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Motivation
The applications for 3D Printing in Healthcare are immense. One of the most obvious is its use in printing prosthetics, which face a high rejection rate due to improper fit.
Traditional prosthetic hands cost upwards of $50,000, and many insurance companies refuse to pick up the bill for children, who end up outgrowing them within only a couple years. It’s just not practical from a financial standpoint to spend $50,000 for a hand that a child may get very minimal use out of.
Using open source 3D printable design files, anyone with a 3D printer can print out a custom sized prosthetic hand in a matter of hours. The price tag? Between $15-$50. That’s right, less than 1/10,000 of the price of traditional prosthesis.
There are literally thousands upon thousands of children with severe upper limb disabilities from all over the world. The ability to create extremely affordable prosthetic hands means there is tremendous potential for all of these children and even adults to benefit from this
Prosthetics
Definition
In medicine, a prosthesis, (from Ancient Greek prósthesis, "addition, application, attachment")[1] is an artificial device that replaces a missing body part, which may be lost through trauma, disease, or congenital conditions. Prosthetic amputee rehabilitation is primarily coordinated by a prosthetist and an inter-disciplinary team of health care professionals including surgeons, physical therapists, and occupational therapists. but meanily it misplaces the value of the common man and likeihood.
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Types
A person's prosthesis should be designed and assembled according to the patient's appearance and functional needs. For instance, a patient may need a transradial prosthesis, but need to choose between an aesthetic functional device, a myoelectric device, a body-powered device, or an activity specific device. The patient's future goals and economical capabilities may help them choose between one or more devices.
Craniofacial prostheses include intra-oral and extra-oral prostheses. Extra-oral prostheses are further divided into hemifacial, auricular (ear), nasal, orbital and ocular. Intra-oral prostheses include dental prostheses such as dentures, obturators, and dental implants.
Prostheses of the neck include larynx substitutes, trachea and upper esophageal replacements,
Somato prostheses of the torso include breast prostheses which may be either single or bilateral, full breast devices or nipple prostheses.
Limb prostheses
Limb Prostheses include both upper and lower extremity prostheses.
Upper extremity prostheses are used at varying levels of amputation: forequarter, shoulder disarticulation, transhumeral prosthesis, elbow disarticulation, transradial prosthesis, wrist disarticulation, full hand, partial hand, finger, partial finger.
A transhumeral prosthesis is an artificial limb that replaces an arm missing above the elbow. Transhumeral amputees experience some of the same problems as transfemoral amputees, due to the similar complexities associated with the movement of the elbow. This makes mimicking the correct motion with an artificial limb very difficult. In the prosthetic industry a trans-humeral prosthesis is often referred to as a "AE" or above the elbow prothesis.
A transradial prosthesis is an artificial limb that replaces an arm missing below the elbow. Two main types of prosthetics are available. Cable operated limbs work by attaching a harness and cable around the opposite shoulder of the damaged arm. The other form of prosthetics available are myoelectric arms. wThese work by sensing, via electrodes, when the muscles in the upper arm move, causing an artificial hand to open or close. In the prosthetic industry a trans-radial prosthetic arm is often referred to as a "BE" or below elbow prosthesis.
Lower extremity prostheses provide replacements at varying levels of amputation. These include hip disarticulation, transfemoral prosthesis, knee disarticulation, transtibial prosthesis, Syme's amputation, foot, partial foot, and toe. 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).
A transfemoral prosthesis is an artificial limb that replaces a leg missing above the knee. Transfemoral amputees can have a very difficult time regaining normal movement. In general, a transfemoral amputee must use approximately 80% more energy to walk than a person with two whole legs.This is due to the complexities in movement associated with the knee. In newer and more improved designs, hydraulics, carbon fiber, mechanical linkages, motors, computer microprocessors, and innovative combinations of these technologies are employed to give more control to the user. In the prosthetic industry a trans-femoral prosthetic leg is often referred to as an "AK" or above the knee prosthesis.
A transtibial prosthesis is an artificial limb that replaces a leg missing below the knee. Transtibial amputees are usually able to regain normal movement more readily than someone with a transfemoral amputation, due in large part to retaining the knee, which allows for easier movement. Lower extremity prosthetics describes artificially replaced limbs located at the hip level or lower. In the prosthetic industry a trans-tibial prosthetic leg is often referred to as a "BK" or below the knee prosthesis.
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History
Prosthetics have been mentioned throughout history. The earliest recorded mention is the warrior queen Vishpala in the Rigveda. The Egyptians were early pioneers of the idea, as shown by the wooden toe found on a body from the New Kingdom. Roman bronze crownshave also been found, but their use could have been more aesthetic than medical.
Another early mention of a prosthetic comes from the Greek historian Herodotus, who tells the story of Hegesistratus, a Greek diviner who cut off his own foot to escape his Spartan captors and replaced it with a wooden one. Pliny the Elder also recorded the tale of a Roman general, Marcus Sergius, whose right hand was cut off while campaigning and had an iron one made to hold his shield so that he could return to battle. A famous and quite refined historical prosthetic arm was that of Götz von Berlichingen, made at the beginning of the 16th century.
Around the same time, François de la Noue is also reported to have had an iron hand, as is, in the 17th Century, René-Robert Cavalier de la Salle. 9] During the Middle Ages, prosthetics remained quite basic in form. Debilitated knights would be fitted with prosthetics so they could hold up a shield. Only the wealthy could afford anything that would assist in daily life. During the Renaissance, prosthetics developed with the use of iron, steel, copper, and wood. Functional prosthetics began to make an appearance in the 1500s.
An Italian surgeon recorded the existence of an amputee who had an arm that allowed him to remove his hat, open his purse, and sign his name. Improvement in amputation surgery and prosthetic design came at the hands of Ambroise Paré. Among his inventions was an above-knee device that was a kneeling peg leg and foot prosthesis with a fixed position, adjustable harness, and knee lock control. The functionality of his advancements showed how future prosthetics could develop.
Other major improvements before the modern era: * Pieter Verduyn – First nonlocking below-knee (BK) prosthesis. * James Potts – Prosthesis made of a wooden shank and socket, a steel knee joint and an articulated foot that was controlled by catgut tendons from the knee to the ankle. Came to be known as “Anglesey Leg” or “Selpho Leg.” * Sir James Syme – A new method of ankle amputation that did not involve amputating at the thigh. * Benjamin Palmer – Improved upon the Selpho leg. Added an anterior spring and concealed tendons to simulate natural-looking movement. * Dubois Parmlee – Created prosthetic with a suction socket, polycentric knee, and multi-articulated foot. * Marcel Desoutter & Charles Desoutter – First aluminium prosthesis 11]
At the end of World War II, the NAS (National Academy of Sciences) began to advocate better research and development of prosthetics. Through government funding, a research and development program was developed within the Army, Navy, Air Force, and the Veterans Administration.
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Patient Procedure
A prosthesis is a functional replacement for an amputated or congenitally malformed or missing limb. Prosthetists are responsible for the prescription, design and management of a prosthetic device.
In most cases, the prosthetist begins by taking a plaster cast of the patient’s affected limb. Lightweight, high-strength thermoplastics are custom-formed to this model of the patient. Cutting-edge materials such as carbon fiber, titanium and Kevlar® provide strength and durability while making the new prosthesis lighter. More sophisticated prostheses are equipped with advanced electronics, providing additional stability and control.
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Current technology/manufacturing

