Editing Prosthesis (section)

==Current technology and manufacturing==
[[File:WorkNC-Knee prosthesis.jpg|right|thumb|Knee prosthesis manufactured using [[WorkNC]] [[Computer Aided Manufacturing]] software]]
Over the years, there have been advancements in artificial limbs. New plastics and other materials, such as [[carbon fiber]], have allowed artificial limbs to be stronger and lighter, limiting the amount of extra energy necessary to operate the limb. This is especially important for trans-femoral amputees. Additional materials have allowed artificial limbs to look much more realistic, which is important to trans-radial and transhumeral amputees because they are more likely to have the artificial limb exposed.<ref name="three">{{cite web|url=http://www.madehow.com/Volume-1/Artificial-Limb.html |title=How artificial limb is made&nbsp;– Background, Raw materials, The manufacturing process of artificial limb, Physical therapy, Quality control |publisher=Madehow.com |date=1988-04-04 |access-date=2010-10-03}}</ref>
[[File:Journal.pone.0019508.g004 prosthetic finger.png|left|thumb|Manufacturing a prosthetic finger]]

In addition to new materials, the use of electronics has become very common in artificial limbs. Myoelectric limbs, which control the limbs by converting muscle movements to electrical signals, have become much more common than cable operated limbs. Myoelectric signals are picked up by electrodes, the signal gets integrated and once it exceeds a certain threshold, the prosthetic limb control signal is triggered which is why inherently, all myoelectric controls lag. Conversely, cable control is immediate and physical, and through that offers a certain degree of direct force feedback that myoelectric control does not. Computers are also used extensively in the manufacturing of limbs. [[CAD/CAM|Computer Aided Design and Computer Aided Manufacturing]] are often used to assist in the design and manufacture of artificial limbs.<ref name="three" /><ref name="sapphire">{{cite journal |last1=Mamalis |first1=AG |last2=Ramsden |first2=JJ |last3=Grabchenko |first3=AI |last4=Lytvynov |first4=LA |last5=Filipenko |first5=VA |last6=Lavrynenko |first6=SN |title=A novel concept for the manufacture of individual sapphire-metallic hip joint endoprostheses |journal=Journal of Biological Physics and Chemistry |date=2006 |volume=6 |issue=3 |pages=113–117 |doi=10.4024/30601.jbpc.06.03|hdl=1826/2527 |hdl-access=free }}</ref>

Most modern artificial limbs are attached to the residual limb (stump) of the amputee by belts and cuffs or by [[suction]]. The residual limb either directly fits into a socket on the prosthetic, or—more commonly today—a liner is used that then is fixed to the socket either by vacuum (suction sockets) or a pin lock. Liners are soft and by that, they can create a far better suction fit than hard sockets. Silicone liners can be obtained in standard sizes, mostly with a circular (round) cross section, but for any other residual limb shape, custom liners can be made. The socket is custom made to fit the residual limb and to distribute the forces of the artificial limb across the area of the residual limb (rather than just one small spot), which helps reduce wear on the residual limb.

=== Production of prosthetic socket ===
The production of a prosthetic socket begins with capturing the geometry of the residual limb; this process is called shape capture. The goal of this process is to create an accurate representation of the residual limb, which is critical to achieve good socket fit.<ref name=":6">{{Cite journal|last1=Suyi Yang|first1=Eddie|last2=Aslani|first2=Navid|last3=McGarry|first3=Anthony|date=October 2019|title=Influences and trends of various shape-capture methods on outcomes in trans-tibial prosthetics: A systematic review|url=https://pubmed.ncbi.nlm.nih.gov/31364475/|journal=Prosthetics and Orthotics International|volume=43|issue=5|pages=540–555|doi=10.1177/0309364619865424|issn=1746-1553|pmid=31364475|s2cid=198999869}}</ref> The custom socket is created by taking a plaster cast of the residual limb or, more commonly today, of the liner worn over their residual limb, and then making a mold from the plaster cast. The commonly used compound is called Plaster of Paris.<ref>{{Cite journal|last1=Sharma|first1=Hemant|last2=Prabu|first2=Dhanasekara|date=September 2013|title=Plaster of Paris: Past, present and future|journal=Journal of Clinical Orthopaedics and Trauma|volume=4|issue=3|pages=107–109|doi=10.1016/j.jcot.2013.09.004|issn=0976-5662|pmc=3880430|pmid=26403547}}</ref> In recent years, various digital shape capture systems have been developed which can be input directly to a computer allowing for a more sophisticated design. In general, the shape capturing process begins with the digital acquisition of three-dimensional (3D) geometric data from the amputee's residual limb. Data are acquired with either a probe, laser scanner, structured light scanner, or a photographic-based 3D scanning system.<ref>{{Cite journal|last1=Herbert|first1=Nicholas|last2=Simpson|first2=David|last3=Spence|first3=William D.|last4=Ion|first4=William|date=March 2005|title=A preliminary investigation into the development of 3-D printing of prosthetic sockets|url=https://pubmed.ncbi.nlm.nih.gov/15944878/|journal=Journal of Rehabilitation Research and Development|volume=42|issue=2|pages=141–146|doi=10.1682/jrrd.2004.08.0134|doi-broken-date=1 November 2024 |issn=1938-1352|pmid=15944878|s2cid=9385882 }}</ref>

After shape capture, the second phase of the socket production is called rectification, which is the process of modifying the model of the residual limb by adding volume to bony prominence and potential pressure points and remove volume from load bearing area. This can be done manually by adding or removing plaster to the positive model, or virtually by manipulating the computerized model in the software.<ref>{{Cite journal|last1=Sewell|first1=P.|last2=Noroozi|first2=S.|last3=Vinney|first3=J.|last4=Andrews|first4=S.|date=August 2000|title=Developments in the trans-tibial prosthetic socket fitting process: a review of past and present research|url=https://pubmed.ncbi.nlm.nih.gov/11061196/|journal=Prosthetics and Orthotics International|volume=24|issue=2|pages=97–107|doi=10.1080/03093640008726532|issn=0309-3646|pmid=11061196|s2cid=20147798}}</ref> Lastly, the fabrication of the prosthetic socket begins once the model has been rectified and finalized. The prosthetists would wrap the positive model with a semi-molten plastic sheet or carbon fiber coated with epoxy resin to construct the prosthetic socket.<ref name=":6" /> For the computerized model, it can be 3D printed using a various of material with different flexibility and mechanical strength.<ref>{{Cite journal|last1=Ribeiro|first1=Danielle|last2=Cimino|first2=Stephanie R.|last3=Mayo|first3=Amanda L.|last4=Ratto|first4=Matt|last5=Hitzig|first5=Sander L.|date=2019-08-16|title=3D printing and amputation: a scoping review|url=https://pubmed.ncbi.nlm.nih.gov/31418306/#:~:text=A%20scoping%20review%20was%20conducted,in%20the%20field%20of%20amputation.&text=Conclusions:%20The%20use%20of%203D,lower%20and%20upper%20limb%20loss.|journal=Disability & Rehabilitation: Assistive Technology|volume=16|issue=2|pages=221–240|doi=10.1080/17483107.2019.1646825|issn=1748-3115|pmid=31418306|s2cid=201018681}}</ref>

