Browsing by Author "Martin, David C."
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Item Cholesterol-substituted 3,4-ethylenedioxythiophene (EDOT-MA-cholesterol) and Poly(3,4-ethylenedioxythiophene) (PEDOT-MA-cholesterol)(Giant, 2023-05-23) Wu, Yuhang; Nagane, Samadhan S.; Baugh, Quintin; Lo, Chun-Yuan; Chhatre, Shrirang S.; Lee, Junghyun; Sitarik, Peter; Kayser, Laure V.; Martin, David C.Cholesterol is a rigid, crystalline, non-polar natural substance that exists in animal blood and cell membranes. Some of its derivatives are known to form ordered liquid crystalline mesophases under suitable conditions. In this work, we carefully examined the influence of cholesterol substitution on the characteristics of 3,4-ethylenedioxythiophene (EDOT-MA-cholesterol) and its corresponding polymer poly(3,4-ethylenedioxythiophene) (PEDOT-MA-cholesterol) synthesized by both chemical and electrochemical polymerization. We found evidence for an ordered lamellar (smectic-like) structure in the EDOT-MA-cholesterol monomer by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction techniques. The ordered phase was observed to form on cooling from the isotropic melt at about 80 °C. Due to the insulating and bulky cholesterol side group on the EDOT monomer, we found that there was a maximum charge density for electrodeposition at ∼ 0.155 C.cm−2. A series of electrodepositions were performed from 0 to 0.155 C.cm−2 for probing the change of the charge transport with more charges used for the electrodeposition. We found that the impedance increased in the high-frequency range (above 104 Hz) and decreased in the low-frequency range (below 102 Hz). Three equivalent circuit models were proposed for fitting impedance data at different charge densities for a better understanding of the film growth process. The suppressed cyclic voltammogram (CV) of PEDOT-MA-cholesterol showed that the charge storage capability was essentially eliminated in the thickest films. The limited doping of the films was corroborated by their diminished electrochromic behavior, polaron-dominating absorption in UV-vis, overoxidized S 2p X-ray Photoelectron Spectroscopy (XPS) signal of electrodeposited films, and proton Nuclear Magnetic Resonance (1H NMR) of chemically polymerized samples. Dense film morphologies were confirmed by scanning electron microscopy (SEM). Grazing incident X-ray diffraction (GIWAXS) indicated the disrupted stacking of conjugated chains, which correlated with the decreased conductivity of the PEDOT-MA-cholesterol films. The measurement of the electrical conductivity gave a value of around 3.30 × 10−6 S.cm−1 which is about six orders of magnitude lower than has been seen in PEDOT (∼3 S.cm-1). Graphical abstract available at: https://doi.org/10.1016/j.giant.2023.100163Item Development of a Regenerative Peripheral Nerve Interface for Control of a Neuroprosthetic Limb(Hindawi Publishing Corporation, 2016-04-17) Urbanchek, Melanie G.; Kung, Theodore A.; Frost, Christopher M.; Martin, David C.; Larkin, Lisa M.; Wollstein, Adi; Cederna, Paul S.; Melanie G. Urbanchek, Theodore A. Kung, Christopher M. Frost, David C.Martin, Lisa M. Larkin, Adi Wollstein, and Paul S. Cederna; Martin, David C.The purpose of this experiment was to develop a peripheral nerve interface using cultured myoblasts within a scaffold to provide a biologically stable interface while providing signal amplification for neuroprosthetic control and preventing neuroma formation. Methods. A Regenerative Peripheral Nerve Interface (RPNI) composed of a scaffold and cultured myoblasts was implanted on the end of a divided peroneal nerve in rats (𝑛��� = 25). The scaffold material consisted of either silicone mesh, acellular muscle, or acellular muscle with chemically polymerized poly(3,4-ethylenedioxythiophene) conductive polymer. Average implantation time was 93 days. Electrophysiological tests were performed at endpoint to determine RPNI viability and ability to transduce neural signals. Tissue samples were examined using both light microscopy and immunohistochemistry. Results. All implanted RPNIs, regardless of scaffold type, remained viable and displayed robust vascularity. Electromyographic activity and stimulated compound muscle action potentials were successfully recorded from all RPNIs. Physiologic efferent motor action potentials were detected from RPNIs in response to sensory foot stimulation. Histology and transmission electron microscopy revealed mature muscle fibers, axonal regeneration without neuroma formation, neovascularization, and synaptogenesis. Desmin staining confirmed the preservation and maturation of myoblasts within the RPNIs. Conclusions. RPNI demonstrates significant myoblast maturation, innervation, and vascularization without neuroma formation.Item