Digital Light 3D Printing of PEDOT-Based Photopolymerizable Inks for Biosensing

3D conductive materials such as polymers and hydrogels that interface between biology and electronics are actively being researched for the fabrication of bioelectronic devices. In this work, short-time (5 s) photopolymerizable conductive inks based on poly(3,4-ethylenedioxythiophene) (PEDOT):polystyrene sulfonate (PSS) dispersed in an aqueous matrix formed by a vinyl resin, poly(ethylene glycol) diacrylate (PEGDA) with different molecular weights (M _n = 250, 575, and 700 Da), ethylene glycol (EG), and a photoinitiator have been optimized. These inks can be processed by Digital Light 3D Printing (DLP) leading to flexible and shape-defined conductive hydrogels and dry conductive PEDOTs, whose printability resolution increases with PEGDA molecular weight. Besides, the printed conductive PEDOT-based hydrogels are able to swell in water, exhibiting soft mechanical properties (Young's modulus of ∼3 MPa) similar to those of skin tissues and good conductivity values (10^-2 S cm^-1) for biosensing. Finally, the printed conductive hydrogels were tested as bioelectrodes for human electrocardiography (ECG) and electromyography (EMG) recordings, showing a long-term activity, up to 2 weeks, and enhanced detection signals compared to commercial Ag/AgCl medical electrodes for health monitoring.

Ionic Hydrogel for Accelerated Dopamine Delivery via Retrodialysis

Local drug delivery directly to the source of a given pathology using retrodialysis is a promising approach to treating otherwise untreatable diseases. As the primary material component in retrodialysis, the semipermeable membrane represents a critical point for innovation. This work presents a new ionic hydrogel based on polyethylene glycol and acrylate with dopamine counterions. The ionic hydrogel membrane is shown to be a promising material for controlled diffusive delivery of dopamine. The ionic nature of the membrane accelerates uptake of cationic species compared to a nonionic membrane of otherwise similar composition. It is demonstrated that the increased uptake of cations can be exploited to confer an accelerated transport of cationic species between reservoirs as is desired in retrodialysis applications. This effect is shown to enable nearly 10-fold increases in drug delivery rates from low concentration solutions. The processability of the membrane is found to allow for integration with microfabricated devices which will in turn accelerate adaptation into both existing and emerging device modalities. It is anticipated that a similar materials design approach may be broadly applied to a variety of cationic and anionic compounds for drug delivery applications ranging from neurological disorders to cancer.

Electrophoretic drug delivery for seizure control

The persistence of intractable neurological disorders necessitates novel therapeutic solutions. We demonstrate the utility of direct in situ electrophoretic drug delivery to treat neurological disorders. We present a neural probe incorporating a microfluidic ion pump (μFIP) for on-demand drug delivery and electrodes for recording local neural activity. The μFIP works by electrophoretically pumping ions across an ion exchange membrane and thereby delivers only the drug of interest and not the solvent. This "dry" delivery enables precise drug release into the brain region with negligible local pressure increase. The therapeutic potential of the μFIP probe is tested in a rodent model of epilepsy. The μFIP probe can detect pathological activity and then intervene to stop seizures by delivering inhibitory neurotransmitters directly to the seizure source. We anticipate that further tailored engineering of the μFIP platform will enable additional applications in neural interfacing and the treatment of neurological disorders.

Conducting Polymer Scaffolds Based on Poly(3,4-ethylenedioxythiophene) and Xanthan Gum for Live-Cell Monitoring

Conducting polymer scaffolds can promote cell growth by electrical stimulation, which is advantageous for some specific type of cells such as neurons, muscle, or cardiac cells. As an additional feature, the measure of their impedance has been demonstrated as a tool to monitor cell growth within the scaffold. In this work, we present innovative conducting polymer porous scaffolds based on poly(3,4-ethylenedioxythiophene) (PEDOT):xanthan gum instead of the well-known PEDOT:polystyrene sulfonate scaffolds. These novel scaffolds combine the conductivity of PEDOT and the mechanical support and biocompatibility provided by a polysaccharide, xanthan gum. For this purpose, first, the oxidative chemical polymerization of 3,4-ethylenedioxythiophene was carried out in the presence of polysaccharides leading to stable PEDOT:xanthan gum aqueous dispersions. Then, by a simple freeze-drying process, porous scaffolds were prepared from these dispersions. Our results indicated that the porosity of the scaffolds and mechanical properties are tuned by the solid content and formulation of the initial PEDOT:polysaccharide dispersion. Scaffolds showed interconnected pore structure with tunable sizes ranging between 10 and 150 μm and Young's moduli between 10 and 45 kPa. These scaffolds successfully support three-dimensional cell cultures of MDCK II eGFP and MDCK II LifeAct epithelial cells, achieving good cell attachment with very high degree of pore coverage. Interestingly, by measuring the impedance of the synthesized PEDOT scaffolds, the growth of the cells could be monitored.

Conducting Polymer Iongels Based on PEDOT and Guar Gum

Conducting polymer hydrogels are attracting much interest in biomedical and energy-storage devices due to their unique electrochemical properties including their ability to conduct both electrons and ions. They suffer, however, from poor stability due to water evaporation, which causes the loss of mechanical and ion conduction properties. Here we show for the first time a conducting polymer gel where the continuous phase is a nonvolatile ionic liquid. The novel conducting iongel is formed by a natural polysaccharide (guar gum), a conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT), and an ionic liquid (IL) 1-butyl-3-methylimidazolium chloride (BMIMCl). First, an aqueous dispersion of PEDOT:guar gum is synthesized by an oxidative polymerization process of EDOT in the presence of the polysaccharide as stabilizer. The resulting PEDOT:guar gum was isolated as a powder by removing the water via freeze-drying process. In the final step, conducting iongels were prepared by the PEDOT:guar gum mixed with the ionic liquid by a heating-cooling process. The rheological properties show that the material exhibits gel type behavior between 20 and 80 °C. Interestingly, the conducting polymer iongel presents redox properties as well as high ionic conductivities (10^-2 S cm^-1). This material presents a unique combination of properties by mixing the electronic conductivity of PEDOT, the ionic conductivity and negligible vapor pressure of the ionic liquid and the support and flexibility given by guar gum.

Comparison of semi-batch vs. continuously fed anaerobic bioreactors for the treatment of a high-strength, solids-rich pumpkin-processing wastewater

The objective of this work was to compare two different high-rate anaerobic bioreactor configurations--the anaerobic sequencing batch reactor (ASBR) and the upflow anaerobic solid removal (UASR) reactor--for the treatment of a solid-rich organic wastewater with a high strength. The two, 4.5-L reactors were operated in parallel for close to 100 days under mesophilic conditions (37°C) with non-granular biomass by feeding a pumpkin wastewater with ∼4% solids. The organic loading rate of pumpkin wastewater was increased periodically to a maximum of 8 g COD L(-1) d(-1) by shortening the hydraulic retention time to 5.3 days. Compositional analysis of pumpkin wastewater revealed deficiencies in the trace metal cobalt and alkalinity. With supplementation, the ASBR outperformed the UASR reactor with total chemical oxygen demand (COD) removal efficiencies of 64% and 53%, respectively, achieving a methane yield of 0.27 and 0.20 L CH4 g(-1) COD fed to the ASBR and UASR, respectively. The better performance realized with the ASBR and this specific wastewater was attributed to its semi-batch, dynamic operating conditions rather than the continuous operating conditions of the UASR reactor.