Optimal socket fit between the residual limb and socket is critical to the function and usage of the entire prosthesis. If the fit between the residual limb and socket attachment is too loose, this will reduce the area of contact between the residual limb and socket or liner, and increase pockets between residual limb skin and socket or liner. Pressure then is higher, which can be painful. Air pockets can allow sweat to accumulate that can soften the skin. Ultimately, this is a frequent cause for itchy skin rashes. Over time, this can lead to breakdown of the skin.<ref name="four">{{cite web|url=http://www.abc.net.au/science/slab/leg/default.htm |title=Getting an artificial leg up&nbsp;– Cathy Johnson |publisher=Australian Broadcasting Corporation |access-date=2010-10-03 }}</ref> On the other hand, a very tight fit may excessively increase the interface pressures that may also lead to skin breakdown after prolonged use.<ref>{{Cite journal|last1=Mak|first1=A. F.|last2=Zhang|first2=M.|last3=Boone|first3=D. A.|date=March 2001|title=State-of-the-art research in lower-limb prosthetic biomechanics-socket interface: a review|url=https://pubmed.ncbi.nlm.nih.gov/11392649/|journal=Journal of Rehabilitation Research and Development|volume=38|issue=2|pages=161–174|issn=0748-7711|pmid=11392649}}</ref>

Artificial limbs are typically manufactured using the following steps:<ref name="three" />
# Measurement of the residual limb
# Measurement of the body to determine the size required for the artificial limb
# Fitting of a silicone liner
# Creation of a model of the liner worn over the residual limb
# Formation of [[thermoplastic]] sheet around the model&nbsp;– This is then used to test the fit of the prosthetic
# Formation of permanent socket
# Formation of plastic parts of the artificial limb&nbsp;– Different methods are used, including [[vacuum forming]] and [[injection molding]]
# Creation of metal parts of the artificial limb using [[die casting]]
# Assembly of entire limb

===Body-powered arms===

Current technology allows body-powered arms to weigh around one-half to one-third of what a myoelectric arm does.

====Sockets====
Current body-powered arms contain sockets that are built from hard epoxy or carbon fiber. These sockets or "interfaces" can be made more comfortable by lining them with a softer, compressible foam material that provides padding for the bone prominences. A self-suspending or supra-condylar socket design is useful for those with short to mid-range below elbow absence. Longer limbs may require the use of a locking roll-on type inner liner or more complex harnessing to help augment suspension.

====Wrists====
Wrist units are either screw-on connectors featuring the UNF 1/2-20 thread (USA) or quick-release connector, of which there are different models.

====Voluntary opening and voluntary closing====
Two types of body-powered systems exist, voluntary opening "pull to open" and voluntary closing "pull to close". Virtually all "split hook" prostheses operate with a voluntary opening type system.

More modern "prehensors" called GRIPS utilize voluntary closing systems. The differences are significant. Users of voluntary opening systems rely on elastic bands or springs for gripping force, while users of voluntary closing systems rely on their own body power and energy to create gripping force.

Voluntary closing users can generate prehension forces equivalent to the normal hand, up to or exceeding one hundred pounds. Voluntary closing GRIPS require constant tension to grip, like a human hand, and in that property, they do come closer to matching human hand performance. Voluntary opening split hook users are limited to forces their rubber or springs can generate which usually is below 20 pounds.

====Feedback====
An additional difference exists in the biofeedback created that allows the user to "feel" what is being held. Voluntary opening systems once engaged provide the holding force so that they operate like a passive vice at the end of the arm. No gripping feedback is provided once the hook has closed around the object being held. Voluntary closing systems provide directly [[Proportional Myoelectric Control|proportional control]] and biofeedback so that the user can feel how much force that they are applying.

In 1997, the [[Colombians|Colombian]] Prof. [[Álvaro Ríos Poveda]], a researcher in bionics in [[Latin America]], developed an upper limb and hand prosthesis with [[sensory feedback]]. This technology allows amputee patients to handle prosthetic hand systems in a more natural way.<ref>{{Cite book|last=Rios Poveda|first=Alvaro|url=https://dukespace.lib.duke.edu/dspace/handle/10161/2661|title=Myoelectric Prostheses with Sensorial Feedback|date=2002|publisher=Myoelectric Symposium|isbn=978-1-55131-029-9|language=en-US}}</ref>

A recent study showed that by stimulating the median and ulnar nerves, according to the information provided by the artificial sensors from a hand prosthesis, physiologically appropriate (near-natural) sensory information could be provided to an amputee. This feedback enabled the participant to effectively modulate the grasping force of the prosthesis with no visual or auditory feedback.<ref name="pmid 24500407">{{cite journal|s2cid=206682721 |display-authors=6|last1=Raspopovic |first1=Stanisa |last2=Capogrosso |first2=Marco |last3=Petrini |first3=Francesco Maria |last4=Bonizzato |first4=Marco |last5=Rigosa |first5=Jacopo |last6=Di Pino |first6=Giovanni |last7=Carpaneto |first7=Jacopo |last8=Controzzi |first8=Marco |last9=Boretius |first9=Tim |last10=Fernandez |first10=Eduardo |last11=Granata |first11=Giuseppe |last12=Oddo |first12=Calogero Maria |last13=Citi |first13=Luca |last14=Ciancio |first14=Anna Lisa |last15=Cipriani |first15=Christian |last16=Carrozza |first16=Maria Chiara |last17=Jensen |first17=Winnie |last18=Guglielmelli |first18=Eugenio |last19=Stieglitz |first19=Thomas |last20=Rossini |first20=Paolo Maria |last21=Micera |first21=Silvestro |title=Restoring Natural Sensory Feedback in Real-Time Bidirectional Hand Prostheses |journal=Science Translational Medicine |date=5 February 2014 |volume=6 |issue=222 |pages=222ra19|pmid=24500407 |doi=10.1126/scitranslmed.3006820|url=http://infoscience.epfl.ch/record/198047}}</ref>

