- Open Access
- Authors : Sahla Yoosuf Husain Ahmed
- Paper ID : IJERTCONV8IS04004
- Volume & Issue : NSDARM – 2020 (Volume 8 – Issue 04)
- Published (First Online): 17-03-2020
- ISSN (Online) : 2278-0181
- Publisher Name : IJERT
- License: This work is licensed under a Creative Commons Attribution 4.0 International License
Sahla Yoosuf Husain Ahmed
Department of Computer Science
Ansar Womens College, Perumpilavu, P.O Karikkad, Thrissur -680 519
Background : Bionic prosthetic hands are rapidly evolving. An in-depth knowledge of this field of medicine is currently only required by a small number of individuals working in highly specialist units. How- ever, with improving technology it is likely that the demand for and application of bionic hands will continue to increase and a wider understanding will be necessary.
Methods : We review the literature and summaries the important advances in medicine, computing and engineering that have led to the development of cur- rently available bionic hand prostheses.
Findings: The bionic limb of today has pro- gressed greatly since the hook prostheses that were introduced centuries ago. We discuss the ways that major functions of the human hand are being replicated artificially in mod- ern bionic hands. Despite the impressive ad- vances bionic prostheses remain an inferior replacement to their biological counterparts. Finally we discuss some of the key areas of research that could lead to vast improvements in bionic limb functionality that may one day be able to fully replicate the biological hand or perhaps even surpass its innate capabilities.
Conclusion: It is important for the health- care community to have an understand- ing of the development of bionic hands and the technology underpinning them as this area of medicine will expand.
Keywords: Bionic hand, Prosthesis, Amputees, Bionic limb, Robotic hand.
The human hand is able to perform a complex repertoire of sophisticated movements that en-
ables us to interact with our environment and communicate with one another. The oppos- able thumb, a rarity in nature, has helped us achieve high levels of dexterity allowing our evolution to proceed rapidly over other crea- tures. To perform complex hand movements we need to synthesize an enormous amount of somesthetic information about our envi- ronment including fine touch, vibration, pain, temperature and proprioception.
The sensory and motor cortices span large, complex areas of the brain and are devoted to interpreting the vast sensory input and using it to fine-tune the motor control of over forty sep- arate muscles of the forearm and hand. This delicate, sophisticated arrangement allows us to perform precision activities such as writing and opening doors whilst simultaneously avoid- ing noxious stimuli.
Loss of a hand can be devastating and un- like losing a leg the functional limitations fol- lowing hand loss are catastrophic. The primary causes of hand loss are trauma, dysvascular- ity and neoplasia. Men are significantly more likely than women to lose their hands with 67% of upper limb amputees being male. Upper limb amputations most commonly occur dur- ing the productive working years with 60% be- tween the ages of 16 and 54. The functional de- mands in this patient group are high and their expectations of a prosthetic limb mirror this.
A few hundred years ago a hand amputee would have been condemned to a hook pros- thesis that had limited function and carried significant social stigma. However in todays society a hand amputee can expect a replace- ment hand that replicates a whole host of nor- mal hand functions and looks remarkably life like. Significant advancements in bionic hand technology have occurred and this field is now considered to be a triumph of medical engineer- ing excellence.
The alternative option to a bionic hand is a hand transplant, which was first performed in 1999. There have been successes in this
field but there are major drawbacks to the widespread use of transplantation. The re- quirement for a donor limb that matches the recipient in terms of size and shape mean suit- able donor limbs are rare. The recipients re- liance on long-term immunosuppression and the complexity of transplant surgery are likely to limit transplantation as the major recon- structive option for amputees. Therefore the more widespread option for an upper limb am- putee is to opt for an artificial replacement.
The modern prosthetic hand has been de- signed to closely approximate the natural limb in both form and function. Despite the fact that the bionic hand was recently hailed as a triumph of engineering excellence it remains an inferior replacement to the real thing and con- sequently there are a number of barriers to its uptake amongst the upper limb amputee popu- lation. These prevent the prosthetic hand from achieving the ultimate goal of any prosthesis: 100% acceptance by its users.
So, how close are we to creating an artificial hand that is a perfect replica of the real thing? Can we expect that medical and engineering advancements will continue to improve upon nature and eventually deliver a bionic hand that enhances our strength, speed and abili- ties far above human norms? Will we all be like the Six Million Dollar Man or the Bionic Woman one day?
Classification of Prosthetic
Similar to the other consumer products the prosthesis has followed the stages of evolution, development and innovation. Replicating any human part is not an easy task. Researchers have to repeatedly reanalyze the need of the prosthesis on the basis of the expectations of the patient keeping in mind age, sex and the profession. This literature survey revealed many researchers in race to design most effi- cient and perfect machine which exactly looks like a real hand and works like a real hand.
