Until recently, people who lose their limbs or are born without them have been forced to use prosthetics little advanced from the stereotypical wooden peg leg of yore. Today, 60 million people around the world and nearly 2 million in the US live with limb loss. That number in the US is expected to double by 2050, mostly due to the type 2 diabetes epidemic, as well as vascular disease, trauma and cancer. The good news: prosthetics are getting better, smarter and cheaper thanks to ever-increasing AI brainpower and the democratization of 3D manufacturing.
Today, implanted neuroprosthetic devices help restore functionality across a wide range of neurological and behavioral issues, from seizures and Parkinson’s to loss of hearing and sight—and, recently, targeting OCD and obesity. The list of deep brain stimulation (DBS)–treatable conditions will grow exponentially. Within a decade, new neuroprosthetic techniques and interfaces will make it unnecessary to perform surgery to implant these life-saving devices.
BUILDING A BETTER ARTIFICIAL LIMB
A new generation of “smart” prosthetic limbs, designed using 3D modeling tools and made with 3D printers, is on the horizon. These include bionic legs that create an effortless gait by anticipating the movements of wearers by continuously monitoring trajectory in relation to the body and the ground. Some plug directly into human nerve tissue for high-fidelity access to electrical signals and muscle movements, while others use sensors in the prosthetic socket to foster neurological connections.
TrueLimb, a durable, 3D-printed prosthetic arm with more than 30 sensors guiding its bionic functionality, is tailored to a user’s exact size, shape and even skin tone. Myoelectric sensors in BrainRobotics’ prosthetic hands connect to muscles and nerves in residual limbs, converting electrical signals from the brain into precise finger movements or programmed actions. Laurent Frossard, a bionic limb scientist at Australia’s Griffith University, and David Lloyd, a Boston University mechanical engineer, are combining biomechanics and computational modeling to create wearable and noninvasive diagnostic devices that rely on designing a precise “digital twin” of each user’s own unique residuum (residual limb). This allows for virtual design and easier refitting and replacements as improved prostheses become available.
Nearly a century ago, one of the world’s first pacemakers revived a stillborn baby in Sydney, Australia. Today, about 40,000 people worldwide have had DBS devices surgically implanted in their brains to control tremors from Parkinson’s disease and other conditions. Surgeons have implanted hundreds more responsive neurostimulation (RNS) devices in patients with drug-resistant epileptic seizures. Both devices work like heart pacemakers to monitor and sense tremors or seizures as they begin and then activate to stop or mitigate them. More than 100,000 people in the US have restored or improved hearing thanks to cochlear nerve implants.
Other brain prosthetics are on the way:
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Surgically implanted devices that access the optic nerve to restore basic levels of sight in the same way cochlear implants have restored hearing.
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Implants in the motor cortex allow paralyzed patients to operate prosthetic limbs, use computer interfaces and control machines using only their thoughts.
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The Defense Advanced Research Projects Agency (DARPA) has developed a brain-computer interface system that will enable a military pilot with an implant to operate multiple aircraft simultaneously via thought. In the next 15 years pilots may be able to control drones and fighter jets with noninvasive or superficially embedded devices that connect with genetically modified brain cells via infrared light signals; no surgery required—DARPA plans to modify the brain cells using nasally inhaled nanomolecular gene therapeutics.
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Neurointerventional electrophysiology is another emerging approach to accessing brain activity without major surgery. Vascular neurosurgeons at the University at Buffalo in partnership with the Jacobs Institute can now insert stent-mounted electrode arrays made by neurotech startup Synchron through blood vessels rather than opening the cranium. The surgeons guide the devices into specific locations, allowing signals from the brain to operate mobile devices and computers.
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40 KPeople, globally, with deep brain stimulation implants for tremor control
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100MAmericans who could benefit from regenerative, bioengineered-cell therapies
The NIH has estimated that over 100 million Americans could benefit from regenerative therapies that use bioengineered cells to repair damaged tissue after a heart attack, cancer surgery or a car crash. Programmed stem cells have regenerated muscle in mice. The first human trials are underway in China, the UK and the US to test stem-cell generated heart patches. Dr. Anthony Atala at Wake Forest has successfully implanted lab-grown organs like esophagi and bladders into human patients.
