Patterned and switchable surfaces for biomaterial applications

Andrew Hook – Patterned and switchable surfaces for biomaterial applicationsThe adsorption and desorption of DNA to ALAPP was quantified by experimentswhere ALAPP surfaces were exposed to pEGFP-N1 solution in a custom builtelectrochemical cell. Initially the ALAPP sample was incubated with the plasmidDNA solution for 24 hr, after which a positive voltage was applied, furtherstimulating DNA adsorption. Subsequently, the bias was reversed and a negativevoltage was applied, stimulating DNA desorption. The concentration of DNA insupernatant was quantified using the minor groove binder PicoGreen®, enabling thecalculation of DNA surface concentration ( DNA ). The results are shown in Figure2.7.After 24 hr incubation, an increase in DNA on the ALAPP from 0.0 mg/m 2 to 0.4mg/m 2 was observed (Figure 2.7), corresponding to the ‘spontaneous’ adsorption ofDNA to the ALAPP surface. In identical control experiments, conducted with Teflonsamples, no adsorbed DNA was detected. Electrophoretic analysis of the DNAadsorbed to the ALAPP surface showed three distinct DNA bands (results notshown) corresponding to the plasmid existing in three forms. Quantification of thesebands determined that 85% of the plasmid DNA was in the supercoiled form whilstthe remaining 15% were distributed between the linear and relaxed circular forms.Assuming the spontaneous adsorption of DNA to ALAPP went to saturation (timetaken for saturation of adsorbed DNA to occur on other substrates is typically 10-60min [23, 30]), the surface concentration of DNA at saturation ( sat ) was 0.4 mg/m 2 . Ifdouble-stranded DNA is considered as a cylinder with diameter 2 nm, as determinedby the crystal structure of B-DNA, then the predicted sat value for a monolayer oflinear DNA would be 1.7 mg/m 2 . Thus, 25% surface coverage for spontaneousadsorption was observed. This result is similar to the sat reported for pUC18 DNAadsorbed onto silica by Melzak et al., 1996 [20]. The thermodynamic driving force2-87