On-demand local release of biomolecules enables fine-tuned stimulation for the next generation of neuromodulation therapies. Such chemical stimulation is achievable using iontronic devices based on microfabricated, highly selective ion exchange membranes (IEMs). Current limitations in processability and performance of thin film LEMs hamper future developments of this technology. Here we address this limitation by developing a cationic IEM with excellent processability and ionic selectivity: poly(4-styrenesulfonic acidco-maleic acid) (PSS-co-MA) cross-linked with polyethylene glycol (PEG). This enables new design opportunities and provides enhanced compatibility with in vitro cell studies. PSSA-co-MA/PEG is shown to out-perform the cation selectivity of the previously used iontronic material.

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.

Technologies that restore or augment dysfunctional neural signaling represent a promising route to deeper understanding and new therapies for neurological disorders. Because of the chemical specificity and subsecond signaling of the nervous system, these technologies should be able to release specific neurotransmitters at specific locations with millisecond resolution. We have previously demonstrated an organic electronic lateral electrophoresis technology capable of precise delivery of charged compounds, such as neurotransmitters. However, this technology, the organic electronic ion pump, has been limited to a single delivery point, or several simultaneously addressed outlets, with switch-on speeds of seconds. We report on a vertical neurotransmitter delivery device, configured as an array with individually controlled delivery points and a temporal resolution of 50 ms. This is achieved by supplementing lateral electrophoresis with a control electrode and an ion diode at each delivery point to allow addressing and limit leakage. By delivering local pulses of neurotransmitters with spatiotemporal dynamics approaching synaptic function, the high-speed delivery array promises unprecedented access to neural signaling and a path toward biochemically regulated neural prostheses.

Current neural interfaces rely on electrical stimulation pulses to affect neural tissue. The development of a chemical delivery technology, which can stimulate neural tissue with the bodys own set of signaling molecules, would provide a new level of sophistication in neural interfaces. Such technology should ideally provide highly local chemical delivery points that operate at synaptic speed, something that is yet to be accomplished. Here, the development of a miniaturized ionic polarization diode that exhibits many of the desirable properties for a chemical neural interface technology is reported. The ionic diode shows proper diode rectification and the current switches from off to on in 50 mu s at physiologically relevant electrolyte concentrations. A device model is developed to explain the characteristics of the ionic diode in more detail. In combination with experimental data, the model predicts that the ionic polarization diode has a delivery delay of 5 ms to reach physiologically relevant neurotransmitter concentrations at subcellular spatial resolution. The model further predicts that delays of amp;lt;1 ms can be reached by further miniaturization of the diode geometry. Altogether, the results show that ionic polarization diodes are a promising building block for the next generation of chemical neural interfaces.