Electronically Conductive Hydrogels by in Situ Polymerization of a Water-Soluble EDOT-Derived Monomer(Advanced Engineering Materials, 2022-05-13) Nguyen, Dan My; Wu, Yuhang; Nolin, Abigail; Lo, Chun-Yuan; Guo, Tianzheng; Dhong, Charles; Martin, David C.; Kayser, Laure V.Electronically conductive hydrogels have gained popularity in bioelectronic interfaces because their mechanical properties are similar to biological tissues, potentially preventing scaring in implanted electronics. Hydrogels have low elastic moduli, due to their high water content, which facilitates their integration with biological tissues. To achieve electronically conductive hydrogels, however, requires the integration of conducting polymers or nanoparticles. These “hard” components increase the elastic modulus of the hydrogel, removing their desirable compatibility with biological tissues, or lead to the heterogeneous distribution of the conductive material in the hydrogel scaffold. A general strategy to transform hydrogels into electronically conductive hydrogels without affecting the mechanical properties of the parent hydrogel is still lacking. Herein, a two-step method is reported for imparting conductivity to a range of different hydrogels by in-situ polymerization of a water-soluble and neutral conducting polymer precursor: 3,4–ethylenedioxythiophene diethylene glycol (EDOT-DEG). The resulting conductive hydrogels are homogenous, have conductivities around 0.3 S m−1, low impedance, and maintain an elastic modulus of 5–15 kPa, which is similar to the preformed hydrogel. The simple preparation and desirable properties of the conductive hydrogels are likely to lead to new materials and applications in tissue engineering, neural interfaces, biosensors, and electrostimulation.Item Poly[3,4-ethylene dioxythiophene (EDOT)-co-1,3,5-tri[2-(3,4-ethylene dioxythienyl)]-benzene (EPh)] copolymers (PEDOT-co-EPh): optical, electrochemical and mechanical properties(Royal Society of Chemistry., 2015-02-09) Ouyang, Liangqi; Kuo, Chin-Chen; Farrell, Brendan; Pathak, Sheevangi; Wei, Bin; Qu, Jing; Martin, David C.; Liangqi Ouyang, Chin-chen Kuo, Brendan Farrell, Sheevangi Pathak, Bin Wei, Jing Qu and David C. Martin; Ouyang, Liangqi; Kuo, Chin-chen; Farrell, Brendan; Wei, Bin; Qu, Jing; Martin, David C.PEDOT-co-EPh copolymers with systematic variations in composition were prepared by electrochemical polymerization from mixed monomer solutions in acetonitrile. The EPh monomer is a trifunctional crosslinking agent with three EDOTs around a central benzene ring. With increasing EPh content, the color of the copolymers changed from blue to yellow to red due to decreased absorption in the near infrared (IR) spectrum and increased absorption in the visible spectrum. The surface morphology changed from rough and nanofibrillar to more smooth with rounded bumps. The electrical transport properties dramatically decreased with increasing EPh content, resulting in coatings that either substantially lowered the impedance of the electrode (at the lowest EPh content), leave the impedance nearly unchanged (near 1% EPh), or significantly increase the impedance (at 1% and above). The mechanical properties of the films were substantially improved with EPh content, with the 0.5% EPh films showing an estimated 5× improvement in modulus measured by AFM nanoindentation. The PEDOT-co-EPh copolymer films were all shown to be non-cytotoxic toward and promote the neurite outgrowth of PC12 cells. Given these results, we expect that the films of most interest for neural interface applications will be those with improved mechanical properties that maintain the improved charge transport performance (with 1% EPh and below).Item Post-polymerization functionalization of poly(3,4-propylenedioxythiophene) (PProDOT) via thiol–ene “click” chemistry(Royal Society of Chemistry., 2015-02-25) Wei, Bin; Ouyang, Liangqi; Liu, Jinglin; Martin, David C.; Bin Wei, Liangqi Ouyang, Jinglin Liua and David C. Martin; Wei, Bin; Ouyang, Liangqi; Liu, Jinglin; Martin, David C.The surface functionalization of conjugated polymers such as the poly(alkoxythiophenes) poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-propylenedioxythiophene) (PProDOT) provides a potential means for systematically tailoring their physical properties. We previously reported the synthesis of an alkene-functionalized 3,4-propylenedioxy-thiophene (ProDOT) derivative that could be readily modified through thiol–ene “click” chemistry. Here, we investigated the post-polymerization modification of PProDOT surfaces by using a dialkene functionalized variant (ProDOT-diene). The chemical structure of the ProDOT-diene monomer was confirmed by Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared spectroscopy (FTIR). The