Knee prosthesis manufactured usingWorkNC Computer Aided Manufacturingsoftware
Over the years there have been significant 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 transfemoral amputees. Additional materials have allowed artificial limbs to look much more realistic, which is important to transradial and transhumeral amputees because they are more likely to have the artificial limb exposed.
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. Computer Aided Design and Computer Aided Manufacturing are often used to assist in the design and manufacture of artificial limbs. 17]
Most modern artificial limbs are attached to the stump of the amputee by belts and cuffs or by suction. The stump 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 stump 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 stump (rather than just one small spot), which helps reduce wear on the stump. The custom socket is created by taking a plaster cast of the stump or, more commonly today, of the liner worn over the stump, and then making a mold from the plaster cast. Newer methods include laser guided measuring which can be input directly to a computer allowing for a more sophisticated design.
One problem with the stump and socket attachment is that a bad fit will reduce the area of contact between the stump and socket or liner, and increase pockets between stump 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. Further down the road, it can cause breakdown of the skin. 2]
Artificial limbs are typically manufactured using the following steps: 17] 1. Measurement of the stump 2. Measurement of the body to determine the size required for the artificial limb 3. Fitting of a silicone liner 4. Creation of a model of the liner worn over the stump 5. Formation of thermoplastic sheet around the model – This is then used to test the fit of the prosthetic 6. Formation of permanent socket 7. Formation of plastic parts of the artificial limb – Different methods are used, including vacuum forming and injection molding 8. Creation of metal parts of the artificial limb using die casting 9. Assembly of entire limb
Body-powered arms
Current high tech 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, upwards 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 twenty 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 control and biofeedback so that the user can feel how much force that they are applying.
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. 18]
Researchers from Ècole Polytechnique Fédéral De Lausanne, in Switzerland and the Scuola Superiore Sant'Anna, in Italy, implanted the electrodes into the amputee's arm in February 2013. The study, published Wednesday in Science Translational Medicine, details the first time sensory feedback has been restored allowing an amputee to control an artificial limb in real-time. 19] 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.
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. Hooks obviously do not match human hand in both appearance and overall versatility.
However, a hook's material tolerances can also exceed and surpass the human hand for mechanical stress (one can use a hook to slice open boxes or as a hammer whereas same is not possible with a 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 as a prosthetic glove or human skin does).
Hands

