Patterned and switchable surfaces for biomaterial applications

Andrew Hook – Patterned and switchable surfaces for biomaterial applications1.3.2. Switchable surfaces for the control of proteins and cellsControlling the behaviour of cells firstly requires the ability to manipulate theproteins that cells use to mediate their attachment to surfaces. Since a major drivingforce for protein adsorption is the surface dehydration associated with hydrophobicinteractions, a focus for switching protein and cell attachment has been theproduction of surfaces that are able to alter their wettability when stimulatedappropriately.Okano’s research group has developed a switchable polymeric surface for cellattachment using poly(N-isopropylacrylamide) (PNIPAAm), which switches from ahydrophilic state to a hydrophobic state by increasing the temperature above itsLCST of 32 °C. Mammalian cells grew on the hydrophobic polymer, but not thehydrophilic polymer enabling cell adhesion to be turned on and off [110]. A patternof the PNIPAAm was formed on a surface by UV-initiated polymerisation of thepolymer through a metal photomask (Figure 1.7A) in direct contact with the surfacesuch that PNIPAAm was only formed where the UV was not blocked. Using thistechnique, Yamato et al., [73] were able to produce an array of 1 mm diametercircular domains of PNIPAAm on a background of tissue culture grade PS. Seededrat hepatocytes grew on both the PNIPAAm and the PS (Figure 1.7B), however,upon lowering the temperature, the cells detached from the PNIPAAm regions(Figure 1.7C). Upon raising the temperature to 37 °C seeded endothelial cells thenattached to the PNIPAAm, generating a patterned cell co-culture (Figure 1.7D).Alternatively, Yamato et al., [64] seeded rat hepatocytes on the patterned PNIPAAmat 20 °C, below the LCST, such that cells only attached to the unmodified tissueculture grade PS. Subsequently seeded human fetal lung fibroblasts at 37 °C, above1-35