Antimicrobial Interfaces - Biointerfaces: Where Material Meets Biology - page 407

Table 14.1 Bacteria-material surface interactions and distances. 79

Distance (nm) Nature of the interactions

o 5 Short-range interactions: electrostatic forces,

specific and hydrophobic groups

d n 3 r 4 n g | 9

10-20 van der Waals forces and electrostatic forces

450 van der Waals forces

interconnecting layer between substrate and adhering bacteria and mediates
their direct interactions. 79 Adhesion of bacteria onto static surfaces can be
explained based on their specific as well as nonspecific interactions 79
(Table 14.1). Specific interactions normally function over short distances
(about 5 nm) and are directional, while the non-specific interaction is the
result of interactive forces between every molecules on the whole cell and
substratum (which are normally long-range in nature, typically more than
50 nm). Once a bacterium gets in touch with a surface through these broad
macroscopic interactive forces, interaction amongst the stereochemical
cluster (short range and specific ones) will start to occur by means of sig-
nificantly elevated attractive interaction energy. 80
There are many features on the surface of materials which were projected
to influence the primary stage in attachment of bacteria. Such factors
comprise of material stiffness, surface charge, surface roughness, hydro-
phobicity, zeta potential, hydrogen bonding capacity, 81 Lewis acid-base
character, specific receptor-adhesion interactions 82 and van der Waals for-
ces. The involvement of so many factors in the colonisation of bacteria on an
implant surface obscure the contribution made by each of these factors in
bacterial attachment. Furthermore, it is dicult to devise universal con-
clusions for adhesion mechanisms of bacteria as the environmental con-
ditions (which include concentrations of glucose and oxygen, temperature,
flow conditions and presence of adsorbed proteins) in which bacterial
strains proliferate vary considerably. Therefore environmental stimuli can
influence the comparative significance of material surface characters and
adhesion mechanisms even in the case of a single strain of bacteria and
material surface. Thus no particular material characteristic or bacterial trait
can wholly illustrate or manage bacterial adhesion. 78 In order to analyse
familiar strategies and draw universal conclusions polymer based bio-
material and bacterial interfaces is predominantly discussed in the following
sections.
Designs of antibacterial interfaces have focussed on limiting or preventing
colonisation of bacteria to material surfaces. Different strategies are pursued
which include exploiting material surface characteristics such as anti-
adhesiveness, antimicrobial activity of material by contact and the controlled
release of antibacterial agents. 83 One of the important factors that play a
significant role in bacterial attachment is the overall surface properties of
bacteria. The relative degree of hydrophobicity in relation to both bulk liquid
and the substratum has been demonstrated to influence attachment. 84

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