The TF8 actuator is an untethered, lower-extremity powered-prostheses designed to replicate biological kinetic and kinematic function of ankles. An energy optimal hardware specification was found by kinematically clamping walking gait data to the dynamic model of a series elastic actuator (SEA). We searched for a minimal electrical energy configuration of motor, reduction ratio, and spring, subject to specified constraints and ultimately discretely available components. The outcome translated into a mechanical design that heavily weighted the importance of mechanical energy storage in springs. The resulting design is a moment-coupled cantilever-beam reaction-force SEA (RFSEA) that has a nominal torque rating of 85Nm, peak torque of 175Nm, 105 degree range of motion, and a hardware mass of 1.6kg.

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For persons with lower extremity (LE) amputation, acquisition of surface electromyography (sEMG) from within the prosthetic socket remains a significant challenge due to the dynamic loads experienced during the gait cycle. However, these signals are critical for both understanding the clinical effects of LE amputation and determining the desired control trajectories of active LE prostheses. Current solutions for collecting within-socket sEMG are generally (i) incompatible with a subject's prescribed prosthetic socket and liners, (ii) uncomfortable, and (iii) expensive. This study presents an alternative within-socket sEMG acquisition paradigm using a novel flexible and low-profile electrode. First, the practical performance of this Sub-Liner Interface for Prosthetics (SLIP) electrode is compared to that of commercial Ag/AgCl electrodes within a cohort of subjects without amputation. Then, the corresponding SLIP electrode sEMG acquisition paradigm is implemented in a single subject with unilateral transtibial amputation performing unconstrained movements and walking on level ground. Finally, a quantitative questionnaire characterizes subjective comfort for SLIP electrode and commercial Ag/AgCl electrode instrumentation setups. Quantitative analyses suggest comparable signal qualities between SLIP and Ag/AgCl electrodes while qualitative analyses suggest the feasibility of using the SLIP electrode for real-time sEMG data collection from load-bearing, ambulatory subjects with LE amputation.

Background Neuroprosthetic devices controlled by persons with standard limb amputation often lack the dexterity of the physiological limb due to limitations of both the user’s ability to output accurate control signals and the control system’s ability to formulate dynamic trajectories from those signals. To restore full limb functionality to persons with amputation, it is necessary to first deduce and quantify the motor performance of the missing limbs, then meet these performance requirements through direct, volitional control of neuroprosthetic devices. Methods We develop a neuromuscular modeling and optimization paradigm for the agonist-antagonist myoneural interface, a novel tissue architecture and neural interface for the control of myoelectric prostheses, that enables it to generate virtual joint trajectories coordinated with an intact biological joint at full physiologically-relevant movement bandwidth. In this investigation, a baseline of performance is first established in a population of non-amputee control subjects ($$n = 8$$ n = 8 ). Then, a neuromuscular modeling and optimization technique is advanced that allows unilateral AMI amputation subjects ($$n = 5$$ n = 5 ) and standard amputation subjects ($$n = 4$$ n = 4 ) to generate virtual subtalar prosthetic joint kinematics using measured surface electromyography (sEMG) signals generated by musculature within the affected leg residuum. Results Using their optimized neuromuscular subtalar models under blindfolded conditions with only proprioceptive feedback, AMI amputation subjects demonstrate bilateral subtalar coordination accuracy not significantly different from that of the non-amputee control group (Kolmogorov-Smirnov test, $$P \ge 0.052$$ P ≥ 0.052 ) while standard amputation subjects demonstrate significantly poorer performance (Kolmogorov-Smirnov test, $$P < 0.001$$ P < 0.001 ). Conclusions These results suggest that the absence of an intact biological joint does not necessarily remove the ability to produce neurophysical signals with sufficient information to reconstruct physiological movements. Further, the seamless manner in which virtual and intact biological joints are shown to coordinate reinforces the theory that desired movement trajectories are mentally formulated in an abstract task space which does not depend on physical limb configurations.

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We present an actuator designed for untethered, lower-extremity powered-prostheses that replicates biological kinetic and kinematic function of both human knees and ankles. An electric energy optimal hardware specification is defined by kinematically clamping walking gait data to the dynamic model of a series elastic actuator (SEA) and searching for motor, reduction ratio, and spring. The actuator is shown to achieve the required torque, angle, and velocity requirements for nominal walking conditions on level ground as well as varied terrain. The performance of the actuator is demonstrated on benchtop and as worn by a human subject with unilateral below knee amputation. The resulting design is a moment-coupled cantileverbeam reaction-force SEA (MC-RFSEA) that has a nominal torque rating of 85Nm, repeated peak torque of 175Nm, 105 o range of motion, and a hardware mass of 1.6kg. Preliminary results from level-ground walking with the actuator tested in an ankle configuration show an electric cost of transport of 0.053J/kg when walking at 1.5m/s.