Antimicrobial Interfaces - Biointerfaces: Where Material Meets Biology - page 409

blended forms) are extensively utilised to produce antimicrobial surfaces on
implant materials. These polymers could either be employed in isolation or
used in conjunction with different materials or molecules in order to gen-
erate superior quality composite materials. Polymer-based materials are
prepared by surface adsorption driven by electrostatic interactions. These
polyelectrolyte multi-layers include, for example, poly(acrylic acid), poly-
(methacrylic acid), poly(allylamine hydrochloride), sulfonated polystyrene, 95
polyethyleneimine, 96 chitosan 97 and hyaluronic acid. 98 Different studies
have shown that the presence of cationic groups correlated with potent
antimicrobial effects. 76 It was reported that surfaces coated with a cationic
N,N-dimethyl-2-morpholinone are capable of inactivating bacteria in dry
environment while a zwitterionic carboxybetaine help surfaces to defy bac-
terial adhesion in wet environments. 99 Surfaces were also prepared using
polyelectrolyte that can stop the first attachment of cells thus avoiding
steady bacterial attachment on material surface. One such polymer, poly-
ethylene glycol (PEG), which has a strong anity for water molecules,
showed drastically reduced adsorption of E. coli cells when immobilised or
grafted onto surfaces due to the development of a highly hydrated layer. 82
But PEG is reported to be susceptible to oxidation impairment which re-
stricted lasting application of it in complex media. 100 Other developments
include the anti-adhesive polymer heparin (which is negatively charged)
embedded into the antibacterial biopolymer chitosan (which is positively
charged) to generate surfaces that inhibit E. coli cells. 97 Likewise hyaluronan
incorporated into a multi-layer showed reduced adhesion of S. epidermidis
due to its hydrophilicity. 98

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14.5.2 Contact-active Materials
Contact active materials are known to cause death or impairment of bacteria
that which firmly attached to its surfaces. A number of these materials are
prepared based on the antibacterial properties of surface immobilised
polycations. 76,101 It was hypothesised that the antibacterial mechanism is
based on the destabilisation and permeation of bacteria resulted from the
dislocation of charges on the cell membrane. 76 The antimicrobial peptide
defensin was also incorporated into polyelectrolyte multi-layers that in-
activated bacteria. 102 Other contact killing species including particles of
titanium 103 and groups of transition metals (polyoxometalates) 104 were also
exploited. The development of light-activated antimicrobial surfaces such as
crystal violet and nanogold incorporated silicone which kill S. epidermidis
and E. coli by the action of light have been developed recently. 105 Likewise it
was reported that light activation led to a decrease in S. aureus attachment
among certain Ni-Ti alloy surface materials covered with titanium di-
oxide. 106 This was suggested to be due to the photon accumulation in the
surface and likely increase in defects which could have resulted in free
oxygen. These approaches have potential applications in domestic and
healthcare settings and the topic is reviewed elsewhere. 107