Engineering

"For Wright, the prosthetic had to have a purpose. She wasn’t interested in something that made her look “normal” if it wasn’t going to help her actually do anything better. And she isn’t alone. More and more amputees, engineers, and prospective cyborgs are rejecting the idea that the “average” human body is a necessary blueprint for their devices. “We have this strong picture of us as human beings with two legs, two hands, and one head in the middle,” says Stefan Greiner, the founder of Cyborgs eV, a Berlin-based group of body hackers. “But there’s actually no reason that the human body has to look like as it has looked like for thousands of years.” Greiner himself has magnetic implants in his fingers and an RFID chip in his skin. “We actually already live in a cyborg society,” he said."

"Traditionally, a prosthetist would wrap a stump with plaster of Paris bandages to make a reverse mold and let it dry, then fill it with more plaster that must harden. From this a socket can be forged that fits, with more modifications for precision, to the bone on the stump. Great care must be taken to avoid nerves and tender areas that are not tolerant of pressure. The key for the technician is to understand the pathology of a stump, which differs for each person. This is a cumbersome process that can take a week, especially with gait training for new patients that lasts three days. It can also be messy work, mixing up and molding the plaster, while a prosthetist visiting a rural area must cart around 20-kilo packs of plaster. But with a 3-D scanner, a digital image can be made in half an hour and sent by email, and there is no mess."

"“If you wear a prosthesis you are disabled for about ten minutes in the morning while you have a shower, then you put your leg on and go to work. If you do not have one, then your hands are out of use with crutches so you can’t even take drinks to the table,” said Carson Harte, a 59-year-old prosthetist and chief executive of Exceed. “Without a prosthesis there are no expectations. You just go back and rely on the goodwill of your family.”"

"Yet for all the agonies and difficulties associated with arm loss, the bigger problem in low-income countries is when lower limb disability leads to loss of mobility. Wheelchairs are expensive and can be difficult to use when roads are pot-holed, streets are muddy and pavements are non-existent. Without a prosthetic limb, people struggle to fetch water, to prepare food and, above all, to work. This throws them back on their families and communities, intensifying any hardship and poverty."

"Stories of lives devastated by conflict or disease are all too common across low-income countries. Lack of an arm or leg can be tough anywhere, but for people in poorer parts of the planet, with so much less support and more rickety infrastructure, it is especially challenging. Some are victims of conflict, others were born with congenitall conditions. Many more are injured on roads, the casualty toll soaring in low-income nations even as it plummets in wealthier ones. Every minute, 20 people are seriously injured worldwide in road crashes. In Kenya, half the patients on surgical wards have road injuries. The World Health Organization (WHO) estimates there are about 30 million people like Nhial and Lam who require prosthetic limbs, braces, or other mobility devices. These can be simple to make and inexpensive. As one veteran prosthetist told me, his specialism is among the most instantly gratifying areas of medicine. “A patient comes in on Monday on crutches that leave them unable to carry anything. By Wednesday they are walking on a new leg and on Friday they leave with their life transformed.” Yet more than eight in 10 of those people needing mobility devices do not have them. They take a lot of work and expertise to produce and fit, and the WHO says there is a shortage of 40,000 trained prosthetists in poorer countries. There is also the time and cost to patients, who may have to travel long distances for treatment that can take five days—to assess need, produce a prosthesis and fit it to the residual limb. The result is that unglamorous items such as braces and artificial limbs are among the most-needed devices to assist lives. Yet, as in so many other areas, technology may be hurtling to the rescue, this time in the shape of 3-D printing."

"The earliest example of a prosthesis ever discovered is not a leg, arm, or even a fake eye, it’s a toe. A big toe, belonging to a noblewoman, was found in Egypt and dated to between 950-710 B.C.E. We all know that toes are important, but it’s interesting that our earliest physical example of the history of prosthetics is a toe and not something that might seem more important, like a leg or an arm."