In February 2013, researchers from [[École Polytechnique Fédérale de Lausanne]] in Switzerland and the [[Sant'Anna School of Advanced Studies|Scuola Superiore Sant'Anna]] in Italy, implanted electrodes into an amputee's arm, which gave the patient sensory feedback and allowed for real time control of the prosthetic.<ref>[https://www.usatoday.com/story/news/nation/2014/02/05/bionic-hand-amputee-feels/5229665/ "With a new prosthetic, researchers have managed to restore the sense of touch for a Denmark man who lost his left hand nine years ago."], ''USA Today'', February 5, 2014</ref> With wires linked to nerves in his upper arm, the Danish patient was able to handle objects and instantly receive a sense of touch through the special artificial hand that was created by Silvestro Micera and researchers both in Switzerland and Italy.<ref>[http://www.channelnewsasia.com/news/health/artificial-hand-offering/986332.html "Artificial hand offering immediate touch response a success"], ''Channelnewsasia'', February 7, 2014</ref>

In July 2019, this technology was expanded on even further by researchers from the [[University of Utah]], led by Jacob George. The group of researchers implanted electrodes into the patient's arm to map out several sensory precepts. They would then stimulate each electrode to figure out how each sensory precept was triggered, then proceed to map the sensory information onto the prosthetic. This would allow the researchers to get a good approximation of the same kind of information that the patient would receive from their natural hand. Unfortunately, the arm is too expensive for the average user to acquire, however, Jacob mentioned that insurance companies could cover the costs of the prosthetic.<ref>{{Cite web|last=DelViscio|first=Jeffery|title=A Robot Hand Helps Amputees "Feel" Again|url=https://www.scientificamerican.com/article/a-robot-hand-helps-amputees-feel-again/|access-date=2020-06-12|website=Scientific American|language=en}}</ref>

====Terminal devices====
Terminal devices contain a range of hooks, prehensors, hands or other devices.

=====Hooks=====
Voluntary opening split hook systems are simple, convenient, light, robust, versatile and relatively affordable.

A hook does not match a normal human hand for appearance or overall versatility, but its material tolerances can exceed and surpass the normal human hand for mechanical stress (one can even use a hook to slice open boxes or as a hammer whereas the same is not possible with a normal hand), for thermal stability (one can use a hook to grip items from boiling water, to turn meat on a grill, to hold a match until it has burned down completely) and for chemical hazards (as a metal hook withstands acids or lye, and does not react to solvents like a prosthetic glove or human skin).

=====Hands=====
[[File:Myoelectric prosthetic arm.jpg|right|thumb|Actor [[Owen Wilson]] gripping the myoelectric prosthetic arm of a United States Marine]]

Prosthetic hands are available in both voluntary opening and voluntary closing versions and because of their more complex mechanics and cosmetic glove covering require a relatively large activation force, which, depending on the type of harness used, may be uncomfortable.<ref>{{Cite journal
  |vauthors=Smit G, Plettenburg DH | title = Efficiency of Voluntary Closing Hand and Hook Prostheses
  | journal = Prosthetics and Orthotics International
  | volume = 34
  | issue = 4
  | pages = 411–427
  | year = 2010
  | doi = 10.3109/03093646.2010.486390
  | pmid = 20849359| s2cid = 22327910
 | url = http://repository.tudelft.nl/islandora/object/uuid%3A8c18e55f-842a-4a74-9b62-4b7fd23d9756/datastream/OBJ/view
  }}</ref> A recent study by the Delft University of Technology, The Netherlands, showed that the development of mechanical prosthetic hands has been neglected during the past decades. The study showed that the pinch force level of most current mechanical hands is too low for practical use.<ref>{{cite journal|last1=Smit|first1=G|last2=Bongers|first2=RM|last3=Van der Sluis|first3=CK|last4=Plettenburg|first4=DH|title=Efficiency of voluntary opening hand and hook prosthetic devices: 24 years of development?|journal=Journal of Rehabilitation Research and Development|date=2012|volume=49|issue=4|pages=523–534|doi=10.1682/JRRD.2011.07.0125|pmid=22773256}}</ref> The best tested hand was a prosthetic hand developed around 1945. In 2017 however, a research has been started with bionic hands by [[Laura Hruby]] of the [[Medical University of Vienna]].<ref>{{cite magazine |last1=Robitzski |first1=Dan|orig-date=First published 18 April 2017 as "A Spare Hand" |title= Disabled Hands Successfully Replaced with Bionic Prosthetics|magazine=Scientific American |date=May 2017 |volume=316 |issue=5 |page=17 |doi=10.1038/scientificamerican0517-17}}</ref><ref>{{cite journal |last1=Hruby |first1=Laura A. |last2=Sturma |first2=Agnes |last3=Mayer |first3=Johannes A. |last4=Pittermann |first4=Anna |last5=Salminger |first5=Stefan |last6=Aszmann |first6=Oskar C. |title=Algorithm for bionic hand reconstruction in patients with global brachial plexopathies |journal=Journal of Neurosurgery |date=November 2017 |volume=127 |issue=5 |pages=1163–1171 |doi=10.3171/2016.6.JNS16154|pmid=28093018 |s2cid=28143731 }}</ref> A few open-hardware 3-D printable bionic hands have also become available.<ref>[https://bionico.org/mains-low-cost/ 3D bionic hands]</ref> Some companies are also producing robotic hands with integrated forearm, for fitting unto a patient's upper arm<ref>[https://www.theguardian.com/uk-news/2015/jun/16/uk-woman-ride-bike-first-time-worlds-most-lifelike-bionic-hand UK woman can ride bike for first time with 'world's most lifelike bionic hand' ]</ref><ref>[https://www.mirror.co.uk/news/technology-science/technology/revolutionary-1m-bionic-hand-allows-5895366 Bebionic robotic hand]</ref> and in 2020, at the Italian Institute of Technology (IIT), another robotic hand with integrated forearm (Soft Hand Pro) was developed.<ref>[https://www.euronews.com/2020/03/02/a-helping-hand-eu-researchers-develop-bionic-hand-that-imitates-life A helping hand: EU researchers develop bionic hand that imitates life]</ref>

====Commercial providers and materials====
Hosmer and [[Otto Bock]] are major commercial hook providers. Mechanical hands are sold by Hosmer and Otto Bock as well; the Becker Hand is still manufactured by the Becker family. Prosthetic hands may be fitted with standard stock or custom-made cosmetic looking silicone gloves. But regular work gloves may be worn as well. Other terminal devices include the V2P Prehensor, a versatile robust gripper that allows customers to modify aspects of it, Texas Assist Devices (with a whole assortment of tools) and TRS that offers a range of terminal devices for sports. Cable harnesses can be built using aircraft steel cables, ball hinges, and self-lubricating cable sheaths. Some prosthetics have been designed specifically for use in salt water.<ref>{{cite web|last1=Onken|first1=Sarah|title=Dive In|url=http://www.cityviewnc.com/2014/01/06/20010/dive-in|website=cityviewnc.com|access-date=24 August 2015|archive-url=https://web.archive.org/web/20150910011729/http://www.cityviewnc.com/2014/01/06/20010/dive-in|archive-date=10 September 2015|url-status=dead|df=dmy-all}}</ref>

