Model of electrically stimulated hernia mesh electrode for soft tissue healing

Abstract

Hernia repair is a common surgery that repairs tissues that have torn due to strain, allowing the internal organs to protrude from the body cavity [1,2]. Hernioplasty, which is hernia repair surgery with incorporation of a mesh to prevent retearing by mechanically supporting the tissues, has various levels of success. Factors such as infection, comorbidities, and age all play a role in how quickly the body can recover. To allow the tissues to be strengthened more naturally, an incorporation of electrical stimulation of the tissues would encourage faster cellular proliferation and therefore wound healing for strengthening the soft tissues [3]. An alternating current (AC) that creates an electric field in the region surrounding a wound has shown in other studies to encourage cellular proliferation and faster healing [3-5]. Previous related research utilized piezoelectric materials to output small amounts of voltage by stimulating the piezoelectric material [6]. This output voltage has been shown to be achievable in soft tissues through transcutaneous medically safe 1MHz ultrasound waves stimulation of the piezoelectric material that mimic the effect of mechanical loading [7]. A literature review of stimulation of cells within soft tissue indicates that fibroblasts proliferate within a sinusoidal AC electric field range of 20-300 mV/mm [3-6]. In this study, the output created by ultrasound loaded piezoelectric device was incorporated into a computational COMSOL® model of a conductive hernia mesh. COMSOL®, a multiphysics finite element analysis software, was used to model the conductive electrode, determine voltage inputs and their resulting electric fields, and to test designs for creating a clinically relevant electric field stimulation within the proliferation range for fibroblasts. The model shows an electrically stimulated hernia mesh devised from the current methods of implanted polypropylene (PP) hernia mesh, by overlaying a thin gold surface onto the polymer mesh, which is proposed to be connected to a small piezoelectric device. For maximized area of stimulation, one of the electrode connection points is insulated from the body environment to conduct the positive and negative electrode points to opposite sides of the wound, creating an electric field across the wound site. Electrode materials for the mesh conductance layer were tested within the model, which showed similar electric fields for each material. The small differences were shown to be based on the material properties, which allowed higher or lower conductance through the surrounding solution, phosphate buffered saline. Gold was chosen to be the conductive metal based on its moderate electric field and biocompatibility. A range of possible output voltages from the piezoelectric device were also modeled in a voltage sweep to show the maximum and minimum electric fields the tissues would experience within the previously set range. When several set points in the electric field were measured at a value of Vin=100 mV, the electric field average was 5.93 ± 1.24. The overall electric field showed maximum values at the anode and cathode, but there was also stimulation midway between the nodes that could supply moderate stimulation to cells wherever they may lie within the electric field. It was concluded from these computations that a voltage of 20mV – 250mV should allow for increased tissue healing through cellular proliferation when connected to gold coated polypropylene hernia mesh.