Effect of electrochemical oxidation and reduction on cell de-adhesion at the conducting polymer-live cell interface as revealed by single cell force spectroscopy.

Cell adhesion on conducting polymers is important in organic bioelectronics, including applications such as electronically switchable surfaces and electrochemical transistors. There is a fundamental interest in understanding the conducting polymer-cellular interface though as yet no direct measurements to quantify the cell adhesion forces and energies, particularly at the molecular level, have been undertaken. Here, the authors apply electrochemical-single cell force spectroscopy (EC-SCFS) to directly quantify the de-adhesion forces between single L929 fibroblast cells and polypyrrole doped with dodecylbenzene sulfonate (PPy-DBSA) under electrical stimulation. The EC-SCFS reveals single cell de-adhesion forces of 0.65 nN on PPy-DBSA films with adsorbed fibronectin (FN) protein. Blocking experiments by introducing antibodies show that cell de-adhesion is largely due to the binding (∼60% of interactions) of cell-surface α5β1 integrin receptors. Electrochemical oxidation and reduction of PPy-DBSA during initial adsorption of fibronectin cause a significant decrease in the single cell de-adhesion forces to ∼0.4 nN, which is suggested to relate to electrical stimulation effects on reducing FN adsorption on the polymer. In contrast, when electrical stimulation is applied after protein adsorption is established and during the EC-SCFS measurements, the single cell de-adhesion is significantly enhanced on the oxidized polymer compared to the reduced and nonbiased polymer. The study highlights the use of EC-SCFS to directly quantify cell adhesion on electrode surfaces, as well as the ability to probe molecular-level interactions such as integrin receptor-FN complexes with forces of ∼50-100 pN.