"An effective prosthesis delivers renewed functionality and is cosmetically pleasing, but it also serves to complete the wearer’s sense of wholeness. A prosthesis then, is as much medical device as it is an emotional comfort, and so the history of prosthetics is not only a scientific history, but the story of human beings since the dawn of civilization who by birth, wound, or accident were left with something missing."

"“There’s a dream that in the future, we’ll be sitting in our home and hit a button to print our prosthetics from scratch,” Sadler says. “That might be a further out vision.” But some people think we’re already there. Sadler agrees with Kuniholn about the difficulty of attaching printed prosthetics, saying, “The fitting is a whole other black art. 3-D printing only gets you part of the way.” Of course, that’s for high-end prosthetics, the kind you hope to have. In some parts of the world, the choice is between having a mediocrely-fitting prosthetic and not having one at all. This is the situation that spurred Summit to action, as well as Patrice Johnson, who, according to Sadler, is, “the only person to have successfully designed and sold [a] functional upper limb prosthesis that used 3-D printing.”"

"“Right on the border of Burma and Thailand, there are landmines like you wouldn’t believe,” he says. These landmines leave many residents as amputees, residents who “would typically never see a prosthesis because of [the] fitting and time it would take.” Armed with Physionetics’ technology and good will, Johnson went to Burma and fitted two amputees with the printed arms. “We donated them,” he says. “All I had to do is go out there, show them how it was fit, and within an hour and a half, we had them on these two guys.” Stories like this are what drive Summit to continue his quest for a “self-use viral app for developing countries” that can create prosthetics. “There will simply never be enough prosthetists to meet their needs.” This isn’t his dream for the future; he thinks it’s a scientific possibility now. And he strongly disagrees that the materials 3-D printing can handle aren’t strong enough to work as limbs. He points out that, “the [human] bones that we have are not as strong as titanium,” a material used in many prosthetic limbs. “When you have great flexibility of geometry, as we do with 3-D printing, you can overcome what strength you don’t have,” Summit says. He says he’s found a way to overcome this strength barrier by creating a hollow prosthetic, then filling it with a lattice structure, similar to the construction of a bird’s bone. “Nature’s been doing this for a long time,” he says."

"In 1948, Reinhold Reiter, a physics student at Munich University (Munich, Germany), created the first myoelectric prosthesis, a device that amplifies surface electromyography (EMG) potentials to power motorized parts. Although Reiter published his work, it was not widely appreciated, and this potentially ground-breaking invention did not gain commercial or clinical acceptance."

"In 1919, a German book titled Ersatzglieder und Arbeitshilfen (Limb Substitutes and Work Aids) contained conceptual designs for the first externally powered prostheses, using pneumatic and electric power sources. Unfortunately, these revolutionary designs were too complex to be feasible with contemporary technology."

"During World War II (1939 to 1945), improved shock management and antibiotics saved lives but resulted in 3475 upper limb amputees in the US (9). The huge demand for artificial limbs led to the creation of a US Committee on Prosthetics Research and Development in 1945 and the Canadian Association of Prosthetics and Orthotics in 1955. The thalidomide tragedy (1958 to 1962) resulted in the birth of many children with shortened limbs, further driving demand and investment for improved prosthetics. In 1948, the Bowden cable body-powered prosthesis was introduced, replacing bulky straps with a sleek, sturdy cable. Despite new materials and improved craftsmanship, today’s body-powered prostheses are essentially adaptations of the Bowden design. Durable, portable and relatively affordable, body-powered prostheses allow the user an impressive range of motion, speed and force in operating a terminal device – most commonly a two-pronged hook – by changing the tension in a cable via preserved shoulder and body movements. The ability to use both hands simultaneously, rather than requiring a healthy hand to control the prosthesis, permits the user to complete tasks more efficiently. Furthermore, by sensing cable tension, the amputee is able to predict and adjust the position of the prosthesis without visual feedback. Although prolonged wearing can be uncomfortable, complicated motor tasks are limited and appearance is not human-like, body-powered prostheses are widely used"

