Strain- and Strain-Rate-Invariant Conductance in a Stretchable and Compressible 3D Conducting Polymer Foam

Abstract

A stretchable conductor is a crucial component required as electrodes for signal probing or interconnects between various electrical components in stretchable electronics. Current approaches for stretchable conductors use strain engineering or composite materials. Here, we demonstrate a conducting polymer foam in which strain-and strain-rate-invariant conductance and compliance are synergistically engineered into a singular entity. The cellular nature of the materials also provides accommodation for both compressive and tensile strains while offering breathability, which opens up new possibilities for stretchable conductors.

Ambient‐Dried, 3D‐Printable and Electrically Conducting Cellulose Nanofiber Aerogels by Inclusion of Functional Polymers

“…The normalized conductivity of the PEDOT‐functionalized aerogels was calculated to be 146 ± 8 S m −1 . This value compares well with the one reported in recently published studies regarding aerogels solely made from freeze‐dried PEDOT:PSS dispersions . This result is remarkable since the cellulose and alginate represent a large weight fraction of the material (37% at a loading of 1.7 g g −1 ), and can be considered as electrical insulators.…”

An Electrochemical Gelation Method for Patterning Conductive PEDOT:PSS Hydrogels

“…Such materials represent a significant advance for resolving the mechanical mismatch between electronics and biological systems that currently prohibits long‐term bioelectronic interfacing . Additional postprocessing treatments for PEDOT:PSS hydrogels, including lyophilization, have also been reported in the literature as methods for fabricating porous scaffolds and aerogels . In these cases, the high water content of PEDOT:PSS hydrogels is critical to generate the desired porous structure, which is templated by freezing entrapped water.…”

“…This is particularly challenging for PEDOT:PSS, since its irreversible gelation mechanism is incompatible with standard nozzle‐based printing methods and because it does not contain moieties that can be readily crosslinked by light for photolithography . Thus far, the primary way to pattern these materials is to shape them with an appropriate mold, but these mold‐based methods are difficult to integrate into conventional, on‐chip device fabrication processes; are hard to scale, since new 3D molds must be fabricated whenever a new pattern is desired; and do not lend themselves to patterning onto curvilinear surfaces or coating 3D objects. In this work, we address these limitations by presenting a novel method for patterning PEDOT:PSS hydrogels on arbitrary surfaces using electrochemical gelation, or “electrogelation,” based on the unique ionically induced gelation mechanism of PEDOT:PSS.…”

“…Moving forward, electrogelation may enable electrode arrays of soft conductors with a variety of desired mechanical properties, including high stretchability, since our PEDOT:PSS electrogels are compatible with hydrogel postprocessing techniques like acid treatment, incorporation of secondary networks, drying methods including lyophilization, and drying followed by reswelling . To demonstrate compatibility with postprocessing treatments, we backfilled an X‐shaped PEDOT:PSS gel patterned using electrogelation with a secondary network of polyacrylic acid, as reported in our previous work .…”

Rapid Custom Prototyping of Soft Poroelastic Biosensor for Simultaneous Epicardial Recording and Imaging

“…Herein, we introduce a sponge-like form of poroelastic silicone composite with optimal rheological properties that allow it to be printed in a nozzle injection system with high fidelity. The resulting composite material provides the following unique features: (1) poroelastic behavior (rather than viscoelastic behavior) with reversible compressibility that can effectively suppress both mechanical and electrical hysteresis against repetitive loading; 16 (2) exceptional softness due to the ultralow mechanical modulus (E < 30 kPa) of the sponge-like foam, which is lower than that of commercial dispensable inks (E > 1.11 MPa; SE 1700, Dow Corning) by more than 10-fold and comparable to that of human cardiac tissues (29-41 kPa); 17 and (3) monolithic structure in which the nanofillers are embedded through the internal pores in a way that eliminates the risk of compromising the structural integrity even under large deformations. 18 In this report, we elucidated the structure-property relationships of this composite material at the molecular and microsystemic levels and then evaluated its applicability in rapid custom prototyping of stretchable biosensors.…”