Timeline (12.5% completed)
|Phase 2||Functional bionic human arm replacement with equal weight/strength profile to human arm|
|Phase 3||Bionic hand with full mobility and articulation|
|Phase 4||Basic sense of touch in a bionic hand|
|Phase 5||Full sense of texture and temp in a bionic hand|
|Phase 6||Customized bio-printing therapies that can repair arm tissue|
|Phase 7||Customized bio-printed arm ready for reattachment|
|Phase 8||Bionic arm with superior specs to human arm|
|0.3||February 3, 2021||– assorted changes requested by r/transhumanism|
|0.2||February 1, 2021||– Added the ‘the task ahead section’ |
– Added ‘what to look forward to section’
|0.1||January 29, 2021||– Initial Upload|
|Project Name||Project Type||Technology||Project Status|
|Arm Transplant (VCA)||Procedure, Research||Surgical||Ongoing|
|Targeted Sensory Reinnervation (TSR)||Procedure, Research||Surgical, EMG||Ongoing|
|Motor Cortex Stimulation||Procedure, Research||Surgical, BMI||Ongoing|
|Epibone Engineered Bone Graphs||Procedure, Product||Surgical, Stem Cell||Ongoing|
|EMG Control System||Research||EMG, Robotics||Ongoing|
|Salamander Blastema Formation||Research||Stem Cell||Ongoing|
|Shadow Dexterous Hand||Research, Hand/Arm||Robotics||Ongoing|
|Modular Prosthetic Limb (MPL)||Research, Hand/Arm||Prosthetic, Robotics, EMG, BMI, Surgical||Ongoing|
|Luke Arm||Research, Product, Hand/Arm||Prosthetic, Robotics, EMG||Completed|
|Taska Hand||Product, Hand/Arm||Prosthetic, Robotics||Completed|
|I-Limb Hand||Product, Hand/Arm||Prosthetic, Robotics||Completed|
|Bebionic Hand||Product, Hand/Arm||Prosthetic, Robotics||Completed|
|Psyonic Ability Hand||Product, Hand/Arm||Prosthetic, Robotics||Completed|
|Atom Touch||Product, Hand/Arm||Prosthetic, Robotics, EMG, BMI, Surgical||Ongoing|
How close are we to Arm 2.0?
We don’t recommend an arm replacement yet — why not? No arm replacement today comes close to the functionality of the human arm.
Lab grown arms are a hypothetical, transplanted arms come with a high degree of risk, and only a fifth of arm amputees choose to use a prosthetic. So for amputees who do not want to take immunosuppressants for the rest of their lives, prosthetics are the only option. The reality is that today’s arm prosthetics have sub-optimal mobility and control. Although modern day prosthetics are marketed as functional replacements, the stories we hear from amputees tell a different story. Amputees report discomfort and limited mobility particularly related to socket attachments.
Complex robotic arms exist, but are mainly in R&D and cannot yet be controlled by intuitive techniques. The main way that amputees move their prosthetics is via proxies. Triggers like foot controls, upper arm sensors, and iPhone apps are used to initiate movement. Although triggers make the arms functional, the amputee’s experience is far from intuitive. The best that we can get to parity on human hand control right now requires an invasive surgery (motor cortex stimulation surgery) that accesses the brain’s motor control center. However, recent developments have shown the promise of a non-invasive solutions when EMG sensors are paired with AI.
The issue of sensory perception for artificial limbs is relatively unaddressed. A handful of manufacturers have built haptic feedback systems for touch but their attempts are rudimentary at best. Experimentation on the topic is accelerating quickly via university and private-sector research (Johns Hopkins APL and CTRL Labs respectively) but viable commercial solutions are non-existent.
