Nanotopographic surfaces
are proven to be successful in killing
bacterial cells upon contact. This non-chemical bactericidal property
has paved an alternative way of fighting bacterial colonization and
associated problems, especially the issue of bacteria evolving resistance
against antibiotic and antiseptic agents. Recent advancements in nanotopographic
bactericidal surfaces have made them suitable for many applications
in medical and industrial sectors. The bactericidal effect of nanotopographic
surfaces is classically studied under static conditions, but the actual
potential applications do have fluid flow in them. In this study,
we have studied how fluid flow can affect the adherence of bacterial
cells on nanotopographic surfaces. Gram-positive and Gram-negative
bacterial species were tested under varying fluid flow rates for their
retention and viability after flow exposure. The total number of adherent
cells for both species was reduced in the presence of flow, but there
was no flowrate dependency. There was a significant reduction in the
number of live cells remaining on nanotopographic surfaces with an
increasing flowrate for both species. Conversely, we observed a flowrate-independent
increase in the number of adherent dead cells. Our results indicated
that the presence of flow differentially affected the adherent live
and dead bacterial cells on nanotopographic surfaces. This could be
because dead bacterial cells were physically pierced by the nano-features,
whereas live cells adhered via physiochemical interactions with the
surface. Therefore, fluid shear was insufficient to overcome adhesion
forces between the surface and dead cells. Furthermore, hydrodynamic
forces due to the flow can cause more planktonic and detached live
cells to collide with nano-features on the surface, causing more cells
to lyse. These results show that nanotopographic surfaces do not have
self-cleaning ability as opposed to natural bactericidal nanotopographic
surfaces, and nanotopographic surfaces tend to perform better under
flow conditions. These findings are highly useful for developing and
optimizing nanotopographic surfaces for medical and industrial applications.