New bionic leg allows amputees to walk easily, it is light, powerful and can generate its own electricity

In life, everyone may encounter some misfortunes to a greater or lesser extent, such as car accidents, fires, diseases, etc., which may cause certain material losses.

Worse still, these misfortunes could cause millions, or even more, of people to lose the limbs that enable them to move, making them unable to obtain spiritual satisfaction in a world of material abundance.

Now, a new type of bionic leg (powered prosthetic leg) promises to greatly increase the mobility of amputees.

A team of researchers from the University of Utah has developed a bionic leg for amputees that has biomechanical knee, ankle and toe joints. The leg is lightweight and can regenerate energy as the wearer walks, extending the operating time of its internal battery.

Moreover, preclinical trials have shown that the bionic leg can perform common walking activities with close to standard kinematics and dynamics, helping amputees walk on level ground and stairs.

The related research paper, titled “A lightweight robotic leg prosthesis replicating the biomechanics of the knee, ankle, and toe joint,” was published as a cover article in the scientific journal Science Robotics. Tommaso Lenzi, assistant professor of mechanical engineering at the University of Utah, is the corresponding author of the paper.

(Source: Science Robotics)

It is reported that the bionic leg is expected to support amputees to walk 15,460 steps on a full charge (the average number of steps for a normal person is 7,500-10,000 per day). It is suitable for amputees with a height between 1.60-1.91 meters and a weight between 59-91 kilograms.

Lightweight, flexible, self-generating

As the name suggests, bionic legs can improve the mobility and quality of life of patients with limb amputations by mimicking the biomechanics of the missing limb.

However, in previous studies, most prosthetic limbs used by patients with above-knee amputations are passive devices controlled by microprocessors, which cannot well replicate the key biomechanical functions of the missing biological leg, such as actively generating movement or injecting energy into the gait cycle.

In addition, biomechanical simulations and non-computerized individual experiments have shown that the ankle joint of the leg can provide considerable net positive energy during walking. If the ankle joint is damaged or missing, the amputee must compensate for the missing ankle energy by increasing the strength of the residual limb and the intact limb, resulting in an unnatural, asymmetric, or even ineffective gait pattern.

Therefore, for amputees, walking with ordinary prostheses is quite strenuous, and climbing stairs, climbing slopes, standing up, sitting down, etc. is also more challenging.

(Source: Pixabay)

Although traditional powered prostheses can provide a certain amount of power for amputees, they are also heavier and larger than passive prostheses and have shorter battery life, which greatly limits their clinical feasibility and practicality.

In previous research, Lenzi's team developed a lightweight powered exoskeleton that uses motors, microprocessors and advanced algorithms to help lower-limb amputees walk, just as an electric bicycle helps a rider pedal uphill .

In this study, Lenzi's team went a step further and replicated the key biomechanical functions of the biological knee, ankle, and toes in the sagittal plane, while also achieving the level of traditional microprocessor-controlled prostheses in terms of weight, size, and battery life.

Figure | Three above-knee amputees walking on a treadmill and stairs. (Source: The paper)

According to the paper, the powered knee joint uses a unique torque-sensing mechanism that combines the advantages of both an elastic brake and a variable transmission.

Figure ｜Main electrical and mechanical components in the knee model. (Source: The paper)

Furthermore, a single actuator can power both the ankle and toe joints via a compatible, underactuated mechanism.

Figure ｜Main electrical and mechanical components in the ankle model. (Source: The paper)

As the wearer walks, the underactuated system not only regenerates significant amounts of mechanical energy, but also replicates key biomechanical functions of the ankle/foot complex.

Furthermore, all mechanical and electrical components are integrated into a compact prosthetic frame, increasing the robustness and efficiency of the bionic leg.

Figure ｜ Actual picture of the bionic leg, and the main electrical and mechanical components in the bionic leg model. (Source: The paper)

When switched to passive mode, the bionic leg can regenerate 2J of electrical energy with each step taken by the wearer, allowing for unlimited walking even if the battery is depleted. This is a very important feature in the real world, as amputees may sometimes forget to bring their charger or charge their prostheses. This has not been possible in previous bionic leg research.

Therefore, the research team believes that bionic legs with these characteristics have the potential to improve the practical mobility of people with above-knee amputations, including the elderly and participants with vascular disorders who lack the strength and balance required to use heavy powered equipment.

Can everyone use it?

However, although the bionic leg has demonstrated superior performance to other mechanical prosthetic legs, there are still some areas that need improvement.

For example, the bionic leg cannot control the ankle and toe joints independently, and the ratio between ankle and toe torque is fixed and cannot be changed based on the user's needs or preferences.

Simulation results show that more flexible springs can improve dynamic performance and electrical efficiency, but longer springs also mean a reduction in the range of motion of the ankle and toe joints.

Moreover, even with an underactuated design, the addition of toe joints will increase the weight of the bionic leg. Therefore, it is necessary to conduct comparative trials with and without toe joints or with different ankle/toe torque ratios to evaluate the impact of toe joints on clinical outcomes.

Additionally, similar to most microprocessor-controlled and powered ankle joints/prostheses, this bionic leg design does not have frontal plane actuation. Although adding frontal plane actuation may increase the size and weight of the prosthesis, it may also improve clinical outcomes, especially when walking on slopes and rough terrain, and more trials are needed to further verify this.

Perhaps, there is still some way to go before everyone can customize their use .

Paper link:

https://www.science.org/doi/10.1126/scirobotics.abo3996