Limb amputation causes severe loss of motor and sensory function for about 2 million Americans. Current limb prostheses (artificial body parts), which are all worn externally on the body, fall short of restoring realistic motor and sensory function. This is partly because most external prostheses remain physically detached from muscles, which play a key role in generating and sensing movements in biological limbs. To facilitate physical muscle-prosthesis attachment, this CAREER project will develop “endoprostheses,†which are limb prostheses that can be fully implanted within living skin. Such muscle-driven endoprostheses (MDEs) represent an important, essential step toward limb prostheses whose function and appearance are indistinguishable from those of the biological limb. Eventually, MDEs could dramatically improve the function, independence, and quality of life for people living with amputation and other severe musculoskeletal defects due to trauma or cancer tissue removal. The project will integrate research and education activities to provide research and career development training to talented graduate and undergraduate students, to develop interactive, hands-on education modules that teach project-related biomedical engineering concepts to K-12 students and to provide opportunities for involving high school students in the research.
The principal investigator's overarching research goal is to develop and promote clinical translation of muscle-driven endoprostheses (MDEs), jointed skeletal devices that are implanted within skin and physically attached to muscles, which will enable anatomically realistic musculoskeletal reconstruction and restore near-normal sensorimotor function. Towards this goal, this CAREER project will design and quantify the motor function of an MDE prototype to replace the hindlimb foot and ankle in an animal (rabbit) model. The project's central hypothesis is that an MDE prototype with one degree of freedom (ankle dorsi/plantar flexion) and attached to select lower limb muscles (gastrocnemius, soleus, and tibialis anterior) can contribute to locomotion. The prototype will consist of rigid tibial and foot segments, bone pins to anchor the MDE in the tibia bone, the ankle joint, an over-molded silicone sleeve and suture-based synthetic tendons that will be used to attach muscles to foot segments. The Research Plan is organized under two thrusts. The FIRST Thrust is to create computational musculoskeletal models to identify an MDE prototype design to replace the rabbit hindlimb ankle that can meet the biomechanical demands of locomotion and determine the relative influence of MDE design parameters on motor function. Steps include compiling musculoskeletal data needed to construct the rabbit model (architecture, geometry, kinematics, elastic properties, etc.), implementing the musculoskeletal data in OpenSim, validating the model for the intact-limb situation, using numerical optimization methods to identify the optimal MDE geometry and performing biomechanical sensitivity analysis to determine the relative influence of design parameters. The SECOND Thrust is to iteratively implant pre-MDE and MDE prototypes in a rabbit model and assess the resulting motor function. Iterative experiments include implanting a series of pre-MDE prototypes that each includes a subset of features of the MDE prototype. After each successful implantation, the size and number of features will be increased. The iterative design facilitates identifying and addressing potential issues with the prototypes. Steps include using Computer Aided Design (CAD) and finite-element analysis (FEA) to define geometry and estimate mechanical stresses and strains, fabricating prototypes, radiography, surgery, recovery and tissue evaluation. Motor Function recovery experiments include following a formal rehabilitation protocol, testing locomotion to determine the extent to which the rabbits choose to load and move the ankle during a functional task and testing biomechanical capacity by measuring the capacity of the ankle independent of how the rabbits choose to use it during locomotion. Research outcomes are expected to address two critical questions: 1) do residual muscles have sufficient biomechanical capacity to generate joint torque and displacement to enable useful motor function with MDEs? and 2) can patients adapt their neuromuscular control to use an MDE effectively to perform motor tasks?
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
