Overcoming transport limitations in miniaturized electrophoretic delivery devices

Organic electronic ion pumps (OEIPs) have been used for delivery of biological signaling compounds, at high spatiotemporal resolution, to a variety of biological targets. The miniaturization of this technology provides several advantages, ranging from better spatiotemporal control of delivery to reduced invasiveness for implanted OEIPs. One route to miniaturization is to develop OEIPs based on glass capillary fibers that are filled with a polyelectrolyte (cation exchange membrane, CEM). These devices can be easily inserted and brought into close proximity to targeted cells and tissues and could be considered as a starting point for other fiber-based OEIP and iontronic technologies enabling favorable implantable device geometries. While characterizing capillary OEIPs we observed deviations from the typical linear current-voltage behavior. Here we report a systematic investigation of these irregularities by performing experimental characterizations in combination with computational modelling. The cause of the observed irregularities is due to concentration polarization established at the OEIP inlet, which in turn causes electric field-enhanced water dissociation at the inlet. Water dissociation generates protons and is typically problematic for many applications. By adding an ion-selective cap that separates the inlet from the source reservoir this effect is then, to a large extent, suppressed. By increasing the surface area of the inlet with the addition of the cap, the concentration polarization is reduced which thereby allows for significantly higher delivery rates. These results demonstrate a useful approach to optimize transport and delivery of therapeutic substances at low concentrations via miniaturized electrophoretic delivery devices, thus considerably broadening the opportunities for implantable OEIP applications.Funding Agencies|Swedish Foundation for Strategic Research; Advanced Functional Materials SFO-center at Linkoping University; Onnesjo Foundation; Knut and Alice Wallenberg Foundation</p

An electronic proton-trapping ion pump for selective drug delivery

The organic electronic ion pump (OEIP) delivers ions and charged drugs from a source electrolyte, through a charge-selective membrane, to a target electrolyte upon an electric bias. OEIPs have successfully delivered γ-aminobutyric acid (GABA), a neurotransmitter that reduces neuronal excitations, in vitro, and in brain tissue to terminate induced epileptic seizures. However, during pumping, protons (H+), which exhibit higher ionic mobility than GABA, are also delivered and may potentially cause side effects due to large local changes in pH. To reduce the proton transfer, we introduced proton traps along the selective channel membrane. The traps are based on palladium (Pd) electrodes, which selectively absorb protons into their structure. The proton-trapping Pd-OEIP improves the overall performance of the current state-of-the-art OEIP, namely, its temporal resolution, efficiency, selectivity, and dosage precision.Funding agencies:Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research; Swedish Research CouncilSwedish Research CouncilEuropean Commission; Advanced Functional Materials SFO-Center at Linkoping University; Onnesjo Foundation; Knut and Alice W</p

Segmental expression of Hoxa-2 in the hindbrain is directly regulated by Krox-20

The hindbrain is a segmented structure divided into repeating metameric units termed rhombomeres (r). The Hox family, vertebrate homologs of the Drosophila HOM-C homeotic selector genes, are expressed in rhombomere-restricted patterns and are believed to participate in regulating segmental identities. Krox-20, a zinc finger gene, has a highly conserved pattern of expression in r3 and r5 and is functionally required for their maintenance in mouse embryos. Krox-20 has been shown to directly regulate the Hoxb-2 gene and we wanted to determine if it was involved in regulating multiple Hox genes as a part of its functional role. Hoxa-2 is the only known paralog of Hoxb-2, and we examined the patterns of expression of the mouse Hoxa-2 gene with particular focus on r3 and r5 in wild type and Krox-20(-/-) mutant embryos. There was a clear loss of expression in r3, which indicated that Hoxa-2 was downstream of Krox-20. Using transgenic analysis with E. coli lacZ reporter genes we have identified and mapped an r3/r5 enhancer in the 5' flanking region of the Hoxa-2 gene. Deletion analysis narrowed this region to an 809 bp BglII fragment, and in vitro binding and competition assays with bacterially expressed Krox-20 protein identified two sites within the enhancer. Mutation of these Krox-20 sites in the regulatory region specifically abolished r3/r5 activity, but did not affect neural crest and mesodermal components. This indicated that the two Krox-20 sites are required in vivo for enhancer function. Furthermore, ectopic expression of Krox-20 in r4 was able to transactivate the Hoxa-2/lacZ reporter in this rhombomere. Together our findings suggest that Krox-20 directly participates in the transcriptional regulation of Hoxa-2 during hindbrain segmentation, and is responsible for the upregulation of the r3 and r5 domains of expression of both vertebrate group 2 Hox paralogs. Therefore, the segmental phenotypes in the Krox-20 mutants are likely to reflect the role of Krox-20 in directly regulating multiple Hox genes.link_to_OA_fulltex

