Introduction: Bacteria are highly effective at populating living or inanimate surfaces, which causes significant problems in the healthcare industry, such as hospital-acquired infections, and persistent biofilm infection of medical devices. There is much to learn on the roles of surface topology at nano and micro scales, wettability and local adhesion forces on bacterial attachment and growth. This talk will present recent results on non-wetting materials engineered to prevent bacterial attachment, based on superhydrophobic surface microtopographies[1]. Further, we have designed a novel class of ultra low-adhesion surfaces that incorporate a micron-scale thick lubricant layer immobilized at a surface, inspired by the Nepenthes pitcher plant[2],[3].
Materials and Methods: Herein we demonstrate the role for superhydrophobic non-wetting surfaces to control (short-term) cell attachment, and the role of surface feature size on cellular attachment. Micropost arrays were molded in polyurethane (PU) with increasing diameter, from 300 nm to 20 µm, from Si masters etched by photolithography. Samples were exposed to P. aeruginosa and E. coli for 5 min contact time, and compared to flat PU and commercial medical gloves. Silicone-based ‘slips’ samples were exposed to continuous flow culture of P. aeruginosa for up to 30 days.
Results and Discussion: We have modelled bacterial cell attachment as particles acting under a balance of local surface tension forces[1]. Superhydrophobic surfaces, also bio-inspired based on non-wetting natural surfaces, were found to be highly effective to prevent bacterial cell attachment (reduced from 104 to 100 cells/mm2), when the micropost diameter was smaller than the cell size (1.5 µm or less), which points to a new paradigm of antimicrobial surface design. Silicone-based ‘slips’ surfaces were also found to effectively prevent bacterial cell adhesion (3 log to 4 log reduction in CFU), due to the inert, stabilized surface liquid interface (Fig 1)[4].
Conclusions: Engineering non-wetting microstructured surfaces can effectively prevent bacterial attachment by physical mechanisms, and can be effective for a broad range of cell types. As a result, these are not biologically-specific and are not susceptible to resistance.
Figure 1. Suppression of bacterial cells attachment and biofilm formation by SLIPS under continuous flow conditions for up to 30 days. (A) Fluorescence imaging of P. aeruginosa overproducing Psl biofilm attached to the micro-structured PDMS control (a-e), and micro-structured PDMS SLIPS (f-l) surfaces, respectively.
References:
[1] Hatton BD & Aizenberg J Nano Letters (2012)12(9):4551-4557
[2] Wong TS, et al. Nature (2011) 477(7365):443-447
[3] Vogel N, Belisle R, Hatton BD, Wong TS, & Aizenberg J Nature Communications (2013) 4(2167).
[4] MacCallum N et al, ACS Biomaterials Science and Engineering (2015), 1, 43.