Strategies for optimizing urea removal to enable portable kidney dialysis: A reappraisal.

Background: Portable hemodialysis has the potential to improve health outcomes and quality of life for patients with kidney failure at reduced costs. Urea removal, required for dialysate regeneration, is a central function of any existing/potential portable dialysis device. Urea in the spent dialysate coexists with non-urea uremic toxins, nutrients, and electrolytes, all of which will interfere with the urea removal efficiency, regardless of whether the underlying urea removal mechanism is based on urease conversion, direct urea adsorption, or oxidation.

Solid-Binding Peptide-Guided Spatially Directed Immobilization of Kinetically Matched Enzyme Cascades in Membrane Nanoreactors.

Biocatalysis is a useful strategy for sustainable green synthesis of fine chemicals due to its high catalytic rate, reaction specificity, and operation under ambient conditions. Addressable immobilization of enzymes onto solid supports for one-pot multistep biocatalysis, however, remains a major challenge. In natural pathways, enzymes are spatially coupled to prevent side reactions, eradicate inhibitory products, and channel metabolites sequentially from one enzyme to another.

Electrically controlled nicotine delivery through Carbon nanotube membranes via electrochemical oxidation and nanofluidically enhanced electroosmotic flow.

A promising tool for nicotine addiction treatment is a programmable nicotine delivery device coupled to smart phone-assisted behavioral therapies. Key metrics for such a device are delivery of adjustable nicotine doses tailored to individual needs, compact size and power efficiency. Reported here is a detailed optimization of carbon nanotube (CNT) membrane fabrication based on electrochemical oxidation, to improve its electrically driven performance for nicotine fluxes and switching ON (-1.

Catalytic Reduction of Graphene Oxide Membranes and Water Selective Channel Formation in Water-Alcohol Separations.

Graphene oxide (GO) is a promising membrane system for chemical separation applications due to its 2-D nanofluidics properties and an ability to control interplanar spacing for selectivity. The permeance of water, methanol (MeOH) and isopropyl alcohol (IPA) through 5 µm thick membranes was found to be 0.38 ± 0.

Smoking Cessation Potential of Smartphone-Assisted Behavioral Therapy Coupled to Programmable Carbon Nanotube Membrane Nicotine Delivery Device.

Smoking tobacco continues to be a worldwide major cause of premature death. Although combined behavioral and pharmacotherapy interventions can increase the smoking cessation rate to nearly 25%, the combined approach is generally economically unattainable, and the low success rate leaves large populations at risk. Reviewed are treatments following primarily the principles of cognitive behavioral therapy (CBT) and nicotine replacement therapy (NRT), based on an addiction disease model with reduced dopamine receptors.

A preclinical evaluation of a programmable CNT membrane device for transdermal nicotine delivery in hairless Guinea pigs.

Nicotine replacement therapy in the form of transdermal nicotine patches and nicotine gums combined with behavioral counseling still has a low smoking cessation rate of 25%. A promising approach to smoking cessation is to remotely program variable transdermal nicotine delivery rates, with inputs from counselor and patient through a smartphone counseling application. A switchable carbon nanotube (CNT) membrane device has been developed for transdermal nicotine delivery that can be programmed to deliver variable doses matching those of nicotine patches (7, 14 and 21 mg/24 h) and nicotine gums (2 mg /4 mg).

Monolayer Growth Front of Precious Metals through Insulating Mesoporous Membranes.

Monolayers of precious metals are deposited within the pores of insulating mesoporous anodized aluminum oxide (AAO) membranes via a new electrochemical underpotential Cu deposition growth front mechanism, followed by spontaneous galvanic replacement of copper by platinum or iridium as demonstrated by XPS, ICP-OES, conductivity, and current analysis. Applications include fuel cells, hydrogen storage, flow batteries, and electrocatalytic conversions.

Programmable carbon nanotube membrane-based transdermal nicotine delivery with microdialysis validation assay.

To evaluate the performance of switchable carbon nanotubes (CNT) membrane devices for transdermal nicotine delivery, we have developed an in-vitro microdialysis method that allow us to detect variable transdermal fluxes of nicotine through CNT devices and can be applied directly to in-vivo studies. Microdialysis membranes were placed beneath the porcine skin and its nicotine levels increased 6-8 times when the CNT membrane on skin was turned from OFF to ON state by application of bias. Fluxes in the ON state were approximately 3 times that of commercial nicotine patches and switching times were less than two hours, thus suggesting the improved therapeutic potential of our device.

Flow-Through Electroporation of HL-60 White Blood Cell Suspensions using Nanoporous Membrane Electrodes.

A flow-through electroporation system, based on a novel nanoporous membrane/electrode design, for the delivery of cell wall-impermeant molecules into model leukocytes, HL-60 promyelocytes, was demonstrated. The ability to apply low voltages to cell populations, with nm-scale concentrated electric field in a periodic array, contributes to high cell viability. With applied biases of 1-4V, delivery of target molecules was achieved with 90% viability and up to 65% transfection efficiency.

Dynamic Electrochemical Membranes for Continuous Affinity Protein Separation.

A membrane system with nm-scale thick electrodes is able to selectively bind genetically modified proteins and pump them across the membrane with sequential voltage pulses. The electrodes are located at the first 20nm of pore entrances to specifically capture targeted proteins and block non-specific protein transport through the pores during the binding cycle. During the release cycle, concentration of imidazole is controlled to keep the pore blocked while releasing proteins at the bottom edge of the electrode.

Functionalized anodic aluminum oxide membrane-electrode system for enzyme immobilization.

