Localized chemical release from an artificial synapse chip

Abstract

A device that releases chemical compounds in small volumes and at multiple, well defined locations would be a powerful tool for clinical therapeutics and biological research. Many biomedical devices such as neurotransmitter-based prostheses or drug delivery devices require precise release of chemical compounds. Additionally, the ability to control chemical gradients will have applications in basic research such as studies of cell microenvironments, stem cell niches, metaplasia, or chemotaxis. We present such a device with repeatable delivery of chemical compounds at multiple locations on a chip surface. Using electroosmosis to drive flow through microfluidic channels, we pulse minute quantities of a bradykinin solution through four 5-m apertures onto PC12 cells and show stimulation of individual cells using a Ca 2؉ -sensitive fluorescent dye. We also present basic computational results with experimental verification of both fluid ejection and fluid withdrawal by imaging pH changes by using a fluorescent dye. This ''artificial synapse chip'' is a prototype neural interface that introduces a new paradigm for neural stimulation, with eventual application in treating macular degeneration and other neurological disorders. D evices that can repeatedly release chemical compounds in small volumes and at multiple locations would be powerful clinical and laboratory tools. Some clinical therapeutics such as implantable drug-delivery devices (1) and neurotransmitterbased neural prostheses (2, 3) require the controlled release of chemical compounds. However, many of the current devices have limited control or repeatability. In addition, basic research requiring control over chemical gradients, such as studies of cell microenvironments (4-6), stem cell niches (7,8), metaplasia (9), or chemotaxis (10-12), can benefit from a general chemicalrelease device. In these areas of study, the local cellular environment plays a significant role in function; a device that enables control over cellular microenvironments may prove to be a powerful research tool.In this article, we present such a device, with repeatable delivery of chemical compounds at multiple locations on a chip surface. The device consists of an array of four 5-m circular apertures, each connected to a microfluidic channel. Using electroosmosis to drive fluid flow, we show ejection of minute quantities of a bradykinin solution through these apertures onto PC12 cells; with a Ca 2ϩ -sensitive fluorescent dye, we measure stimulation of individual cells. In addition, we use a finite element model to derive basic computational results and provide experimental verification of both fluid ejection and fluid withdrawal through imaging pH changes of a fluorescent dye.We labeled our device an ''artificial synapse chip.'' We built the device for application to a neurotransmitter-based retinal prosthesis, a device that, in essence, mimics a synapse by controlled, repeatable release of neurotransmitters. The use of neurotransmitters for stimulation instead of electric fields provides...

Cognitive Enhancement: Methods, Ethics, Regulatory Challenges

“…Development is rapid, both on the hardware side, where multielectrode recordings from more than 300 electrodes permanently implanted in the brain are currently state-of-the art, and on the software side, with computers learning to interpret the signals and commands (Nicolelis et al 2003;Shenoy et al 2003;Carmena et al 2003). Early experiments on humans have shown that it is possible for profoundly paralyzed patients to control a computer cursor using just a single electrode (Kennedy and Bakay 1998) implanted in the brain, and experiments by Parag Patil and colleagues have demonstrated that the kind of multielectrode recording devices used in monkeys would most likely also function in humans (Peterman et al 2004;Patil et al 2004). Experiments in localized chemical release from implanted chips also suggest the possibility of using neural growth factors to promote patterned local growth and interfacing (Peterman et al 2004).…”

“…Early experiments on humans have shown that it is possible for profoundly paralyzed patients to control a computer cursor using just a single electrode (Kennedy and Bakay 1998) implanted in the brain, and experiments by Parag Patil and colleagues have demonstrated that the kind of multielectrode recording devices used in monkeys would most likely also function in humans (Peterman et al 2004;Patil et al 2004). Experiments in localized chemical release from implanted chips also suggest the possibility of using neural growth factors to promote patterned local growth and interfacing (Peterman et al 2004).…”

Spatially resolved non-invasive chemical stimulation for modulation of signalling in reconstructed neuronal networks

“…The concept mentioned above has been advanced by Peterman et al (2004) and Takoh et al (2005). They developed a porous membrane-based substrate to provide localized chemical release of substances to cultured cells via a microfluidic interface from below.…”

“…Intercellular communications of cardiac myocytes cultured on porous polycarbonate membranes (Takoh et al 2005) were detected by observing cytosolic Ca 2C transients using fluo-4. The same detection method was employed to observe repeated stimulation of PC12 cells with bradykinin (Peterman et al 2004). In these experiments, the PC12 cells were cultured on silicon nitride membranes integrated into silicon chips.…”

Integrated flow sensing for focal biochemical stimulation

“…Microfluidic dosing devices have been introduced that enable selective stimulation of cells and study of cell membrane receptors and pathways [1][2][3][4][5][6]. Patterned laminar flows confined by polymer or glass microchannels demonstrate the microfluidic control of cell inactivation with cellular and sub-cellular resolution [1,4,5].…”