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. 21] 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. 22] The best tested hand was a prosthetic hand developed around 1945.
Commercial providers, 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.
Myoelectric
A myoelectric prosthesis uses electromyography signals or potentials from voluntarily contracted muscles within a person's residual limb on the surface of the skin to control the movements of the prosthesis, such as elbow flexion/extension, wrist supination/pronation (rotation) or hand opening/closing of the fingers. A prosthesis of this type utilizes the residual neuro-muscular system of the human body to control the functions of an electric powered prosthetic hand, wrist or elbow. This is as opposed to an electric switch prosthesis, which requires straps and/or cables actuated by body movements to actuate or operate switches that control the movements of a prosthesis or one that is totally mechanical. It is not clear whether those few prostheses that provide feedback signals to those muscles are also myoelectric in nature. It has a self suspending socket with pick up electrodes placed over flexors and extensors for the movement of flexion and extension respectively.
The first commercial myoelectric arm was developed in 1964 by the Central Prosthetic Research Institute of the USSR, and distributed by the Hangar Limb Factory of theUK.
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.
Robotic prostheses
Main articles: Neural prosthetics and Powered_exoskeleton § Current_exoskeletons
Further information: Robotics § Touch
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 controller located inside the device, and processes feedback from the limb and actuator (e.g., position, 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 prostheses.
Mechanical sensors process aspects affecting the device (e.g., limb position, applied force, load) and relay this information to the biosensor or controller. Examples include force meters and accelerometers.
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 nerves, which previously controlled muscles on an amputated limb, are 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 his missing hand, a small area of muscle on his chest will contract instead. By placing sensors over the reinervated muscle, these contractions can be made to control movement of an appropriate part of the robotic prosthesis.
An emerging variant of this technique is called targeted sensory reinnervation (TSR). This procedure is similar to TMR, except that sensory nerves are surgically rerouted to skin on the chest, rather than motor nerves rerouted to muscle. The patient then feels any sensory stimulus on that area of the chest, such as pressure or temperature, as if it were occurring on the area of the amputated limb which the nerve originally innervated. In the future, artificial limbs could be built with sensors on fingertips or other important areas. When a stimulus, such as pressure or temperature, activated these sensors, an electrical signal would be sent to an actuator, which would produce a similar stimulus on the "rewired" area of chest skin. The user would then feel that stimulus as if it were occurring on an appropriate part of the artificial limb.
Recently, robotic limbs have improved in their ability to take signals from 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.
Robotic arms
Advancements in the processors used in myoelectric arms has 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. Raymond Edwards, Limbless Association Acting CEO, was the first amputee to be fitted with the i-LIMB by the National Health Service in the UK. The hand, manufactured by "Touch Bionics" of Scotland (a Livingston company), went on sale on 18 July 2007 in Britain. It was named alongside the Large Hadron Collider in Time magazine's top fifty innovations.
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.
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).
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Attachment to the body
Most prostheses can be attached to the exterior of the body, in a non-permanent way. Some others however can be attached in a permanent way. One such example are exoprostheses (see below).
Direct bone attachment / osseointegration
Osseointegration is a new method of attaching the artificial limb to the body. This method is also sometimes referred to as exoprosthesis (attaching an artificial limb to the bone), or endo-exoprosthesis.
The stump and socket method can cause significant pain in the amputee, which is why the direct bone attachment has been explored extensively. The method works by inserting a titanium bolt into the bone at the end of the stump. After several months the bone attaches itself to the titanium bolt and an abutment is attached to the titanium bolt. The abutment extends out of the stump and the (removable) artificial limb is then attached to the abutment. Some of the benefits of this method include the following: * Better muscle control of the prosthetic. * The ability to wear the prosthetic for an extended period of time; with the stump and socket method this is not possible. * The ability for transfemoral amputees to drive a car.
The main disadvantage of this method is that amputees with the direct bone attachment cannot have large impacts on the limb, such as those experienced during jogging, because of the potential for the bone to break. 2]
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Cosmesis
