Atomic force microscopy (AFM) in conjunction with cross-section analysis was applied to determine the distribution,
position and contact angle of spray-deposited water micro-droplets on micro-structured arrays. For this investigation, two
micro-structured arrays on silicon wafers with a chessboard pattern of depressions and protrusions of various sizes were
manufactured by e-beam lithography. The first array had a silicon oxide/silicon structure (hydrophilic/hydrophilic) with
an elevated silicon oxide layer of 40 nm and the second had a gold/silicon structure (hydrophobic/hydrophilic) with an
elevated gold layer of 35 nm. On the first array with only hydrophilic surfaces, the behavior of the water droplets was
mainly affected by topography, whereby the contact angles on the structures were considerably higher than the contact
angles of droplets on unstructured reference surfaces. On the second array the water micro-droplets were confined in the
hydrophilic depressions by the hydrophobic boundary whereby the highest contact angle was measured on the smallest
squares and the lowest contact angle was found on the largest μm exceeding the contact angles of the droplets on the unstructured reference materials.
In this work, we have investigated the effect of nanostructured surfaces on the attachment and viability of two bacterial
species of medical relevance. Surfaces having squares, channels and dots in the nano size range with intermittent
hydrophobicity and hydrophilicity showed complex effects on both live and dead E. coli cells. Nevertheless the
behaviour of S. aureus was found to be less modulated by the surface properties. The square structures had promising
repellent effect on both live and dead E. coli species while S. aureus populated these surfaces very well. On dot
nanostructures the population by E. coli was considerably higher than on the surrounding spaces while the distribution of
S. aureus cells remained uniform on both structured and unstructured areas. When the bacteria were applied to surfaces
with channels, live E. coli cells showed a very interesting fluctuation in function depending on the width of the channels
but this fluctuation was not observed in case of dead cells. Because of its spherical form, lacking flagellae and production
of extracellular substances, S. aureus adhered to this structure more evenly and no fluctuation was observed. Strain
specific bacterial physiology and reactivity to these surfaces may possibly also be a factor in influencing the interaction.
These initial results contribute to the purposeful design of species-specific pro- or anti-bacterial surfaces for the use of
lab-on-a-chip devices and various types of medical devices.
In this work, we have investigated the effect of changes in the properties of planar surfaces on the attachment and
viability of two bacterial species of medical relevance. Polydimethylsiloxane (PDMS) surfaces showed a promising
repellent effect on both live and dead E. coli and S. aureus cells. When the hydrophilicity of the PDMS was increased by
UV-radiation this repellent effect disappeared. On gold surfaces coated with hydrophobic and hydrophilic self assembled
monolayers (SAM) very few bacterial cells were found, compared to plain gold. Moreover, the behaviour of E. coli and
S. aureus was modulated differently by the surface properties. Thus, while S. aureus cells lived in slimy conglomerates
and colonised the surfaces at the same high density from both diluted and concentrated solutions, in contrast, single cells
of E. coli colonised the surfaces at lower densities from diluted solutions. Also, dead E. coli cells were easily washed off from most surfaces, whilst dead S. aureus cells were frequently found attached to the surfaces, which may also be
explained by its occurrence in conglomerates. Strain specific bacterial physiology and reactivity to these surfaces may
possibly also be a factor in influencing the interaction. These initial results contribute to the purposeful design of species-specific
pro- or anti-bacterial surfaces for the use of lab-on-a-chip devices and medical devices.
Many bacterial species are able to colonize the surfaces of biomedical tools or devices and form biofilms creating a
source of infection and other deleterious effects. Biofilms constitute environments in which bacteria grow and are
protected from the host's immune system and antimicrobial medications. The bacterial adhesion, which is an important
and first step in biofilm formation, is influenced by several physico-chemical and topographical factors at the interfaces
between the bacterial cell and the surface. Therefore, the mechanism of initial adhesion needs to be investigated to better
understand the events of anchorage and film formation as bacteria colonise surfaces. In this work, atomic force
microscopy (AFM) in the tapping mode of imaging has been employed to investigate the attachment of bacteria onto a
structured surface patterned with different hydrophilic and hydrophobic areas. The interactions of Escherichia coli and
Staphylococcus aureus with these structures were also monitored by fluorescence microscopy. AFM was successfully
employed for the study of the cell responses to both nanotopography and the surface chemistry via observation of various
cell functions; including extracellular polymeric substance (EPS) mediated cellular adhesion.
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