Surface modification of polypyrrole via affinity peptide: quantification and mechanism

Area of Science:

• Biomaterials Science
• Polymer Chemistry
• Neuroscience Engineering

Background:

• Conducting polymers like polypyrrole (PPy) are promising for neural electrodes but are hindered by conductivity loss during surface modification.
• Previous research identified a peptide, T59, that binds to PPy without compromising its electrical properties.

Purpose of the Study:

• To quantify the binding affinity and kinetics of the T59 peptide to polypyrrole.
• To elucidate the binding mechanism between T59 and PPy.
• To establish T59 as a viable tool for modifying PPy for biomedical applications.

Main Methods:

• Equilibrium binding assays were used to determine binding affinity and surface density.
• Force spectroscopy was employed to measure binding kinetics (on-rate and off-rate).
• Computational or biochemical methods were used to investigate the binding mechanism.

Main Results:

• T59 exhibits a high affinity for PPy with a binding constant of 92.6 ± 21.4 nM.
• The maximum surface density of T59 on PPy was determined to be 5.1 ± 1.7 fmol/cm².
• Binding occurs rapidly, with an off-rate of 2.5 s⁻¹ and an on-rate of 2.6 × 10⁷ M⁻¹ s⁻¹, indicating a fast equilibrium.
• The binding mechanism involves an electrostatic interaction between aspartic acid (D8) on T59 and the positively charged backbone of oxidized PPy.

Conclusions:

• The T59 peptide demonstrates robust and rapid binding to polypyrrole, making it an effective non-compromising surface modification strategy.
• The identified electrostatic interaction provides a mechanistic basis for T59-PPy binding.
• This research paves the way for advanced PPy-based neural interfaces with enhanced biocompatibility and functionality.