Patterned Live Neural Networks by Induced Electrical Fields for Bio-Sensing

It is estimated that about 18 million people worldwide suffer from dementia and it is projected to increase to about 35 million by the year 2025. All types of dementia occur due to an aberration in memory retention and development, caused by malfunctioning neurons. Experimental investigation of the dynamics of biological networks is a fundamental step towards understanding how the nervous system works. Activity-dependant modification of synaptic strength is widely recognized as cellular basis of learning, memory and developmental plasticity. Understanding memory formation and development, thus translates to changes in the electrical activity of the neurons. It is not possible to achieve this understanding at a cellular level by in vivo studies. To map the changes in the electrical activity it is essential to conduct in-vitro studies on individual neurons. Hence there is an enormous need to develop novel ways for assembly of highly controlled neuronal networks. To this end, we used a 5x5 multiple microelectrode array system to spatially arrange neurons, by combination of applied DC and AC fields We characterized electric field distribution inside our test platform by using two dimensional finite element modeling (FEM). As the first stage in the formation of a neural network dielectrophoretic AC fields were used to position the neurons over the electrodes. We used DC electric field to control axon growth direction within the network. Applied electric field direction is found to be an important parameter for axon growth. Electrical impulses were recorded from the individual neurons in the network during positioning and network formation. Materials and Methods We employed dielectrophoretic forces in our experiment to achieve the separation of neurons from glial cells. Dielectrophoretic cell separation exploits dielectrophoretic forces that are created on cells when a non uniform electrical field interacts with the fieldinduced electrical polarization on the cells. Depending on the dielectric properties of the cells relative to the suspending medium, these forces can be either positive or negative and can direct the cells toward strong or weak electrical field regions, where cells with distinct intrinsic dielectric properties can be controlled. Figure 1 depicts the principle of action of dielectrophoretic forces on mammalian cells. The Force equation for dielectrophoresis and the cross over frequency (fCM) are also shown. The cross over frequency is that frequency at which a particle does not experience any dielectrophoretic force for a given solution conductivity, applied amplitude and applied frequency. The substrate has a 5x5 electrode array pattern, with electrode diameter of 80mm with a 200mm center to center spacing and covering an area of 0.8x0.8 mm. Two platinum plated leads (6mm, thick) from each electrode terminate at two separate electrode pads. The dimension of the electrode pads are 100mm x 20mm. The electrode array is shown in figure 2. Figure 1. Representation of the principle of action of dielectrophoretic forces on mammalian cells. Figure 2. Optical micrograph of the 5x5 electrode array. 80 μm