User-oriented novel electric upper limb prosthesis with flexible sensors for detecting skin deformation

Abstract

Conventional myoelectric hands need to detect muscle activities in stumps; therefore, they are not applicable in amputees with short stumps or with paralyzed limbs. We developed a novel electric upper limb prosthesis that functions without myoelectricity, based on the shape deformation of the amputated upper limb. This bioinstrument includes a bridge circuit and multiple amplifier circuits that are calibrated to amplify minute voltages from a skin sensor with multiple strain gauges placed on the soft and stretchy skin surface within a specified range of output voltages. The aim of this study is to compare the novel electric upper limb prosthesis with a conventional myoelectric hand (Myoboy system with System Electric Hand DMC plus, Ottobock). Eight healthy participants were enrolled in this study. Clinical evaluation of each hand was performed using the Simple Test for Evaluating Hand Function (STEF) and the Action Research Arm Test (ARAT). Additional tests based on activities of daily living, such as holding a ballpoint pen, grasping an eraser, holding a plastic bottle, and holding an umbrella, were also performed. Each hand was fixed to the participants’ forearm after placing sensors to detect myoelectricity or the shape deformation of the forearm. Performing the last 4 tasks of the STEF; that is, pinching small metallic circular disks, small wooden circular disks, small pins, and pieces of cloth—and the first task of ARAT; that is, grasping a big wooden block—was difficult with both prosthetic hands. The remaining tasks could be performed only with the novel prosthesis. We developed a novel prosthetic hand with unique sensors to detect skin deformation that enables better grasping than that with conventional myoelectric hands. Additional tests on activities of daily living will be effective in evaluating the function of this prosthesis.