Table 1: Presents Classification of Prosthetic as per amputation
Type of amputation
Type of prosthetic
Trans carpel disarticulation
Automated Prosthetic arms are considered as biomedical devices and developing the same is interdisciplinary activity i.e. combination of mechanisms and electronics. The selection of prosthetic arm depends upon type of the dis- articulation the patient has undergone and the patients need. Please refer figure 1.
Figure 1: Amputation level
Amputation above elbow (AE) or Transhumeral Prosthesis
It is an artificial limb which replaces an arm missing above the elbow. It has complexities related to movements to the fingers, wrist and elbow. Refer figure 2.
Figure 2: Transhumeral Prosthesis
Amputation Below elbow (BE) or Transradial Prosthesis
It is an artificial limb which replaces missing arm below the elbow.
Figure 3: Transradial Prosthesis
Electronic Transradial or Wrist Disarticulation Prosthesis
Figure 4: Wrist Disarticulation Prosthesis
Finger Disarticulation Prosthe- sis
Figure 5: Finger Disarticulation Prosthesis
he human hand is by nature so com- plex that replicating its functions using
residual limb relative to the patients body con- trols the movement of the prosthesis. These limbs require the user to have enough strength to operate them and they are limited to a small epertoire of movements. However they are cheap to produce and are relatively easy to use, so they can be a suitable option for people with low demands.
Traditional Prosthetic Hooks/ Body Powered Hooks
Prosthetic hooks were originally developed in the early 1900s. They have proven to be an effective and reliable tool for amputees to use in their daily lives. Although there are several variations of prosthetic hooks, they all behave in the same general way. There are two hook shaped metal prongs which pivot at the rear section. The prongs are normally held together through spring force. The spring force is sup- plied by what are known as tension bands in the industry, essentially strong rubber bands. The users can decide how much spring force is required for a given task, and may manually add or remove tension bands as needed with their other hand. The prong hooks are opened by a cable placed under tension. The cable is pulled by a harness being worn by the user consisting of a strap going across the torso and both shoulders. This means that a user must flex their back or shoulders to accomplish the opening action of the terminal hook.
Figure 6: Prosthetic Hook and Harness
a bionic device is a significant challenge. Con-
trolling a bionic limb must be quick, easy and reliable for it to have any advantage over a non- functioning alternative.
The most basic, controllable, artificial limbs rely on a system of cables attached to a harness that the user wears. Motion of the
Figure 7: Body Powered Harness Motion There are several advantages to using pros-
thetic hooks. Hooks are incredibly reliable;
there is only one or two moving parts the entire system. There are no batteries to be charged and there are no electronic components which could possibly fail. In general if something needs to be adjusted with the system common hand tools can be used. The hooks can handle high mechanical loading which are useful for physical labor and strenuous tasks. Users have no fear of damaging components of the hook through rough usage. The inside of the hooks are generally lined with a high grip rubber ma- terial. Overall the prosthetic hook systems are very cost effective considering their long lifes- pan. An entire strap and harness with hook would usually cost less than $9,000 and last many years very easily. Simply put, a user would have no worry about component fail- ure on a day-to-day basis. The bulk of that cost comes from the custom molded socket. The socket is usually made of carbon fiber and molded individually for each user depending on their unique amputation.
Prosthetic hooks come with their own limitations. The single greatest limita- tion stems from the fact that the holding force of the hooks is supplied ready man- ually adjusted spring tension bands. In order to have a high gripping force, the user would have to strain their muscles to open the hooks which can lead to muscle fatigue or pain. High gripping force is generally desired when handling a large or heavy object. For example, holding onto a broom handle or rake proves to be quite challenging due to the large amount of force required. Related to the limi- tation of muscle force required to open prosthetic hooks, users often report pain from a strap and harness during activities
which require frequent opening and clos- ing of the end effector. One frustration with prosthetic hooks comes from having to change the tension bands manually in order to adjust the gripping force. Multi- ple tension bands have to be carried at all times and require use of a secondary hand and earth to make changes. The same force desired to securely hold a heavy ob- ject is enough to crush a lightweight ob- ject such as a thin plastic bottle or some foods.