===Lower-extremity prosthetics===
[[File:AustralianParalympianOfTheYear 468.JPG|thumb|right|A prosthetic leg worn by [[Ellie Cole]]]]
Lower-extremity prosthetics describes artificially replaced limbs located at the hip level or lower. Concerning all ages Ephraim et al. (2003) found a worldwide estimate of all-cause lower-extremity amputations of 2.0–5.9 per 10,000 inhabitants. For birth prevalence rates of congenital limb deficiency they found an estimate between 3.5 and 7.1 cases per 10,000 births.<ref>{{cite journal|pmid=12736892|year=2003|last1=Ephraim|first1=P. L.|title=Epidemiology of limb loss and congenital limb deficiency: A review of the literature|journal=Archives of Physical Medicine and Rehabilitation|volume=84|issue=5|pages=747–61|last2=Dillingham|first2=T. R.|last3=Sector|first3=M|last4=Pezzin|first4=L. E.|last5=MacKenzie|first5=E. J.|doi=10.1016/S0003-9993(02)04932-8}}</ref>

The two main subcategories of lower extremity prosthetic devices are trans-tibial (any amputation transecting the tibia bone or a congenital anomaly resulting in a tibial deficiency), and trans-femoral (any amputation transecting the femur bone or a congenital anomaly resulting in a femoral deficiency). In the prosthetic industry, a trans-tibial prosthetic leg is often referred to as a "BK" or below the knee prosthesis while the trans-femoral prosthetic leg is often referred to as an "AK" or above the knee prosthesis.

Other, less prevalent lower extremity cases include the following:
# Hip disarticulations&nbsp;– This usually refers to when an amputee or congenitally challenged patient has either an amputation or anomaly at or in close proximity to the hip joint. ''See [[hip replacement]]''
# Knee disarticulations&nbsp;– This usually refers to an amputation through the knee disarticulating the femur from the tibia. ''See [[knee replacement]]''
# Symes&nbsp;– This is an ankle disarticulation while preserving the heel pad.

====Socket====
The socket serves as an interface between the residuum and the prosthesis, ideally allowing comfortable weight-bearing, movement control and [[proprioception]].<ref>{{cite journal|pmid=11392649|year=2001|last1=Mak|first1=A. F.|title=State-of-the-art research in lower-limb prosthetic biomechanics-socket interface: A review|journal=Journal of Rehabilitation Research and Development|volume=38|issue=2|pages=161–74|last2=Zhang|first2=M|last3=Boone|first3=D. A.}}</ref> Socket problems, such as discomfort and skin breakdown, are rated among the most important issues faced by lower-limb amputees.<ref>{{cite journal |last1=Legro |first1=MW |last2=Reiber |first2=G |last3=del Aguila |first3=M |last4=Ajax |first4=MJ |last5=Boone |first5=DA |last6=Larsen |first6=JA |last7=Smith |first7=DG |last8=Sangeorzan |first8=B |title=Issues of importance reported by persons with lower limb amputations and prostheses. |journal=Journal of Rehabilitation Research and Development |date=July 1999 |volume=36 |issue=3 |pages=155–63 |pmid=10659798 }}</ref>

====Shank and connectors====
This part creates distance and support between the knee-joint and the foot (in case of an upper-leg prosthesis) or between the socket and the foot. The type of connectors that are used between the shank and the knee/foot determines whether the prosthesis is modular or not. Modular means that the angle and the displacement of the foot in respect to the socket can be changed after fitting. In developing countries prosthesis mostly are non-modular, in order to reduce cost. When considering children modularity of angle and height is important because of their average growth of 1.9&nbsp;cm annually.<ref name="ReferenceA"/>

====Foot====
Providing contact to the ground, the foot provides shock absorption and stability during stance.<ref>{{cite journal|doi=10.1097/00008526-200510001-00007|title=Perspectives on How and Why Feet are Prescribed|journal=Journal of Prosthetics and Orthotics|volume=17|pages=S18–S22|year=2005|last1=Stark|first1=Gerald}}</ref> Additionally it influences gait biomechanics by its shape and stiffness. This is because the trajectory of the center of pressure (COP) and the angle of the ground reaction forces is determined by the shape and stiffness of the foot and needs to match the subject's build in order to produce a normal gait pattern.<ref>{{cite journal|doi=10.1016/0966-6362(93)90038-3|title=Trajectory of the body COG and COP during initiation and termination of gait|journal=Gait & Posture|volume=1|pages=9–22|year=1993|last1=Jian|first1=Yuancheng|last2=Winter|first2=DA|last3=Ishac|first3=MG|last4=Gilchrist|first4=L}}</ref> Andrysek (2010) found 16 different types of feet, with greatly varying results concerning durability and biomechanics. The main problem found in current feet is durability, endurance ranging from 16 to 32 months<ref name="ReferenceB">{{cite journal |last1=Andrysek |first1=Jan |title=Lower-limb prosthetic technologies in the developing world: A review of literature from 1994–2010 |journal=Prosthetics and Orthotics International |date=December 2010 |volume=34 |issue=4 |pages=378–398 |doi=10.3109/03093646.2010.520060 |pmid=21083505 |s2cid=27233705 }}</ref> These results are for adults and will probably be worse for children due to higher activity levels and scale effects. Evidence comparing different types of feet and ankle prosthetic devices is not strong enough to determine if one mechanism of ankle/foot is superior to another.<ref name=":2">{{cite journal |last1=Hofstad |first1=Cheriel J |last2=van der Linde |first2=Harmen |last3=van Limbeek |first3=Jacques |last4=Postema |first4=Klaas |title=Prescription of prosthetic ankle-foot mechanisms after lower limb amputation |journal=Cochrane Database of Systematic Reviews |issue=1 |pages=CD003978 |date=26 January 2004 |volume=2010 |doi=10.1002/14651858.CD003978.pub2 |pmid=14974050 |pmc=8762647 |url=https://pure.rug.nl/ws/files/67438636/Hofstad_et_al_2004_Cochrane_Database_of_Systematic_Reviews.pdf }}</ref> When deciding on a device, the cost of the device, a person's functional need, and the availability of a particular device should be considered.<ref name=":2" />

====Knee joint====
{{Main article|Knee replacement}}
In case of a trans-femoral (above knee) amputation, there also is a need for a complex connector providing articulation, allowing flexion during swing-phase but not during stance. As its purpose is to replace the knee, the prosthetic knee joint is the most critical component of the prosthesis for trans-femoral amputees. The function of the good prosthetic knee joint is to mimic the function of the normal knee, such as providing structural support and stability during stance phase but able to flex in a controllable manner during swing phase. Hence it allows users to have a smooth and energy efficient gait and minimize the impact of amputation.<ref>{{Cite journal|last1=Andrysek|first1=Jan|last2=Naumann|first2=Stephen|last3=Cleghorn|first3=William L.|date=December 2004|title=Design characteristics of pediatric prosthetic knees|url=https://pubmed.ncbi.nlm.nih.gov/15614992/|journal=IEEE Transactions on Neural Systems and Rehabilitation Engineering |volume=12|issue=4|pages=369–378|doi=10.1109/TNSRE.2004.838444|issn=1534-4320|pmid=15614992|s2cid=1860735}}</ref> The prosthetic knee is connected to the prosthetic foot by the shank, which is usually made of an aluminum or graphite tube.

