Soft Synergy-Based Artificial Hand for Prosthetic Applications

Project: Research project

Project Details


Specific Aims The human hand is critically important for performance of many activities of daily living (ADL), including selffeeding, tool use, and recreation. Therefore, loss of the hand due to traumatic injury or disease significantly limits persons with limb loss ability to perform ADL and work, thus greatly affecting overall quality of life. In the U.S., one person in 200 has lost a limb3. While worldwide statistics are more difficult to estimate, the WHO estimates 16% of amputations affect the upper extremity48. The significance of this problem is exemplified by efforts made over the past few decades in designing engineering solutions to maximize the functionality of prosthetic hands, ranging from relatively simple body-powered (i.e., split hook) prostheses to more advanced myoelectric prostheses controlled by electromyographic (EMG) activity of forearm muscles. Despite advances in hand prostheses design and research, several barriers remain against widespread acceptance of prosthetic hands by persons with limb loss. The adult rejection rate for myoelectric upper limb prostheses is estimated at 23%5. Non-wear and passive use of upper limb prostheses (regardless of type) is estimated at 20 and 27%, respectively5. Level of limb loss is one the most significant factors in prosthesis acceptance25, although this is likely largely caused by associated technological challenges. The two most significant deterrents to prosthetic use are prostheses limited functionality, e.g., limited ability to perform ADL, and comfort, which includes fit and weight of prosthesis5, 25. Additional factors associated with abandonment of hand prostheses are durability of the prosthetic hand; lack of sensory feedback; cost, which can be significant when considering both the initial and maintenance costs of the more sophisticated hand prostheses, i.e., myoelectric models; and the aesthetic appearance of the prosthetic hand7. Therefore, todays commercially available hand prostheses fail to address the needs of individuals with limb loss, i.e., regaining some degree of autonomy and functionality, and re-entering the work force. To address the above gaps in hand prosthetic research and access to persons with limb loss, we propose to design a new prosthetic hand, the University of Pisa/IIT SoftHand (SH), based on the recently proposed approach of soft synergies. This approach, which capitalizes on the combination of the concept of human hand synergies and novel soft robotics technologies, has introduced a new viewpoint on prosthesis design. The functionality of this new design has been preliminarily demonstrated by one of the co-investigators, Dr. Antonio Bicchi. The SH was originally designed and implemented for robotics applications. However, the SH design is biologically inspired as it embeds experimental observations by the PI and colleagues of how humans coordinate motion at multiple joints of the digits during grasping of a wide variety of object shapes and sizes10. Our recent modeling work has identified important advantages of using the concept of hand synergies as an approach for robotics and applications to prosthetic grasp control8. The SH hand uses a radically new technology based on soft robotics and adaptive mechanics27. Most importantly, preliminary tests of the SH on intact individuals suggest that it can be used to grasp a wide variety of common objects with very limited training and minimum cognitive load for the user. Furthermore, the SH is mechanically simple and resistant to large impacts. However, a number of important steps have to be taken to adapt the current design of the SH to that of a functional and effective prosthetic hand. We will pursue the following aims: Specific Aim 1: To quantify the functional capabilities of the Pisa/IIT SoftHand for prosthetic applications on intact individuals. Preliminary data suggest that the SH is extremely versatile and can be used to grasp and manipulate common objects. We will perform extensive testing of the myoelectric SH by asking intact subjects (controls) to perform a wide variety of ADL tasks. We will also determine the extent to which grasping performance benefits from adding force feedback capabilities. These data will be used by the Mayo Clinic and the IIT research teams to modify the SH design to adapt it for use by persons with limb loss (Aim 2) while focusing on the SH socket design, EMG-based control, and force feedback interface. Specific Aim 2: To quantify the functional capabilities of the modified Pisa/IIT SoftHand on persons with limb loss. We will quantify the ability of patients with transradial amputation to perform the same tasks tested in Aim 1 using the prosthetic version of the SH. The best-performing force feedback modality identified in Aim 1 will be implemented in the prosthetic SH. We hypothesize that patients will learn to use the SH and perform grasp and manipulation tasks with greater proficiency than allowed by their current terminal devices. The long-term objectives of this exploratory study are to design and build a low-cost and high-performance hand prosthesis that will be accepted by patients with transradial amputation, and enable performance of a wider range of ADL tasks than allowed by todays commercially available prostheses. The data collected through the proposed studies will provide an important foundation for optimizing the design of the SH prosthesis for testing on a large number of persons with limb loss. Future studies will also assess the extent to which the SHs functionality and acceptance might benefit from embedding additional synergistic digit motion patterns in the prosthesis.
Effective start/end date8/31/147/31/17


  • HHS: National Institutes of Health (NIH): $398,834.00

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