Flexible Organic Electronic Ion Pump for Flow-Free Phytohormone Delivery into Vasculature of Intact Plants

Plant vasculature transports molecules that play a crucial role in plant signaling including systemic responses and acclimation to diverse environmental conditions. Targeted controlled delivery of molecules to the vascular tissue can be a biomimetic way to induce long distance responses, providing a new tool for the fundamental studies and engineering of stress-tolerant plants. Here, a flexible organic electronic ion pump, an electrophoretic delivery device, for controlled delivery of phytohormones directly in plant vascular tissue is developed. The c-OEIP is based on polyimide-coated glass capillaries that significantly enhance the mechanical robustness of these microscale devices while being minimally disruptive for the plant. The polyelectrolyte channel is based on low-cost and commercially available precursors that can be photocured with blue light, establishing much cheaper and safer system than the state-of-the-art. To trigger OEIP-induced plant response, the phytohormone abscisic acid (ABA) in the petiole of intact Arabidopsis plants is delivered. ABA is one of the main phytohormones involved in plant stress responses and induces stomata closure under drought conditions to reduce water loss and prevent wilting. The OEIP-mediated ABA delivery triggered fast and long-lasting stomata closure far away from the delivery point demonstrating systemic vascular transport of the delivered ABA, verified delivering deuterium-labeled ABA

pH Dependence of γ‑Aminobutyric Acid Iontronic Transport

The organic electronic ion pump (OEIP) has been developed as an “iontronic” tool for delivery of biological signaling compounds. OEIPs rely on electrophoretically “pumping” charged compounds, either at neutral or shifted pH, through an ion-selective channel. Significant shifts in pH lead to an abundance of H⁺ or OH^–, which are delivered along with the intended substance. While this method has been used to transport various neurotransmitters, the role of pH has not been explored. Here we present an investigation of the role of pH on OEIP transport efficiency using the neurotransmitter γ-aminobutyric acid (GABA) as the model cationic delivery substance. GABA transport is evaluated at various pHs using electrical and chemical characterization and compared to molecular dynamics simulations, all of which agree that pH 3 is ideal for GABA transport. These results demonstrate a useful method for optimizing transport of other substances and thus broadening OEIP applications

Design and Operation of Hybrid Microfluidic Iontronic Probes for Regulated Drug Delivery

Highly controlled drug delivery devices play an increasingly important role in the development of new neuroengineering tools. Stringent - and sometimes contradicting - demands are placed on such devices, ranging from robustness in freestanding devices, to overall device miniaturization, while maintaining precise spatiotemporal control of delivery with high chemical specificity and high on/off ratio. Here, design principles of a hybrid microfluidic iontronic probe that uses flow for long-range pressure-driven transport in combination with an iontronic tip that provides electronically fine-tuned pressure-free delivery are explored. Employing a computational model, the effects of decoupling the drug reservoir by exchanging a large passive reservoir with a smaller microfluidic system are reported. The transition at the microfluidic-iontronic interface is found to require an expanded ion exchange membrane inlet in combination with a constant fluidic flow, to allow a broad range of device operation, including low source concentrations and high delivery currents. Complementary to these findings, the free-standing hybrid probe monitored in real time by an external sensor is demonstrated. From these computational and experimental results, key design principles for iontronic devices are outlined that seek to use the efficient transport enabled by microfluidics, and further, key observations of hybrid microfluidic iontronic probes are explained.Additional Funding agencies: FLAG‐ERA. Grant Number: JTC2017; EPIGRAPH. Grant Number: ANR‐17‐GRF2‐0001; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linköping University. Grant Number: 2009‐00971; A*MIDEX ION. Grant Number: 2IONXXID/REID/ID17HRU208</p