Geometric Properties and Hand Grasping Dynamics: a Useful Approach to Bionic Hands

Physical properties such as shape, volume, and size influence the dynamics of biological systems. In this context, we focus on the geometric properties of limb movements and their physiological and biomechanical effects. Using hand grasping as a paradigmatic example, we describe how dynamic changes in geometric configuration can affect the pathophysiology of grasping. We focus on precision pinch, the simplest and most basic form of grasping, where one finger remains stable while another moves against it (Brand and Hollister, 1999). The thumb and index finger come together to grasp small objects with great precision, such as a pen. During the precision pinch, the geometric configuration of the hand changes, modifying the distribution of forces and the functional connectivity between the fingers. These changes may offer a new approach to the biomechanics of artificial arms. While current approaches consider grasps as homogeneous structures, we argue that local variations in hand geometry can lead to new biomedical effects with intriguing operational implications.