Dec 152010

Chemical stimulation using channels in a so-called “puffer” neural probe has been a challenging endeavor, originated by Prof. Kendal Wise’s laboratory in U. Michigan back in 1997. The early probes were fabricated using the reactive ion etching (RIE) technology, and despite their initial promise, so far have not been successfully used in chronic animal studies.  Multiple issues, ranging from the outlet biofouling to the hydraulic resistance inside a microfluidic channel, have been identified. A commercial probe combining the drug delivery and electrical recording/stimulation was recently developed by the NeuroNexus Technologies (D/DM-series); it consists of the silicone probe glued to the fused silica fluidic channel. Opting for an integrated probe solution, engineers at the Institute of Micromachining and Information Technology and the Institute of Microsystem Technology at the University of Freiburg etched the channels with heights of 50 µm and more inside the wafer using the deep RIE (DRIE) technology. Their effort is a part of the NeuroProbes project, funded by a European Sixth Framework Programme (FP6), which includes 13 other partners from Belgium, Germany, Sweden, Switzerland, UK, Italy, France, Hungary, Spain, and Netherlands. The probes, fabricated by German engineers, remained unclogged in an acute in vivo test, while the chronic implant studies are still ongoing. The fluid pumping action inside the microfluidic channels was achieved by a MEMS device built into the probe. The MEMS device functions by constricting fluid-filled micro-chambers (volume = 0.25 μL each) using a thermally expandable material coupled to heating microelements. The microchambers are connected in series and can be constricted individually with a 3-second temporal precision. Having the chemical stimulation and electrical recording on the same probe, may soon allow a detailed examination the chemical signaling inside the brain in vivo with a high spatiotemporal precision.

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