Patterned and switchable surfaces for biomaterial applications

Chapter 4 – Formation of a chemically patterned substrate for cell microarray applicationsNSANB was reacted with amine functional synthetic polymers in aqueous mediain order to produce phenylazide modified polymers, as shown in Figure 4.3A [220,226]. Two amine functional polymers were used, PEI and PLL (Figure 4.3C and D).In addition, two polymers without amine groups were used as negative controls;PAA and PVP (Figure 4.3B and E). The NSANB concentration was altered from 0 to2 mg/ml, resulting in molar ratios of cross-linker to amine groups for the aminefunctional polymers of 0.24, 0.12, 0.06 and 0.00. In order to functionalise the PAAwith NSANB, the NSANB was initially incubated with ethylenediamine before beingcovalently linked to PAA in the presence of EDC and NHS. This approach will alsoresult in the formation of some diazide crosslinker, whereupon a NSANB moleculelinks to both ends of the ethylenediamine, however, this side reaction should assist inthe surface immobilisation and inter- and intra-molecular crosslinking of PAA spots.NSANB concentrations were altered from 0 to 2 mg/ml, resulting in molar ratios ofcross-linker to carboxylic acid groups for the PAA of 0.12, 0.06, 0.03 and 0.00,assuming the functionalisation reaction went to completion. This process is shownschematically in Figure 4.3A. After reaction with the crosslinker, the polymers werespotted onto the PEG coated glass slide surfaces in an array format using a roboticcontact spotter. This was done in a dark room. Once an array of polymer spots wasformed, the slide was irradiated with UV light for 10 min to form highly reactivenitrene species that readily insert into nearby C-H bonds, enabling the formation ofcovalent bonds between the printed polymer and the underlying PEG coating as wellas inter- and intra-molecular crosslinking (Figure 4.3A). The advantage of thisapproach is that the underlying surface chemistry is not limited to the PEG surfacedescribed, but can be readily applied to other organic surface coatings such as selfassembledmonolayers of PEGylated-thiols on a gold substrate. After washing to4-142