One of the most important aspect of a prosthetic knee joint would be its stance-phase control mechanism. The function of stance-phase control is to prevent the leg from buckling when the limb is loaded during weight acceptance. This ensures the stability of the knee in order to support the single limb support task of stance phase and provides a smooth transition to the swing phase. Stance phase control can be achieved in several ways including the mechanical locks,<ref>{{Cite thesis|title=Evaluation and Design of a Globally Applicable Rear-locking Prosthetic Knee Mechanism|url=https://tspace.library.utoronto.ca/handle/1807/33575|date=2012-11-27|degree=Thesis|language=en-ca|first=Dominik|last=Wyss}}</ref> relative alignment of prosthetic components,<ref name=":5">R. Stewart and A. Staros, "Selection and application of knee mechanisms," Bulletin of Prosthetics Research, vol. 18, pp. 90-158, 1972.</ref> weight activated friction control,<ref name=":5" /> and polycentric mechanisms.<ref>M. Greene, "Four bar linkage knee analysis," Prosthetics and Orthotics International, vol. 37, pp. 15-24, 1983.</ref>

=====Microprocessor control=====
To mimic the knee's functionality during gait, microprocessor-controlled knee joints have been developed that control the flexion of the knee. Some examples are [[Otto Bock]]'s C-leg, introduced in 1997, [[Ossur]]'s Rheo Knee, released in 2005, the Power Knee by Ossur, introduced in 2006, the Plié Knee from Freedom Innovations and DAW Industries' Self Learning Knee (SLK).<ref>[http://www.daw-usa.com/Pages/SLK3.html "The SLK, The Self-Learning Knee"] {{Webarchive|url=https://web.archive.org/web/20120425081600/http://www.daw-usa.com/Pages/SLK3.html |date=2012-04-25 }}, DAW Industries. Retrieved 16 March 2008.</ref>

The idea was originally developed by Kelly James, a Canadian engineer, at the [[University of Alberta]].<ref>{{Cite news|url= https://www.nytimes.com/2005/06/20/health/menshealth/20marrbox.html |title = Titanium and Sensors Replace Ahab's Peg Leg |access-date=2008-10-30 |work= The New York Times |date= 2005-06-20 | first=Michel | last=Marriott}}</ref>

A microprocessor is used to interpret and analyze signals from knee-angle sensors and moment sensors. The microprocessor receives signals from its sensors to determine the type of motion being employed by the amputee. Most microprocessor controlled knee-joints are powered by a battery housed inside the prosthesis.

The sensory signals computed by the microprocessor are used to control the resistance generated by [[hydraulic cylinders]] in the knee-joint. Small valves control the amount of [[hydraulic fluid]] that can pass into and out of the cylinder, thus regulating the extension and compression of a piston connected to the upper section of the knee.<ref name=PikeAlvin>Pike, Alvin (May/June 1999). "The New High Tech Prostheses". InMotion Magazine 9 (3)</ref>

The main advantage of a microprocessor-controlled prosthesis is a closer approximation to an amputee's natural gait. Some allow amputees to walk near walking speed or run. Variations in speed are also possible and are taken into account by sensors and communicated to the microprocessor, which adjusts to these changes accordingly. It also enables the amputees to walk downstairs with a step-over-step approach, rather than the one step at a time approach used with mechanical knees.<ref name=MartinCraigW>Martin, Craig W. (November 2003) [http://www.ibrarian.net/navon/paper/Evidence_Based_Practice_Group__EBPG_.pdf?paperid=2575568 "Otto Bock C-leg: A review of its effectiveness"] {{Webarchive|url=https://web.archive.org/web/20161228231356/http://www.ibrarian.net/navon/paper/Evidence_Based_Practice_Group__EBPG_.pdf?paperid=2575568 |date=2016-12-28 }}. WCB Evidence Based Group</ref> There is some research suggesting that people with microprocessor-controlled prostheses report greater satisfaction and improvement in functionality, residual limb health, and safety.<ref name="Kannenberg 2014 1469–1496">{{cite journal |last1=Kannenberg |first1=Andreas |last2=Zacharias |first2=Britta |last3=Pröbsting |first3=Eva |title=Benefits of microprocessor-controlled prosthetic knees to limited community ambulators: Systematic review |journal=Journal of Rehabilitation Research and Development |date=2014 |volume=51 |issue=10 |pages=1469–1496 |doi=10.1682/JRRD.2014.05.0118 |pmid=25856664 |s2cid=5942534 }}</ref> People may be able to perform everyday activities at greater speeds, even while multitasking, and reduce their risk of falls.<ref name="Kannenberg 2014 1469–1496"/>

However, some have some significant drawbacks that impair its use. They can be susceptible to water damage and thus great care must be taken to ensure that the prosthesis remains dry.<ref>{{cite journal |last1=Highsmith |first1=M. Jason |last2=Kahle |first2=Jason T. |last3=Bongiorni |first3=Dennis R. |last4=Sutton |first4=Bryce S. |last5=Groer |first5=Shirley |last6=Kaufman |first6=Kenton R. |title=Safety, Energy Efficiency, and Cost Efficacy of the C-Leg for Transfemoral Amputees: A Review of the Literature |journal=Prosthetics and Orthotics International |date=December 2010 |volume=34 |issue=4 |pages=362–377 |doi=10.3109/03093646.2010.520054 |pmid=20969495 |s2cid=23608311 }}</ref>

