Effects of Nanopillar Size and Spacing on Mechanical Perturbation and Bactericidal Killing Efficiency

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.

Nature-Inspired Surface Structures Design for Antimicrobial Applications

“…This discrepancy was resolved by Yarlagadda, in which the simulation parameters were not consistent with a real experimental study. Therefore, Yarlagadda agreed with Modaresifar et al that smaller interspaces increase sterilization efficiency [ 93 ].…”

Nanospikes on Customized 3D‐Printed Titanium Implant Surface Inhibits Bacterial Colonization

“…[ 48 ] It is worth to note that the bactericidal efficiency of nanospiked surface on 3D‐printed parts is higher than the previously reported flat surfaces with thinner and sharper nanostructures. [ 30,31,49 ]…”

“…Such tip‐localized mechanism rules the major proportion of the cell–nanospike interaction especially for multidrug‐resistant Gram‐negative strains like P. aeruginosa. [ 49 ] The rod‐shape structure of P. aeruginosa enables multiple nanospike contact points within a single cell. Hence, upon contact with the sharp apex of the nanospike, the thin peptidoglycan layer (≈2.5 nm) of P. aeruginosa is easily deformed and penetrated into the nanospike.…”

“…[48] It is worth to note that the bactericidal efficiency of nanospiked surface on 3D-printed parts is higher than the previously reported flat surfaces with thinner and sharper nanostructures. [30,31,49] When cells were left for 18 h on the nanospiked implant surface, almost all cell which came into contact with the implant surface got lysed (Figure 6). Lysed cell get sunk into the nanospikes as shown in Figure 6a, allowing more room for further cell death.…”

Design and Properties of Antimicrobial Biomaterials Surfaces

“…[243] The bacteria membrane experiences stress and tension resulting in rupture and death. [213][214][244][245][246][247][248] Besides the applied stress, a model suggests that gravity and non-specific forces such as van der Waals forces play crucial roles in stretching the cell wall. [249] Rupturing commonly occurs at the contact area between the tips and bacteria or the cell membrane trapped between two adjacent tips.…”