, increasing the ultimate tensile strength of the composite by about 10%.