A nanoporous membrane system with directed flow carrying reagents to sequentially attached enzymes to mimic nature’s enzyme complex system was demonstrated. Genetically modified glycosylation enzyme, OleD Loki variant, was immobilized onto nanometer-scale electrodes at the pore entrances/exits of anodic aluminum oxide membranes through His6-tag affinity binding. The enzyme activity was assessed in two reactions—a one-step “reverse” sugar nucleotide formation reaction (UDP-Glc) and a two-step sequential sugar nucleotide formation and sugar nucleotide-based glycosylation reaction.

Programmable transdermal clonidine delivery through voltage-gated carbon nanotube membranes.

Oral dosage forms and traditional transdermal patches are inadequate for complex clonidine therapy dosing schemes, because of the variable dose/flux requirement for the treatment of opioid withdrawal symptoms. The purpose of this study was to evaluate the in vitro transdermal flux changes of clonidine in response to alterations in carbon nanotube (CNT) delivery rates by applying various electrical bias. Additional skin diffusion studies were carried out to demonstrate the therapeutic feasibility of the system.

Single-step electrochemical functionalization of double-walled carbon nanotube (DWCNT) membranes and the demonstration of ionic rectification.

Carbon nanotube (CNT) membranes allow the mimicking of natural ion channels for applications in drug delivery and chemical separation. Double-walled carbon nanotube membranes were simply functionalized with dye in a single step instead of the previous two-step functionalization. Non-faradic electrochemical impedance spectra indicated that the functionalized gatekeeper by single-step modification can be actuated to mimic the protein channel under bias.

Programmable transdermal delivery of nicotine in hairless guinea pigs using carbon nanotube membrane pumps.

A compact switchable transdermal nicotine patch device was demonstrated to be effective in vivo in a hairless guinea pig animal model. This required the development and validation of a quantitative method for the simultaneous determination of cotinine and nicotine in hairless guinea pig plasma by liquid chromatography-mass spectrometry. Nicotine metabolism in hairless guinea pigs is rapid and cotinine was found to be the viable nicotine marker.

Ionic rectification by electrostatically actuated tethers on single walled carbon nanotube membranes.

Large electrostatically actuating charged tethers (~2.5 nm) at the tip entrances of single walled carbon nanotubes (i.d.

Electrochemical water oxidation with carbon-grafted iridium complexes.

Hydrogen production from water splitting provides a potential solution to storing harvested solar energy in chemical fuels, but this process requires active and robust catalysts that can oxidize water to provide a source of electrons for proton reduction. Here we report the direct, covalent grafting of molecular Ir complexes onto carbon electrodes, with up to a monolayer coverage. Carbon-grafted Ir complexes electrochemically oxidize water with a turnover frequency of up to 3.

Electrophoretically induced aqueous flow through single-walled carbon nanotube membranes.

Electrophoresis, the motion of charged species through liquids and pores under the influence of an external electric field, has been the principle source of chemical pumping for numerous micro- and nanofluidic device platforms. Recent measurements of ion currents through single or few carbon nanotube channels have yielded values of ion mobility that range from close to the bulk mobility to values that are two to seven orders of magnitude higher than the bulk mobility. However, these experiments cannot directly measure ion flux.

Highly efficient electroosmotic flow through functionalized carbon nanotube membranes.

Carbon nanotube membranes with inner diameter ranging from 1.5-7 nm were examined for enhanced electroosmotic flow. After functionalization via electrochemical diazonium grafting and carbodiimide coupling reaction, it was found that neutral caffeine molecules can be efficiently pumped via electroosmosis.

Mass transport through carbon nanotube membranes in three different regimes: ionic diffusion and gas and liquid flow.

Transport phenomena through the hollow conduits of carbon nanotubes (CNTs) are subjects of intense theoretical and experimental research. We have studied molecular transport over the large spectrum of ionic diffusion to pressure-driven gaseous and liquid flow. Plasma oxidation during the fabrication of the membrane introduces carboxylic acid groups at the CNT entrance, which provides electrostatic "gatekeeper" effects on ionic transport.

Catalytic Activity of Ultrathin Pt Films on Aligned Carbon Nanotube Arrays.

Uniform ultrathin Pt films were electrodeposited onto an aligned array of carbon nanotubes (CNTs) for high-area chemically stable methanol fuel cell anodes. Electrochemical treatment of the graphitic CNT surfaces by diazoniumbenzoic acid allowed for uniform Pt electroplating. The mass activity of the Pt thin film can reach 400 A/g at a scan rate of 20 mV/s and in a solution of 1 M CHOH/0.

Electrophoretic transport of biomolecules through carbon nanotube membranes.

Electrophoretic transport of proteins across electrochemically oxidized multi-walled carbon nanotube (MWCNT) membranes has been investigated. A small charged protein, lysozyme, was successfully pumped across MWCNT membranes by an electric field while rejecting larger bovine serum albumin (BSA). Transport of lysozome was reduced by a factor of about 30 in comparison to bulk mobility and consistent with the prediction for hindered transport.

Programmable transdermal drug delivery of nicotine using carbon nanotube membranes.

Carbon nanotube (CNT) membranes were employed as the active element of a switchable transdermal drug delivery device that can facilitate more effective treatments of drug abuse and addiction. Due to the dramatically fast flow through CNT cores, high charge density, and small pore dimensions, highly efficient electrophoretic pumping through functionalized CNT membrane was achieved. These membranes were integrated with a nicotine formulation to obtain switchable transdermal nicotine delivery rates on human skin (in vitro) and are consistent with a Fickian diffusion in series model.