Hybrid bionic systems for the replacement of hand function

In recent years, thanks to the advancement of robotics and mechatronics, new and more effective devices for the restoration and replacement of sensory-motor function in disabled people have been developed. In all these systems, user acceptability is strictly connected to several issues such as the residual abilities of the subject, the mechatronic characteristics of the robot, and also the interface chosen to link them. It is possible to figure out different "human-interface-device" combinations [also defined as "hybrid bionic systems" (HBSs)] characterized by different properties in terms of level of hybridness, connection, and augmentation. In particular, in HBSs the interface has to be customized according to the characteristics of the robotic artefact to be controlled and to the desires and needs of the final users. In this paper, our attention has been focused on the problem of the replacement of hand function after amputation. Three HBSs characterized by different levels of complexity, dexterity, and sensorization are presented in order to show the possibility of developing acceptable and effective systems.by choosing different levels of connection and hybridness (i.e., different interfaces) for different devices and applications. The following case studies are presented: 1) the use of invasive interfaces to the peripheral nervous system to control a dexterous and highly sensorized hand prosthesis; 2) the use of electromyographic signals recorded using surface electrodes to control a compliant adaptive prosthesis; and 3) the use of a foot interface to control a two-degrees-of-freedom prosthesis. The preliminary results achieved so far seem to confirm the idea that the correct choice of the proper interface while developing an HBS can increase effectiveness and usability.