Transfemoral prosthesis users typically perform the sit-to-stand motion unilaterally, placing minimal load on the prosthetic side. This increases the risk of injury and accelerates the degeneration of the intact limb. To address this, understanding compensation strategies is essential. Predictive neuromusculoskeletal modeling offers a method to investigate this. The aim of this study was to develop and validate a neuromusculoskeletal model with reflex-based muscle control to simulate the sit-tostand motion in non-amputees and transfemoral amputees with a passive prosthesis. We developed a three-dimensional sit-tostand musculoskeletal model of a non-amputee (20 degrees of freedom, 24 muscles) and a transfemoral amputee (20 degrees of freedom, 19 muscles), both incorporating a two-phase stand-up controller based on an existing two-dimensional reflex controller. We compared the simulation framework to measured kinematics, muscle activations, ground reaction forces, and existing literature on degrees of asymmetry and muscle forces. The developed framework was used to optimize prosthetic knee and ankle stiffness and damping for the sit-to-stand motion with a passive prosthesis. The simulated kinematics of the non-amputee matched measured kinematics. The prosthesis model indicated compensation strategies involving increased thoracic and lumbar extension, lumbar bending towards the non-amputated side,
increased pelvic tilt combined with decreased hip flexion, and heightened muscle activation and force. Optimization results suggested a knee stiffness of 0.1432 [Nm/deg] and damping of 0.0246 [Nm·s/deg], while the ankle required a stiffness of 0.1968 [Nm/deg] and damping of 0.1350 [Nm·s/deg]. These values are recommended for testing in future experiments.

Background: Pneumatic actuators are widely used in applications like (medical) robots, or prostheses. Pneumatic actuators require a complex manufacturing process and are produced in standardized dimensions to reduce costs. Over the last decade 3D-printing has emerged as a cost-effective and efficient production method in medical applications. 3D-printing can also function as a cost-efficient alternative production method for pneumatic actuators. Objective: The goal of this research is to study the possibility of creating a pneumatic linear actuator with 3D-printing. Furthermore, the aim is to use the advantage of 3D-printing to create pneumatic actuators with non-circular cross-sections. Methodology: To evaluate the performance of a 3D-printed pneumatic actuator, a test setup was designed and built to measure the leakage and sliding friction force. Furthermore, two pneumatic actuators with a non-conventional cross-sectional shape were designed and their performance was tested and compared with a 3D-printed cylindrical pneumatic actuator, since these tests only ran once, the results are more a guideline. During the manufacturing of the cylinders, no post-processing techniques were used. Results: The functioning of a 3D-printed circular pneumatic actuator was proven with low static leakage rates of 2.5%, low dynamic leakage rates of approximately 1%, and a maximum friction force of [Formula presented]. Furthermore, the results show that it is possible to print functioning pneumatic cylinders with a non-cylindrical concave cross-section. The non-conventional cylinders were tested up to [Formula presented] with maximum dynamic leakage of [Formula presented]. Conclusion: This study demonstrates a method to create functional pneumatic linear actuators with 3D-printing. It was possible to create 3D-printed actuators with a conventional shape, e.g. circular and unconventional shapes e.g. stadium/oval shape and a kidney shape. The leak rates for conventional and unconventional shapes were in the same range. This opens up the world for more design freedom in pneumatic actuators.

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