Design of a multichannel indentation system for measuring biomechanical properties of forearm soft tissues in vivo

Accurate biomechanical measurement systems are critical tools in advanced prosthetic socket designs. However, an efficient active measurement system of soft tissues, particularly for amputees in vivo, has proved lacking and challenging since rapidly changeable force and deformation of soft tissues under slope retention tests have to be captured within minimum milliseconds. In this paper, we propose a multichannel indentation system with 8 active indentation units, 8 force sensors, and a high-speed control system. The forearm diameter is measured ranging from 10mm to 140mm, which satisfies the need for forearm amputees. The FSM (finite-state machine) based control system is also designed for enhancing safety and improving the real-time properties of data acquisition. The measurement accuracies and performance are verified respectively by an accuracy experiment using a high-precision load cell and a practical test experiment recruiting a forearm amputee. As a whole, the average linearity L, hysteresis H, and repeatability R of all the 8 channel indentation units are 0.34 (%F・S), 0.69(%F・S), and 0.99 (%F・S), respectively. The detected data from the practical experiment within 75s shows viscoelastic properties of the soft tissues. Results demonstrate that the proposed measurement system can be used for efficient biomechanical data acquisition of forearm soft tissue in vivo and has the potential clinical utility for forearm amputees.