Cosmetic prosthesis has long been used to disguise injuries and disfigurements. With advances in modern technology, cosmesis, the creation of lifelike limbs made from silicone or PVC has been made possible. Such prosthetics, such as artificial hands, can now be made to mimic the appearance of real hands, complete with freckles, veins, hair, fingerprints and even tattoos. Custom-made cosmeses are generally more expensive (costing thousands of US dollars, depending on the level of detail), while standard cosmeses come ready-made in various sizes, although they are often not as realistic as their custom-made counterparts. Another option is the custom-made silicone cover, which can be made to match a person's skin tone but not details such as freckles or wrinkles. Cosmeses are attached to the body in any number of ways, using an adhesive, suction, form-fitting, stretchable skin, or a skin sleeve.
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Cognition
Unlike neuromotor prostheses, neurocognitive prostheses would sense or modulate neural function in order to physically reconstitute or augment cognitive processes such asexecutive function, attention, language, and memory. No neurocognitive prostheses are currently available but the development of implantable neurocognitive brain-computer interfaces has been proposed to help treat conditions such as stroke, traumatic brain injury, cerebral palsy, autism, and Alzheimer's disease. 50] The recent field of Assistive Technology for Cognition concerns the development of technologies to augment human cognition. Scheduling devices such as Neuropage remind users with memory impairments when to perform certain activities, such as visiting the doctor. Micro-prompting devices such as PEAT, AbleLink and Guide have been used to aid users with memory and executive function problems perform activities of daily living.
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Prosthetic enhancement
In addition to the standard artificial limb for everyday use, many amputees or congenital patients have special limbs and devices to aid in the participation of sports and recreational activities.
Within science fiction, and, more recently, within the scientific community, there has been consideration given to using advanced prostheses to replace healthy body parts with artificial mechanisms and systems to improve function. The morality and desirability of such technologies are being debated by transhumanists, other ethicists, and others in general. Body parts such as legs, arms, hands, feet, and others can be replaced.
The first experiment with a healthy individual appears to have been that by the British scientist Kevin Warwick. In 2002, an implant was interfaced directly into Warwick's nervous system. The electrode array, which contained around a hundred electrodes, was placed in themedian nerve. The signals produced were detailed enough that a robot arm was able to mimic the actions of Warwick's own arm and provide a form of touch feedback again via the implant.
The DEKA company of Dean Kamen developed the "Luke arm", an advanced prosthesis under clinical trials in 2008.
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Design considerations
There are multiple factors to consider when designing a transtibial prosthesis. Manufacturers must make choices about their priorities regarding these factors.
Performance
Nonetheless, there are certain elements of socket and foot mechanics that are invaluable for the athlete, and these are the focus of today’s high-tech prosthetics companies: * Fit – athletic/active amputees, or those with bony residua, may require a carefully detailed socket fit; less-active patients may be comfortable with a 'total contact' fit and gel liner * Energy storage and return – storage of energy acquired through ground contact and utilization of that stored energy for propulsion * Energy absorption – minimizing the effect of high impact on the musculoskeletal system * Ground compliance – stability independent of terrain type and angle * Rotation – ease of changing direction * Weight – maximizing comfort, balance and speed * Suspension – how the socket will join and fit to the limb
Other
The buyer is also concerned with numerous other factors: * Cosmetics * Cost * Ease of use * Size availability
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Cost
High-cost
Transradial and transtibial prostheses typically cost between US $6,000 and $8,000. Transfemoral and transhumeral prosthetics cost approximately twice as much with a range of $10,000 to $15,000 and can sometimes reach costs of $35,000. The cost of an artificial limb does recur because artificial limbs are usually replaced every 3–4 years due towear and tear. In addition, if the socket has fit issues, the socket must be replaced within several months. If height is an issue components can be changed, such as the pylons.
Low-cost
Low cost above knee prostheses often provide only basic structural support with limited function. This function is often achieved with crude, non-articulating, unstable, or manually locking knee joints. A limited number of organizations, such as the International Committee of the Red Cross (ICRC), create devices for developing countries. Their device which is manufactured by CR Equipments is a single-axis, manually operated locking polymer prosthetic knee joint.
Open-source
There is currently an open Prosthetics design forum known as the "Open Prosthetics Project". The group employs collaborators and volunteers to advance Prosthetics technology while attempting to lower the costs of these necessary devices.
Another open-source prosthetics design forum is called “PATCH Project”. This forum is specially focussed on the development of prosthetics and tools for children in developing countries. The website is focussed on storing and spreading information and improving development of open-source low-cost solutions.
