We continue to investigate the design, synthesis, and characterization of electrically and ionically active conjugated polythiophene copolymers for integrating a variety of biomedical devices with living tissue. This paper will describe some of our most recent results, including the development of several new monomers that can tailor the surface chemistry, adhesion, and biointegration of these materials with neural cells. Our efforts have focused on copolymers of 3,4 ethylenedioxythiophene (EDOT), functionalized variants of EDOT (including EDOT-acid and the trifunctional EPh), and dopamine (DOPA). The resulting PEDOT-based copolymers have electrical, optical, mechanical, and adhesive properties that can be precisely tailored by fine tuning the chemical composition and structure. Here we present results on EDOT-dopamine bifunctional monomers and their corresponding polymers. We discuss the design and synthesis of an EDOT-cholesterol that combines the thiophene with a biological moiety known to exhibit surface-active behaviour. We will also introduce EDOT-aldehyde and EDOT-maleimide monomers and show how they can be used as the starting point for a wide variety of functionalized monomers and polymers.
Here we examined the capacitive behavior of electrodeposited poly(2’-maleimideomethyl-3,4-ethylenedioxythiophene) (PEDOT-maleimide) and compared it to poly(3,4-ethylenedioxythiophene) (PEDOT). According to results of linear cyclic voltammetry (linear CV) and galvanostatic charging/discharging (GCD) in...
Organic electrochemical transistors (OECTs) are promising bioelectronic devices, especially because of their ability to transport charge both ionically and electronically. Conductive polymers are typically used as the active materials of OECTs. Crosslinked, cast, and dried films of commercially available poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PE-DOT:PSS) suspensions are commonly and widely used for OECTs so far. Electrochemical polymerization of PEDOT from 3,4-ethylenedioxythiophene (EDOT) monomer can also be used to fabricate OECTs; however, this approach has not been investigated in as much detail. In particular, the role of various counterions that can be incorporated into the PEDOT films of OECTs has not been systematically studied. Here, we report the electrochemical fabrication and characterization of OECTs using PEDOT with several different counterion salts including lithium perchlorate (LiClO 4 ), sodium p-toluene sulfonate (pTS), and poly(sodium 4-styrene sulfonate) (PSS). We found that the characteristic dimensions of PEDOT films deposited on the electrodes could be precisely controlled by total charge density, with a nominal thickness of about one micron requiring a current density of about 0.6 C/cm 2 regardless of the choice of counterion. The films with the PSS counterion were relatively smooth, while PEDOT films prepared with the pTS and LiClO 4 were much rougher due to the sizes of counterions. The PEDOT films with pTS and PSS grew along the substrate surface (in-plane direction) much faster than with LiClO 4 . The maximum transconductance (g m ) of a PEDOT OECT was 46 mS with pTS as the counterion with the high on-current level (>10 mA) based on the large channel area. These results provide an effective and efficient way to fabricate OECTs with various monomers and additives as active materials in order to modify the device characteristics for further applications.
The ability to interface electronic materials with the peripheral nervous system is required for stimulation and monitoring of neural signals. Thus, the design and engineering of robust neural interfaces that maintain material-tissue contact in the presence of material or tissue micromotion offer the potential to conduct novel measurements and develop future therapies that require chronic interface with the peripheral nervous system. However, such remains an open challenge given the constraints of existing materials sets and manufacturing approaches for design and fabrication of neural interfaces. Here, we investigated the potential to leverage a rapid prototyping approach for the design and fabrication of nerve cuffs that contain supporting features to mechanically stabilize the interaction between cuff electrodes and peripheral nerve. A hybrid 3D printing and robotic-embedding (i.e., pick-and-place) system was used to design and fabricate silicone nerve cuffs (800 µm diameter) containing conforming platinum (Pt) electrodes. We demonstrate that the electrical impedance of the cuff electrodes can be reduced by deposition of the conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on cuff electrodes via a post-processing electropolymerization technique. The computer-aided design and manufacturing approach was also used to design and integrate supporting features to the cuff that mechanically stabilize the interface between the cuff electrodes and the peripheral nerve. Both ‘self-locking’ and suture-assisted locking mechanisms are demonstrated based on the principle of making geometric alterations to the cuff opening via 3D printing. Ultimately, this work shows 3D printing offers considerable opportunity to integrate supporting features, and potentially even novel electronic materials, into nerve cuffs that can support the design and engineering of next generation neural interfaces.
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