ProDOT-diene monomer was either chemically or electrochemically polymerized into the PProDOT-diene polymer, and then subsequently modified with alkyl, PEG, or ferrocene moieties via radical-based thiol–ene chemistry. We found that the normally insoluble PProDOT-diene could be converted into a soluble derivative by grafting alkyl groups onto the polymer chains after chemical polymerization. When electrochemically deposited on indium-tin oxide (ITO) glass electrodes, the conductivity, electroactivity and contact angles of the modified PProDOT-diene films could be tuned over a broad range. Scanning Electron Microscopy (SEM) revealed that post-polymerization modification did not significantly alter the surface morphology of the PProDOT-diene films. Overall, this method allows for efficient, facile tuning of the surface chemistry of poly(alkylthiophene) films, making it possible to tailor properties such as conductivity and wettability for different applications.Item Salt Solution Concentration Effects on the Electrochemical Impedance Spectroscopy of Poly(3,4-ethylenedioxythiophene) (PEDOT)(ChemElectroChem, 2022-05-09) Sitarik, Peter; Martin, David C.Poly(3,4-ethylenedioxythiophene) (PEDOT) has become a widely used modifier for biomedical electrodes because of its ability to significantly decrease the impedance at low frequencies (below 1 kHz). However, in past studies the role of the solution concentration (ionic conductivity) on the electrochemical impedance behavior has not been well established. Here we describe the electrochemical impedance spectroscopy of the conjugated polymer (PEDOT) using standard screen-printed electrodes and various standard salt (NaCl) solutions with known conductivities from 1.0E-2 S/cm to 3.1E-6 S/cm. Changing the conductivity of the salt solution used for impedance measurements had a dramatic influence on the experimentally obtained spectra. An equivalent circuit consisting of a constant phase element in series with a parallel resistor and second constant phase element was used to match and describe these systems. Our results make it possible to better elucidate the influence of electrode, solution, and polymer coating on the resulting impedance response.Item Synthesis and characterization of bicontinuous cubic poly(3,4-ethylene dioxythiophene) gyroid (PEDOT GYR) gels(Royal Society of Chemsitry, 2015-01-12) Cho, Whirang; Wu, Jinghang; Shim, Bong Sup; Kuan, Wei-Fan; Mastroianni, Sarah E.; Young, Wen-Shiue; Kuo, Chin-Chen; Epps, Thomas H. III; Martin, David C.; Whirang Cho, Jinghang Wu, Bong Sup Shim, Wei-Fan Kuan, Sarah E. Mastroianni, Wen-Shiue Young, Chin-Chen Kuo, Thomas H. Epps, III and David C. Martin; Cho, Whirang; Wu, Jinghang; Shim, Bong Sup; Kuan, Wei-Fan; Mastroianni, Sarah E.; Young, Wen-Shiue; Kuo, Chin-Chen; Epps, Thomas H. III; Martin, David C.We describe the synthesis and characterization of bicontinuous cubic poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer gels prepared within lyotropic cubic poly(oxyethylene)10 nonylphenol ether (NP-10) templates with Ia[3 with combining macron]d (gyroid, GYR) symmetry. The chemical polymerization of EDOT monomer in the hydrophobic channels of the NP-10 GYR phase was initiated by AgNO3, a mild oxidant that is activated when exposed to ultraviolet (UV) radiation. The morphology and physical properties of the resulting PEDOT gels were examined as a function of temperature and frequency using optical and electron microscopy, small-angle X-ray scattering (SAXS), dynamic mechanical spectroscopy, and electrochemical impedance spectroscopy (EIS). Microscopy and SAXS results showed that the PEDOT gels remained ordered and stable after the UV-initiated chemical polymerization, confirming the successful templated-synthesis of PEDOT in bicontinuous GYR nanostructures. In comparison to unpolymerized 3,4-ethylenedioxythiophene (EDOT) gel phases, the PEDOT structures had a higher storage modulus, presumably due to the formation of semi-rigid PEDOT-rich nanochannels. Additionally, the storage modulus (G′) for PEDOT gels decreased only modestly with increasing temperature, from ∼1.2 × 105 Pa (10 °C) to ∼7 × 104 Pa (40 °C), whereas G′ for the NP-10 and EDOT gels decreased dramatically, from ∼5.0 × 104 Pa (10 °C) to ∼1.5 × 102 Pa (40 °C). EIS revealed that the impedance of the PEDOT gels was smaller than the impedance of EDOT gels at both high frequencies (PEDOT ∼102 Ω and EDOT 2–3 × 104 Ω at 105 Hz) and low frequencies (PEDOT 103–105 Ω and EDOT ∼5 × 105 Ω at 10−1 Hz). These results indicated that PEDOT gels were highly ordered, mechanically stable and electrically conductive, and thus should be of interest for applications for which such properties are important, including low impedance and compliant coatings for biomedical electrodes.