There are more than two million Americans living with limb loss, including nearly 200,000 lower-leg amputations. And that number is expected to rise 145 percent by 2060. Bionic legs — robotic prostheses that use sensors, actuators and microprocessors to replicate natural human movement — offer a promising path to restored mobility, but the technology is still a work in progress.
“It’s a very difficult thing to lose a limb,” Pierre Cherelle, CEO of Belgian startup Axiles Bionics, told Built In. “And seeing that in 2025 — when everyone has three personal computers at home — and we still have non-articulated feet as being the standard is just sad.”
Bionic Leg Definition
A bionic leg is an electronically controlled lower limb prosthetic. It uses microprocessors, sensors and, at times, powered joints to replicate natural leg movement and restore mobility for those with limb loss.
What Is a Bionic Leg?
A bionic leg is a high-tech, lower limb prosthetic that’s designed to simulate natural movement. Outfitted with microprocessors, sensors and actuators, these electronic extremities rely on integrated control systems to facilitate movement. They’re often built from lightweight materials, like carbon fiber or titanium, and may include individual components — like a knee, ankle or foot — or be a fully integrated system combining them all.
Similar to traditional prosthetics, bionic legs are meant to restore mobility to people who have lost their lower limbs as a result of trauma, illness or congenital conditions. But unlike standard devices, they adapt in real time to a wearer’s gait and terrain, offering more precise, responsive and intuitive control as they stand, walk, climb stairs, descend slopes and more.
“Bionic technology simply makes people’s lives better through intuitive operation, improved security and lower effort,” Helgi Hall, vice president of global prosthetics at bionic orthopedics company Össur, told Built In. “It gradually restores lost function in a way that feels seamless, so users can get back to doing what they love.”
Bionic Legs vs. Prosthetic Legs
Both prosthetic and bionic legs replace missing lower limbs, but they differ in how they restore mobility. Traditional prosthetics are generally passive mechanical devices. They offer basic stability, but they cannot actively respond to changing conditions like walking speed, terrain or posture — so users must compensate with their own effort. Bionic legs, on the other hand, use sensors and control systems to adjust in real time to their wearer’s gait and environment. Some newer models also incorporate artificial intelligence to learn from an individual’s unique movements, gradually improving responsiveness, balance and energy efficiency over time.
“A bionic leg takes in information about the user’s activity and their environment, and it uses this information — in conjunction with firmware control algorithms — to make decisions about the type of action to apply to the joint that will assist the user with that activity,” Hall said. “Thus, the user can do the activity with less thought and effort” compared to a purely mechanical device.
Still, regular prosthetic legs tend to be more reliable, lighter in weight and a lot more accessible compared to their costly, computerized counterparts. An entry level bionic leg can cost around $60,000 or more.
Examples of Bionic Legs
Because of the technical challenges involved in developing bionic lower limbs, only a small number of companies are working in this field. Here are some of the key pioneers — and their signature bionic leg products.
Ottobock — C-Leg 4
Developed by Ottobock, the C-Leg 4 is a microprocessor-controlled prosthetic knee designed for individuals with above-knee amputations for everyday use. Since its introduction in 1997, it has become a staple in lower limb prostheses as the most widely fitted microprocessor knee globally, with more than 100,000 fittings to date. It features a lightweight design and comes with an intuitive app and extended battery life that lasts two days of regular use or 16 straight hours of continuous walking.
More recently, the German company upgraded its more rugged model, the Genium X3, which was developed in collaboration with the U.S. Military, to the Genium X4 — a waterproof, bionic leg with a microprocessor that processes sensor data 100 times per second.
Össur — Power Knee
Iceland-based Össur created the world’s first actively powered bionic knee. Called the Power Knee, it features a motor that generates force when walking, stair climbing and standing up, mimicking natural muscle function. It also uses artificial intelligence to replicate muscle activity, providing powered extension and flexion for more natural, less tiring movement, while also learning from the wearer’s gait over time.
For users looking for a more passive model, Össur’s Rheo Knee is built with a magnetorheological actuator, which provides smart dampening to increase or decrease resistance during different phases of a user’s gait. Or the Navvii, a waterproof alternative.
Blatchford — Linx
Linx is a fully integrated bionic limb system, combining a microprocessor knee and ankle into one coordinated limb. Developed by UK-based company Blatchford, it uses sensors to continuously adjust across its joints and hydraulics, ensuring smoother transitions from flat surfaces to stairs. Linx’s sensor system also enables stumble recovery, which optimizes knee stability during a user’s swing phase in order to prevent falls.
