Bacteriostatic, silver-doped, zirconia-based thin coatings for temporary fixation devices tuning stem cells' expression of adhesion-relevant genes and proteins

Temporary fixation devices must support bone healing, be easily removed without bone tissue overgrowth, and reduce the risk of infection. To match these needs, mechanically and chemically stable thin coatings, based on a zirconia matrix doped with silver (ZrO2-Ag), were sputtered on Ti6Al4V. Coatings with two silver concentrations were produced: a low (0.2 % at Ag) concentration (AL) for bacteriostatic effect and a high (0.5 % at Ag) concentration (AH) for antibacterial properties. Surfaces were characterized for silver content and release, mechanical adhesion, morphology, roughness, wettability, and surface zeta potential, reporting high stability and a continuous Ag release over 28 days. Direct cytocompatibility was shown for human mesenchymal stem cells (hMSC), while antibacterial properties were verified towards Staphylococcus aureus. Results revealed non-toxic and anti-adhesion effects of AL that were deeply investigated towards hMSC by a multi-omics approach. Transcriptomics revealed a down-regulation of cadherins- and integrins-related genes involved in the cell-to-cell and cell-to-substrate adhesion, whereas proteomics confirmed a reduced expression of adhesion proteins (Talin and Ras homolog family member A - RhoA). The OMICS profiles were matched by bioinformatics analysis, confirming a cluster of preserved biological functions strongly related to the cells' adhesion but not to apoptosis. Therefore, AL is a good candidate for bone temporary fixation devices, not interfering with bone healing (cytocompatible), avoiding bone adhesion on the implant surface, and being bacteriostatic.