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

International audienceNew and highly specific drug delivery tools will facilitate a better understanding of the complex neurobiological environment, and pave the way to highly localized and precise drug delivery technology. To work optimally, such devices need to achieve great chemical and biotarget specificity, while simultaneously limiting biocompatibility issues or pharmaceutical side effects. If these devices are implemented as minimized free-standing probes, they can easily be manipulated to target specific cells or be combined with different experimental setups and sensing technologies to facilitate a wide range of diagnostic and therapeutic capabilities, in particular at deep tissue/organ sites. [3] Here, we compare the capabilities and limitations of two high precision drug delivery techniques, pressure-based microfluidics, and iontronics. In microfluidics, drug transport is highly controlled by regulation of fluidic pressure in miniaturized fluid channels. [4,5] By connecting several fluidic sources and microfabricated fluid channels, mixing, switching, screening, and delivery of various drugs can be easily achieved. The field of microfluidics includes a multitude of experimental setups from lab-on-a-chip devices to free standing microfluidic neural probes. [4,6] The other technique of interest is iontronics, where regulation of applied potentials enables precise dose control and chemical specificity, as long as the drug or neurotransmitter of interest is positively or negatively charged. [7] The most basic iontronic component is the organic electronic ion pump (OEIP). OEIPs are based on a well-defined and encapsulated ion exchange membrane (IEM) separating a source electrolyte reservoir from a target electrolyte (generally referred to as the "ion channel"). Broadly speaking, selectivity of the IEM is dependent on the inherent polarity of the fixed charge, its degree of charge, and its pore size and density. Transport from the source reservoir, through the IEM ion channel, and to the target electrolyte is achieved actively by migration of ions and passive diffusion. By varying an applied potential across the IEM, the migrational ionic delivery rate is controlled electronically and a direct correspondence in applied electronic current and quantity of drug delivered can be established. Planar OEIP devices have been successfully demonstrated for a variety of neurological applications, e.g., by delivery of gamma-aminobutyric acid to suppress epileptiform activity. [8