One overarching issue found the pros-
thetic hooks stems from the social stigma of people who are seen as different in so- ciety. Everyone in the world strives to be seen as normal and lead a normal func- tioning life. Far too often, amputees re- port discomfort in social situations from being stared at or treated differently. Prosthetic hooks standout easily with their unusual shape and function. Many people still associate prosthetic hooks with pirate hooks sadly. In addition to social issues, wearers of prosthetic hooks report dissatisfaction in their personal lives in and relationships with friends and family. Users find it more challenging to show affection through their prosthetic hook because of its unusual shape and feel. It can be challenging to care the harness with certain styles of clothing.
chieving a more complex set of move- ments relies on integration with a digi-
tal control method. These can be very ba- sic, such as placing a controlling unit into the users shoe, or very complex such as myoelec- tric control that interprets electrical activity in the neuromusculature of the limb stump to al- low motion.
Myoelectric control is the most widely used control in commercially available bionic limbs. It relies on complex algorithms to make sense of the massive amount of electrical activity in the stump, which is affected by everything from movement in the shoulder or elbow to the heartbeat. Techniques such as electrical pat- tern recognition can be used to activate whole muscle groups that form components of cer- tain movements. For instance electrical activ- ity in the flexor compartment of the forearm
will lead to flexing of the bionic hand. Never- theless learning how to use a myoelectrically controlled prosthesis can be time consuming and difficult and there must be enough elec- trical activity in the limb stump for them to work. Improving the accuracy of computer al- gorithms that decode the signals is a substan- tial area of research at present.
Myoelectric upper limb technologies use elec- trical signals generated by muscles in the resid- ual limb to control the movements of prosthe- sis. When the user contracts certain muscles, surface electrodes in the socket detect the mus- cle signals and send them to a controller, which triggers tiny, battery-powered motors to move the fingers, hand, wrist or elbow. The advan- tages of myoelectric prostheses include more in- tuitive control of the prosthesis, increased grip strength, access to multiple grip patterns and more natural hand movements.
Myoelectric technologies are available for all levels of upper limb loss.
Electric finger solutions for those with finger amputations consist of individually-powered prosthetic fingers that can bend, touch, pick up and point. Electric finger solutions are cus- tom built to replace any missing fingers and work in harmony with any remaining fingers.
Figure 8: Myoelectric finger
Fully articulating myoelectric hands are avail- able from a variety of manufacturers in multi- ple sizes and configurations. Some of the most popular devices are:
The Taska Hand
The Michelangelo Hand
BeBionic and iLimb Hands
Figure 9: BeBionic Hand
Figure 10: iLimb Hand
Several years ago, robotic prosthetic hands with individually articulated fingers were re- leased onto the market. These hands were com- pletely revolutionary in their look and function compared with other prosthetic options that existed. Touch Bionics was the first company to release one of these hands known as the iL- imb. The iLimb is based around the design of an individual finger, known as digits by 14 Touch Bionics. Each finger contains its own motor and gearbox which is very helpful when designing a prosthetic hand which must fit in- side human proportions. In fact, amputees who are only missing partial fingers may sim- ply use as many Digits as they need in a cus- tom solution from Touch Bionics. Each finger has a joint at the ase and one pivot point at the first knuckle. The fingertip is passively actuated by being pulled on by a cable. One interesting mechanical aspect of the fingers is a spring linkage which allows the fingers to be manually bent inwards to prevent damage if the hand hits into a hard object. Altogether, the iLimb has 5 degrees of freedom. User in- put is controlled through myoelectric sensors reading the muscle signals remaining on a por- tion of an amputees arm. The control is de- signed to be intuitive in this sense that a per- son should optimally be able to open and close
their hand with the same muscle signals they would normally send them to an actual human hand. Touch bionics boasts 14 different grip patterns which are all subtle variations of the most commonly used patterns.
Figure 11: Myoelectric Control Example
How it works
The iLimb is an externally powered prosthesis often controlled by myoelectric signals, mean- ing it uses muscle signals in the patients resid- ual limb to move the device. Electrodes are placed on the users bare skin above two pre- selected muscle sites. When a user contracts these muscles, the electrodes pick up subtle changes in the electrical patterns and send these signals to a microprocessor which in- structs the iLimb to open and close.
The iLimb can open and close into several dif- ferent grip such as a lateral grip or precision pinch. Users can assign their most commonly used grip to up to four different muscle trig- gers.
hold open (using the open signal for a set period of time)
double impulse (two quick open signals after the hand is fully open)
triple impulse (three quick open signals after the hand is fully open)
co-contraction (contracting both the open and close muscles simultaneously)
When the user activates any one of these trig- gers, the iLimb will move into the grip that has been assigned to it.
The number of triggers programmed de- pends on each individuals ability to control
and activate the signals. As the users control and strength improves over time with practice, the user can assign more triggers to grips for improved dexterity and function.
