The surface properties effect on bacterial attachment and biofilm formation

Abstract

Many microorganisms form sessile communities, called biofilms, in self-produced extracellular polymeric substances (EPS), which often attach to solid surfaces. Biofilms are central to addressing the most pressing global challenges in every sector application, from medicine to industry to the environment, and play a considerable economic and social influence. The surface roughness and wettability can affect bacterial attachment and biofilm formation. However, there was a lack of studies about how the surface roughness and wettability will affect bacterial attachment and biofilm formation in both static and flow conditions. In this Ph.D. project, we started with studying the surface roughness and wettability effect of typical biomaterials polydimethylsiloxane (PDMS) on bacterial attachment and biofilm formation of the key biofilm-forming pathogens Staphylococcus epidermidis and Pseudomonas aeruginosa. The plain PDMS was cast on a petri dish and different sandpapers (P240 and P120) to create different roughness (0.0768 to 15.51µm). These surfaces with different roughness led to contact angles of 117.5 ± 1.1°, 129 ± 5.0°and 115.0 ± 3.1°, respectively. And their corresponding contact angle hysteresis is 21.4 ±2.1°, 20.6 ± 3.5°, and 17.1 ± 5.8°. The results have demonstrated that the roughened surfaces led to much dense and thicker biofilms for both bacteria, although the initial bacterial attachment on rough surfaces with Ra=15.51µm did not differ much. This could be due to stronger adhesion of bacterial attachment on rougher surfaces. Then, we use both plain PDMS and roughened PDMS to prepare slippery surfaces (with very low contact angle hysteresis) by infusing silicone oil. We fabricated the materials with varied oil thicknesses (50, 20, 5, 2μm) atop the surface. In the static conditions, all slippery surfaces only have little bacterial adhesion for Staphylococcus epidermidis and Pseudomonas aeruginosa, even for the 14days long-term culture. However, the significant bacterial attachment was found for surfaces with initial thin oil (5, 2μm) after 7 days of dynamic culture (the wall shear stress=0.01Pa). This is due to flow shear-induced oil depletion. ii Finally, we fabricated another two slippery surfaces with very low contact angle hysteresis: Slippery Omnipobic Covalently Attached Liquid-like (SOCAL) surface, and Polyethylene glycol (PEG) surface. As silver nanoparticles (AgNPs) are commercially used antimicrobial surfaces. We also prepared AgNPs-coated PDMS as comparisons. All these surfaces have demonstrated excellent resistance against biofilm formation under static and dynamic conditions (with a reduction of biofilm by 2-4 orders of magnitude) compared to plain PDMS, even after 14 days of culture. Notably, the total biomass of Staphylococcus epidermidis on SOCAL is 1-2 orders of magnitude larger than that on PEG in static and dynamic culture, and vice versa when culturing Pseudomonas aeruginosa. This suggests that Staphylococcus epidermidis may be preferable to the hydrophilic surface and it is vice versa for Pseudomonas aeruginosa. In addition, when cultured Pseudomonas aeruginosa after 2 days, 7 days, and 14 days in static, much EPS has produced on AgNPs-coated PDMS surface. Since the adhesion between EPS and the coating is stronger than that between the coating and the PDMS surface, the coating will be easily peeled off when using the Phosphate Buffered Saline (PBS) to wash the surface. However, silver ions are still present in the solution, which can also kill bacteria. These slippery surfaces offer a new antibiofilm strategy for medical device applications, while other areas where biofilm development is problematic. The liquid-like solid surfaces demonstrated better antibiofilm performance in flow conditions, compared to liquid-infused surfaces.