Patterned and switchable surfaces for biomaterial applications

Chapter 3 – Comparison of the binding mode of plasmid DNA to allylamine plasma polymer and poly(ethyleneglycol) surfacespolymerisation [33-35, 38]. The key advantage of plasma polymerisation over wetchemical procedures is the ability to produce pinhole free, adherent films on almostany substrate with the ability to incorporate a desired functionality by the judiciouschoice of monomer. However, plasma polymer films exhibit complicated, crosslinkedchemistries that are difficult to characterise and often change over time due toaging processes [183, 189]. Allylamine has been used extensively for the formationof plasma polymer films with amine functionality [180, 186, 190-193] and has beenemployed in a number of studies where DNA immobilisation/hybridisation [34, 36,37] and mammalian cell attachment was desired [33, 35, 192, 194-197]. The successof the allylamine plasma polymer (ALAPP) to interact favourably with both DNAand cells makes this polymer a highly attractive surface for biodevice applicationsrequiring biomolecule manipulation [1]. Despite the interest in ALAPP, themechanism of DNA binding to this surface has not been studied in depth.In general terms, it has been observed that higher salt concentrations and lowerpH increase the propensity for DNA adsorption and vice versa [20, 23]. This effecthas been studied for a number of different surfaces including glass, modified glass,mica, various minerals, silica particles, silica wafers, modified silica and latexparticles and is generally assumed to be driven by a shielding of the anionic chargesof the DNA [20, 22, 23, 30, 43, 198-200]. This is also useful for the purpose of DNApurification [198]. Apart from the influence of pH or ionic strength on DNAadsorptivity, fundamental studies of the driving forces of DNA adsorption to varioussurfaces are limited. Adsorption studies of DNA to silica surfaces modified with bothanionic and cationic moieties suggest that DNA adsorption is driven by more thanjust electrostatic interactions [27]. Melzak et al. [20] undertook an in-depth study ofthe driving forces of DNA to silica wafers in perchlorate solutions and determined3-98