===Myoelectric===
A '''myoelectric prosthesis''' uses the electrical tension generated every time a muscle contracts, as information. This tension can be captured from voluntarily contracted muscles by electrodes applied on the skin to control the movements of the prosthesis, such as elbow flexion/extension, wrist supination/pronation (rotation) or opening/closing of the fingers. A prosthesis of this type utilizes the residual neuromuscular system of the human body to control the functions of an electric powered prosthetic hand, wrist, elbow or foot.<ref>{{cite news|title=Amputees control bionic legs with their thoughts|url=https://www.reuters.com/article/us-iceland-mind-controlled-limb-idUSKBN0O51EQ20150520|work=Reuters|date=20 May 2015}}</ref> This is different from an electric switch prosthesis, which requires straps and/or cables actuated by body movements to actuate or operate switches that control the movements of the prosthesis. There is no clear evidence concluding that myoelectric upper extremity prostheses function better than body-powered prostheses.<ref name=Carey2015 /> Advantages to using a myoelectric upper extremity prosthesis include the potential for improvement in cosmetic appeal (this type of prosthesis may have a more natural look), may be better for light everyday activities, and may be beneficial for people experiencing [[phantom limb]] pain.<ref name=Carey2015>{{cite journal |last1=Carey |first1=Stephanie L. |last2=Lura |first2=Derek J. |last3=Highsmith |first3=M. Jason |last4=CP. |last5=FAAOP. |title=Differences in myoelectric and body-powered upper-limb prostheses: Systematic literature review |journal=Journal of Rehabilitation Research and Development |date=2015 |volume=52 |issue=3 |pages=247–262 |doi=10.1682/JRRD.2014.08.0192 |pmid=26230500 }}</ref> When compared to a body-powered prosthesis, a myoelectric prosthesis may not be as durable, may have a longer training time, may require more adjustments, may need more maintenance, and does not provide feedback to the user.<ref name=Carey2015 />

[[:es:Álvaro Ríos Poveda|Prof. Alvaro Ríos Poveda]] has been working for several years on a non-invasive and affordable solution to this feedback problem. He considers that: "Prosthetic limbs that can be controlled with thought hold great promise for the amputee, but without sensorial feedback from the signals returning to the brain, it can be difficult to achieve the level of control necessary to perform precise movements. When connecting the sense of touch from a mechanical hand directly to the brain, prosthetics can restore the function of the amputated limb in an almost natural-feeling way." He presented the first Myoelectric prosthetic hand with sensory feedback at the ''XVIII World Congress on Medical Physics and Biomedical Engineering'', 1997, held in [[Nice, France]].<ref>{{cite web |author1=((International Federation for Medical and Biological Engineering)) |author1-link=International Federation for Medical and Biological Engineering |title=World Congress on Medical Physics and Biomedical Engineering |url=https://ifmbe.org/events/world-congress/ |website=IFMBE |access-date=19 March 2022 |date=17 December 2012}}</ref><ref>{{cite conference |last1=Rios |first1=Alvaro |title=Microcontroller system for myoelectric prosthesis with sensory feedback |conference=World Congress on Medical Physics and Biomedical Engineering: XVIII International Conference on Medical and Biological Engineering and XI International Conference on Medical Physics |year =1997 |location=Nice, France}}</ref>

The USSR was the first to develop a myoelectric arm in 1958,<ref>{{cite journal|pmid=365281|year=1978|last1=Wirta|first1=R. W.|title=Pattern-recognition arm prosthesis: A historical perspective-a final report|journal=Bulletin of Prosthetics Research|pages=8–35|last2=Taylor|first2=D. R.|last3=Finley|first3=F. R.|url=http://www.rehab.research.va.gov/jour/78/15/2/wirta.pdf}}</ref> while the first myoelectric arm became commercial in 1964 by the Central Prosthetic Research Institute of the [[Soviet Union|USSR]], and distributed by the Hangar Limb Factory of the [[United Kingdom|UK]].<ref>{{Cite journal
  | last = Sherman
  | first = E. David
  | title = A Russian Bioelectric-Controlled Prosthesis: Report of a Research Team from the Rehabilitation Institute of Montreal
  | journal = Canadian Medical Association Journal
  | volume = 91
  | issue = 24
  | pages = 1268–1270
  | year = 1964
| pmc=1927453
| pmid=14226106}}</ref><ref>{{Cite book
  | last = Muzumdar
  | first = Ashok
  | title = Powered Upper Limb Prostheses: Control, Implementation and Clinical Application
  | publisher = Springer
  | year = 2004
  | isbn = 978-3-540-40406-4}}</ref> Myoelectric prosthesis are expensive, require regular maintenance, and are sensitive to sweat and moisture.

===Robotic prostheses===
[[File:An-Electrocorticographic-Brain-Interface-in-an-Individual-with-Tetraplegia-pone.0055344.s009.ogv|thumb|Brain control of 3D prosthetic arm movement (hitting targets). This movie was recorded when the participant controlled the 3D movement of a prosthetic arm to hit physical targets in a research lab.]]
{{Main|Neural prosthetics|Powered exoskeleton#Current products (powered exoskeletons)}}
{{Further|Robotics#Touch|3-D printing|Open-source hardware}}

Robots can be used to generate objective measures of patient's impairment and therapy outcome, assist in diagnosis, customize therapies based on patient's motor abilities, and assure compliance with treatment regimens and maintain patient's records. It is shown in many studies that there is a significant improvement in upper limb motor function after stroke using robotics for upper limb rehabilitation.<ref>{{cite journal | author = Reinkensmeyer David J | year = 2009 | title = Robotic Assistance For Upper Extremity Training After Stroke | journal = Studies in Health Technology and Informatics | volume = 145 | pages = 25–39 | pmid = 19592784 | url = http://computational.eu/emerging//book9/chapter_2.pdf | access-date = 2016-12-28 | archive-url = https://web.archive.org/web/20161228195545/http://computational.eu/emerging//book9/chapter_2.pdf | archive-date = 2016-12-28 | url-status = dead }}</ref>
In order for a robotic prosthetic limb to work, it must have several components to integrate it into the body's function: [[Biosensors]] detect signals from the user's nervous or muscular systems. It then relays this information to a [[microcontroller]] located inside the device, and processes feedback from the limb and actuator, e.g., position or force, and sends it to the controller. Examples include surface electrodes that detect electrical activity on the skin, needle electrodes implanted in muscle, or solid-state electrode arrays with nerves growing through them. One type of these biosensors are employed in [[myoelectric prosthesis|myoelectric prostheses]].

A device known as the controller is connected to the user's nerve and muscular systems and the device itself. It sends intention commands from the user to the actuators of the device and interprets feedback from the mechanical and biosensors to the user. The controller is also responsible for the monitoring and control of the movements of the device.

An [[actuator]] mimics the actions of a muscle in producing force and movement. Examples include a motor that aids or replaces original muscle tissue.

