Electrokinetic confinement of axonal growth for dynamically configurable neural networks

Abstract

Axons in the developing nervous system are directed via guidance cues, whose expression varies both spatially and temporally, to create functional neural circuits. Existing methods to create patterns of neural connectivity in vitro use only static geometries, and are unable to dynamically alter the guidance cues imparted on the cells. We introduce the use of AC electrokinetics to dynamically control axonal growth in cultured rat hippocampal neurons. We find that the application of modest voltages at frequencies on the order of 105 Hz can cause developing axons to be stopped adjacent to the electrodes while axons away from the electric fields exhibit uninhibited growth. By switching electrodes on or off, we can reversibly inhibit or permit axon passage across the electrodes. Our models suggest that dielectrophoresis is the causative AC electrokinetic effect. We make use of our dynamic control over axon elongation to create an axon-diode via an axon-lock system that consists of a pair of electrode `gates' that either permit or prevent axons from passing through. Finally, we developed a neural circuit consisting of three populations of neurons, separated by three axon-locks to demonstrate the assembly of a functional, engineered neural network. Action potential recordings demonstrate that the AC electrokinetic effect does not harm axons, and Ca2+ imaging demonstrated the unidirectional nature of the synaptic connections. AC electrokinetic confinement of axonal growth has potential for creating configurable, directional neural networks.

Brain cells and neuronal networks: Encounters with controlled microenvironments

“…In short, microfluidic and electric fields can be combined to control neuronal connectivity [127]. In this line, the next section deals with the control of neuronal architectures combined with the implementation of recording/stimulation electronics.…”

“…Adhesive patterns in the millimeter range have also been employed to create another type of axonal diodes: in the work of Feinerman et al [126], the 50 lm wide restricted contact zones joining millimeter sized triangles induced a preferential unidirectional crossing of the axons toward the tip of these geometric shapes. Dielectrophoresis was also used to dynamically control axonal growth through electrical axon-lock [127]. By a ''Stop and go'' electrokinetic effect on axonal growth, configurable and directional mature neural networks between up to three different neuronal compartments were implemented (Fig.…”

Thermal effect of dielectrophoresis manipulation on cerebrospinal fluid

“…Consequently, the use of intensive electrical fields in direct contact with brain tissue leads to a temperature increase which may have an impact on the conductivity of CSF and other side effects. In fact, recent advances in microfabrication has resulted in very compact microelectrodes which can produce intensive electrical fields with a lower voltage as in the case with recent dielectrophoresis-based devices to monitor neuronal activities [4]. Indeed Honegger et al, showed in their work that it was possible to dynamically control axonal growth in cultured rat hippocampal neurons through the use of AC electrokinetics.…”

A cell-based sensor of fluid shear stress for microfluidics

“…In another flow regime, many devices are meant to apply very low flow rates for long durations. Typical examples of such microfluidic devices are those used for long-term static 5 or perfusion cell culture 6, 7 .…”