طراحی الکترود آرایه ای برای تحریک الکتریکی جلدی: یک مطالعه شبیه سازی

Array electrodes are a promising technology that is likely to bring transcutaneous electrical stimulation (TES) a step forward. The dynamic adaptation of electrode size and position helps to simplify the use of electrical stimulation systems and to increase their clinical efficacy. However, up to now array electrodes were built by trial and error and it is unclear how, for example, the gaps between the array elements or the resistivity of the electrode–skin interface material influence the current distribution. A TES model that comprises a finite element model and a nerve model has been used to analyze the influence of array electrode gaps and gel resistivities on nerve activation. Simulation results indicate that the resistivity of the electrode–skin interface layer should be adapted depending on the size of the gaps between the array elements. Furthermore, the gap sizes should be smaller than 3 mm in order to keep losses small.

In transcutaneous electrical stimulation (TES) pairs of surface electrodes are placed on the skin in order to stimulate motor nerves. Clinically, TES is often applied in the rehabilitation of stroke subjects or spinal cord injured subjects [1], or for supporting tasks of daily living [2] using so called neuroprostheses. In the past such neuroprostheses used single stimulation electrodes [3] and [4]. Recently array electrodes were proposed to improve the efficacy of such TES systems [5] and [6]. Array electrodes consist of multiple elements which can be individually activated to form a virtual electrode of arbitrary size and location. The position and size of the activated region (virtual electrode) can be dynamically changed [7] and [8]. For good wearability textile array electrodes are produced by embroidering silver coated fibers in the form of array electrodes into garments [9]. One large layer of self-adhesive hydrogel is used as skin interface between the skin and the array electrode [10]. The gaps between array elements and the resistivity of the interface layer (gel) influence the current distribution flowing into the human limb. In previous works the sizes of the gaps between array elements and the resistivity of the gel layer were chosen intuitively [5], [6] and [10]. In this paper a TES model comprising a finite element (FE) and a nerve model is used in order to analyze and better understand the influence of the gap sizes and the gel resistivity on nerve activation. Using the TES model it was investigated how large the gaps are allowed to be and how this decision is related to the choice of the gel resistivity. Previously, the indifferent electrode (anode) was placed separately from the array [5] and [6]. However, in [9] it was shown that the active (cathode) and the indifferent electrode (anode) can be placed on the same array. This simplifies the application of TES because only one electrode has to be applied to the human body instead of one array plus a separate indifferent electrode. Obviously, a part of the applied current is lost because it will directly flow from the cathode to the anode through the hydrogel. It is unclear how much of the applied current is lost in the gel layer depending on different parameters (e.g., gel resistivity, skin resistivity, …). To address these issues different parameter combinations were applied to the TES model in order to quantify and to reduce these losses.