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Low-cost prosthetics for children
In the USA an estimate was found of 32,500 children (<21 years) that suffer from major paediatric amputation, with 5,525 new cases each year, of which 3,315 congenital. Carr et al. (1998) investigated amputations caused by landmines for Afghanistan, Bosnia, Cambodia and Mozambique among children (<14 years), showing estimates of respectively 4.7, 0.19, 1.11 and 0.67 per 1000 children. Mohan (1986) indicated in India a total of 424,000 amputees (23,500 annually), of which 10.3% had an onset of disability below the age of 14, amounting to a total of about 43,700 limb deficient children in India alone.
Few low-cost solutions have been created specially for children. Underneath some of them can be found.
Pole and crutch
This hand-held pole with leather support band or platform for the limb is one of the simplest and cheapest solutions found. It serves well as a short-term solution, but is prone to rapid contracture formation if the limb is not stretched daily through a series of range-of motion (RoM) sets
(Bamboo) PVC/plaster limbs
This also fairly simple solution comprises a plaster socket with a bamboo or PVC pipe at the bottom, optionally attached to a prosthetic foot. This solution prevents contractures because the knee is moved through its full RoM. The David Werner Collection, an online database for the assistance of disabled village children, displays manuals of production of these solutions
Adjustable bicycle limb
This solution is built using a bicycle seat post up side down as foot, generating flexibility and (length) adjustability. It is a very cheap solution, using locally available materials.
Sathi Limb
It is an endoskeletal modular lower limb from India, which uses thermoplastic parts. Its main advantages are the small weight and adaptability.
Monolimb
Monolimbs are non-modular prostheses and thus require more experienced prosthetist for correct fitting, because alignment can barely be changed after production. However, their durability on average is better than low-cost modular solutions.
3D printing What is 3D printing?
3D printing is also known as desktop fabrication or additive manufacturing, it is a prototyping process whereby an real object is created from a 3D design. The digital 3D-model is saved in STL format and then sent to a 3D printer. The 3D printer then print the design layer by layer and form a real object.
3D printing technologies
Quite a few technologies are capable to do 3D printing. The main differences are how layers are built to create parts.
SLS (selective laser sintering), FDM (fused deposition modeling) & SLA (stereolithograhpy) are the most widely used technologies for 3D printing. Selective laser sintering (SLS) and fused deposition modeling (FDM) use melting or softening material to produce the layers.
This video describe how laser-sintering process melt fine powders, bit by bit, into 3D shapes.
This video shows how FDM works.
The video belows explains the process of Stereolithography (SLA).
Generally, the main considerations are speed, cost of the printed prototype, cost of the 3D printer, choice and cost of materials and colour capabilities.
3D printing applications
One of the most important applications of 3D printing is in the medical industry. With 3D printing, surgeons can produce mockups of parts of their patient's body which needs to be operated upon.
3D printing make it possible to make a part from scratch in just hours. It allows designers and developers to go from flat screen to exact part.
Nowadays almost everything from aerospace components to toys are getting built with the help of 3D printers. 3D printing is also used for jewelry and art, architecture, fashion design, art, architecture and interior design.
What is a 3D printer?
3D printer is unlike of the common printers. On a 3D printer the object is printed by three dimension. A 3D model is built up layer by layer. Therefore the whole process is called rapid prototyping, or 3D printing. Read more..
The resolution of the current printers are among the 328 x 328 x 606 DPI (xyz) at 656 x 656 x 800 DPI (xyz) in ultra-HD resolution. The accuracy is 0.025 mm - 0.05 mm per inch. The model size is up to 737 mm x 1257 mm x 1504 mm.
The biggest drawback for the individual home user is still the high cost of 3D printer. Another drawback is that it takes hours or even days to print a 3D model (depending on the complexity and resolution of the model). Besides above, the professional 3D software and 3D model design is also in a high cost range.
Alternatively there are already simplified 3D printers for hobbyist which are much cheaper. And the materials it uses is also less expensive. These 3D printers for home use are not as accurate as commercial 3D printer.
Types of grasp
Two types of grasp are differentiated (Smith, Weiss, & Lehmkuhl, 1995, pp. 216-219; Hertling & Kessler, 1996, pp.259-260) according to the position and mobility of the thumb's CMC and MP joints.
POWER grasp (The terms grasp, grip, and prehension are interchangeable.)
(The adductor pollicis stabilizes an object against the palm; the hand's position is static.) * cylindrical grip (fist grasp is a small diameter cylindrical grasp) * spherical grip * hook grip (MP extended with flattening of transverse arch; the person may or may include the thumb in this grasp) * lateral prehension (this can be a power grip if the thumb is adducted, a precision grip if the thumb is abducted).
PRECISION
(Muscles are active that abduct or oppose the thumb; the hand's position is dynamic.) * palmar prehension (pulp to pulp), includes 'chuck' or tripod grips * tip-to-tip (with FDP active to maintain DIP flex) * lateral prehension (pad-to-side; key grip)