Axiles Bionics — Lunaris
Developed by Belgian startup Axiles Bionics, the Lunaris is a biomimetic ankle-foot prosthesis with an elastic tendon and anatomical ankle joint. Offering a 39-degree range of motion it mimics the Achilles tendon, providing a more natural gait and better adaptability in dynamic terrains. The Lunaris was constructed with advanced composite materials, including carbon and glass fibers, aerospace-grade aluminum and titanium alloys. It also offers a lightweight and compact design without compromising on strength. Integrated sensors and smart connectivity enable real-time adjustments, enhancing user comfort and stability during daily activities.
How Do Bionic Legs Work?
Bionic legs work by continuously monitoring their wearers’ movements and surroundings. Tiny sensors built into the leg measure things like force, speed, knee angle, torque and how the limb is positioned. This data is then processed by a control algorithm — software that interprets the input and decides how the leg should respond. Based on these calculations, an actuator (typically a smart damper or motor) is instructed to apply the appropriate movement or resistance to assist the user in real time, whether it’s flexing the knee or adjusting the ankle to mimic a natural gait, allowing the user to move smoothly and naturally.
Depending on the model, a bionic leg may be powered by external sources like batteries or motors, or operate passively using mechanical components like springs. In both cases, effective energy management — whether generating it during push-off or dissipating it to absorb shock — is essential to replicating the mechanics of a natural gait.
Unlike bionic upper-limb prostheses like arms or hands, bionic legs rarely use myoelectric control, which links sensors to healthy nerves and muscle signals above the amputation site to trigger movement. The catch is that this requires the user to retrain their body, which can be difficult and unnatural — or, in the case of lower limb biomechanics, nearly impossible.
“Walking is something that’s deeply wired in our brains,” Cherelle said. It is a full-body balancing act, requiring our legs to coordinate weight, shock and push-off in perfect rhythm. Biarticular muscles also have a more pronounced role in lower limbs, spanning multiple joints and making organic motion that much harder to copy with machines. “Learning to walk again by activating other muscles — forget about it.”
Even so, higher-tech models are not always the obvious choice. It will always be a matter of what works best for the user, Cherelle added.
Most bionic limbs can fit into one of three categories: passive, active and semi-active.
- Passive limbs are non-motorized mechanical devices that rely on the user’s body movement; they can still be considered “bionic,” as many incorporate advanced materials and engineering, as well as high-tech components like sensors, when compared to traditional prostheses.
- Active limbs are typically powered by motors and batteries, and use sensors and processors to adapt in real time.
- Semi-active limbs include some powered elements — like microprocessor-controlled knees or ankles — but don’t actively generate motion; instead, they adjust resistance or stiffness based on user feedback. “Think of [semi-active limbs] as an electric bike — the battery and the motors are there for the assistance, but you can still operate it like a regular bike when the battery is dead,” Cherelle said.
Future of Bionic Legs
Bionic leg technology is quickly shifting from developing motorized mechanical devices to neuroprostheses directly connected to the brain, thanks to a recent study from Massachusetts Institute of Technology. The research introduces a novel surgical approach called the agonist-antagonist myoneural interface, or AMI, which surgically reconnects pairs of residual muscles to restore natural muscle dynamics and sensory signaling.
Plugged directly into the nervous system, the new neuroprosthetic interface restores about 18 percent of the muscle feedback found in a biological limb, allowing users to walk with lifelike motion without relying on rigid, pre-programmed robotics. Sensors placed between the reconstructed amputation site and the bionic leg transmit electrical signals from the brain to the prosthesis and send movement data back to the user. This two-way communication gives patients a sense of proprioception — the brain’s ability to perceive the body’s position and movement in space — which is essential for stable, intuitive walking.
Compared to those with traditional amputations, users of this interface walked 41 percent faster and moved more naturally, showing that even a small boost in neural feedback can make a big difference in how a prosthetic leg feels and functions.
To date, only about 60 people in the world have undergone the AMI procedure, which has now become standard at leading institutions like the Brigham and Women’s Hospital in Massachusetts.
Frequently Asked Questions
How much does a bionic leg cost?
Battery-powered bionic legs that feature computerized parts start at $60,000, according to the MIT Media Lab.
What does a bionic leg do?
A bionic leg is a prosthetic that uses sensors, microprocessors and powered joints to restore a user’s mobility by replicating natural bipedal movement. By adapting to a user’s unique gait and environment, it allows the user to walk and maintain balance while standing and taking on more challenging activities, such as climbing stairs and navigating uneven terrain.
What is the difference between a prosthetic leg and a bionic leg?
A prosthetic leg is a passive, mechanical device that relies on the user's own movement to function properly, while a bionic leg integrates advanced technology, such as sensors, AI and microprocessors to adapt to a user’s gait and surroundings in real time.
How long do bionic legs last?
While this factor will vary from person to person and is based on a device’s frequency of use, a bionic limb may last three to five years on average before needing to be replaced or taken in for major repairs, according to Robo Bionics.
