Antimicrobial Interfaces - Biointerfaces: Where Material Meets Biology - page 408

Differences in surface hydrophobicity are believed to result to form the net
surface properties conferred upon the cell surface molecules such as pro-
teins and lipids. The production of these molecules at the surface of the
bacterial envelope is inducible in at least some instances. Bacteria might
also be capable of adjusting their surface hydrophobicity in ways that would
either enhance or diminish attachment to a substratum.
The diverse physicochemical tactics reported so far are rooted on detailed
analyses of the interaction energy between surface characters and the mi-
crobial system. However, limitations in the systems design to study these
interactions do not provide the overall picture. For example, cell surfaces of
bacteria are structurally heterogeneous and possess an intricacy that is not
routinely considered while contemplating physicochemical modelling at the
molecular level. More importantly concepts such as distance between the
bacterial surface to that of biomaterial surface partly lose its sense when
taking into account that some of the bacterial cell surface appendages such
as pili can become as long as 1 mm. 85 Adhesion of bacteria to surface of
materials may be predicted as means of reassigning disorganised cells (bulk
phase) to almost firmly connected status at the interface. 86 In order to
forecast the behaviour of bacteria on various surfaces, physicochemical
approaches such as the thermodynamic approach 87 and the Derjaguin-
Landau-Verwey-Overbeek; (DVLO) theory 88 are being explored. It is envis-
aged that the mechanistic data on bacterial adhesion derived from the
extended DVLO theory could provide developmental strategies for new sur-
faces displaying nominal bacterial adhesion. A comprehensive discussion on
the subject is reported elsewhere. 85
The fact that surface irregularities of material generally encourage at-
tachment of bacteria, while ultra smooth surfaces inhibit biofilm formation
was approved in many reports. 89-91 The initial bacterial adhesion is likely to
favour locations where bacterial cells can be shielded from shear forces.
Therefore increasing the surface roughness can lead to enhancement of the
overall surface accessible for adhesion. 92 However, the concept that ultra-
smooth surfaces prevent attachment of bacteria and subsequent biofilm
formation has been challenged recently by the finding that bacteria
could effectively colonise surfaces that possess very low (nanometre or sub-
nanometre range) surface roughness (Ra). 93 Therefore new advances in
techniques to modify the nanotopography of surfaces can be used as a
valuable technique for the production of antibacterial materials. It was re-
ported that physical parameters such as stiffness, in particular Young's
modulus, alter the mechano-selective adhesion of bacteria such as
S. epidermidis and E. coli. 94 An elevated level of Young's modulus of the
material was found to be positively correlated with the attachment of
S. epidermidis and E. coli in the range of 1 MPa to 100 MPa. 94
Even though it is not widely included in antimicrobial investigations, the
fundamental features, which include the evaluation of the biocompatibility
of the antibacterial surfaces, require comprehensive analysis while de-
signing such materials. Polymers (including naturally derived, synthetic or

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