Patterned and switchable surfaces for biomaterial applications

Andrew Hook – Patterned and switchable surfaces for biomaterial applications1.3.3. Alternative switchable surfacesSwitchability is not only limited to hydrogel systems. There is no lack of other,alternative strategies for the development of switchable surfaces with biodeviceapplications.Lahann et al., [112] developed a surface coating on gold that transducedconformational changes in a low density SAM initiated by a voltage bias intowettability changes. The SAM was formed by attaching a large, cleavable headgrouponto the alkanethiol used (16-mercapto)hexanoic acid (MHA), which limitedthe packing density of the SAM. After cleavage of the head group, a low densitySAM remained. By application of a voltage bias, the ionised carboxylic acid groupwas attracted to the surface, producing a conformational change in the MHAbackbone that exposed a hydrophobic loop at the solid liquid/interface, producing areversible change in hydrophilicity, which was observed as a change in contactangle. Development of these self assembled surfaces offers exciting opportunitieswhen applied to the manipulation of biomolecules.Gillies et al., [113] developed a one-off switchable system using pH sensitivemicelles. Linear-dendritic block copolymers containing hydrophobic head groupsand PEG tails were formed, which spontaneously formed micelles in aqueousconditions. The hydrophobic head group contained a cyclic acetal linker that, uponhydrolysis at lower pH, decomposed, releasing trimethoxy benzene and producing adiol end group. This reaction increased the hydrophilicity of the head group andessentially removed the driving force for micelle formation, which led to theirbreakdown. The micelles were stable at physiological pH, however, lowering the pHto 5 caused the hydrolysis of the acetal group, initiating the destabilisation of the1-39