The ability of polymers displaying lower critical solution temperatures (LCSTs) to mediate bioadsorptive
processes was assessed. Three carboxyl-terminated polymers P1
−
3 with LCSTs respectively of 20, 32, and
42 °C were prepared by free-radical polymerization of N-isopropylacrylamide with and without comonomers
acrylamide and N-tert-butylacrylamide. The polymers were grafted to amine-functionalized glass substrates,
and their surface properties were investigated by contact angle goniometry and atomic force microscopy.
Increases in water contact angle of up to 24° were observed between 10 and 37 °C for polymers with LCSTs
of 20 and 32 °C, whereas no change was apparent for control amine-functional and the LCST 42 °C polymer
surfaces over this temperature range. Variations in topography in water were also apparent from atomic
force microscopy (AFM) studies for all the polymer grafts but not the amine surfaces over these temperatures.
Adsorption of 3H-labeled bovine serum albumin and cytochrome c also increased to polymer grafts above
the LCST, with the greatest change in the amount of attached protein being exhibited by polymer P1 (1.13
pmol·cm-2 cytochrome c at 10 °C, 3.95 pmol·cm-2 at 37 °C): adsorption to control surfaces varied by less
than 10% in this assay. Incubation of the graft and control substrates with a gram negative and motile
bacterium (Salmonella typhimurium) and gram positive, nonmotile species (Bacillus cereus) showed the
same overall pattern of attachment as the protein adsorption experiments, with polymers P1 and P2
retaining more bacteria (increases of up to 1350%) at 37 °C than at temperatures below their LCST, while
amine-functional and P3 polymer surfaces showed less than 20% changes in the number of attached
microorganisms. Further incubations at temperatures below polymer LCST resulted in fewer adsorbed
cells at the surfaces showing the reversibility of short-term attachment to these materials. The results
show that protein adsorption and short-term bacterial attachment correlate well with observed changes
in surface properties as determined by contact angle goniometry and indicate that control of bioadhesion
is possible by grafting suitably functionalized polymers capable of temperature-mediated hydrophilic−hydrophobic switching.
A systematic investigation into the effect of surface chemistry on bacterial adhesion was carried out. In particular, a number of physicochemical factors important in defining the surface at the molecular level were assessed for their effect on the adhesion ofListeria monocytogenes, Salmonella typhimurium,Staphylococcus aureus, and Escherichia coli. The primary experiments involved the grafting of groups varying in hydrophilicity, hydrophobicity, chain length, and chemical functionality onto glass substrates such that the surfaces were homogeneous and densely packed with functional groups. All of the surfaces were found to be chemically well defined, and their measured surface energies varied from 15 to 41 mJ · m−2. Protein adsorption experiments were performed with3H-labelled bovine serum albumin and cytochromec prior to bacterial attachment studies. Hydrophilic uncharged surfaces showed the greatest resistance to protein adsorption; however, our studies also showed that the effectiveness of poly(ethyleneoxide) (PEO) polymers was not simply a result of its hydrophilicity and molecular weight alone. The adsorption of the two proteins approximately correlated with short-term cell adhesion, and bacterial attachment for L. monocytogenes and E. coli also correlated with the chemistry of the underlying substrate. However, for S. aureus and S. typhimurium a different pattern of attachment occurred, suggesting a dissimilar mechanism of cell attachment, although high-molecular-weight PEO was still the least-cell-adsorbing surface. The implications of this for in vivo attachment of cells suggest that hydrophilic passivating groups may be the best method for preventing cell adsorption to synthetic substrates provided they can be grafted uniformly and in sufficient density at the surface.
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