Enhancement and suppression effects of a nanopatterned surface on bacterial adhesion

We present a quantitative thermodynamic model to elucidate the effects of a nanopatterned surface on bacterial adhesion. Based on the established model, we studied the equilibrium state of rodlike bacterial cells adhered to a nanopillar-patterned surface. Theoretical analyses showed the physical origin of bacterial adhesion on a nanopatterned surface is actually determined by the balance between adhesion energy and deformation energy of the cell membrane. We found that there are enhancement effects on bacterial adhesion to the patterned surface with large radius and small spacing of nanopillars, but suppression effects for nanopillars with a radius smaller than a critical value. In addition, according to our model, a phase diagram has been constructed which can clarify the interrelated effects of the radius and the spacing of nanopillars. The broad agreement with experimental observations implies that these studies would provide useful guidance to the design of nanopatterned surfaces for biomedical applications.

Figure 1

(a) Schematic illustration of a rodlike bacterial cell adhered to a nanopatterned surface with nanopillars. (b) The cross section along the radius direction of bacterial cell. (c) The enlarged view of the membrane adhered to a nanopillar.

Figure 2

(a) The calculated values of the total free energy change as a function of bottom width $\left(r\right)$ at different contact angles $\theta$, from left to right, 170° (red), 160° (green), 150° (blue), 140° (cyan), 130° (magenta), and 120° (olive) when the radius and spacing of nanopillars are $R_p=40\mathrm{nm}$ and $D_p=150\mathrm{nm}$. (b) The minima of the free energy change as a function of $\theta$.

Figure 3

(a) The calculated values of the minima of free energy change as a function of $\theta$ for different radii of nanopillars [from top to bottom, 20 nm (red), 30 nm (green), 40 nm (blue), 50 nm (cyan), and 60 nm (magenta)] with the spacing of $D_p=150\mathrm{nm}$. (b) The calculated stretching degree of bacterial membrane at the equilibrium stage under different radii of nanopillars.

Figure 4

The calculated stretching degree of bacterial membrane at the equilibrium stage under different radii and spacing of nanopillars.

Figure 5

The phase diagram of the bactericidal activity in the space of $R_p-D_p$ (radius versus spacing of nanopillars). The color bar indicates the values of stretching degree of bacterial membrane [the red indicates high value (enhancement phase), and blue indicates low value (suppression phase)]. The white dashed line is the critical radius for bacterial adhesion based on Eq. (11). The squares represent the experimental results [15, 19].