Patterned and switchable surfaces for biomaterial applications

Chapter 1 - IntroductionFor some applications it has been desirable to adsorb DNA to negatively chargedsurfaces. This has been the case for atomic force microscopy (AFM) experimentswith DNA, which commonly require adsorption of DNA to atomically flat,hydrophilic mica and also for adsorption to silica, which is an important andubiquitous material for many biodevices [20]. The electrostatic repulsion betweenDNA and mica or other negatively charged surfaces or particles can be overcome,enabling DNA adsorption, in the presence of a divalent cation such as Mg 2+ , whichcan act as bridging cations [20, 23, 43]. Generally, trivalent cations are moreeffective than divalent cations, which in turn are more effective than monovalentcations at enabling DNA adsorption. Hansma et al., [44] used AFM to study theeffect of the type of divalent cation on binding of dsDNA of lengths from 79-1057 bpto mica. High amounts of DNA adsorbed to mica in the presence of Ni, Co and Znions, however, weak adsorption was seen with Mn, Hg and Cd ions. This effect wasexplained in terms of the structure of mica and how each type of ion interacted withthe mica as opposed to a specific ion-DNA interaction, suggesting that the type ofion most suitable at enhancing DNA adsorption is dependant on the particularsubstratum surface.1.1.3. Surface manipulation of proteins and cellsMany biodevice applications, including tissue engineering, cell microarrays andimplants [4, 45-47], require the ability to manipulate proteins, and concurrently cells,at interfaces. The fundamental nature of how proteins behave at surfaces dependslargely upon their primary structure, that is, the sequence of amino acids making upthe protein. There are four main properties of amino acids that influence thebehaviour of proteins; polar, non-polar, negatively charged and positively charged. It1-10