Electronically Conductive Hydrogels by in Situ Polymerization of a Water‐Soluble EDOT‐Derived Monomer

Abstract

Biomedical electronic devices can be interfaced with the human body to measure physiological signals [1,2] or to provide electrical stimulation for treatment. [3,4] Electronic materials that can be seamlessly interfaced with human tissues or cells are, therefore, essential to study or stimulate the nervous system, or to serve as neural tissue scaffolds. But, materials challenges remain to be addressed to bridge the gap between "soft" biological tissues and "hard" electronics. The mechanical mismatch between biological tissues and electronics can lead to scar formation between the electronics and the target tissue, which significantly hampers the performance and efficacy of bioelectronic stimulation and recording. [3,5,6] Conductive hydrogels are a promising strategy for interfacing electronic materials with biological tissues. [6,7] Due to their high water content (70-99 wt%), hydrogels can be as soft and flexible as biological tissues, including skin, muscle, heart, spinal cord, and brain (E < 100 kPa). [6] To impart electrical conductivity, conductive nanoparticles, such as metal nanowires (NWs) [8,9] carbon nanotubes (CNTs), [7] and conductive polymers [5,7,10] can be incorporated inside the hydrogel. NWs and CNTs, while effective at achieving electronically conductive hydrogels, were shown to lead to heterogeneities in the network and hydrogels with a high elastic modulus; overall leading to a poor interface with biological entities. [8] Compared to these nanocomposite hydrogels, conductive hydrogels made from conducting polymers (CPs), including poly(3,4-ethylenedioxythiophene) (PEDOT), [11,12] polypyrrole (PPy), [13][14][15] or polyaniline (PANI) [15,16] offer a higher compatibility with biological systems, by virtue of their flexibility and potential for ionic-as well as electronic-conductivity.Several methods have been envisioned for the preparation of conductive hydrogels from CPs. [17,18] The conducting polyelectrolyte complex of PEDOT with poly(styrene sulfonate) (PEDOT:PSS) can be gelled directly from its aqueous solution by increasing the ionic strength with bivalent ions Mg 2þ , Ca 2þ , or multivalent ions Fe 3þ , Ce 4þ . [19,20] These conductive hydrogels, however, are only weakly crosslinked leading to poor strength and contain residual ions, which could lead to potential inflammation and cell toxicity. [21] Thus, the purification process requires a large amount of distilled water for at least a week to wash out excess ions. [20] Another method is the use of secondary dopants, including sulfuric acid and dimethyl sulfoxide, as both

One Pot Photomediated Formation of Electrically Conductive Hydrogels

“…Notably, at an identical gel volume, the hydrogel with a 100:13 ratio of SS to EDOT displayed the lowest impedance magnitude. The Nyquist plot of the hydrogels (Figure b) were analyzed and fitted to the equivalent circuit model commonly used for PEDOT-based conductive hydrogels (Figure c). ,, The tabulated values extracted from this model are presented in Table and show small χ 2 values, indicating a good fit for the model. The values of R c , R e , and R i are, respectively, the resistive contributions from the assembled cell used for the test and the electronic and ionic resistance from the conductive hydrogel.…”

“…However, bioelectronic devices made from conductive hydrogels are currently limited by their fabrication methods and our ability to control the shape and position of the hydrogel. Conventional methods such as molding ,, have been frequently used to fabricate conductive hydrogels but can only provide simple structures with low resolution (>100 μm) . This large size may not be compatible with bioelectronic applications requiring small electrodes.…”

Engineering Multi‐Scale Organization for Biotic and Organic Abiotic Electroactive Systems

“…In another work, a parallel approach was demonstrated by mold casting hydrogels composed of water‐soluble EDOT‐diethylene glycol that are electronically conductive upon in situ polymerization and can maintain the mechanical properties of the gel. [ 107 ] In the future, a better understanding of polymer chain entanglements and formation of nanofibril networks in PEDOT‐based or PEDOT:PSS solutions will advance the development of these 3D printable polymer systems. Moreover, the flexibility and reproducibility of 3D printing of conductive PEDOT: PSS allows the fabrication of bioelectronic signal recording probe with PDMS (Figure 8d,e ).…”

Gels of Semiconducting Polymers in Benign Solvents

“…32 Another method begins with a polymer precursor, 3,4ethylenedioxythiophene diethylene glycol, to create a hydrogel. 33 In a recent study, PBLG, a biocompatible polypeptide, was used to enhance the assembly of poly(3-hexylthiophene) (P3HT) into a network structure. 34 Here, the interactions between PBLG and P3HT led to an ordered structure of P3HT growing between bundled PBLG helices.…”

“…The process involves mixing DMSO into aqueous PEDOT: PSS solutions to develop interconnected networks of PEDOT: PSS nanofibrils . Another method begins with a polymer precursor, 3,4-ethylenedioxythiophene diethylene glycol, to create a hydrogel . In a recent study, PBLG, a biocompatible polypeptide, was used to enhance the assembly of poly­(3-hexylthiophene) (P3HT) into a network structure .…”