Patterned and switchable surfaces for biomaterial applications

Andrew Hook – Patterned and switchable surfaces for biomaterial applicationsThe DNA on PEG was found to be significantly lower than for ALAPP over thebulk DNA concentration range studied (Figure 3.4A) confirming that, as expected,PEG resists adsorption of DNA as compared with the ALAPP film. By applying theLangmuir model to the data sets shown in Figure 3.4, the s and K for DNAadsorption to PEG were found to be 1.75 mg/m 2 and 680 ml/mg respectively, whichis significantly lower than the equivalent values of 4.96 mg/m 2 and 1600 ml/mgmeasured for ALAPP. The small amount of DNA adsorption observed on the PEGfilms is presumably due to weak Van der Waals interactions or hydrogen bonding.At pH 7.4 a more negative -potential was measured for ALAPP than for PEG. Assuch, electrostatic interactions with the ALAPP film should be less favourable thanfor the PEG film. Significantly, a contact angle difference of 57° was measured forthe two films, with the PEG film being more hydrophilic, an important disparitybetween these two films at a pH of 7.4. Thus, rather than the stabilisation of a DNAon an ALAPP film being predominantly due to electrostatic interactions,hydrophobic effects between the hydrophobic nucleobases and hydrophobicfunctionalities within the ALAPP film were suspected to contribute significantly [18,19]. It is suspected that the brush character of the PEG film, as discussed previously,also contributes to the low DNA seen on the PEG films.To further investigate how DNA interacts with ALAPP surfaces, a series ofexperiments monitoring DNA adsorption in various solvents of varying pH, ionconcentration and hydrophobicity were conducted. The results are shown in Figure3.5-Figure 3.8. Entropically, the adsorption of DNA is driven by surface dehydration,that is, the removal of water molecules from the surface [20]. However, in order forthis thermodynamically favourable process to occur, the DNA molecules mustdiffuse close enough to the surface to displace water molecules at the solid/liquid3-117