Development of Two-Dimensional Biomechanical Modeling of the Thumb for Pipetting

The aim of this study is to develop a two-dimensional biomechanical static thumb model based on the posture of the hand using pipette. This model used hand anatomy and static equilibrium conditions to estimate internal tendon forces against a given external force. The input variables can be divided into two groups: 1) joint angle, external load and bone length, which are directly measured from the test; and 2) tendon force ratio and moment arm, which are adopted from previous studies. The thumb model was simulated using an FSR (forcesensing resistor) and validated using an Electromyography (EMG) system with four grip heights from 1 to 4 cm and with two tasks: Aspirating and Dispensing. A similar trend was observed between the simulation and EMG results. The average thumb pressure for Dispensing tasks is about 3.1 times greater than that for Aspirating, and the overall force efficiency ratio for both tasks is around 8 times the external load. The optimal grip height is 3 cm in terms of grip strength, 1 or 3 cm in terms of minimum internal force and 1 cm in terms of force efficiency. Overall, the optimal grip height is 1 or 3 cm.