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For years, traditional rigid prosthetic knees have been associated with challenges such as excessive weight, complex design, and discomfort, especially for those living with above-knee limb loss. However, recent advances in soft materials, robotics, and biomimicry have opened new avenues for developing solutions that are both functional and comfortable.
Researchers at Peking University have introduced an innovative prosthetic knee that promises to transform mobility for above-knee amputees. Unlike conventional metal designs, this new device employs origami-inspired soft robotics, offering a combination of flexibility, shock absorption, and affordability—all within a lightweight framework. The detailed findings of the study were published in December 2024 in Nature Communications.
What makes this design special?
Origami-Based Design
To mimic how a human knee works, researchers tapped into the principles of origami. By folding a thermoplastic polyurethane (TPU) structure using a precise crease pattern, the prosthetic knee mimics a portion of the instantaneous center of rotation (ICR) found in biological knees, especially during walking.
Horsetail-Inspired Load Stability
The team also drew inspiration from nature, specifically from horsetails—plants known for their strength. Horsetails have internal structures that use pressure and hollows to stay strong.
Similarly, the origami prosthetic knee contains small air chambers within its folds. When weight is applied, these chambers stiffen automatically, making the knee very strong yet lightweight—only about 300 grams—while supporting over 75 kilograms, which is roughly 250 times its own weight.
Enhanced Comfort via Shock Absorption
For comfort, the prosthetic knee features a soft, rubber-like chamber that absorbs shocks—about 11.5 to 17.3% better than rigid knee designs. This not only helps cushion the impact but also improves walking gait and reduces muscle strain for users, making it more comfortable and easier to use than traditional rigid prosthetic knees.
Real-World Use
The prosthetic knee is compact and easy to use, measuring just 15 centimeters in height and 12 centimeters in width. It’s manufactured using 3D printing, which keeps the cost low at under $200. And assembling it takes about two days.
The study’s benchtop tests demonstrated that the origami knee joint closely mimics the natural movement of a real knee. It can produce more than 25 Nm of torque, making it strong enough for daily activities. The device’s loading can also be adjusted using air pressure for different needs.
In trials with study participants, the researchers found that this prosthetic knee allowed people to walk naturally at both normal and faster speeds. They experienced less fatigue because the device is lightweight, which helped improve their walking symmetry. Additionally, the participants felt safe and confident navigating stairs, ramps, and obstacles.
Challenges and Opportunities
As with any breakthrough discovery, this origami-inspired prosthetic knee presents both challenges to overcome and opportunities to explore.
One challenge is ensuring that the soft knee prosthetic remains durable and can perform well over many steps. Researchers still need to test how it holds up during long-term use.
Another challenge is adapting the design for different users. The current lightweight and modular design works well, but it needs more development to fit fully powered prosthetic legs or children.
The origami-inspired design of this prosthetic knee is innovative, but it can only imitate some parts of typical knee movement. Still, it’s a promising step toward creating knee joints that move more like real human knees using origami structures.
Currently, the fastest speed at which an above-knee prosthetic user can walk with a soft knee is approximately 1.25 meters per second. This is slightly slower than the typical fast walking speed of 1.5 meters per second. However, this difference may be due to users still getting accustomed to how the soft knee works.
The bottom line
This prosthetic knee shows how ancient folding techniques and natural designs can inspire cutting-edge prosthetics. It’s lightweight, affordable, strong, and moves in a way that closely mirrors natural leg movement. As new technologies like soft robotics, origami-inspired structures, and air-powered systems come together, the future of prosthetics looks very promising and within reach.
