Self-organised nanoarchitecture of titanium surfaces influences the attachment of Staphylococcus aureus and Pseudomonas aeruginosa bacteria.

The surface nanotopography and architecture of medical implant devices are important factors that can control the extent of bacterial attachment. The ability to prevent bacterial attachment substantially reduces the possibility of a patient receiving an implant contracting an implant-borne infection. We now demonstrated that two bacterial strains, Staphylococcus aureus and Pseudomonas aeruginosa, exhibited different attachment affinities towards two types of molecularly smooth titanium surfaces each possessing a different nanoarchitecture. It was found that the attachment of S. aureus cells was not restricted on surfaces that had an average roughness (S a) less than 0.5 nm. In contrast, P. aeruginosa cells were found to be unable to colonise surfaces possessing an average roughness below 1 nm, unless sharp nanoprotrusions of approximately 20 nm in size and spaced 35.0 nm apart were present. It is postulated that the enhanced attachment of P. aeruginosa onto the surfaces possessing these nanoprotrusions was facilitated by the ability of the cell membrane to stretch over the tips of the nanoprotrusions as confirmed through computer simulation, together with a concomitant increase in the level of extracellular polymeric substance (EPS) being produced by the bacterial cells.

Three-dimensional visualization of nanostructured surfaces and bacterial attachment using Autodesk® Maya®.

There has been a growing interest in understanding the ways in which bacteria interact with nano-structured surfaces. As a result, there is a need for innovative approaches to enable researchers to visualize the biological processes taking place, despite the fact that it is not possible to directly observe these processes. We present a novel approach for the three-dimensional visualization of bacterial interactions with nano-structured surfaces using the software package Autodesk Maya. Our approach comprises a semi-automated stage, where actual surface topographic parameters, obtained using an atomic force microscope, are imported into Maya via a custom Python script, followed by a 'creative stage', where the bacterial cells and their interactions with the surfaces are visualized using available experimental data. The 'Dynamics' and 'nDynamics' capabilities of the Maya software allowed the construction and visualization of plausible interaction scenarios. This capability provides a practical aid to knowledge discovery, assists in the dissemination of research results, and provides an opportunity for an improved public understanding. We validated our approach by graphically depicting the interactions between the two bacteria being used for modeling purposes, Staphylococcus aureus and Pseudomonas aeruginosa, with different titanium substrate surfaces that are routinely used in the production of biomedical devices.

Three-dimensional reconstruction of surface nanoarchitecture from two-dimensional datasets.

The design of biomaterial surfaces relies heavily on the ability to accurately measure and visualize the three-dimensional surface nanoarchitecture of substrata. Here, we present a technique for producing three-dimensional surface models using displacement maps that are based on the data obtained from two-dimensional analyses. This technique is particularly useful when applied to scanning electron micrographs that have been calibrated using atomic force microscopy (AFM) roughness data. The evaluation of four different surface types, including thin titanium films, silicon wafers, polystyrene cell culture dishes and dragonfly wings confirmed that this technique is particularly effective for the visualization of conductive surfaces such as metallic titanium. The technique is particularly useful for visualizing surfaces that cannot be easily analyzed using AFM. The speed and ease with which electron micrographs can be recorded, combined with a relatively simple process for generating displacement maps, make this technique useful for the assessment of the surface topography of biomaterials.

Embedding and publishing interactive, 3-dimensional, scientific figures in Portable Document Format (PDF) files.

With the latest release of the S2PLOT graphics library, embedding interactive, 3-dimensional (3-d) scientific figures in Adobe Portable Document Format (PDF) files is simple, and can be accomplished without commercial software. In this paper, we motivate the need for embedding 3-d figures in scholarly articles. We explain how 3-d figures can be created using the S2PLOT graphics library, exported to Product Representation Compact (PRC) format, and included as fully interactive, 3-d figures in PDF files using the movie15 LaTeX package. We present new examples of 3-d PDF figures, explain how they have been made, validate them, and comment on their advantages over traditional, static 2-dimensional (2-d) figures. With the judicious use of 3-d rather than 2-d figures, scientists can now publish, share and archive more useful, flexible and faithful representations of their study outcomes. The article you are reading does not have embedded 3-d figures. The full paper, with embedded 3-d figures, is recommended and is available as a supplementary download from PLoS ONE (File S2).

