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Patterned and switchable surfaces for biomaterial applications

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Andrew Hook – <strong>Patterned</strong> <strong>and</strong> <strong>switchable</strong> <strong>surfaces</strong> <strong>for</strong> <strong>biomaterial</strong> <strong>applications</strong>In order to characterise the extent of hydrophobic interactions between theAOLG-modified tip <strong>and</strong> the polymer coatings F-D curves were conducted in TEbuffer supplemented with different % (v/v) of ethanol. The added ethanol decreasesthe free energy of the liquid/solid interface by decreasing the thermodynamic penalty<strong>for</strong> having a polar solvent exposed to hydrophobic moieties on the surface [213].Thus, increasing ethanol content should decrease the driving <strong>for</strong>ce <strong>for</strong> DNAadsorption if hydrophobic interactions play a role [188].A summary of the pull off <strong>for</strong>ces measured between the polymer samples <strong>and</strong> theDNA is shown as Figure A1.2. Interestingly, no polymer showed a decrease in thepull off <strong>for</strong>ce at higher ethanol concentrations, suggesting that hydrophobicinteractions do not play a significant role <strong>for</strong> the interactions being studied. However,the <strong>for</strong>ce between the tip <strong>and</strong> PALA, PEI <strong>and</strong> PLL was observed to greatly increaseat higher ethanol concentrations. Ethanol weakly solvates charge compared withwater, thus, at higher ethanol concentrations it is entropically favourable <strong>for</strong> the<strong>for</strong>mation of polar interactions. Thus, the increase in ethanol concentration enhancedthe electrostatic interactions between the AOLG-modified tip <strong>and</strong> the polycationicpolymers. This clearly demonstrates the presence of the strong electrostaticinteractions possible between DNA <strong>and</strong> PALA, PEI <strong>and</strong> PVP, whilst the ability ofPAA <strong>and</strong> PVP to repel DNA.K

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