Patterned and switchable surfaces for biomaterial applications

Andrew Hook – Patterned and switchable surfaces for biomaterial applicationsless polar than water or containing regions less polar than water will be driven toadsorb to hydrophobic surfaces by hydrophobic interactions [11].1.1.1.2. The multivalent effectGenerally, interactions of biomolecules with surfaces are based upon weak forces.Thus, a key factor to ensure that any biomolecule remains adsorbed to the surface isthe multivalent effect, whereupon many small bonds form and the combination ofthese many bonds leads to the formation of an overall strong interaction. Themultivalent effect is thermodynamically favourable due to the increase in entropyintroduced when a single large molecule adsorbs to the surface, displacing multiplesmaller molecules. This effect pertains particularly to biomolecules due to theirlarger size. It is on the basis of the multivalent effect that surface diffusion can beexplained. As any biomolecule is held to the surface by a number of weakinteractions, at any time some of these bonds can break and reform at anotherlocation, however, provided enough bonds remain intact the molecule itself will notbreak from the surface. In such a manner the biomolecule is able to ‘roll’ along thesurface where the molecule only partially adsorbs and desorbs [12]. The introductionof stronger biomolecule-surface interactions would, thus, also decrease the rate ofsurface diffusion due to a decreased rate of bond breakage [13].1.1.2. Surface manipulation of DNAIn applications such as DNA microarrays, DNA based-biosensors and transfectedcell microarrays (TCMs) [1, 14-17], the adsorption or desorption of DNA to or froma surface is required. The adsorption of DNA to a surface is governed by two forcesassociated with the functional groups of DNA; electrostatic forces associated withthe negative charge of the phosphate groups and hydrophobic forces associated with1-5