Biophysical model of bacterial cell interactions with nanopatterned cicada wing surfaces.

The nanopattern on the surface of Clanger cicada (Psaltoda claripennis) wings represents the first example of a new class of biomaterials that can kill bacteria on contact based solely on their physical surface structure. The wings provide a model for the development of novel functional surfaces that possess an increased resistance to bacterial contamination and infection. We propose a biophysical model of the interactions between bacterial cells and cicada wing surface structures, and show that mechanical properties, in particular cell rigidity, are key factors in determining bacterial resistance/sensitivity to the bactericidal nature of the wing surface. We confirmed this experimentally by decreasing the rigidity of surface-resistant strains through microwave irradiation of the cells, which renders them susceptible to the wing effects. Our findings demonstrate the potential benefits of incorporating cicada wing nanopatterns into the design of antibacterial nanomaterials.

The influence of nano-scale surface roughness on bacterial adhesion to ultrafine-grained titanium.

We discuss the effect of extreme grain refinement in the bulk of commercial purity titanium (CP, Grade-2) on bacterial attachment to the mechano-chemically polished surfaces of the material. The ultrafine crystallinity of the bulk was achieved by severe plastic deformation by means of equal channel angular pressing (ECAP). The chemical composition, wettability, surface topography and roughness of titanium surfaces were characterized using X-ray photoelectron spectroscopy (XPS) and water contact angle (WCA) measurements, as well as atomic force microscopy (AFM) with 3D interactive visualization of the titanium surface morphology. It was found that physico-chemical surface characteristics of the as-received and the ECAP-modified CP titanium did not differ in any significant way, while the surface roughness at the nano-scale did. Optical profilometry performed on large scanning areas of approximately 225 mum x 300 mum showed that there was no significant difference between the roughness parameters R(a) and R(q) for surfaces in the two conditions, the overall level of roughness being lower for the ECAP-processed one. By contrast, topographic profile analysis at the nano-scale by AFM did reveal a difference in these parameters. This difference was sensitive to the size of the scanned surface area. A further two surface roughness parameters, skewness (R(skw)) and kurtosis (R(kur)), were also used to describe the morphology of titanium surfaces. It was found that the bacterial strains used in this study as adsorbates, viz. Staphylococcus aureus CIP 65.8 and Pseudomonas aeruginosa ATCC 9025, showed preference for surfaces of ECAP-processed titanium. S. aureus cells were found to have a greater propensity for attachment to surfaces of ECAP-modified titanium, while the attachment of P. aeruginosa, while also showing some preference for the ECAP-processed material, was less sensitive to the ECAP processing.

Effect of ultrafine-grained titanium surfaces on adhesion of bacteria.

The influence of the ultrafine crystallinity of commercial purity grade 2 (as-received) titanium and titanium modified by equal channel angular pressing (modified titanium) on bacterial attachment was studied. A topographic profile analysis of the surface of the modified titanium revealed a complex morphology of the surface. Its prominent micro- and nano-scale features were 100-200-nm-scale undulations with 10-15 microm spacing. The undulating surfaces were nano-smooth, with height variations not exceeding 5-10 nm. These surface topography characteristics were distinctly different from those of the as-received samples, where broad valleys (up to 40-60 microm) were detected, whose inner surfaces exhibited asperities approximately 100 nm in height spaced at 1-2 microm. It was found that each of the three bacteria strains used in this study as adsorbates, viz. Staphylococcus aureus CIP 68.5, Pseudomonas aeruginosa ATCC 9025 and Escherichia coli K12, responded differently to the two types of titanium surfaces. Extreme grain refinement by ECAP resulted in substantially increased numbers of cells attached to the surface compared to as-received titanium. This enhanced degree of attachment was accompanied with an increased level of extracellular polymeric substances (EPS) production by the bacteria.