Researchers from Imperial College London in the UK and Istituto Italiano di Tecnologia in Italy show how hand and brain movement patterns are related, opening the door to creating bionic limbs that users will find comfortable. The European Research Council supported the study and published in Science Robotics.
Image Credit: Istituto Italiano di Tecnologia
Researchers are facilitating the development of artificial limbs that feel natural to users. They illustrate the relationship between motoneuron control patterns and hand movement patterns. The study also describes how these results were applied to a soft prosthetic hand that people with physical disabilities were able to test effectively.
Two research teams collaborate on the study: one led by Antonio Bicchi at the Istituto Italiano di Tecnologia (Italian Institute of Technology) in Genova, Italy, and another led by Dario Farina at Imperial College London, UK. It is the result of the European Research Council (ERC)-funded “Natural BionicS” project, which aims to go beyond the model of existing prosthetic limbs, which patients frequently give up because they do not respond “naturally” to their movement and control needs.
The prosthesis must interact with the surroundings in the same manner as a real limb for the central nervous system to perceive the bionic limb as “natural.” Because of this, researchers think that the design of prostheses should be founded on the notion of sensorimotor synergies and soft robotics technologies, like the Soft-Hand robotic hand, which was first developed by Antonio Bicchi's group at IIT.
Implications could extend beyond prostheses if a natural-feeling interface between our neural system and an artificial body is developed. For example, it could enable the seamless integration of human beings with robot components to help, empower, and extend ourselves.
For the first time, the study demonstrates the connection between two basic structures that organize the human body: synergies at the level of hand behaviors and those at the level of spinal motoneurons. The human body’s synchronized patterns of joint motions and muscle activation are known as synergies.
Researchers found that the visible results of underlying neural structures in the central nervous system can be translated as hand postures. These structures can be accessed and deciphered using sophisticated algorithms to the electric signals generated by muscles. The activation of the neural cells in the spinal cord that cause muscle contractions is manifested peripherally via these signals. Certain cell groups that underpin the hand behavior can be identified once the activity of these cells has been deciphered.
This finding improves the comprehension of the neural mechanisms that govern motor control and offers new possibilities for creating more intuitive and effective human-machine interactions. Researchers can now co-design multi-synergistic robotic hands and neural decoding algorithms, allowing prosthesis users to gain natural control over limitless postures and perform dexterous activities such as in-hand manipulation that would be impossible with other approaches.
More specifically, the researchers created a soft prosthetic hand with two degrees of actuation, allowing it to perform postures controlled by two basic postural synergies. This novel design was tested in real-time scenarios with 11 volunteers with no physical disabilities and three prosthesis users.
To accomplish seamless control, the scientists devised a sophisticated online approach that converts decoded brain synergies into continuous functioning of the two-synergy prosthetic hand. The findings revealed that integrating neurological and postural synergies enables precise, natural, and coordinated control of multidigit operations. This approach not only provides smoother and more intuitive movements but also marks a significant advancement in the development of prosthetic devices that closely resemble the functioning and fluidity of natural limbs.
These developments significantly impact prosthesis users’ quality of life by giving them more freedom and a more organic relationship with their prosthetic limbs.
Journal Reference:
Capsi-Morales, P., et. al. (2025) Merging motoneuron and postural synergies in prosthetic hand design for natural bionic interfacing. Science Robotics. doi.org/10.1126/scirobotics.ado9509