Patterned and switchable surfaces for biomaterial applications

Chapter 1 - Introductionmicelles. This pH switch was used to deliver a hydrophobic dye encapsulated withinthe micelles on demand.Ionov et al., [114] developed a mixed polyelectrolyte brush consisting ofpoly(acrylic acid) (PAA) and poly(2-vinyl pyridine) (PVPI) chains with pKa valuesof 6.7 and 3.2, respectively, whereupon PAA is negatively charged above pH=6.7and PVPI is positively charged below pH=3.2. Switching of the pH from 3 to 9caused a switching of the surface chemistry from a positive surface charge tonegative. This change also instigated a rearrangement of the surface bound polymer,whereupon, at low pH PVPI was extended and, thus, dominated the surfacecharacter, whilst PAA was collapsed, hidden beneath the PVPI layer. At high pH thiswas reversed, with the PVPI collapsing and PAA extending. Concurrently, changingthe pH altered the contact angle of the mixed polymer brush surface, whereupon thesurface exhibited hydrophilic properties at high and low pH, but was morehydrophobic over the pH range of 4-8, where the surface had a near neutral surfacecharge.Winkelmann et al., [115] produced a patterned surface with conductive and nonconductiveregions of titanium and silicon, respectively by photolithographicmicrofabrication using a patterned photoresist. Surfaces with regions of differentmetals were also formed using this technique, enabling the study of protein and celladhesion to a variety of metal interfaces [116]. Using this substrate, the controlledremoval of adsorbed PLL-g-PEG at conductive regions was demonstrated byapplication of +1800 mV voltage bias, which enables further adsorption of functionalmolecules, in the present case human fibrinogen was adsorbed, to the re-exposedtitanium layer [117].1-40