A team at Tufts University led by biologist Michael Levin and funded by Microsoft cofounder Paul Allen’s Frontiers Group is using guided application of electrical fields to help regrow body parts. Levin’s group recently used instructions formulated in what the group calls “the morphogenic code” to turn frog stem cells into self-organizing teams of programmable “Xenobots” that can develop specialized cell structures to move around and record information about their own movements—a major step toward regrowing human limbs and organs.
If a salamander can regenerate its limbs, why can’t a human? The fact is that humans do regenerate. We’re regenerating all the time. The question therefore is how can you induce further regeneration?
Anthony Atala, MD
Director of the Wake Forest Institute for Regenerative Medicine
The most advanced prosthetic limbs can cost upwards of $70,000. Brain- Robotics’ myoelectric hand, along with next-gen artificial legs being developed at MIT Media Lab and the Bionic Leg from the University of Utah’s Bionic Engineering Lab, will all become commercially available within the next five to ten years, but are likely to be very expensive.
A recent analysis by the RAND Corporation shows why investing in prosthetic technology is worth it. RAND compared health outcomes for people with abovethe- knee limb loss using microprocessorcontrolled prosthetic knees to outcomes for those using analog prosthetic knees. While wearers of microprocessorenhanced knees spent roughly $15,000 a year in prosthetic-related costs— $1,700 more than analog knee users— they saved $4,600 annually in direct and indirect healthcare costs (thanks to fewer injuries and lower caregiving costs) compared to analog-knee wearers—a $2,900 gain. Perhaps most importantly, while wearers of microprocessor-equipped prosthetic knees in the study lived about one month longer than their analog counterparts, RAND determined that they gained almost 11 months of “quality-of-life-adjusted” time per person over the 10-year study. That’s 11 extra months to engage in productive, rewarding activities—aka healthspan—a boon both to those with limb loss and to society.
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11 MONTHSGained by prosthetic users to engage in more demanding, active pursuits
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$4.6 THOUSANDSaved annually by microprocessor controlled knee users vs. analog prosthetic knee users
Cartilage doesn’t have a blood supply, so it’s hard to regenerate. With what we call biologics, we’re trying to grow things before you need them. We will likely be able to regrow a knee in the next 15 years. We can do so in a petri dish, so if we can build the right scaffold to transplant it with robotic assistance, we can make it happen.
Dr. Martin Roche
Orthopedic knee surgeon, Holy Cross Orthopedic Institute
While most high-end bionic limbs are still priced like high-end automobiles, 3D printing is changing the prosthetics market rapidly. Open Bionics’s customizable 3D-printed Hero Arms (including a Black Panther: Wakanda Forever model) start around $10,000 and are covered by Medicare. Unlimited Tomorrow’s 3D-printed TrueLimb, mentioned at left, costs less than $8,000 with capabilities that only a few years ago would have carried a price tag above $50,000.
The future looks even brighter for affordability and access to prosthetic technology. Bioengineer Hugh Herr—a double amputee and cohead of MIT’s Yang Center for Bionics—and his former student David Moinina Sengeh, Sierra Leone’s chief technology offificer, lead Prosthetics for All—a mobile clinic providing affordable or even free 3D-printed prosthetics to Sierra Leoneans who have lost limbs. In India, Rise Bionics makes $300 legs whose wearers have outperformed competitors using $100,000 prosthetics in paralympic competition. The e-NABLE network—comprising thousands of volunteers in more than 100 countries— collaborates to produce free or low-cost 3D-printed prosthetics for anyone in need.
While millions of us have opted to replace worn-out knees and hips with artifificial joints, Herr predicts that as limbs age and become compromised, people will move beyond joints to replace entire flflesh-and-blood limbs with durable prosthetic versions connected to our brains by seamless, AI-augmented neural interfaces.