Electrochemical characterization of the stimuli-response of surface-immobilized elastin-like polymers†
Elastin-like polymers (ELPs) are frequently used in a variety of bioengineering applications because of their stimuli-responsive properties. Above their transition temperature, ELPs will adopt different structures that promote intra- and intermolecular hydrophobic contacts to minimize unfavorable interactions with an aqueous environment. We electrochemically characterize the stimuli-responsive behavior of surface-immobilized ELPs corresponding to two proposed states: extended and collapsed. In the extended state the ELPs are more solvated. In the collapsed state, triggered by introducing an environmental stimulus, non-polar intramolecular contacts within ELPs are favored, resulting in quantifiable morphological changes on the surface characterized using electrochemical impedance spectroscopy (EIS). Charge transfer resistance, a component of impedance, was shown to increase after exposing an ELP modified electrode to a high salt concentration environment (3.0 M NaCl). An increase in charge transfer resistance indicates an increase in the insulating layer on the electrode surface consistent with the proposed mechanism of collapse, as the ELPs have undergone morphological changes to hinder the kinetics of the redox couple exchange. Further characterization of the surface-immobilized ELPs showed a reproducible surface modification, as well as reversibility and tunability of the stimuli-response.