Targeted muscle reinnervation (TMR) is a technique in which [[motor nerve]]s, which previously controlled [[muscle]]s on an amputated limb, are [[surgery|surgically]] rerouted such that they reinnervate a small region of a large, intact muscle, such as the [[pectoralis major]]. As a result, when a patient thinks about moving the thumb of their missing hand, a small area of muscle on their chest will contract instead. By placing sensors over the reinnervated muscle, these contractions can be made to control the movement of an appropriate part of the robotic prosthesis.<ref name="six">{{Cite journal|vauthors=Kuiken TA, Miller LA, Lipschutz RD, Lock BA, Stubblefield K, Marasco PD, Zhou P, Dumanian GA |title=Targeted reinnervation for enhanced prosthetic arm function in a woman with a proximal amputation: a case study |journal=Lancet |date= February 3, 2007 |volume=369 |issue=9559 |pages=371–80 |pmid=17276777 |doi=10.1016/S0140-6736(07)60193-7|s2cid=20041254 }}</ref><ref>{{cite web|url=http://www.technologyreview.com/blog/editors/22730/ |title=Blogs: TR Editors' blog: Patients Test an Advanced Prosthetic Arm |work=Technology Review |date=2009-02-10 |access-date=2010-10-03}}</ref>

A variant of this technique is called targeted sensory reinnervation (TSR). This procedure is similar to TMR, except that [[sensory nerve]]s are surgically rerouted to [[skin]] on the chest, rather than motor nerves rerouted to muscle. Recently, robotic limbs have improved in their ability to take signals from [[Human brain|the human brain]] and translate those signals into motion in the artificial limb. [[DARPA]], the Pentagon's research division, is working to make even more advancements in this area. Their desire is to create an artificial limb that ties directly into the [[nervous system]].<ref name="seven">{{cite web |url=http://www.darpa.mil/dso/solicitations/sn07-43.htm |title=Defense Sciences Office |publisher=Darpa.mil |access-date=2010-10-03 |archive-url=https://web.archive.org/web/20090426080528/http://www.darpa.mil/dso/solicitations/sn07-43.htm |archive-date=2009-04-26 |url-status=dead }}</ref>

====Robotic arms====
Advancements in the processors used in myoelectric arms have allowed developers to make gains in fine-tuned control of the prosthetic. The [[Boston Digital Arm]] is a recent artificial limb that has taken advantage of these more advanced processors. The arm allows movement in five axes and allows the arm to be programmed for a more customized feel. Recently the [[I-LIMB Hand]], invented in Edinburgh, Scotland, by [[David Gow]] has become the first commercially available hand prosthesis with five individually powered digits. The hand also possesses a manually rotatable thumb which is operated passively by the user and allows the hand to grip in precision, power, and key grip modes.<ref>{{Cite journal|last1=Binedell|first1=Trevor|last2=Meng|first2=Eugene|last3=Subburaj|first3=Karupppasamy|date=2020-08-25|title=Design and development of a novel 3D-printed non-metallic self-locking prosthetic arm for a forequarter amputation|url=https://pubmed.ncbi.nlm.nih.gov/32842869/|journal=Prosthetics and Orthotics International|volume=45|pages=94–99|doi=10.1177/0309364620948290|issn=1746-1553|pmid=32842869|s2cid=221326246}}</ref>

Another neural prosthetic is [[Johns Hopkins University Applied Physics Laboratory]] Proto 1. Besides the Proto 1, the university also finished the [[Proto 2]] in 2010.<ref>{{cite web |url=http://www.ric.org/aboutus/mediacenter/press/2007/o501.aspx |title=Proto 1 and Proto 2 |publisher=Ric.org |date=2007-05-01 |access-date=2010-10-03 |archive-url=https://web.archive.org/web/20110727215917/http://www.ric.org/aboutus/mediacenter/press/2007/o501.aspx |archive-date=2011-07-27 |url-status=dead }}</ref> Early in 2013, Max Ortiz Catalan and Rickard Brånemark of the Chalmers University of Technology, and Sahlgrenska University Hospital in Sweden, succeeded in making the first robotic arm which is mind-controlled and can be permanently attached to the body (using [[osseointegration]]).<ref>{{cite web|url=https://www.sciencedaily.com/releases/2013/02/130222075730.htm |title=World premiere of muscle and nerve controlled arm prosthesis |publisher=Sciencedaily.com |date=February 2013 |access-date=2016-12-28}}</ref><ref>{{cite web|url=http://www.gizmag.com/thought-controlled-prosthetic-arm/25216/ |title=Mind-controlled permanently-attached prosthetic arm could revolutionize prosthetics |publisher=Gizmag.com |date=2012-11-30 |access-date=2016-12-28 |author=Williams, Adam }}</ref><ref>{{cite web|last=Ford |first=Jason |url=http://www.theengineer.co.uk/sectors/medical-and-healthcare/news/trials-imminent-for-implantable-thought-controlled-robotic-arm/1014779.article |title=Trials imminent for implantable thought-controlled robotic arm |publisher=Theengineer.co.uk |date=2012-11-28 |access-date=2016-12-28}}</ref>

An approach that is very useful is called arm rotation which is common for unilateral amputees which is an amputation that affects only one side of the body; and also essential for bilateral amputees, a person who is missing or has had amputated either both arms or legs, to carry out activities of daily living. This involves inserting a small permanent magnet into the distal end of the residual bone of subjects with upper limb amputations. When a subject rotates the residual arm, the magnet will rotate with the residual bone, causing a change in magnetic field distribution.<ref>{{cite journal |author1=Li, Guanglin |author2=Kuiken, Todd A | year = 2008 | title = Modeling of Prosthetic Limb Rotation Control by Sensing Rotation of Residual Arm Bone | journal = IEEE Transactions on Biomedical Engineering | volume = 55 | issue = 9| pages = 2134–2142 | doi=10.1109/tbme.2008.923914| pmc=3038244 | pmid=18713682}}</ref> EEG (electroencephalogram) signals, detected using small flat metal discs attached to the scalp, essentially decoding human brain activity used for physical movement, is used to control the robotic limbs. This allows the user to control the part directly.<ref>{{cite journal | author = Contreras-Vidal José L. | year = 2012 | title = Restoration of Whole Body Movement: Toward a Noninvasive Brain-Machine Interface System | journal = IEEE Pulse | volume = 3 | issue = 1| pages = 34–37 | doi=10.1109/mpul.2011.2175635| pmid = 22344949 |display-authors=etal| pmc = 3357625}}</ref>

====Robotic transtibial prostheses ====
The research of robotic legs has made some advancement over time, allowing exact movement and control.

