Colloidal Crystals Delay Formation of Early Stage Bacterial Biofilms

The objective of this work was to examine whether close-packed spheres of polystyrene (colloidal crystals) could be used to delay the development of biofilms. We examined early stage biofilm formation of Pseudomonas aeruginosa after 2 days on a flat sheet of polystyrene and on the same solid coated in polystyrene spheres of 450 or 1500 nm diameter. All materials were coated in fetal bovine serum to enable comparison of the effects of different surface curvature while maintaining constant surface chemistry. After 2 days, fluorescence imaging showed that the volume of bacterial colonies was much smaller on the 1500 nm colloidal crystals than on the flat film. In addition, electron microscopy showed that the area covered by structures containing more than one layer of bacteria was significantly reduced on both the 450 and 1500 nm colloidal crystals compared to the flat sheet. This provides proof of concept of biofilm inhibition of a pathogen by a simple nonchemical coating that may find future application in reducing the incidence of infections. Even though the density of adhered bacteria on 450 and 1500 nm was similar after 1 day, biofilm formation after 2 days was delayed more on the 1500 nm spheres than on the 450 nm spheres. We also observed that bacteria have preferred adsorption sites on the 1500 nm colloidal crystals and that cell bodies were often separated. This leads us to hypothesize that the greater spacing between favorable sites on the 1500 nm colloidal crystal hindered the early stage biofilm formation by separation of cell bodies.