The Task Ahead
There are three paths required to recreate the human arm:
- Recreate the arm’s anatomy
- Recreate the arm’s systems
- Recreate the arm’s functions
The goal of anatomic recreation is to recreate the look & function of an arm. 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 arm 2.0 has one hand, five fingers, and is roughly the same size and weight of a human arm. Biologically, there are two ways that the anatomy of the arm can be recreated. The first is to cheat by reattaching someone else’s arm. This idea may sound arcane, but more than 85 successful arm/hand transplants have been performed. The second is to regrow your own arm using stem cells (a big hypothetical). These ideas are discussed in the ‘Transplanting the human arm’ and ‘Regrowing the human arm’ sections respectively.
There are four major systems in the arm 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 arm is enabled by the veins and arteries that run through nearly every part of the arm.
The arm’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 arm (flexion, extension, abduction, adduction, rotation). Sensory feedback in the arm allows us to spatially map and sense our surroundings. Abnormality alerts refers to strains, compressions, over-use and other injuries to the anatomy that prohibit function. Finally, the arm needs to be able to repair itself on a surface level.
Today’s prosthetics fake human-like arm motion rather than recreating the underlying mechanisms that enable motor control. New research may mean that change is on the horizon.
Aside from exceptions like the LUKE arm, fully robotic prosthetic arms are not commercially available. Instead solutions are modular with motor control function being mainly built into the hand. The best modern day prosthetics have same form factor as the human hand but lack functionality (Ossur i-limb, Ottobock Bebionic hand, Taska hand,and Psyonic Ability hand). All have individually actuating motors but actual movement is limited to 10-15 preset hand positions with pre-programmed motion. These prosthetics are not recreating human arm movement, just basic function.
Bleeding-edge DARPA-funded projects however, have made strides in motor control. The LUKE arm appears similar to other prosthetics but its multi-articulating hand with 10 joints significantly increases dexterity. It is also the only only prosthetic on the market with a powered shoulder allowing users to reach upwards. Unfortunately, control methods for the LUKE arm are fractured and unintuitive. Another DARPA project, the Modular Prosthetic Limb (MPL) out of Johns Hopkins APL, aimed to revolutionize robotic arm control. By using an EMG-based control system augmented by AI the arm is able to be intuitively controlled by the mind. The MPL clocks a human-level strength profile (can lift 35 pounds) with a fully-motorized arm and fingers. In 2022, Atom Limbs will be bringing to market the commercial version of the MPL, the Atom Touch. For successful arm transplant recipients, intuitive motor control of their new arms is a given. The price of process however is a lifetime of immunosuppressive drugs.
In the quest for human like-motion, individual finger articulation is most important and obvious mechanical challenge. The development of systems that can control fingers has largely been left up to research institutions and organizations like DARPA trying to affect change. In that vein, OpenAI is applying their deep learning software to the most advanced robotic hand on the planet in order to solve Rubik’s cubes. That hand, the Shadow Dexterous Hand, uses specialized tendons modeled on the human hand to simulate realistic hand movement. The large external mechanical tendons enable incredibly quick and tactile finger motion – unfortunately this development is not functional outside of the lab.
Sensation & Wiring
Even though we do not have a good understanding of how sensation works in the human body – early rudimentary techniques in stimulating sensation have been largely successful.
Proprioception is defined as the way sensation informs the body’s movements. In the case of the arm, proprioception is a very important part of force feedback – the way that we spatially navigate the world through touch. Force feedback tells us when to stop and start movements. That sensation begins in the nerve endings where fast-adapting receptors interrupt things like texture and slow-adapting receptors tackle lasting sensations. Those nerve endings then relay signals through the periphery nervous system to the brain where the signals are processed and conscious feeling occurs.
Recreating the process of sensation has proved incredibly tricky thus far. Today’s prosthetics generally do not employ any force feedback mechanisms outside of vibrations that shake the whole limb. The lack of force feedback make clumsy prosthetics even harder to use. One possible solution for amputees is targeted sensory reinnervation or TSR surgery. The process reassigns nerves once responsible for arm and hand sensations closer to the surface. Those nerves are then mapped externally by physicians and electrodes are placed on the skin – returning a sense of touch to amputees via connected sensors. This technique was famously demonstrated by the MPL in a video where an amputee receives force feedback while grasping a ball. Atom Limbs plans to integrate the technology into their latest product, the Atom Touch.
