PMMA-based composite bone cements with zirconium oxide fillers of different granulations: structural optimization and
Robert Karpiński1,2, Agata Przekora3, Jakub Szabelski4
1Department of Machine Design and Mechatronics, Faculty of Mechanical Engineering, Lublin University of Technology, Lublin, Poland.
Introduction:
Polymethyl methacrylate (PMMA) bone cements are widely used in orthopaedics, but their limited fatigue resistance, brittleness and lack of biological bonding to bone motivate the search for composite formulations with improved mechanical performance and biofunctional potential. Zirconium oxide (ZrO2) is an attractive radiopaque ceramic filler that may reinforce the PMMA matrix while enabling microstructural optimisation.
Methods:
Commercial Refobacin Plus acrylic bone cement containing 0.6 g gentamicin was modified with ZrO2 particles of three granulations: nanoparticles (<100 nm), microparticles (≈5 μm) and fine powder (<10 μm), introduced at 1-5 wt%. After curing, specimens were subjected to compressive strength testing in accordance with ISO 5833, Shore D microhardness measurements and scanning electron microscopy to assess microstructure, particle dispersion and the occurrence of agglomerates or defects.
Results:
All PMMA/ZrO2 composites exhibited compressive strength above 70 MPa, thus meeting the ISO 5833 requirement. For ZrO2 contents up to about 3 wt%, compressive strength remained similar to the control cement; nanoparticle-filled samples maintained approximately 75-85 MPa, and fine and medium particles at 1-3 wt% often slightly increased average strength, whereas a 5 wt% admixture (especially of larger particles) significantly reduced compressive strength and hardness due to particle agglomeration. Hardness values were comparable to the unmodified cement at ≤3 wt% ZrO2 but decreased by roughly 18-21% at 5 wt%, and at a given concentration hardness was not markedly affected by particle size; SEM imaging revealed that homogeneously dispersed fine ZrO2 supported stress transfer and matrix stiffening, while large agglomerates acted as structural defects.
Discussion:
The results indicate that careful selection of ZrO2 grain size and limiting its content to low concentrations enables PMMA bone cement modification without compromising mechanical integrity, with ZrO2 functioning simultaneously as a reinforcing and radiopaque phase. Such tailored PMMA/ZrO2 composites may support the design of bone cements with optimised strength and biofunctionality, although further studies including fatigue tests and in vitro/in vivo biological evaluations are required to fully validate their clinical potential.
