Patterned and switchable surfaces for biomaterial applications

Andrew Hook – Patterned and switchable surfaces for biomaterial applicationsis no surprise then that the main two interactions of proteins with surfaces, like in thecase of DNA, are electrostatic and hydrophobic interactions.As proteins function predominantly within aqueous environments, with theexception of membrane bound proteins, proteins try to minimise the entropic penaltyof interactions with water with hydrophobic domains by shielding as manyhydrophobic amino acids within the protein core whilst arranging the hydrophilicamino acids on the protein surface. However, this ‘phase separation’ is not alwayscomplete, particularly within smaller proteins that have a larger surface area tovolume ratio. Thus, hydrophobic domains often exist on the surface of proteins, andthose readily adsorb to hydrophobic surfaces even in the presence of electrostaticrepulsion due to the large increase in entropy associated with surface de-solvationand the minimisation of polar/non-polar interfaces [11]. This thermodynamicallyfavourable process is the driving force for protein adsorption. However, adsorption toa surface, particularly a hydrophobic surface, can lead to a rearrangement ofhydrophobic domains within the centre of proteins to enable the formation ofhydrophobic contacts between those domains and the surface. Thus, although highlyhydrophilic surfaces will generally reduce protein adsorption, hydrophobic surfacesor hydrophobic patches on otherwise hydrophilic surfaces can cause therearrangement of proteins resulting in their denaturation and exposure of previouslyburied hydrophobic residues. This protein rearrangement upon surface adsorption isdriven by an increase in entropy due to the destabilisation of ordered proteindomains, such as -helices and -sheets [11].Elwing et al., [48] investigated the adsorption of human -globulin, humanfibrinogen and lysozyme onto a surface with a wettability gradient. This surface wasprepared using silanes onto doped silicon to form a wettability gradient with contact1-11