Patterned and switchable surfaces for biomaterial applications

Chapter 1 - IntroductionSeveral strategies have demonstrated the ability to produce ‘low-fouling’ surfacesthat resist non-specific protein adsorption, including the surface immobilisation ofcarbohydrates, dextrans or hydrogels [64]. However, the most common and the mosteffective method utilises the hydrophilic poly(ethylene glycol) (PEG) molecule eitherimmobilised or polymerised onto the surface or other polymers or biomaterialsfunctionalised with PEG. Three primary factors contribute to PEG’s low-foulingproperties. Firstly, the hydrophilic PEG hydrogen binds extensively to water and dueto its molecular structure fits well into the structure of bulk water. Protein adsorptionwould lead to unfavourable disruption of the hydrogen bonding. Secondly, the freeenergy of the polymer-water interface is minimal, decreasing the driving force ofprotein adsorption. Thirdly, a dense PEG brush has high volume exclusion propertiesdue to high conformational entropy [65]. In the case of end-point grafted PEG, it hasbeen found that the PEG coating provides an interfacial barrier that prevents proteinsfrom interacting with the underlying substrate. Therefore, the molecular weight andinterfacial graft density of PEG chains are important parameters to enable nonfoulingproperties of the coating [66, 67].The production of alternative low-fouling surfaces is limited. Kleinfeld et al., [68]devised a strategy to control the attachment and outgrowth of neuronal cells onsilanised silicon patterned by photolithography to have regions of alkyl silanes andamino functionalised silanes. Interestingly, the alkyl-silanes were able to resist theattachment of cells, leaving the cells to grow only on the amino functionalisedregions. The low-fouling ability of this surface is presumably a result of thedenaturation of secreted proteins that cells use to attach to the surface. The use ofblocking proteins such as bovine serum albumin (BSA) or casein has also been used1-16