Next generation solutions will not just bring back a binary sense of touch. As we better understand nervous system wiring and sensor density increases, a return of texture sensation for amputees is not out of the question. A system for mechanical temperature sensing is also possible. The same electrodes that stimulate touch could have an integrated a heating mechanism connected to temperature sensors on the artificial limb. Further into uncharted territory is the idea of returning a sense of pain to artificial limbs. Even though pain is a useful sense and an evolutionary safeguard against harm, the ethics and demand for such a feature are untested.
Transplanting the human arm
Arm transplants are beginning to be feasible but remain a massive medical effort with many unknowns and dangers.
The arm transplant process is known as Vascularized Composite Allotransplantation (VCA). The process involves bone fixation, reattachment of veins/arteries, and repair of tendons/nerves all in one 12 hour surgery requiring up to 40 physicians. The surgeons align tissue but body that does the actual work of repairing and connecting host tissue to donor tissue. Patients generally have a basic sense of touch restored and are encouraged to move their new hand within the first 24-48 hours. So far, no deaths have been recorded from the procedure.
Even though arm transplants are possible, there are a myriad of potential problems associated with the procedure. The biggest issue is rejection as the body treats new organs as invaders. Patients have to take strong immunosuppressive drugs for the rest of their lives to avoid a rejection. Rejection will first manifest itself as a rash in the skin before the arm will have to be removed. No official donor base exists for arm transplants but the wait is generally only weeks to months. Patients need to match HLA typing, blood type, and other physical characteristics with their donor. Post-surgery, 1-2 years of intensive physical therapy is required. Long term research on arm transplants is extremely limited.
So far, 85 people have received hand or arm transplants beginning 11 years ago. In January 2021, a patient received the first double arm/shoulder transplant. Johns Hopkins Medicine is working on a novel immunosuppression protocol that may significantly improve outcomes for patients.
Regrowing the human arm
Progress is being made towards growing and regrowing human arms but the process does not have an end in sight.
In general the human body is great at healing itself. The human arm can repair surface tissue but major surface injuries require skin grafts to prevent scarring. The next frontier of human arm repair is in targeted stem cell therapies where structural damage to areas like the rotator cuff and even bones can be repaired. That said, larger reconstructive stem cell therapies involving multiple forms of tissue is not currently possible.
When humans lose limbs, a blood clot forms leading to a scab and then to scarring. In nature this process works differently for certain a curious animal. When a salamander looses a limb it forms a blastema, a new limb bud, instead of scar tissue. The blastema will then over the course of a few months form into the shape of the limb that was lost and regrow itself. Researchers hope that by studying the genome of these animals we may be able apply their secrets to humans one day. This process however requires gene therapies – an area only being to be clinically explored.
In time, 3D bio-printing techniques mainly used for organ growth today can and will be applied to limb regrowth. Today problems with scaffolding and complexity keep 3D bio-printing on a small scale. In time companies like Epibone, which allows individuals to regrow bones using their own stem cells, will create the building blocks for commercial personalized limb regeneration. In contrast to transplanted arms, lab grown limbs from a patient’s stem cells means no rejection potential or dangerous immunosuppressive drugs.
What to look forward to
Reality is slowly catching up with science fiction and it is clear that bionic arms will be part of the opening act.
Even though today’s arm replacements are lacking, the future is looking bright. As research in EMG control/BMI control/robotics continues to increase exponentially, reaching human parity with a robotic arm seems inevitable. So once a bionic arm surpasses it’s human equivalent, what types of arms will people want to have? The mind immediately leaps to superhuman strength profiles and Swiss army like utility capabilities for future bionic arms. The reality will likely be in between this and an identical bionic replacement.
Looking ahead, two interesting paths to biological regeneration of the arm emerges. The first as discussed above is gathering stem cells from a patient and growing a replacement arm 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 arm 2.0 discussed above, biological augmentation will change the way that we think about what an arm 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 arm? 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.