Overall, the iLimb is a fantastic product which has given a tremendous amount of in- creased functionality to the lives of many am- putees. The cost of the hand would be a stag- gering $60,000.
Figure 12: Darin Sargent with his i-limb The iLimb however does not have an ac-
tively powered positionable thumb. The user
must use their other hand to manually rotate the angle of the thumb. For example, if a user is eating a meal and has their hand in a key grip mode for holding onto a spoon or fork, and then decides to drink from a glass or cup, the user would have to manually rotate the thumb down until it is in position for a cylin- drical grip. The iLimb does at least contain a sensor to recognize the current position of the thumb to help ensure the hand is not going to damage itself in certain grip modes. There is also no force feedback provided to the user, so it can be difficult to perform precision tasks. As a result of the lack of force feedback, users may inadvertently drop objects because they are not being gripped firmly enough, but there is no indication before it is too late and the object has fallen.
The BeBionic hand is incredibly similar in construction to the iLimb. The BeBionic hand was produced by RSL Steeper with the intention of offering similar functionality to the iLimb at a slightly reduced cost. Some people speculate that the hand is a direct spinoff based on identical mechanical compo- nents. There are little to no functional dif- ferences between the two hands, so they are considered the same for the sake of discussion.
entral and peripheral motor and so- matosensory pathways retain significant residual connectivity and function for many years after limb amputation and this property has been exploited by researchers using a tech- nique called targeted motor reinnervation to increase the accuracy of myoelectrically con-
In this technique the nerves that once sup- plied the amputated limb muscles are surgi- cally anastomosed into the remaining muscles of the amputation stump to create indepen- dently controlled nerve-muscle units. The rein- nervated muscles act as biological amplifiers of motor commands in the amputated nerves and the surface electromyogram (EMG) can be used to enhance control of a robotic arm. This technique has shown promising results with the ability to achieve intuitive control of multiple functions in a bionic hand.
An alternative system being developed to increase accuracy of myoelectric prostheses in- volves the implantation of bipolar differential electromyographic (EMG) electrodes within the muscle to create a system capable of read- ing intra muscular EMG signals that increases the number of control sources available for prosthesis control.
Targeted Muscle Reinnerva- tion(TMR)
Targeted muscle reinnveration, usually referred to as TMR is a complicated surgical proce- dure for high level arm amputees that takes nerves previously dedicated to hand, wrist or elbow motion, and rewires them into adjacent muscles, dramatically amplifying the nerve sig- nals with the goal of providing users with thought control of their myoelectric prosthe- sis.
Current myoelectric prostheses for above-
elbow and shoulder disarticulation levels pro- vide up to three degrees of freedom:
Flexing and extending the elbow hold open (using the open signal for a set pe- riod of time)
Turning the wrist in or out
Opening and closing the hand or elec- tronic terminal device
These motions are typically controlled one at a time by electrical signals from one or two
muscle sites (known as EMG sites) in the residual limb or upper shoulder area.
TMR surgery creates additional EMG sites that are controlled with distinct and intuitive muscle contractions, some of which can oc- cur simultaneously and with less mental ef- fort. When combined with occupational ther- apy, the result is a high level of intuitive con- trol, which can significantly enhance the func- tional use of the prosthesis.
Mind Controlled Bionic Arm
The Rehabilitation Institute of Chicago intro- duced the first woman to be fitted with its bionic arm technology. Claudia Mitchell, who had her left arm amputated at the shoul- der after a motorcycle accident, can now grab a drawer pull with her prosthetic hand by think- ing, grab drawer pull. That a person can suc- cessfully control multiple, complex movements of a prosthetic limb with his or her thoughts opens up a world of possibility for amputees.
Figure 13: Claudia Mitchell with her bionic arm
How it works
The bionic arm technology is possible pri- marily because of two facts of amputation. First, the motor cortex in the brain (the area that controls voluntary muscle movements) is still sending out control signals even if certain voluntary muscles are no longer available for control; and second, when doctors amputate a limb, they dont remove all of the nerves that once carried signals to that limb. So if a persons arm is gone, there are working nerve stubs that end in the shoulder and simply have nowhere to send their information. If those nerve endings can be redirected to a working muscle group, then when a person thinks grab handle with hand, and the brain sends out the corresponding signals to the nerves that should communicate with the hand, those signals end
up at the working muscle group instead of at the dead end of the shoulder.