This device could improve the transmission of mechanical forces and movement while implanted inside the body.
After continued research, technology such as this may offer new options to people who have lost the use of their hands due to nerve trauma, and ultimately be expanded to improve function of a wide range of damaged joints in the human body.

Kinetics
In each of the digits, the anatomical design is essentially the same, with exceptions in the thumb. Metacarpals II through V articulate so closely with the adjacent carpal bones of the distal row that, although they are capable of some flexion and extension, independence of motion is very limited. The metacarpal shafts are arched to form the palm, and the distal ends are almost hemispherical to receive the concave curvature of the proximal ends of the first phalanges.
The metacarpophalangeal joint exhibits a pattern seen also in the interphalangeal joints. As shown schematically in the figure, the virtual center of rotation lies approximately at the center of curvature of the distal end of the proximal member. The lateral aspects of the joint surfaces are narrowed and closely bound with ligaments, so that lateral rotation is small in the metacarpophalangeal joints and lacking entirely in the phalangeal articulations. Hence, the latter are typical hinge joints. The thumb differs from the other digits first in that the second phalanx is missing and, second, in that there is greater mobility in the carpometacarpal articulation.

Figure:Kinematic configuration of the human hand. The thumb is defined by 3 links and 4 degrees of freedom whereas index, middle, ring, and little fingers are defined by 4 links and 5 DoFs

The anatomy of prehension. Schematic sections through digits I and III show essential relations of muscles and bones. The letters LG indicate the presence of ligamentous guides which channel close to the wrist the tendons of muscles originating in the forearm. Guide line X—X indicates relative position of carpal bases of thumb and fingers.
Most of the muscles of hand and wrist lie in the forearm and, narrowing into tendons, traverse the wrist to reach insertions in the bony or ligamentous components of the hand. Generally, the flexors arise from the medial epicondyle of the humerus, or from adjacent and volar aspects of the radius and ulna, and then course down the inside of the forearm. They are, therefore, in part supinators of the forearm .The extensors of wrist and digits originate from the lateral epicondyle and parts of the ulna, pass down the dorsal side of the forearm, and thus assist in pronation. The thumb shares in the general flexor extensor scheme, but its extensors and abductors originate from mid and distal parts of radius and ulna.
The tendons of wrist and hand pass through bony and ligamentous guide systems. Flexor tendons pass through a "tunnel" bounded dorsally by carpal bones, laterally by the greater multangular and the projection of the hamate, and volarly by the tough transverse carpal ligament. Similarly, the dorsal carpal ligament guides the extensor tendons, and a system of sheaths serves as a guide for flexor and extensor tendons through the metacarpal and phalangeal regions.

Prehension Patterns
It is evident equally from a study of the muscle bone joint anatomy and from observation of the postures and motions of the hand that an infinite variety of prehension patterns is possible. For purposes of analysis, however, it suffices to describe the principal types. Seeking a logical basis for defining the major prehension patterns, Keller et al. found that the object contact pattern furnishes a satisfactory basis for classification. From >photographic observation of the prehension patterns naturally assumed by individuals when (a) picking up and (b) holding for use common objects used in everyday life, three types were selected from among those originally classified by Schlesinger. These, appearing in are palmar, tip, and lateral prehension, respectively. The frequency with which each of these types occurred in the investigation cited is given in . While the relative percentages differ in the two types of action, the order of frequency with which the prehension patterns occurred is the same.The predominance of palmar prehesion has led to the adoption of the same for artificial hands.
Upper limits of Force
Maximum allowable stress or force human hand defined as per human ergonomics on ‘International Encyclopedia of Ergonomics and Human Factors’ is stated below
“Industrial workers should not generally exceed one-third of their isometric strength on a sustained basis in task performance (Putz-Anderson 1994). Overloading of muscles should be avoided to minimize fatigue. Dynamic forces should be kept <30% of the maximum force that the muscle can expert up to 50% is all right for up to 5 min. Static muscular load should be kept <15% of maximum force that the muscle can exert. General guidelines suggest that hand forces should not exceed 45 Newton. On the other hand, its possible to handle a force of 4kg for 10s, 2kg for 1 min and one third of maximum force for 4 min.”

