🦿 Leg 2.0


Timeline (12.5% completed)

Phase 1Functional bionic Human leg replacement
Phase 2Functional bionic human leg replacement with equal weight/gait profile to human leg
Phase 3Bionic leg with full mobility and articulation
Phase 4Basic sense of touch in a bionic foot
Phase 5Full sense of texture and temp for bionic foot
Phase 6Customized bio-printing therapies that can repair leg tissue
Phase 7Customized bio-printed leg ready for reattachment
Phase 8Bionic leg with superior specs to human leg

Changelog

VersionPublish DateChanges
0.1February 3, 2021– Initial Upload

Project Index

Project NameProject TypeTechnologyProject Status
Leg TransplantProcedure, ResearchSurgicalOngoing
Ewing AmputationProcedure, ResearchSurgical, EMGOngoing
Motor Cortex StimulationProcedure, ResearchSurgical, BMIOngoing
Epibone Engineered Bone GraphsProcedure, ProductSurgical, Stem CellOngoing
EMG Control SystemResearchEMG, RoboticsOngoing
Salamander Blastema Formation ResearchStem CellOngoing
Utah Bionic LegLeg, Product, ResearchProsthetic, Robotics, EMGOngoing
Blatchford LynxProduct, LegProsthetic, Robotics, EMGCompleted

    How close are we to Leg 2.0?


    Although we don’t recommend a leg replacement yet, we are getting damn close

    Bionic legs are particularly effective for two reasons, robotics can accurately emulate the gait cycle and myoelectric control of the legs is relatively simple compared to hand control. That said, bionic legs are mainly only good at walking and are extremely expensive. As of now, there is only one full bionic leg replacement on the market (bionic knee and ankle). Because of the non-conformity of leg amputations, commercial bionic replacements are sold in a modular fashion, bionic knees, bionic feet/ankles, and feet attachments are the main components.

    Less complicated solutions also exist — simple prosthetic legs with no moving parts are still the cheapest and most popular form of leg replacements on the market. As the industry evolves, prosthetics with specific applications have emerged. Most prolific are the blade legs worn by Paralympic sprinters that store and release kinetic energy. Specialized legs are needed for and optimized for most activities (running, swimming, showering, biking). Hugh Herr, an MIT professor and mountaineer, famously built his own bionic leg so he could get back on the mountain.

    Like with arms, transplanting legs comes with a high degree of risk and lab grown legs are still a hypothetical. So for amputees who do not want to take immunosuppressants for the rest of their lives, prosthetics are the only option. Differing from arm amputees, leg amputees almost always get a prosthetic of some form. Prosthetic legs are necessary for walking, and are far more advanced than prosthetic arms at the moment.

    The Task Ahead


    There are three paths required to recreate the human leg:

    1. Recreate the leg’s anatomy
    2. Recreate the leg’s systems
    3. Recreate the leg’s functions

    The goal of anatomic recreation is to recreate the look & function of an leg. That doesn’t necessarily require the same underlying anatomy. If we can accomplish the same functions, while looking the same, the job is done. For the sake of argument, we are assuming that leg 2.0 has a thigh, knee (hinge joint), shin, ankle (synovial joint) and foot component. Biologically, there are two ways that the anatomy of the leg can be recreated. The first is to cheat by reattaching someone else’s leg. This idea may sound arcane, but as of 2012 two patients have undergone leg transplants. The second is to regrow your own leg using stem cells (a big hypothetical). These ideas are discussed in the ‘Transplanting the human leg’ and ‘Regrowing the human leg’ sections respectively.

    There are four major systems in the leg that need to be recreated. Structure, enabled by bones, is the most basic and important system. Movement, enabled by ligaments and tendons, creates an incredibly complex pulley system that facilitates motor control. Sensation, enabled by the peripheral nervous system, is responsible for a sense of touch, texture, and temperature. Finally, the energy system that powers the leg is enabled by the veins and arteries that run through nearly every part of the leg.

    The leg’s functions that need to be recreated can be bucketed into the following categories: motor control, sensory feedback, abnormality alerts, and repair. Motor control includes every permutation of movement in the leg (flexion, extension, abduction, adduction, rotation). Sensory feedback in the leg allows us to spatially map and sense our surroundings. The unconscious calculation the brain makes allows us to adjust our gait basted on terrain/density prediction. Abnormality alerts refers to strains, compressions, over-use and other injuries to the anatomy that prohibit function. Finally, the leg needs to be able to repair itself on a surface level.

    Motor Control


    Motor control research for legs is promising — human parity will certainly be reached within the next decade

    Assuming the leg amputation is done above the knee, there are six components for a bionic leg with full motor control. Sensors at stump of the leg, a microprocessor for the knee, a knee module and hinge, a microprocessor for the ankle, an ankle module and synovial joint, and a foot competent. Unlike arm movements, there is a specific gait cycle that the leg follows for movement. On each side of the body there is a mirror stance and swing phase where of double and single leg support alternately support the body. The predicable nature of this cycle simplifies the task of engineering motor control for replacements legs. The knee module is made up of a relatively simple hinge mechanism and activated via a myoelectric sensor. Knee modules are often less common/developed because most leg amputations are done below the knee. The ankle module operates similarly to the knee module taking in data through a myoelectric sensor but its movement operates in three dimensions instead of one. Motor control of the ankle takes into account a number of factors: impact force, slope degree, speed and EMG sensory data. This data is then fed through the ankle’s microprocessor where the gyroscope makes adjustments that enable a smooth gait. For those that want a superior sense of stability and/or have socket related issues, osseointegration of a leg socket is recommended. When a patient receives a bionic leg, the prosthetist plays a final critical role in motor control. He/she evaluates the modular components of the leg and assembles it in a way that shock absorption is maximized. Shock absorption is taken into account at every part of the prosthetic, not just the socket.