Dr. Todd Kuiken of the RIC developed the procedure, which he calls targeted mus- cle re-innervation. Surgeons basically dissect the shoulder to access the nerve endings that control the movements of arm joints like the elbow, wist and hand. Then, without dam- aging the nerves, they redirect the endings to a working muscle group. In the case of the RICs bionic arm, surgeons attach the nerve endings to a set of chest muscles. It takes sev- eral months for the nerves to grow into those muscles and become fully integrated. The end result is a redirection of control signals: The motor cortex sends out signals for the arm and hand through nerve passageways as it always did; but instead of those signals ending up at the shoulder, they end up at the chest.
To use those signals to control the bionic arm, the RIC setup places electrodes on the surface of the chest muscles. Each electrode controls one of the six motors that move the prosthetic arms joints. When a person thinks open hand, the brain sends the open hand signal to the appropriate nerve, now located in the chest. When the nerve ending receives the signal, the chest muscle its connected to con- tracts. When the open hand chest muscle contracts, the electrode on that muscle detects the activation and tells the motor controlling the bionic hand to open. And since each nerve ending is integrated into a different piece of chest muscle, a person wearing the bionic arm can move all six motors simultaneously, result- ing in a pretty natural range of motions for the prosthesis.
Figure 14: Bionic arm working example
Control bionic hand without help of vision
Theres no arguing that prosthetics have come a long way. Controlling a robotic limb with your brainwaves was impossible a mere decade ago; now it seems routine. More than ever, scientists are squeezing increasingly dense sets of motors and sensors into replacement limbs. The result is sophisticated bionic ap- pendages capable of fine, dexterous movement. But theres a problem: without a di- rect visual, the wearer has absolutely no idea what their bionic arm is up to. They dont know where the arm is in space, how fast its moving, or where its going. This intu- itive sense of body positioning, dubbed kines- thesia, has been hard to build into prosthet- ics. Its not touchkinesthesia uses feedback from the joints and muscles to compute where your limbs are even without direct touch feed- back. Yet, like touch, kinesthesia is essen- tial for fine motor control: this is the sense that lets you shove a handful of popcorn into your mouth while keeping your eyes on the big screen. Its behind seemingly mundane actions such as scratching your back or catching a ball. Somebody with a prosthetic hand, since they cant feel the movement of their device, they es- sentially have to compensate [for] that with vi- sion, said lead author Dr. Paul Marasco at the Cleveland Clinic, who collaborated with the University of Alberta and University of New Brunswick. This kills any sense of ownership of the arm.
The new device restores kinesthesia using a se- riously clever body hack. When you vibrate a tendon at 70 to 115 Hz, it makes it feel like the associated joint is moving. The illusion is strong enough that the person thinks their limbs are contorted into impossible positions or that their nose is growing like Pinocchios. By vibrating multiple tendons, scientists can in- duce the sensation of complex arm movements in space without anything physically moving.
Scientists have known about this phe- nomenondubbed the vibration-induced kinesthetic illusionsince the 1970s, but no ones ever tested it in amputees before.
The volunteers in this study had previ- ously undergone surgery to rewire the remain- ing nerves in their upper bodies to other mus- cles. For example, the nerve that normally controls the elbow is hooked up to chest mus- cles. When the patient thinks about moving his elbow, the nerve sends the command to the chest muscle. This activity is then picked up by a sensor that, in turn, instructs the pros- thetic arms elbow to move accordingly. The team first vibrated the volunteers chest, bi- cep, and triceps tendonswhere the remaining nerves were rerouted toand asked them to mimic the perceived movements in their miss- ing hands with their remaining one.
Incredibly, different vibration paradigms mapped onto a library of complex hand mo- tions. For example, stimulating the biceps in most patients generated the cylinder grip, in which the hand is loosely clenched as if wrap- ping around a tube. Other motions included the thumb and index finger fine pinch, or the thumb, middle, and index finger tripod pinch. In all, the team identified 22 different hand motions, or precepts.
Figure 15: Operating bionic hand without help of vision example
A Kinesthetic Interface
The next step was to put this library to use. The team developed a neural-machine interface with two lines of communication. When the patient thinks about moving the bionic arm, the signal is picked up from the re-innervated muscle to control the prosthesis. At the same time, it also triggers a small but powerful mo- tor to vibrate the muscle, generating the kines- thetic illusion.
The improvement was evident within min- utes. Using computer simulation software, the volunteers could easily close their virtual pros- thetic hands a quarter, half, or three quar- ters of the way without watching the hand. In contrast, with the vibrations turned off they performed significantly worseone pa- tient had nearly no sense of hand position with- out adding the hack.
