The transradial amputation has changed little through recent decades. The procedure is designed just to provide padding for socket comfort and secondarily to allow those muscles to generate myoelectric control signals. With improvements in microsurgery, it has become possible to perform advanced residual limb reconstruction by including neural interfaces that leverage the body's inbuilt neural feedback mechanisms to create a post-amputation residuum with efferent and afferent signaling more similar to the intact limb than under existing techniques, enabling greatly enhanced embodiment and control of a prosthetic limb.
Specifically, by connecting naturally opposed muscles in series to construct the "pulley" of an AMI, muscle mechanoreceptors are activated during volitional movement of the phantom limb and produce proprioceptive afferent signals. Thus, the sensation of movement of the joint is preserved. This antagonist muscle structure additionally provides a mechanism for modulating the impedance of the phantom joint, as the sum of absolute torques produced about the joint determines stiffness while only the net of those torques controls acceleration. The AMI thus enables biomechanically relevant control strategies.
The provision of touch feedback is also possible with the inclusion of the CMI. Cutaneous afferents can be produced when a muscle actuator contracts to cause strain in a skin graft from the fingertips. As the construct preserves the dermis, a full range of cutaneous sensation from the different mechanoreceptors in the skin are elicited. With muscle actuators natively recruited during grasping, graded touch feedback can even be felt reflexively.
In this project, we seek to modify the amputation procedure to include at least one AMI construct for each digit in the hand and for the wrist, and to incorporate CMI construction for all digits. Together, these interfaces contribute to the development of a bionic limb that is capable not only of voluntary efferent control, but also meaningfully senses objects manipulated in the hand.