    Sensation & Wiring


    Sensation research for bionic legs is underwhelming, wired EMG control solutions have advanced significantly in the last decade

    Wiring for bionic legs is the process through which nerve signals of the ankle and/or knee are read by an EMG sensor placed on the residual limb. The electrodes relay the sensory data through a microprocessor which calculates movement based on this data and additional environmental factors. For above the knee amputees, latency may be a problem as bionic knee and ankle products are sold separately. As of 2021, there is only one fully bionic leg on the market. Continued vertical integration of these two products will certainly improve mobility and outcomes for patients. All of the above mentioned bionic products require a power source to operate, an exciting alternative is passively powered bionics, which this University of Utah based team has achieved.

    Proprioception is the way that our feet and legs are able to inform the body of anticipated terrain. So far there has been no commercial progress in attempting to bring sensation back to the legs and feet. It can be inferred that once bionic hand sensation research progresses, the technology will be transferred to lower limb bionics. On the research side, one MIT engineer who received reinnervation surgery returned some sensation to his feet by placing sensors on the bottom of his foot connected to his amputated toes’ nerve endings. The little research that has been done implies that restoring sensory feedback restoration in leg amputees improves walking speed, metabolic cost and phantom pain. One of the most promising areas of the field is a procedure known as the Ewing amputation. This procedure is a new amputation strategy that preserves muscles, tendons, and nerves in a way that they can be better read read by advanced bionics systems. According to peer reviewed research, this method enables “improved prosthetic control and restoration of muscle-tendon proprioception.” 20 patients have received the surgery so far.

    Exoskeletons


    For patients that cannot move themselves exoskeletons provide a potential lifeline to movement

    BMI controlled bionics may be promising for paraplegics who want control of an arm, but connecting a paraplegic to bionic legs will not solve the issue of stabilization and balance. Exoskeletons however, by creating a rigid structure around the body controlled by the mind, solve this problem. Exoskeletons have long been a sci-fi favorite but recently came into the public consciousness after a man paralyzed from the waist down kicked the ceremonial first goal in Rio’s 2014 World Cup.

    Although promising, the expense and upkeep of exoskeletons compared to bionic limbs is an order of magnitude more. Motor cortex stimulation surgery must be preformed and and a permanent implant must be implanted. Then there is the cost of a reliable BMI and the price of the actual exoskeleton which are only beginning to become commercialized. Further, any sort of commercial application of this technology would require a mechanism for independently loading the user into the exoskeleton that would likely be just as complex as the exoskeleton itself. Finally, in the case of malfunction, exoskeleton field repairs obviously cannot be done by the user. Clearly exoskeletons are not ready for prime time today, but they do offer an exciting glimpse into the future for disabled people.

    Transplanting the human leg


    Section coming soon.

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    Regrowing the human leg


    Section coming soon.

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    What to look forward to


    Someday soon, bionic legs will jump higher and run faster than their biological counterparts. So what will it take for bionic legs to get across the finish line?

    To achieve human parity bionic legs need to improve in a few key areas. Versatility of the leg is the first key step, bionic legs need to be able to run, walk, and get wet while functioning in the same way that human legs can. The next area is the addition of sensation, at the very least the user should be able to feel the ground underneath them to get a mental sense of the terrain. Eventually toes could be roboticized, but it is possible that advances in gyroscopic technology may soon surpass the stabilization provided by biological toes. Finally, battery technology needs to advance to provide a bulletproof all day battery — no one should have to worry about their leg running out of battery. Alternatively, we could see passively powered bionic legs take the reigns in the next couple years. In any case, bionic parity with the human leg is almost within grasp.

    Within human body 2.0, there are few things as certain as the idea of bionic supremacy for the bionic leg. From the actual technology to our sci-fi aspirations, leg 2.0 has progressed over the last decade with blinding speed. With the addition of AI, better EMG sensors, and more powerful motors, the sky is the limit for this technology. Expect highly engineered modifications for every activity (skiing, biking, mountaineering) allowing amputees not just to enjoy these activities but to make them superior athletes to their non-cyborg counterparts.

    Looking ahead, two interesting paths to biological regeneration of the leg emerges. The first as discussed above is gathering stem cells from a patient and growing a replacement leg that will be be surgically attached. The second, a more far fetched option, is the idea that self assembling cell regeneration will one day function in the same way that salamanders regenerate limbs. An ethical gray area is the idea of further biological augmentation. Far different from the human leg 2.0 discussed above, biological augmentation will change the way that we think about what a leg is, both from a visual and functional standpoint.

    Finally as sensation research is in its infancy, future of engineered senses is up to the imagination. What will the sensation of touch be like between someone with artificial sensations and an unmodified person? Will we we recreate the feeling, temperature, and sensitivity of human skin or build something wildly different? Will additional senses be added to the leg? Will we voluntarily choose to take away pain and other senses? We are not close to answering these questions, but imagining the answers sure is fun.