Kinesthetic feedback was even more pow- erful than vision for fine motor control. When asked to catch a virtual ball using their vir- tual hands, kinesthetic reflexes kicked in far faster than visual feedback, allowing the vol- unteers to reach out precisely and intuitively. Even with blindfolds and noise-canceling head- phones on to block off the world, the volunteers easily followed instructions to close the bionic hand into a cylinder grip. Whats more, they had no trouble reporting the status of the pros- theticswhether they were open or closed.
When you reach your hand out to grab your coffee cup or another object, your brain is sig- naling certain muscles to move. As your hand moves in response, nerves for those muscles send a message back to the brain about the
movement. You dont have to see your hand to know that youve grabbed your cup. You can feel it. Without these messages from the muscles and nerves, a person with a prosthetic hand or arm must rely on the eyes to relay messages about movement to the brain. But feedback from vision alone can be a clumsy substitute for complex sensory feedback.
Osseointegration Osseointegration(OI) is a surgical procedure that enables amputees to attach a prosthesis directly to the bone of their residual limb with a titanium implant, eliminating the need for a socket. By making it possible to safely attach a prosthetic limb directly to the body with- out the need for a socket, OI is improving the lives of amputees around the world through the comfort and natural movement of an OI pros-
surgery by the renowned Dr. Albert Chi, M.D., FACS, Oregon Health Science University (OHSU). By taking advantage of existing neu- rological pathways, Dr. Chi rewired the nerves that once controlled Moores hand and arm to control the prosthetic device.
Moore was initially fit with a LUKE arm prosthesis but quickly realized he wanted more than what the socket technology could provide. He opted to undergo osseointegration surgery by Dr. Munjed Al Muderis, orthopedic sur- geon and clinical lecturer at Macquarie Uni- versity and The Australian School of Advanced Medicine, Sydney, Australia. Osseointegration allows the prosthesis to be anchored directly to the bone, giving patients freedom of move- ment, eliminating the need for a socket.
ur hands allow us to interact with our en-
O vironment. We use the sensory input for
Figure 16: Luke arm prosthetic recipient Ju- nius Moore: and Matt Albuquerque, president and founder of Next StepBionics & Prosthetics Junius Moore, 35, is the worlds first recip- ient of an osseointegrated LUKE arm com- bined with post targeted muscle reinnervation (TMR) surgery. This first-of-its-kind pros- thetic advancement will pave the way for simi- lar procedures in the United States, benefiting trans-radial (lower arm), trans-humeral (mid-
arm), and shoulder disarticulation amputees.
Next Step conducted the first public demonstration of the LUKE arm prosthesis and the fitting that makes it possible to have it integrated into the patients living bone and controlled by muscle movements in the remain- ing limb at a news conference on 12 DEC 2018 at Next Steps headquarters in the Med-Tech Mill Yard in Manchester.
Moore, a trans-humeral (mid-arm) am- putee due to a motor vehicle accident, un- derwent targeted muscle reinnervation (TMR)
touch, to fine-tune movements and to avoid
harm. A continuing challenge for prostheses developers is to replicate the sensory function of the hand. Sensation in a bionic limb can be divided into two distinct categories e sensory information interpreted by the device itself and sensation that is perceived by the user.
Modern units have developed simple tech- niques for interpreting tactile sensory informa- tion that the devices use intrinsically to mod- ify their activity. For example information on grasp strength ensures a user will not break objects by holding them too tightly whilst in- formation provided by detection of sound from microphones embedded in the hand ensures that the object will not slip out of the grip and be dropped. This information, required for di- rect control of the device, can be interpreted via a low-level control loop thus decreasing the cognitive load of the user and increasing pa- tient acceptability. These features improve the functionality of the device but do not provide the user with any sensory information about their surroundings.
Providing a sensory input from a bionic limb that is capable of being perceived by the user is far more complex. One approach is to utilize the concept of multimodal plastic- ity where loss of one sensory modality can be compensated by another. For example hearing can partly compensate for the loss of touch if auditory feedback is given when a bionic limb
comes into contact with an object.
Another approach is to try to replicate sen-
sation by transferring stimuli from electronic sensors in the bionic limb to natural sensors on the skin of the limb stump which the patient perceives as coming from the amputated limb. This has been difficult to achieve but recent work has successfully replicated more complex sensory modalities such as cutaneous propri- oception alongside fine touch and pain sensa- tion. It is hoped that this technique can be further developed to provide a complete range of sensations.
Direct interfaces with the peripheral or cen- tral nervous systems may provide the solution to enhanced sensation from bionic hands and ultimately come closest to restoring the origi- nal sensory perceptions of the hand. The use of intraneural electrodes that are capable of delivering information directly to the periph- eral afferent nerves within the residual limb has shown promising results in delivering meaning- ful sensations to amputees. Delivering sensa- tions through this approach has been shown to improve control as it allowed amputees to con- trol the grip force and joint position of their artificial limb more accurately without relying on visual input. One of the main advantages of a sensitized bionic limb is the accelerated reha- bilitation program as the patient finds it more intuitive to learn how to control when they are receiving tactile feedback from the device.
