Introduction: Biological responses to materials are controlled primarily by surface properties like roughness and chemistry, which affect cell attachment, proliferation, and differentiation. Physical or chemical modifications of the implant allow surface properties to be tailored to direct the response of mammalian cells and modulate the local microenvironment. Nevertheless, surface properties can also influence microbial adhesion, which may limit their clinical success. Recently, zirconium oxide (ZrO2) has been used in orthopedic and dental applications. However, it is unknown if mesenchymal stem cells (MSCs) respond similarly to ZrO2 as to other implant materials. The aim of this study was to examine whether MSCs are sensitive to ZrO2 and if changes in atomic ordering affect MSC response and bacterial adhesion.
Materials and Methods: ZrO2 thin films (80nm) were deposited by magnetron sputtering on titanium substrates (smooth (S): Ra=0.4 um; sandblasted/acid-etched (SLA): Ra=3.0) in a reactive 80% Ar:20% O2 atmosphere at 200W RF power. Amorphous ZrO2 films were deposited at 22°C and crystalline films at substrate temperatures of 250°C. Chemistry (X-ray diffraction, XRD), topography (scanning electron microscopy, SEM), and roughness (confocal microscopy) were characterized. Human MSCs were cultured on ZrO2 surfaces or uncoated titanium for seven days. Osteoblastic markers (RUNX2 mRNA, alkaline phosphatase activity in cell lysates, and secreted osteocalcin) and related growth factors [secreted vascular endothelial growth factor (VEGF), bone morphogenetic protein 2 (BMP2) and osteoprotegerin (OPG)] were assessed. Adhesion of bacterial strains Escherichia coli and Staphylococcus aureus was measured after 24 hours by colony-forming unit (CFU) assay. Statistical significance was examined by ANOVA with posthoc Bonferroni’s modification of Student’s t-test.
Results and Discussion: ZrO2 thin films did not alter submicron/micron topography but generated 5-10nm structures across the surface. XRD confirmed the crystalline or amorphous nature of the films. MSC attachment was higher on amorphous ZrO2 than on crystalline ZrO2 or titanium, an effect more robust on microstructured SLA surfaces. Cell number, ALP, OCN, OPG, BMP2, and VEGF levels were higher on amorphous ZrO2 than crystalline ZrO2 or pure titanium. Both E. coli and S. aureus adhered to all surfaces tested, but there was no difference in CFUs on ZrO2 surfaces.
Conclusions: The present study indicates that ZrO2 modifications produced a better MSC response than titanium surfaces, characterized by the higher production of osteoblastic markers. Atomic ordering seems to have no effect on bacterial adhesion or CFUs formed. In contrast, atomic ordering affected osteoblastic differentiation of MSCs, with the highest levels induced on amorphous ZrO2 surfaces, suggesting that ZrO2 modifications with atomic ordering may enhance bone formation around implants.
CONACYT-152995; DGAPA-PAPIIT #IN118814, #IN118914, and #IG100113).