Electro-assisted assembly of conductive polymer and soft hydrogel into core-shell hybrids

Abstract

Soft hydrogels have become an important class of materials for mimicking and interfacing biological soft tissues with potential applications in drug delivery, tissue engineering and bioelectronics. Creative methods for integrating hydrogels with other materials such as organic conductors are highly desired. Here, we describe the single-step electrosynthesis of PEDOT/alginate into core-shell hybrid structures via an electrochemical-chemical-chemical mechanism. Using a pulsed electropolymerisation protocol, we generated PEDOT in either oxidized or reduced form. By-products of this electrochemical step trigger the chemical reactions for the concomitant assembly of alginate hydrogels. Characterization evidences that PEDOT (core) and alginate (shell) compartments form an electrochemically integrated interface. During growth, both can be loaded with useful cargo. We loaded a negatively charged small molecule and investigated passive and electroactive release mechanisms from the two compartments. Our electro-assisted assembly/crosslinking of integrated PEDOT/alginate hybrids contributes a promising approach to the design of functional interfaces for applications in controlled release and soft electronics.

Electrochemically Driven Assembly of Chitosan Hydrogels on PEDOT Surfaces

“…PEDOT/Chitosan Presolutions: The solution composition was adapted from a previous work. [7,23] For the PEDOT:TPP, 150 mM of TPP, 70 mM of SDS (ten times critical micellar concentration), and 50 mM of EDOT is dissolved in 24.3 mL of deionized water. For the electro-assisted crosslinking: 1% (v/v) of acetic acid was diluted in 24.3 mL of deionized water, followed by the dissolution of 150 mM of sodium chloride.…”

“…Here, we used a pulsed electropolymerization method where the potential at the working electrode (WE) is held at oxidative potentials (+1.2 V vs AgAg/Cl) for a brief time (0.5 s), followed by holding it at the open-circuit potential (OCP) for interpulse periods lasting 5 s. As reported previously, this method allows time for diffusion and thus for more efficient doping of PEDOT. [7] The PEDOT:TPP-coated wire is then transferred to a chitosan solution and in step (3) PEDOT is reduced at −1.2 V, releasing the TPP dopant to cross-link the chitosan hydrogel. Figure 1b illustrates steps in the gel formation that correspond to the chemical reactions described in Figure 1a.…”

“…The pulsed electropolymerization method generates PEDOT:TPP coatings with a rough surface morphology, enabling higher doping of the structure as compared with smooth coatings. [7] The chitosan hydrogel fully envelops the PEDOT creating a smooth outer surface. The adherent coating of i-C produced by our electro-assisted method is in contrast with the microspheres typically observed with chitosan hydrogels cross-linked with TPP.…”

“…[5] Hydrogel coatings can improve the electrical properties of the interface by reducing impedance and increasing the charge injection capacity. [6][7][8] The hydrogel coating may support the release of therapeutic agents such as neurotrophin or dexamethasone. [9,10] Encapsulation of living cells in the coating may enable reduction of fibrotic scars forming around the electrode.…”

“…[18][19][20][21][22] These methods have the advantage that gelation occurs only over the conductive surface (conformal coating), the rate of gelation can be potentiostatically controlled and interfaces with a smooth transition zone can be formed. [7,23] In the context of electrodes, the electrical interface between hydrogel and rigid (conductive) substrate is of key importance. This is challenging to achieve because hydrogels typically are ionic conductors while metals are electronic conductors.…”