Patterned and switchable surfaces for biomaterial applications

Chapter 5 – Surface plasmon resonance imaging of polymer microarraysbetween CN and FN with PAAc, an entropy effect as a result of proteinrearrangement or conformational changes upon surface adsorption that may exposepositively charged domains embedded with the protein resulting in a change in theprotein pI upon adsorption [293].The k a measured for FN adsorption to PAAc, PEIc and PLLc were 69.9x10 3 ,35.9x10 3 and 88.6x10 3 s -1 M -1 , respectively (Table 5.1). Interestingly, FN adsorptionto PLLc had a higher k a than to PEIc, despite both polymer being positively charged.Moreover, FN adsorption to PAAc also had a higher k a than to PEIc. The reason forthe relatively fast rate of adsorption of FN to PLL is unclear.BSA adsorption was observed on both PEIc and PLLc, with adsorption for 1500 sat 10 mg/ml resulting in protein layers of thickness 0.4 and 0.2 nm, respectively(Figure 5.16B and C). Conversely, little to no BSA adsorption was measurable on thePAAc (Figure 5.16A). In fact, a negative change in mass was measured for PAAc(Figure 5.16A). Since the SPR sensorgrams shown in Figure 5.14-Figure 5.16 havehad the signal from the unmodified HDI PEG background subtracted, this negativeresult is likely due to the PAAc resisting BSA adsorption more effectively than thePEG background. BSA has a pI of 4.7 [294] and is, thus, negatively charged atphysiological pH. The resistance of BSA adsorption by PAAc is therefore likely tobe due to the electrostatic repulsion of the overall negative charge of the protein withthe negative charge of PAA. Likewise, the adsorption to PEIc and PLLc is likely dueto electrostatic attraction between the overall negative charge of BSA and thepositive charge of PEI and PLL. Adsorption of BSA has been previously shown to beelectrostatically mediated [281, 295]. The s∞ of BSA adsorption to PEIc and PLLcwas found to be 3.8 and 3.2 mg/m 2 , respectively (Table 5.1), which is significantlylower than the s∞ of CN type I and FN adsorption to PAAc of 15.7 and 15.3 mg/m 25-200