Role of silver/zinc oxide in affecting de-adhesion strength of Staphylococcus aureus on polymer biocomposites

A single-cell force spectroscopy is utilized to characterize the dynamics of the transient interaction (0-10s) between alive Staphylococcus aureus and ultra-high molecular weight polyethylene (UHMWPE). Adhesion force of bacteria upon addition of antibacterial additives (i.e. silver (Ag) nanoparticles and zinc oxide (ZnO) micro-rods) has been evaluated. Addition of Ag and ZnO reduces the colony forming units (CFUs) from 93±7 (UHMWPE) to 23±5 (U+3wt.% Ag+3wt.% ZnO) on 10×10mm² area of sample surface. Presence of ZnO causes increase in the surface free energy from 29.1 (UHMWPE) to 32.3mJ/m² (UHMWPE+1wt.% ZnO) and 32.3mJ/m² for U+3wt.% ZnO whereas due to Ag the surface free energy decreased to 28.3mJ/m² and 28.4mJ/m² for UHMWPE+1wt.% Ag and U+3wt.% Ag respectively. At a contact time of 10s bacterial adhesion on U+1wt.% Ag+1wt.% ZnO, U+3wt.% Ag and U+3wt.% Ag+3wt.% ZnO showed lowest adhesion forces, ~2.6nN, ~2.9nN and ~3.2N respectively as compared to neat UHMWPE (~4nN) due to a lower surface free energies, but U+1wt.% Ag and U+1wt.% ZnO and U+3wt.% ZnO show higher adhesion force due their higher surface free energy. Ag nanoparticles reduce the live bacteria count whereas ZnO reduces the bacterial retention and combination of both acts synergistically so the count of live bacteria as well as total bacterial density reduced in U-Ag-ZnO composite samples.