Patterned and switchable surfaces for biomaterial applications

Chapter 4 – Formation of a chemically patterned substrate for cell microarray applicationsfor 48 hr. Cells were visualised by fluorescence microscopy. GFP fluorescence wastaken through a 470-495 nm excitation filter and a 510 nm suppression filter. RFPfluorescence was observed through a 530-550 nm excitation filter and a 575 nmsuppression filter.4.3. Results and discussion4.3.1. Optimisation of polymer printingInitially the optimised formation of PEI arrays was of interest, thus, PEI printingwas conducted at varied temperature, humidity, approach speed of the pin to thesurface and dwell time of the pin in contact with the surface. Fluorescence images ofPEI spots formed under these varied conditions are shown in Figure 4.2. Thediameter and variability of the pixel height, calculated as the standard deviation ofthe height of the total number of pixels for each spot, was calculated and alsographed in Figure 4.2. It should be noted that Figure 4.2A and Figure 4.2B wereobtained on separate days such that the pixel intensity values are not quantitativelycomparable. A number of key conclusions can be determined from Figure 4.2.Firstly, printed PEI spots always have a rim as a result of mass transport effects asthe spot dries [225]. Formation of this rim results in an increased variability acrossthe spots. It can be seen from Figure 4.2A that decreasing both temperature andhumidity increases the variability as a result of increasing the thickness and height ofthe rim. Altering humidity does not have any affect on the spot diameter. However,decreasing temperature increases the spot size. In order to minimise variability, ahumidity of 65 % and a temperature of 30 °C was selected for further PEI arrayformation.4-138