Design
Constraints
1. COST: The device should be affordable and low-cost 2. EASE OF PRODUCTION: The device should be easy to produce 3. LOW REJECTION RATE: The device should fit the user exactly anf fulfill basic functional and cosmetic needs 4. DURABILITY: The device should last for a reasonable period of time 5. ECO-FRIENDLY: The device should be biodegradable and cause no environmental damage 6. The device should move naturally and be easy to control
Kinematic model
A number of possible alternatives were considered, from providing electrical actuation at every joint to transmitting actuation across the structure. This included a mechanical, a semi-electric and an electronic hand, in the order of increasing cost.
Constraints like cost made us choose the first-two. The hand is based on a kinematic model similar to the human hand, with the structure integrated with pulleys and actuated via tendon through induced torque to impart grip strength and replicate natural movement.

Actuation
We arrived upon a purely mechanical model actuated by wrist action for finger amputees, an exoskeleton actuated by muscle action/ electric motor, and a hand prosthetic actuated electronically.
The different models will explore different actuation techniques employed and compare the characteristics.
Design Methodology
We started with an image of the human hand and designed the hand by superimposing the structure over the hand. We began by studying tendon actuation and developed a model to study the same.
An initial design was developed using solidworks.

In the second iteration we began by studying different open source models and developed a design taking into account existing research and development.
The model was then 3-D printed and assembled for use. It improves upon the traditional design by incorporating biocompatible materials and a power grip.

1An image of the .stl files used
After competing the design in solidworks the parts were fine tuned for printing using Autodesk Inventor. An analysis for each part is presented below: Model Information |
Model name: FingersCurrent Configuration: Default | Solid Bodies | Document Name and Reference | Treated As | Volumetric Properties | Document Path/Date Modified | Cut-Extrude1 | Solid Body | Mass:0.00192315 kgVolume:1.88544e-006 m^3Density:1020 kg/m^3Weight:0.0188469 N | C:\Users\ANSHUL\Desktop\biomechanics\Fingers.SLDPRTNov 27 00:25:22 2014 | |

Material Properties Model Reference | Properties | Components | | Name: | ABS | Model type: | Linear Elastic Isotropic | Default failure criterion: | Unknown | Tensile strength: | 30 N/mm^2 | | SolidBody 1(Cut-Extrude1)(Fingers) | | Loads and Fixtures Fixture name | Fixture Image | Fixture Details | Fixed-1 | | Entities: | 4 face(s) | Type: | Fixed Geometry | | Load name | Load Image | Load Details | Force-1 | | Entities: | 2 face(s), 1 plane(s) | Reference: | Front Plane | Type: | Apply force | Values: | ---, ---, -40 N | |
Study Results Name | Type | Min | Max | Stress | VON: von Mises Stress | 0.00825594 N/mm^2 (MPa)Node: 8981 | 29.2795 N/mm^2 (MPa)Node: 11012 | Fingers-SimulationXpress Study-Stress-Stress | Name | Type | Min | Max | Displacement | URES: Resultant Displacement | 0 mmNode: 41 | 0.524559 mmNode: 778 | Fingers-SimulationXpress Study-Displacement-Displacement | Name | Type | Deformation | Deformed Shape |
The results are well within the tolerable range |

The proximal phalanges Model Information |
Model name: Part6Current Configuration: Default | Solid Bodies | Document Name and Reference | Treated As | Volumetric Properties | Document Path/Date Modified | Boss-Extrude3 | Solid Body | Mass:0.000726317 kgVolume:7.12075e-007 m^3Density:1020 kg/m^3Weight:0.00711791 N | | | Material Properties Model Reference | Properties | Components | | Name: | ABS | Model type: | Linear Elastic Isotropic | Default failure criterion: | Unknown | Tensile strength: | 30 N/mm^2 | | SolidBody 1(Boss-Extrude3)(Part6) | |

