Peking University, February 25, 2025: Inspired by the horsetail structure, a research team at Peking University has developed the world’s first soft prosthetic knee. Their ingenious lower-limb prosthetic design was recently published in Nature Communications under the title “Bioinspired origami-based soft prosthetic knees”, with Ph.D. student Gao Siyuan as first author and Professor Wang Qining as corresponding author, both from the Department of Advanced Manufacturing and Robotics, College of Engineering, Peking University.

Why it matters:

In contrast to the rigid, high-density metallic mechanics of knee prosthetics, soft materials enable lighter, more flexible designs with better compliance and impact absorption. However, challenges such as inefficient deformation under load have hindered their application of in prosthetics. The new design overcomes these limitations with an innovative solution.

What’s new:

1.Origami-based mechanism: The soft prosthetic knee features an origami structure, reinforced with polymer blocks and a connection system for the thigh and calf. Weighing only 300g and standing at 15cm, the prosthetic’s design allows for a broad range of motion, meeting the dynamic movement needs of the knee.

Origami-based soft prosthetic knee

2.Polycentric rotation: The team introduces a fold structure that mimics the human knee’s polycentric rotation. By adjusting design parameters, the prosthetic achieves highly accurate joint movement that replicates natural knee function.

3.Horsetail-inspired stabilized soft structure: To enhance the prosthetic’s weight-bearing capacity, the back-fold structure creates a pneumatic chamber, simulating the hydraulic pressure of horsetail cells. Reinforced folds reduce unnecessary deformation, improving the accuracy of motion control.

Horsetail-inspired stabilized soft structure

Results:

1.Benchtop testing: The prosthetic demonstrated precise movement under pneumatic control, with performance closely matching theoretical predictions. It also absorbed impact forces by 11.5% to 17.3%, held the weight of over 75kg (250 times its weight) and generated more than 25Nm of torque.

Benchtop testing result

2.Clinical testing: In treadmill walking tasks, participants were able to walk at both normal and fast speeds with improved gait symmetry, experiencing less fatigue and lower impact. Additionally, the prosthetic performed well in multi-terrain and outdoor scenarios, such as walking on stairs and ramps, and crossing obstacles.

Different ambulation tasks with the soft prosthetic knee

Significance:

This innovation represents a paradigm shift in lower-limb prosthetics, offering a flexible, lightweight, and customizable solution for the development of soft robotics by integrating advanced materials, drives, and sensors. The use of 3D printing and other modern manufacturing techniques in prosthetic design opens up possibilities to reduce costs and accelerate the development of next-generation prosthetics.

Link to the paper: https://www.nature.com/articles/s41467-024-55201-1

Written by: He Yike
Edited by: Zhang Jiang
Source: PKU Wechat (Chinese)