In a groundbreaking study, researchers are paving the way for the design of prosthetic limbs that feel and move more naturally for users. This research, published in Science Robotics, highlights an exciting advancement in the field of bionics, demonstrating the connection between hand movement patterns and motoneuron control patterns. The study also reports the successful application of these findings to a soft prosthetic hand that was tested by individuals with physical impairments. The prosthetic hand showed promising results, achieving more natural movement and control than traditional prosthetic models.
The collaborative study, led by two prominent research teams from the Istituto Italiano di Tecnologia (IIT) in Genova, Italy, and Imperial College London, UK, is the outcome of the Natural BionicS project. This project aims to improve upon the limitations of current prosthetic limbs, which are often abandoned by patients due to their inability to respond naturally to the user’s movement and control needs.
The Need for Natural Interaction in Prosthetics
One of the key challenges in designing prosthetic limbs is ensuring that they can interact with the body in the same way as a natural limb. For a prosthesis to be considered truly natural by the central nervous system, it must be able to interact with the environment as a human limb would. This requires a seamless integration between the user’s nervous system and the prosthetic device.
Researchers believe the key to achieving this natural interface lies in the concept of sensorimotor synergies and soft robotics technologies. Antonio Bicchi, one of the leading researchers at IIT, and his team were among the first to propose this concept. They developed the Soft-Hand robotic hand, which uses soft robotics to mimic the behavior of a human hand more closely. The integration of these technologies, along with an understanding of the neural patterns that govern human movement, could enable the creation of prostheses that feel more like an extension of the body.
Understanding Synergies in Human Movement
To create prosthetics that interact with the nervous system in a natural way, researchers first needed to deepen their understanding of the body’s synergies. Synergies refer to the coordinated patterns of muscle activation and joint movements that allow the body to perform various movements efficiently and smoothly. At the core of this study, the researchers demonstrated for the first time how synergies at the level of spinal motoneurons and those in hand behaviors are interconnected.
The researchers found that hand postures and movements are not random but are the observable results of underlying neural patterns in the central nervous system. These patterns can be decoded from the electrical signals generated by our muscles, which are the peripheral signals of neural activity in the spinal cord. This breakthrough offers insights into how the brain controls movement at a deeper, more fundamental level.
By analyzing these electrical signals, researchers are now able to identify the specific groups of motoneurons responsible for different hand movements. These findings could significantly enhance our understanding of motor control and lead to more effective human-machine interfaces, which could bridge the gap between the biological and mechanical systems.
Designing Intuitive Prosthetics
The implications of these findings are profound. By decoding the neural activity that drives hand movements, researchers can create prosthetics that respond more naturally to the user’s intentions. Rather than relying on simplistic, pre-programmed motions, multi-synergistic robotic hands can now be co-designed with neural decoding algorithms, allowing users to control their prosthetics with greater precision and fluidity.
This is a significant step forward in creating prosthetic limbs that can perform a wide range of natural hand postures and execute complex tasks that are difficult or impossible for traditional prosthetics. With these innovations, users may be able to execute more dexterous tasks such as in-hand manipulation, which is often a challenge with current devices.
The research team specifically designed a soft prosthetic hand with two degrees of actuation to perform movements based on two primary postural synergies. This design was tested on 11 participants without physical impairments and three individuals who were prosthetic users. The results demonstrated that the prosthetic hand, when controlled using decoded neural signals, could perform a wide range of natural postures and complex movements with precision.
Real-Time Testing and Results
To achieve seamless control of the soft prosthetic hand, the researchers developed an advanced online method that maps the decoded neural synergies to the hand’s movements in real-time. This method allows the prosthetic hand to operate continuously and smoothly, ensuring that the user’s intentions are carried out with minimal effort.
The results of the tests were promising. By integrating both neural synergies (the patterns of muscle activity controlled by the spinal cord) and postural synergies (the patterns of hand behavior), the researchers were able to achieve precise and coordinated control of multidigit actions. This approach enabled the prosthetic hand to move more fluidly and naturally, mimicking the motion of a human hand more closely than previous models.
One of the standout achievements of this research is its focus on multidigit actions—complex tasks that require the coordinated movement of multiple fingers. These types of movements are challenging for traditional prosthetic hands, which often struggle with precision and coordination. However, by using the synergies identified in the study, the prosthetic hand was able to perform intricate tasks with ease, offering users a more natural experience.
The Path Forward: Empowering Prosthesis Users
The results of this research have profound implications for the future of prosthetics. By enabling prosthetics to mimic the natural movement patterns of the human hand, this research could dramatically improve the quality of life for prosthesis users. It offers them the possibility of achieving greater autonomy and performing everyday tasks with more ease and comfort.
The integration of neural synergies into prosthetics also represents a breakthrough in human-machine interfaces, moving us closer to a future where human bodies can seamlessly integrate with artificial devices. This approach could extend beyond prosthetics, potentially paving the way for cyborg technologies that enable humans to augment their abilities with robotic parts.
In the future, we may see further advancements in prosthetics that incorporate more degrees of freedom, enabling even more complex movements and tasks. Moreover, these innovations could help those with neurological conditions, such as spinal cord injuries or stroke, regain more control over their limbs and improve their overall quality of life.
As prosthetic technology continues to evolve, the research from this study represents an important milestone in the ongoing effort to create devices that are not just functional but that truly feel natural to their users. With the promise of more intuitive, flexible, and precise prosthetic limbs, the future of bionics looks brighter than ever.
Reference: Patricia Capsi-Morales et al, Merging motoneuron and postural synergies in prosthetic hand design for natural bionic interfacing, Science Robotics (2025). DOI: 10.1126/scirobotics.ado9509