Abstract
Nanopatterned surfaces administer antibacterial activity through contact-induced mechanical stresses and strains, which can be modulated by changing the nanopattern’s radius, spacing and height. However, due to conflicting recommendations throughout the theoretical literature with poor agreement to reported experimental trends, it remains unclear whether these key dimensions—particularly radius and spacing—should be increased or decreased to maximize bactericidal efficiency. It is shown here that a potential failure of biophysical models lies in neglecting any out-of-plane effects of nanopattern contact. To highlight this, stresses induced by a nanopattern were studied via an analytical model based on minimization of strain and adhesion energy. The in-plane (areal) and out-of-plane (contact pressure) stresses at equilibrium were derived, as well as a combined stress (von Mises), which comprises both. Contour plots were produced to illustrate which nanopatterns elicited the highest stresses over all combinations of tip radius between 0 and 100 nm and center spacing between 0 and 200 nm. Considering both the in-plane and out-of-plane stresses drastically transformed the contour plots from those when only in-plane stress was evaluated, clearly favoring small tipped, tightly packed nanopatterns. In addition, the effect of changes to radius and spacing in terms of the combined stress showed the best qualitative agreement with previous reported trends in killing efficiency. Together, the results affirm that the killing efficiency of a nanopattern can be maximized by simultaneous reduction in tip radius and increase in nanopattern packing ratio (i.e., radius/spacing). These findings provide a guide for the design of highly bactericidal nanopatterned surfaces.
Highlights
Nanopatterning is the process of physically modifying a surface to impart bacteria killing properties to otherwise innocuous materials
It is understood that nanopatterned surfaces kill bacteria by inducing—through contact—mechanical stress and strain in the envelope which exceeds
The results showed that nanopillar radius played a critical role in controlling contact pressure, and both contact pressure and areal stress could be enhanced using small-tipped radii with tight packing
Summary
Nanopatterning is the process of physically modifying a surface to impart bacteria killing properties to otherwise innocuous materials. The ability of nanopatterning to confer a broad-spectrum killing effect on diverse materials has implied that the resulting surfaces operate on a mechanism that is predominantly physical. This is most directly inferred from electron micrographs of bacteria adhered to nanopatterned surfaces, which often show instances of nanopillar penetration or piercing [12,13,14,15,16]. It is understood that nanopatterned surfaces kill bacteria by inducing—through contact—mechanical stress and strain in the envelope which exceeds
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