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-microm 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.

Fig. 1.

The artificial synapse chip. (A) Top view schematic of the multisite stimulation device (8 × 8 mm). The active area is on the bottom of the device. (B) Scanning electron micrograph of the device. (C) Higher-magnification scanning electron micrograph of the channel corners. The apertures are visible inside the channels, as indicated by the arrows. (D) Cutout schematic at the center of the device. The silicon and SU-8 layers have been removed from one corner, providing a view of the anisotropically etched well in which cells are cultured. (E) Illustration of the acrylic holder used to interface the devices. The polydimethylsiloxane gasket, acrylic base plate, and aluminum foil electrical contacts are shown.

Fig. 2.

Fluorescein bubble size variations as a function of time. (Left) Experimental scanning confocal micrographs at 0.0, 1.5, and 3.8 sec (n = 11). The applied potential began at 1.0 sec. (Scale bar, 25 μm.) (Right) Computational model for concentration above aperture in comparison with experimental data (black squares are data, and the solid red line is the model). The applied pulse is included on the plot in blue. [Reproduced with permission from ref. (copyright 2004, American Chemical Society).]

Fig. 3.

Sequential, multisite PC12 stimulation. (A) Single aperture PC12 stimulation. Scanning confocal micrographs of the device with PC12 cells before (Left), during (Center), and after (Right) stimulation. The channels were filled with combinations of Texas red and fluorescein dyes. The 20-μm circles are concentric with the 5-μm apertures. A fluid puff is visible at the active aperture, as indicated by the arrow in the middle frame. The last frame shows stimulated cells after a background subtraction. (Scale bar, 100 μm.) (B) Sequential, multisite PC12 stimulation. The frames display cell stimulation during sequential activation of three channels. The crosses indicate the location of the apertures, with red indicating the active aperture. The green circles are visual guides to indicate stimulated PC12 cells. A background from before stimulation was subtracted from each frame. (Scale bar, 100 μm.)

Fig. 4.

Repeat stimulation of two PC12 cells. The frame numbers are indicated, with red indicating the frame at which stimulation is activated. The arrows indicate the frames at which the stimulation is a maximum, always two frames after stimulation.