An innovative passive knee prosthesis featuring discrete stiffness levels to provide adaptive support for sit-to-stand and overground walking

For decades, active knee prostheses have demonstrated their effectiveness in assisting people with transfemoral amputation with daily locomotion tasks. However, passive devices remain the preferred choice for most users due to their ease of use, affordability, energy independence, and adaptability to different gait patterns in everyday activities. One of the main challenges in creating unpowered prostheses is achieving support for a broad spectrum of locomotion tasks solely through passive mechanisms. Inspired by the emerging approach of layered prostheses with active as-needed assistance, we designed a passive knee prosthesis allowing level-ground walking and sit-to-stand-to-sit transitions. The core innovation of our concept lies in the use of four kinematically activated mechanisms to achieve various stiffnesses tailored to the selected task or its distinct phases (stance/swing). Following the conceptual design, analytical dimensioning has been conducted to verify structural resistance to typical loading patterns, supporting the viability of the overall device. Next, Finite Element Method simulations have been carried out, incorporating a higher level of complexity for a more accurate representation of real-world conditions. Finaly, the prototype has been fabricated and assembled , paving the way for extensive experimental validations. Initial assessments of the assembled system are currently ongoing, providing qualitative insights into its functionality. Next step of the validation procedure will adhere to ISO-standard testing protocols and additionally, will incorporate in-vivo tests with a newly prototyped able-bodied adapter for improved user fit.