MEMS-based microelectrode technologies capable of penetrating neural tissues

Due to the high spatial selectivity and resolution with high accessibility to single neurons, penetrating neural electrodes have been used for neuronal recording or stimulation in specific applications although they are invasive, thus inducing more inflammatory response and damages to the tissue, compared to non-penetrating electrodes. Penetrating electrodes are mainly made up of stiff materials such as metal wires, silicon, or glass. Compared to microwire electrodes, siliconbased penetrating electrodes are fabricated in precise designs and dimensions, often in forms of array with higher number of independent channels. Although precise 2-D and 3-D electrode structures are used in many applications, efforts to make them more biocompatible and long-lasting have been reported recently. On the other hand, soft materials such as polymers have also been lately used in penetrating electrodes to accommodate their flexibility and mechanical properties that are more favorable to neural tissues, minimizing adverse effects on tissues. Polymer-based electrodes are promising for future applications where better biocompatibility is required although technical hurdles in using them in long term have to be overcome.