Effect of Antibiotic Incorporation on the Porosity of Polymethylmethacrylate (PMMA) Bone Cement: A Comparative Analysis.

Polymethylmethacrylate (PMMA) is widely applied in orthopedics. Antibiotic-loaded PMMA has been extensively used, and its mechanical impact, especially porosity, is of widespread importance. We assessed the effects of commercially available and add-on antibiotic PMMA in terms of porosity. The study evaluated seven high-viscosity bone cement groups (S1-S7), with six specimens per group: an antibiotic-free control, three commercially antibiotic-loaded, and three manually antibiotic-loaded with gentamicin, vancomycin, clindamycin, or their combinations. Total porosity percentage was defined as the primary outcome, while open- and closed-pore parameters were secondary outcomes. Porosity was quantitatively evaluated using micro-computed tomography (μ-CT). Raman spectroscopy was used for complementary chemical characterization, and X-ray diffraction (XRD) was used for exploratory comparison of the relative crystalline contribution of the formulations. μ-CT analysis showed that S1, S3, and S7 had the highest mean total and open porosity values, whereas S2, S4, and S6 demonstrated lower mean values. However, no significant between-group differences were detected for open-porosity or total-porosity percentages. Significant differences were identified for closed-pore number, volume, surface area, and percentage. S7 had the highest number of closed pores, while S4 showed a higher closed-pore volume than S2, S3, S5, and S6 (p < 0.05), a higher closed-pore surface area together with S7 than S1, S2, S3, S5, and S6 (p < 0.05), and a higher closed-pore percentage than S3 and S5 (p < 0.01). Raman spectra showed formulation-dependent spectral differences. Exploratory XRD indicated the highest relative crystalline contribution in S1 and the lowest in S7, without a consistent relationship with μ-CT porosity. Conclusively, the tested formulations differed mainly in closed-pore architecture rather than in total or open porosity percentages. Raman spectroscopy provided complementary chemical information, whereas XRD showed descriptive differences in the crystalline contribution of the formulations. The mechanical and clinical relevance of microstructural findings requires further evaluation with mechanical and antibiotic-elution testing.