Integration of pre-aligned liquid metal electrodes for neural stimulation within a user-friendly microfluidic platform

Abstract

Electrical stimulation of nervous tissue is used clinically for the treatment of multiple neurological disorders and experimentally for basic research. With the increase of optical probes to record neuronal activity, simple and user-friendly methods are desired to stimulate neurons and their subcellular compartments for biological experimentation. Here we describe the novel integration of liquid metal electrodes with microfluidic culture platforms to accomplish this goal. We integrated electrode and cell channels into a single poly(dimethylsiloxane) (PDMS) chip, eliminating entirely the need to align electrodes with microchannels. We designed the electrode channels such that the metal can be injected by hand and when the device is non-covalently bound to glass. We demonstrated the biocompatibility of the electrodes for long-term cultures (12 days) using hippocampal neurons. We demonstrated the use of these electrodes to depolarize neurons and recorded neuronal activity using the calcium indicator dye, Fluo-4. We established optimal stimulation parameters that induce neuronal spiking without inducing damage. We showed that the liquid metal electrode evoked larger calcium responses in somata than bath electrodes using the same stimulus parameters. Lastly we demonstrated the use of these liquid metal electrodes to target and depolarize axons. In summary, the integration of liquid metal electrodes with neuronal culture platforms provides a user-friendly and targeted method to stimulate neurons and their subcellular compartments, thus providing a novel tool for future biological investigations.

Electrophoretic Deposition of Gallium with High Deposition Rate

“…The deposition rate is almost one order of magnitude higher than the previously-reported deposition rate of electroplating (~ 0.067 μm/min) [11]. Relatively thick (e.g., tens of μm) Ga films can be desirable in many applications, including liquid metal electrodes [8,9] and micro switches [10]. Sequential deposition was performed to verify such capability of the reported method and address the concern of self-limited deposition caused by the non-conductive holding layer, which is intentionally kept without being rinsed in this case.…”

“…Gallium and its compounds can find many applications in microelectronics [1], solar cells [2,3], solar water splitting [4,5], microwave circuitry [6], optoelectronics [7], flexible neuroprobes [8], self-repairing electrodes [9], and micro switches [10]. Considerable efforts have already been made to OPEN ACCESS deposit gallium thin films, which typically involve electroplating with highly toxic gallium salts.…”

Cloning SU8 silicon masters using epoxy resins to increase feature replicability and production for cell culture devices

“…Viability was assessed using live/dead stains as described previously. 21 . Neurons grown on SU8-Si derived PDMS chambers were used as a reference control (Fig.…”

“…Hippocampal cells were prepared from embryonic day 17-18 Sprague Dawley embryos of either sex as described previously. 21,22 We used 5-10 ll of cell suspension per well at a density of 12 million cells/ml.…”

Generating electric fields in PDMS microfluidic devices with salt water electrodes

“…Liquid metals, which have both the conductivity of solder and are liquid at room temperature like salt solutions, have also been used for electrodes in microfluidic devices 19,20 . One such liquid metal is Galistan, which freezes at −19°C and is by weight 68% Ga, 22% In, and 10% Sn.…”