With advancements in these technologies we may soon be able to re-wire the sensory input to the peripheral nervous system so that the central nervous system can perceive sensa- tions coming from a bionic limb as if it were the natural limb.
Bionic hand allows patient to feel
Figure 17: Igor Spetic with his bionic arm with realistic finger sensation.
Igor Spetic, 49, lost his right hand in a work related accident five years ago. But on Oct. 9, he got to bring home an innovative prosthetic hand for the first time, one that not only has more precise gripping, but gives him back his sense of touch.
The hand was created by researchers at Case Western Reserve University, which was granted$4.4 million from the Defense Ad- vanced Research Projects Agency (DARPA) for their work creating a prosthetic hand that can feel. The goal is to make a hand that al- lows someone to function in a way that allows him to forget he doesnt have the real version. Whats exciting about Case Westerns tech- nology is that it creates a connection between the prosthetic and the brain, allowing users to actually feel the sensation of picking up on ob-
How it works:
Sensors in the prosthetic hand measure
the pressure applied to various objects as the hand closes around them.
The measurements are then recorded, converted into a neural code, and sent through wires to electrodes that were sur- gically implanted around nerve bundles in Spetics forearm and upper arm.
When the neural code reaches Spetics nerves, the signal is transmitted through
his healthy neural pathways that werent affected by his amputation, to his brain.
The brain interprets the signals as feel- ing, as if from a normal hand.
Figure 18: How finger sensation is achieved: Even though the sensor is gone, the wires that communicate the information to the brain still exits. Devices was developed which can go on to those wires and apply electrical information that communicates with the wires and send it back to the brain.
Electrical impulses in the nervous system con- vey information between brain cells or along the neurons in the peripheral nerves that stretch throughout the body. These signals drive the actuators of the body, such as the muscles, and they provide feedback in the form of sensation, limb position, muscle force, and so on.
By inserting electrodes directly into mus- cles or wrapping them around the nerves that control the contraction of the muscles, we can send commands to those electrodes that roughly replicate the signals associated with moving a hand, standing up, or lifting a foot
Figure 19: An x-ray reveals the sugically im- planted electrode cuffs: in Spetics forearm and the wires in his upper arm that connects to an external computer.
Engineering such an interface is difficult be- cause it has to allow precise patterns of stimu- lation to the persons peripheral nerves, with- out damaging or otherwise altering the nerves. It also must function reliably for years within the harsh environment of the body.
There are several approaches to designing an implanted interface. The least invasive is to embed electrodes in a muscle, near the point where the target nerve enters that muscle. Such systems have been used to restore func- tion following spinal-cord injury, stroke, and other forms of neurological damage. The body tolerates the electrodes well, and surgically re- placing them is relatively easy. When the elec- trodes need to activate a muscle, however, it of- ten requires a current of up to 20 milliamperes, about the same amount you get when you shuf- fle across a carpet and get shocked; even then, the muscle isnt always completely ac- tivated.
The most invasive approach involves insert- ing electrodes deep into the nerve. Placing the stimulating contacts so close to the target ax- onsthe parts of nerve cells that conduct elec- trical impulsesmeans that less current is re- quired and that very small groups of axons can be selectively activated. But the body tends to reject foreign materials placed within the pro- tective layers of its nerves. In animal experi- ments, the normal inflammatory process often pushes these electrodes out of the nerve.Figure 20: Restoring The Sense of Touch:
To allow a person with a prosthetic hand to perceive sensations, researchers at Case West- ern Reserve University surgically implanted
electrode cuffs around the median, radial, and ulnar nerves in the affected arm. The flat- tened cuff [above right] is more effective than the traditional circular cuff [above left] because electrical signals can access the nerve fibers more easily. When precise patterns of electri- cal pulses are sent to each electrode, the sub- ject feels sensations at specific sites on the front and back of his hand, as well as different tex- tures. Although this experimental system uses an external computer, the eventual goal is to implant a controller, which will wirelessly com- municate with the prosthetic hand.
Spetic, the cherry-plucking volunteer, has the flat electrode cuffs placed around the me- dian and ulnar nerves, two of the three main nerves in his arm. He has a traditional circular electrode placed around the radial nerve. This provides a total of 20 stimulation channels in his forearm: eight each on the median and ul- nar nerves and four on the radial nerve. Test- ing revealed that the 20 stimulation points cre- ated sensations at 19 places on Spetics missing hand, including spots on the left and right sides of his palm, the back of his hand, his wrist, his thumb, and his fingertips.
