Prosthetic device is designed to function as a replacement for a missing limb and typically consists of suspension, liner, socket, pylon and foot components. The objectives of this research are to design a pylon component of a transtibial prosthetics by implementing auxetic metamaterial and to also validate performance of the designed pylon under quasi-static and dynamic conditions. The design and analysis processes are conducted using the finite element analysis and its effectiveness is validated by experimental testing of the prototype pylon sample. In the design process, the pylon structure is formulated by rearranging 2D re-entrant hexagon model into 3D model. It is identified from the design evaluation that the pylon exhibits the stiffness of the value of 79.24, 2371.6, and 13344 kN/m for the ligament thickness variation of 0.3 mm, 1 mm, and 2 mm, respectively. This directly indicates a capability of the stiffness tuning of the pylon by changing the ligament thickness. It is evaluated that the pylon with the ligament thickness of 0.3 mm causes the deformation of 0.53 cm during a single period of gait cycle, while the ligament thickness of the 1 mm causes the deformation of 0.4 cm. The deformation physically indicates the energy absorption of the pylon structure and hence the thinner ligament, the higher energy absorption provides. It is also found from the deformation transition of the primary and secondary bends, the negative Poisson’s ratio is occurred in 3D model transformed from 2D re-entrant hexagon.

Background: The standard surgical approach to amputation has failed to evolve significantly over the past century. Consequently, standard amputations often fall short with regards to improving the quality-of-life (QoL) for patients. A modified amputation has been designed at both the transtibial (TTA) and transfemoral (TFA) level that incorporates agonist-antagonist myoneural interface (AMI) constructs to provide patients with a novel alternative to standard amputation. Here, we present the patient reported outcome measures (PROMs) amongst our lower extremity AMI amputees and demonstrate an overall significant improvement in their physical and mental wellbeing. Methods: Four PROMs surveys, 1) EQ-5D-3L, 2) Lower Extremity Functional Scale (LEFS), 3) PROMIS-57, 4) Short Form-36 (SF-36), and 5) Sickness Impact Profile (SIP), were administered to lower extremity AMI amputees pre-operatively (baseline) and at 6 weeks, 3 months, 6 months, 9 months, 12 months, 24 months, 36 months, and 48 months post-operatively between June 24th, 2018, and December 15th, 2022. The surveys were either administered during a clinic visit or emailed at the encounter timepoint. Study data was collected and managed using REDCap (Research Electronic Data Capture) electronic data capture tools hosted at Brigham and Women’s Hospital. Analyses of collated data were performed by fitting a linear mixed model using SAS version 9.4 (SAS Institute, Cary, NC). Results: The cohort’s baseline and 12-month post-operative responses were compared to determine score improvement. The cohort demonstrated a significantly improved EQ-5D-3L index value (p<0.0001) and EQ VAS (p<0.0001) at 12-months post-operatively (n=22) when compared to baseline (n=28). The LEFS score significantly improved at 12-months post-operatively compared to baseline (p<0.0001) with a mean of 59.04 ± 3.14 (SE) at 12-months and a mean of 31.96 ± 2.84 (SE) at baseline. AMI patients demonstrated significantly improved scores across PROMIS-57 domains at 12-months compared to baseline scores; the p-value was <0.0001 for all domains except for the Depression domain where p=0.0181. The health domain scores significantly improved from baseline to 12-months post-operation for all SF-36 domains. Lastly, the SIP indicated a significant decrease in overall dysfunction from baseline to 12-months post-operation (p<0.0001). Conclusions: Modified lower extremity amputation with AMI construction has the potential to provide amputees with increased quality-of-life when compared to the pre-operative state. However, further investigation is necessary to determine whether the patient reported outcome measures of the AMI amputee cohort are superior to those who receive a standard amputation.

Powered ankle prostheses have been proven to improve the walking economy of people with transtibial amputation. All commercial powered ankle prostheses that are currently available can only perform one-degree-of-freedom motion in a limited range. However, studies have shown that the frontal plane motion during ambulation is associated with balancing. In addition, as more advanced neural interfaces have become available for people with amputation, it is possible to fully recover ankle function by combining neural signals and a robotic ankle. Accordingly, there is a need for a powered ankle prosthesis that can have active control on not only plantarflexion and dorsiflexion but also eversion and inversion. We designed, built, and evaluated a two-degree-of-freedom (2-DoF) powered ankle-foot prosthesis that is untethered and can support level-ground walking. Benchtop tests were conducted to characterize the dynamics of the system. Walking trials were performed with a 77 kg subject that has unilateral transtibial amputation to evaluate system performance under realistic conditions. Benchtop tests demonstrated a step response rise time of less than 50 milliseconds for a torque of 40 N·m on each actuator. The closed-loop torque bandwidth of the actuator is 9.74 Hz. Walking trials demonstrated torque tracking errors (root mean square) of less than 7 N·m. These results suggested that the device can perform adequate torque control and support level-ground walking. This prosthesis can serve as a platform for studying biomechanics related to balance and has the possibility of further recovering the biological function of the ankle-subtalar-foot complex beyond the existing powered ankles.