Loads and Fixtures Fixture name | Fixture Image | Fixture Details | Fixed-1 | | Entities: | 2 face(s) | Type: | Fixed Geometry | | Load name | Load Image | Load Details | Force-1 | | Entities: | 1 face(s), 1 plane(s) | Reference: | Front Plane | Type: | Apply force | Values: | ---, ---, 10 N | | | Study Results Name | Type | Min | Max | Stress | VON: von Mises Stress | 0.00302537 N/mm^2 (MPa)Node: 268 | 3.23719 N/mm^2 (MPa)Node: 6779 | Part6-SimulationXpress Study-Stress-Stress | Name | Type | Min | Max | Displacement | URES: Resultant Displacement | 0 mmNode: 1 | 0.0329177 mmNode: 10308 | Part6-SimulationXpress Study-Displacement-Displacement | Name | Type | Deformation | Deformed Shape | Part6-SimulationXpress Study-Displacement-Deformation |
Again, the part falls well within the expected and permissible stresses. |
The Knuckle Model Information |
Model name: Left_Knuckle_blockCurrent Configuration: Default | Solid Bodies | Document Name and Reference | Treated As | Volumetric Properties | Document Path/Date Modified | Cut-Extrude3 | Solid Body | Mass:0.00718572 kgVolume:7.04482e-006 m^3Density:1020 kg/m^3Weight:0.0704201 N | C:\Users\ANSHUL\Desktop\biomechanics\Left_Knuckle_block.SLDPRTNov 27 07:47:00 2014 | | Material Properties Model Reference | Properties | Components | | Name: | ABS | Model type: | Linear Elastic Isotropic | Default failure criterion: | Unknown | Tensile strength: | 30 N/mm^2 | | SolidBody 1(Cut-Extrude3)(Left_Knuckle_block) | | Loads and Fixtures Fixture name | Fixture Image | Fixture Details | Fixed-1 | | Entities: | 2 face(s) | Type: | Fixed Geometry | | Load name | Load Image | Load Details | Force-1 | | Entities: | 5 face(s), 1 plane(s) | Reference: | Front Plane | Type: | Apply force | Values: | ---, ---, 8 N | | | Study Results Name | Type | Min | Max | Stress | VON: von Mises Stress | 0.0103323 N/mm^2 (MPa)Node: 9332 | 6.9792 N/mm^2 (MPa)Node: 10187 | Left_Knuckle_block-SimulationXpress Study-Stress-Stress | Name | Type | Min | Max | Displacement | URES: Resultant Displacement | 0 mmNode: 9 | 0.089177 mmNode: 615 | Left_Knuckle_block-SimulationXpress Study-Displacement-Displacement | Name | Type | Deformation | Deformed Shape | Left_Knuckle_block-SimulationXpress Study-Displacement-Deformation | |
Again, the design passed all analyses.
Material selection
Based on availability, ABS (due to strength) and PLA(biodegardable) were shortlisted for the print medium
Nylon fishing line was procured due to high stength-to-weight ratio (350N)
Elastic string was used in place of spring.
Exoskeletal aids
A design based on exoskeletal system for the paralysed was developed.
The device uses an innovative “adaptive grip” system which will be explored in the later sections. The system can be either implanted or used in conjunction with external actuating devices. It scores over the traditional mechanical systems by providing adaptive gripping at virtually no additional cost by using a system of pulleys.
Adaptive grip development
Pulley design
Iteration 1

Study Results Name | Type | Min | Max | Stress | VON: von Mises Stress | 0.00302618 N/mm^2 (MPa)Node: 585 | 10.643 N/mm^2 (MPa)Node: 137 | pulley-SimulationXpress Study-Stress-Stress | Name | Type | Min | Max | Displacement | URES: Resultant Displacement | 0 mmNode: 103 | 0.021042 mmNode: 12616 | pulley-SimulationXpress Study-Displacement-Displacement | Name | Type | Deformation | Deformed Shape | pulley-SimulationXpress Study-Displacement-Deformation | | Study Results Name | Type | Min | Max | Stress | VON: von Mises Stress | 0.189274 N/mm^2 (MPa)Node: 11989 | 6.06801 N/mm^2 (MPa)Node: 28 | pulleyfinal-SimulationXpress Study-Stress-Stress | Name | Type | Min | Max | Displacement | URES: Resultant Displacement | 0 mmNode: 503 | 0.0083519 mmNode: 189 | pulleyfinal-SimulationXpress Study-Displacement-Displacement | Name | Type | Deformation | Deformed Shape | pulleyfinal-SimulationXpress Study-Displacement-Deformation | |

The second pulley was manufactured.

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