Patterned and switchable surfaces for biomaterial applications

Andrew Hook – Patterned and switchable surfaces for biomaterial applications-potential measurements were taken of various surfaces using a ZetaCAD (CADInstrumentation) using the streaming potential technique. Two identical surfaceswere placed facing each other with a separation of 100 m, which is large comparedwith the double thickness layer. A 0.01 M phosphate buffer of pH 5-7.4 or a 0.01 Macetate buffer of pH 4-5.5 was streamed between the two surfaces at variouspressures ranging from 0-500 mbar in a stepwise fashion with pressure increments of5 mbar. The flow was reversed after each measurement to avoid electrodeasymmetry. For each pressure the temperature, conductivity, viscosity and dielectricconstant of the solution was measured as well as the potential difference between thetwo ends of the surfaces using a multimeter (Keithley 2000) and silver electrodesplaced at either end of the samples. A graph of the voltage difference was plottedagainst pressure to calculate the -potential of the surface according to theHelmholtz-Smoluchowski formula shown as equation 3.1, where is the -potential, is the conductivity of the solution, is the viscosity of the solution, is thepermittivity of the solution, E is the measured potential across the surface and P isthe pressure at which the solution is applied across the surface. EP(3.1)3.2.3. Plasmid preparationPlasmids pEGFP-N1 (4.7 kb) (Clontech), encoding the green fluorescing protein(GFP) (excitation 488 nm, emission 509 nm), were propagated using the JM109Escherichia coli (E-coli) strain (Promega). Cells were transfected with plasmid usingthe heat shock method. Plasmid was isolated using the Promega ®Maxiprep Kit(Promega) according to the manufacturer’s specifications. Isolated plasmid was3-103