Role of nanostructured gold surfaces on monocyte activation and Staphylococcus epidermidis biofilm formation

The role of material surface properties in the direct interaction with bacteria and the indirect route via host defense cells is not fully understood. Recently, it was suggested that nanostructured implant surfaces possess antimicrobial properties. In the current study, the adhesion and biofilm formation of Staphylococcus epidermidis and human monocyte adhesion and activation were studied separately and in coculture in different in vitro models using smooth gold and well-defined nanostructured gold surfaces. Two polystyrene surfaces were used as controls in the monocyte experiments. Fluorescent viability staining demonstrated a reduction in the viability of S. epidermidis close to the nanostructured gold surface, whereas the smooth gold correlated with more live biofilm. The results were supported by scanning electron microscopy observations, showing higher biofilm tower formations and more mature biofilms on smooth gold compared with nanostructured gold. Unstimulated monocytes on the different substrates demonstrated low activation, reduced gene expression of pro- and anti-inflammatory cytokines, and low cytokine secretion. In contrast, stimulation with opsonized zymosan or opsonized live S. epidermidis for 1 hour significantly increased the production of reactive oxygen species, the gene expression of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and IL-10, as well as the secretion of TNF-α, demonstrating the ability of the cells to elicit a response and actively phagocytose prey. In addition, cells cultured on the smooth gold and the nanostructured gold displayed a different adhesion pattern and a more rapid oxidative burst than those cultured on polystyrene upon stimulation. We conclude that S. epidermidis decreased its viability initially when adhering to nanostructured surfaces compared with smooth gold surfaces, especially in the bacterial cell layers closest to the surface. In contrast, material surface properties neither strongly promoted nor attenuated the activity of monocytes when exposed to zymosan particles or S. epidermidis.