Researchers at the [[Rehabilitation Institute of Chicago]] announced in September 2013 that they have developed a robotic leg that translates neural impulses from the user's thigh muscles into movement, which is the first prosthetic leg to do so. It is currently in testing.<ref>{{cite web|url=http://www.medgadget.com/2013/09/robotic-leg-emg.html |title=Rehabilitation Institute of Chicago First to Develop Thought Controlled Robotic Leg |publisher=Medgadget.com |date=September 2013 |access-date=2016-12-28}}</ref>

Hugh Herr, head of the biomechatronics group at MIT's Media Lab developed a robotic transtibial leg (PowerFoot BiOM).<ref>[https://www.smithsonianmag.com/innovation/future-robotic-legs-180953040/ Is This the Future of Robotic Legs?]</ref><ref>{{cite web|url = https://biomech.media.mit.edu/portfolio_page/powered-ankle-foot-prosthesis/ |title = Transtibial Powered Prostheses|website = Biomechatronics|publisher = MIT Media Lab}}</ref>

The Icelandic company Össur has also created a robotic transtibial leg with motorized ankle that moves through algorithms and sensors that automatically adjust the angle of the foot during different points in its wearer's stride. Also there are brain-controlled bionic legs that allow an individual to move his limbs with a wireless transmitter.<ref>{{Cite news|url=https://www.popsci.com/brain-controlled-bionic-legs-are-here-no-really|title=Brain-Controlled Bionic Legs Are Finally Here|work=Popular Science|access-date=2018-12-01|language=en}}</ref>

====Prosthesis design====
The main goal of a robotic prosthesis is to provide active actuation during gait to improve the biomechanics of gait, including, among other things, stability, symmetry, or energy expenditure for amputees.<ref>{{Cite journal|last1=Liacouras|first1=Peter C.|last2=Sahajwalla|first2=Divya|last3=Beachler|first3=Mark D.|last4=Sleeman|first4=Todd|last5=Ho|first5=Vincent B.|last6=Lichtenberger|first6=John P.|date=2017|title=Using computed tomography and 3D printing to construct custom prosthetics attachments and devices|journal=3D Printing in Medicine|volume=3|issue=1|pages=8|doi=10.1186/s41205-017-0016-1|issn=2365-6271|pmc=5954798|pmid=29782612 |doi-access=free }}</ref> There are several powered prosthetic legs currently on the market, including fully powered legs, in which actuators directly drive the joints, and semi-active legs, which use small amounts of energy and a small actuator to change the mechanical properties of the leg but do not inject net positive energy into gait. Specific examples include The emPOWER from BionX, the Proprio Foot from Ossur, and the Elan Foot from Endolite.<ref>{{Cite web|url=http://www.bionxmed.com/|title=Home – BionX Medical Technologies|website=www.bionxmed.com|language=en-US|access-date=2018-01-08|archive-date=2017-12-03|archive-url=https://web.archive.org/web/20171203114709/http://www.bionxmed.com/|url-status=dead}}</ref><ref>{{Cite web|url=https://www.ossur.com/prosthetic-solutions/products/dynamic-solutions/proprio-foot|title=PROPRIO FOOT|last=Össur|website=www.ossur.com|language=en-us|access-date=2018-01-08}}</ref><ref>{{Cite news|url=http://www.endolite.com/products/elan|title=Elan – Carbon, Feet, Hydraulic – Endolite USA – Lower Limb Prosthetics|work=Endolite USA – Lower Limb Prosthetics|access-date=2018-01-08|language=en-US}}</ref> Various research groups have also experimented with robotic legs over the last decade.<ref>{{cite journal |last1=Windrich |first1=Michael |last2=Grimmer |first2=Martin |last3=Christ |first3=Oliver |last4=Rinderknecht |first4=Stephan |last5=Beckerle |first5=Philipp |title=Active lower limb prosthetics: a systematic review of design issues and solutions |journal=BioMedical Engineering OnLine |date=19 December 2016 |volume=15 |issue=S3 |pages=140 |doi=10.1186/s12938-016-0284-9 |pmid=28105948 |pmc=5249019 |doi-access=free }}</ref> Central issues being researched include designing the behavior of the device during stance and swing phases, recognizing the current ambulation task, and various mechanical design problems such as robustness, weight, battery-life/efficiency, and noise-level. However, scientists from [[Stanford University]] and [[Seoul National University of Science and Technology|Seoul National University]] has developed artificial nerves system that will help prosthetic limbs feel.<ref>{{Cite web|url=https://www.engineering.com/DesignerEdge/DesignerEdgeArticles/ArticleID/17049/Researchers-Create-Artificial-Nerve-System.aspx|title=Researchers Create Artificial Nerve System|last=ENGINEERING.com|website=www.engineering.com|language=en-US|access-date=2018-06-08}}</ref> This synthetic nerve system enables prosthetic limbs sense [[braille]], feel the sense of touch and respond to the environment.<ref>{{Cite web|url=http://www.xinhuanet.com/english/2018-06/01/c_137223459.htm|archive-url=https://web.archive.org/web/20180607021506/http://www.xinhuanet.com/english/2018-06/01/c_137223459.htm|url-status=dead|archive-date=June 7, 2018|title=Stanford researchers create artificial nerve system for robots – Xinhua {{!}} English.news.cn|website=www.xinhuanet.com|access-date=2018-06-08}}</ref><ref>{{Cite news|url=https://news.stanford.edu/2018/05/31/artificial-nerve-system-gives-prosthetic-devices-robots-sense-touch/|title=An artificial nerve system gives prosthetic devices and robots a sense of touch {{!}} Stanford News|last=University|first=Stanford|date=2018-05-31|work=Stanford News|access-date=2018-06-08|language=en-US}}</ref>

===Use of recycled materials===
Prosthetics are being made from recycled plastic bottles and lids around the world.<ref>{{cite web | title=Affordable prosthetics made from recycled plastic waste | website=MaterialDistrict | date=14 January 2019 | url=https://materialdistrict.com/article/prosthetics-recycled-plastic/ | access-date=3 November 2020}}</ref><ref name="World Economic Forum 2019">{{cite web | title=These researchers are turning plastic bottles into prosthetic limbs | website=World Economic Forum | date=4 October 2019 | url=https://www.weforum.org/agenda/2019/10/plastic-bottles-waste-prosthetic-limbs/ | access-date=3 November 2020}}</ref><ref>{{cite web | last=Bell | first=Sarah Jane | title=Recycling shampoo bottles to make prosthetic limbs becomes retired hairdresser's dream| website=ABC News|publisher=Australian Broadcasting Corporation | date=21 April 2019 | url=https://www.abc.net.au/news/2019-04-22/recycled-plastic-made-into-prosthetic-limbs/10992038 | access-date=3 November 2020}}</ref><ref name="Conway 2019">{{cite web | last=Conway | first=Elle | title=Canberra family turning bottle caps into plastic hands and arms for children  | website=ABC News|publisher=Australian Broadcasting Corporation | date=26 June 2019 | url=https://www.abc.net.au/news/2019-06-27/lids-for-kids-canberra-collection-volunteer-envision-hands/11249628 | access-date=3 November 2020}}</ref><ref>{{cite web | title=Envision Hands | website=Envision | date=19 February 2020 | url=https://envision.org.au/envision-hands/ | access-date=3 November 2020}}</ref>