Bacterial Interactions with Solids: Topography

We are interested in the general problem of how bacteria respond to surface topography when they adsorb. The chief application of this research is to understand how to make materials resist the formation of bacterial biofilms. Biofilms are three-dimensional collections of bacteria, usually coated in a polymer matrix, that adsorb to surfaces. These biofilms form on medical devices, such as catheters, and are a serious health problem. One possible way of delaying bacterial adsorption, surface transport and biofilm formation is to prepare a solid with surface features that are similar to the scale of the bacterium (µm). Compared to chemical treatments, or nanoscale roughness such surfaces cannot be easily “covered up” by adsorption of polymers from solution—the micron scale is just too large. Our expectation is that “topographical surfaces” will have a much longer antibiofilm lifetime or could be used in conjunction with chemical treatments. The important questions are: do they work, and which topography is optimal? In recent work, we have examined whether deposition of colloidal crystals inhibits the attachment of bacteria and the growth into biofilms.

Fluorescence images showing that when there are many bacteria (red) on a flat surface there are fewer when that surface is coated in 450 nm particles and even fewer when the surface is coated with 1550 nm particles.

SEM image of dehydrated bacteria(green)on colloidal crystal(purple) showing that the bacteria usually adsorb in the gaps between the particles.

Fluorescence Image showing bacteria in the gaps between colloidal particles (particles not shown)

Our research on the bacterium Pseudomonas Aeruginosa shows that:

  • (a) fewer bacteria adsorb to colloidal crystals
  • (b) the progression to a biofilm is delayed on colloidal crystals.
  • (c) the bacteria that do adsorb, do so in the gaps between particles.

Publications on this topic:

Preventing Bacterial Colonization using Colloidal Crystals Kargar, M.; Ducker, W. A. J. Materials Chemistry B., 2014, 2, 5962-5971. DOI 10.1039/C4TB00835A

Antimicrobial Surfaces Using Covalently Bound Polyallylamine, Dmitri D. Iarikov, D. D.; Kargar, M.; Sahari, A.;Russel, L.; Gause, K. T.; Behkam, B.; Ducker, W. A. Biomacromolecules, 2014, 15, 169–176. DOI: 10.1021/bm401440h,

Thermal Rectifiers and Interfacial Resistance

It is well known that, whatever the medium, heat only travels from a hot object to a cold object. However, if the hot and cold object are switched, it is not obvious whether the heat will meet the same resistance going in the opposite direction. If the resistance is different, then the object is called a thermal rectifier, which is analogous to an electrical rectifier, which has a different electric resistance in opposite directions. We are currently performing research to build and understand thermal rectifiers. The main application is heat management. For example, it would be great if a house on a winter day could allow heat in but on a winter night would not allow heat out. Our research in this area also examines heat transfer in thin films.

Publication on this Topic:

The Influence of Interface Bonding on Thermal Transport through Solid–Liquid Interfaces, Harikrishna, H.; Ducker, W. A.; Huxtable, S. T. Applied Physics Letters 2013, 102, 251606.

Interfacial Nanobubbles

Recently it has been found that small bubbles exist at the interface between water and hydrophobic solids. We have been investigating the structure, chemistry and stability of these bubbles. The relationship between interfacial and bulk nanobubbles is being studied in collaboration with the company, Revalesio. Our research has focused on trying to determine whether the features really are in the gas state. In the image to the right, the bright spots show tiny air bubbles under water.

Optical images of nanobubbles. The left image is reflection interference contrast microscopy (RICM). The right image is a fluorescence image where fluorescence is quenched wherever there is water. The bright spots show air pockets that are nanobubbles.

Publications on this Topic:

Phase State of Interfacial Nanobubbles, Seo, D; German, S. R.; Mega, T. L.; Ducker. W.A., Journal of Physical Chemistry C., 2015, 119, 14262-14266.