Patterned and switchable surfaces for biomaterial applications

Chapter 1 - Introductionangles ranging from 20-80˚. Significantly, for all proteins a higher surface coverage( protein ) was attained at the hydrophobic end [48]. However, significant amounts ofprotein adsorption were still observed towards the hydrophilic end of the gradient,suggesting that although surface wettability plays a significant role in proteinadsorption it is still not the only force at play. As a variant of this work, Tilton et al.,[10] investigated the adsorption of ribonuclease A onto polystyrene (PS) in differentalcohol co-solvents of different polarity. Decreasing adsorption propensity wasdemonstrated in solvents of decreasing polarity, which can be explained in terms ofthe minimisation of the driving force of protein adsorption [10].As proteins are usually not geometrically symmetric, the orientation of adsorbedprotein can impact upon its protein . For example, if a protein had an oblong shapesuch that there was a significant difference between the projected areas of the side-onand end-on orientation, then if all proteins were able to adsorb in an end-onorientation, a greater protein would be attained as compared with an all side-onattachment [10]. The orientation of adsorbed proteins impacts not only upon protein .Surface orientation is of even greater importance for protein activity. Even if a high proteinis attained, most applications for protein adsorption are not viable if theadsorbed protein is not bioactive. For this reason, various approaches have beendeveloped to control the orientation of adsorbed proteins. This is often achieved bymodifying proteins at specific points on the protein exterior with molecular tethers ortags. Common approaches include the use of poly-histidine tagged protein, whichforms a complex with surface bound nickel ions [49] and biotin labelled proteins thatcan form a strong biotin-avidin bridge with avidin functionalised surfaces [50]. Acomprehensive review of methods to control protein orientation is available to theinterested reader [51].1-12