The next generation of cuff will have four times as many contacts. The more channels, the more selectively it will be able to access small groups of axons and provide a more use- ful range of sensations. In addition to the tac- tile, research is done to produce sensations like temperature, joint position (known as propri- oception), and even pain. Despite its negative connotation, pain is an important protective mechanism. During the tests, one stimulation channel did cause a painful sensation. Eventu- ally, we will be able to include such protective mechanisms.
The user feels like an actual hand is touching the object. It feels real, says Dustin Tyler, leader of the project and an associate profes- sor of biomedical engineering at Case Western. Until recently, Spetic had been testing Case Westerns technology in the lab, but in Octo- ber he took the prosthetic home, and became one of the first people to test such advanced prosthetics in real world situations, outside of the artificial conditions in a lab.
Already, hes been able to accomplish small tasks that were once extremely difficult, like cutting fruits and
vegetables with a knife, securely holding his coffee cup, and opening bags with both hands instead of using a combination of his teeth and left hand.
What Im excited about is knowing that I can go back from being one-handed to being a two-handed person, says Spetic. Of course its going to be a relearning of using a right hand that I havent had for 5 years, but I can hopefully be a two-handed person again.
Research to Consider
The ultimate goal is to achieve a Bio mecha- tronic design where the mechatronic system of the artificial hand is inspired by and works like the living limb. To achieve this goal there would need to be integration of the prostheses with the central nervous system so that the re- placement moves and is perceived as if it were the natural hand without the requirement for any training or adaptation.
Though the design of prosthetics is con- tinuing to develop and benefits many patients living with an amputated limb, there are still challenges ahead in the design of a prosthetic limb that satisfies intricate requirements, such as easy control of the prosthetic limb and to make this mechanical device cosmetically ap- pealing. There is also the challenge of under- standing the issue of tissue reactions to mate- rial used for the prosthetic limb and how an inflammatory response to such a reaction may interfere with signal transmission of biosensors. In case of integrating feeling of touch, to make a self-contained device that doesnt rely on an external computer, there is a need of miniature processors that can be inserted into the prosthesis to communicate with the im- plant and send stimulation to the electrode cuffs. The implanted electronics must be ro- bust enough to last years inside the human body and must be powered internally, with no wires sticking out of the skin. There is also a need to work out the communication proto- col between the prosthesis and the implanted
The use of intraneural electrodes is perhaps the most promising technology that may hold the key to successful integration of bionic limbs
into the biological system. Intraneural elec- trodes interface directly into the nerves in the limb stump and have the ability to carry a bidirectional flow of information between the bionic limb and patient. It is a daunting en- gineering challenge, but when succeeded, this haptic technology could benefit more than just prosthetic users. Such an interface would al- low people to touch things in a way that were never before possible.
Imagine an obstetrician feeling a fetuss heartbeat, rather than just relying on Doppler imaging. Imagine a bomb disposal specialist feeling the wires inside a bomb that is actually being handled by a remotely operated robot. Imagine a geologist feeling the weight and tex- ture of a rock thats thousands of kilometers away or a salesperson tweeting a handshake to a new customer.
Such scenarios could become reality within the next decade. Sensation tells us what is and isnt part of us. By extending sensation to our machines, we will expand humanitys reacheven if that reach is as simple as hold- ing a loved ones hand.
The prosthetic hand of the middle ages was present merely as a prop. Today we have bionic hand prostheses that give much better func- tionality, are acceptable to more patients and are durable and comfortable. However these prostheses still have to overcome considerable hurdles in order to mimic or even improve upon the intrinsic hand and they carry significant economic implications. The advancements in this field of medicine are exponential and it is likely that within 10 years there will be com- mercially available limbs that provide both sen- sation and accurate motor control from day 1. Being Bionic raises a new question, can a bionic arm outlast the human one?!!! Well,
even the most advanced prosthetic is not a replacement for a flesh and blood limb. As the technology progresses, we are likely to progress with it. Most prosthetics are still in their infancy and are limited to medical use. But what happens when these technologies be- comes more advanced, smarter and stronger. Will normal people want them? Policy makers have already started to bring up the issue that as soon as it becomes more mechanical, our laws will have to evolve
to reflect how we look
at privacy access in domain of our own bodies, making them do what we dont want them to do. I really believe that in the end, we will be able to do those kinds of things but humanity have so much to gain here.
So… YES. I think all these technologies will change us but I dont think thats a bad thing.
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