"World War I (1914 to 1918) resulted in casualties in numbers previously unimagined. In the United States (US), amputee rehabilitation programs were created to help the >4400 amputees, of which the majority (54%) were upper limb, to regain some ability to work on farms or in factories. The distribution of prosthetics with sockets and a universal terminal device allowed the attachment of various work tools. In 1917, the Surgeon General of the US Army is-sued a landmark invitation for limb makers to meet in Washington, DC. The result was the creation of the Association of Limb Manufacturers of America, today the American Orthotic & Prosthetic Association. In Canada, a national charter in 1920 recognized the need to provide support to amputees, leading to the creation of the Amputations Association of The Great War, today known as the War Amps."

"The concept of an ‘automatic’ body-powered upper limb prosthesis was pioneered by German dentist Peter Baliff in 1818. Using transmission of tension through leather straps, Baliff’s device enabled the intact muscles of the trunk and shoulder girdle to elicit motion in a terminal device attached to the amputation stump. For the first time, an amputee was able to operate his prosthesis with fluid body motions, rather than as a distinct foreign object. In the 1860s, the Comte de Beaufort in France adapted the design for use by wounded soldiers. A shoulder harness with a strap buttoned to the trousers was passed through a loop to the contralateral axilla and missing limb, allowing an amputee to manipulate the strap tension to open and close a double spring hook, or flex and extend the thumb on a simple hand with fused fingers. In 1916, German surgeon Dr Ferdinand Sauerbruch described his prosthetic design with digits controlled by transmission of upper arm muscle movements. Video captures from the era show amputees effectively using the prosthesis to drink from a teacup and even to remove a match from a box to light a cigarette. Unfortunately, due to the high cost of production, few individuals were able to afford the device."

"The domes were very easily repaired by replacing the damaged mortar or mesh..."

"Portland cement is generally used, sometimes blended with a . The filler... is usually a well-graded sand capable of passing a 2.36 mm (No. 8) sieve. However, depending upon the... reinforcing material (mesh opening, distribution, etc.), a mortar containing some small-size gravel may be used. ...Addition of short and discrete fibers of different types favorably affects the control of cracking and the capacity... to resist tensile loads. ...[R]elatively short and slender (l/d = 100) steel fibers may be randomly distributed in hydraulic cement mortars... the overall effect being to increase tensile strength and improve the shear resistance..."

"[T]he early work of Lambot... was one of the first applications of , but [was] also... a form of . His patent on wire-reinforced boats that was issued in 1847... This was the birth of reinforced concrete, but subsequent development differed from Lambot’s concept. The technology of the period could not accommodate the time and effort needed to make mesh of thousands of wires. Instead, large rods were used to make what is now called conventional reinforced concrete, and the concept of ferrocement was almost forgotten for 100 years."

"Ferrocement is a form of reinforced concrete... [utilizing] closely spaced multiple layers of mesh or fine rods completely embedded in cement mortar. It can be formed into thin panels or sections, mostly less than 1 in. (25 mm) thick... Unlike conventional concrete, ferrocement reinforcement can be assembled into its final desired shape and the mortar... plastered directly in place without the use of a form."

"Most of the more recent use of ferrocement have been by others, but it is to the insight and pioneering work of that they owe their successes."

"In the 1953 Milan Fair building and in the 1959 Flaminio stadium... Nervi used ferrocement corrugations... in strikingly cantilered roofs. A further use by Nervi of the material has been in... smooth, lightweight forms into which conventional poured concrete could be molded..."

"Nervi's first used of ferrocement in an important public structure was in the 1948 Exposition Hall in Turin. ...The great corrugated roof is... ferrocement panels 1 1/2" thick tied together by ribs of conventional poured concrete..."

"The following year Nervi designed and built a 41' ... the Nennele... the hull's total thickness was less than 1/2"."

"In 1947 [Nervi] built his first ferrocement structure on land, a storage warehouse... 35' x 70' and all four... walls [and] roof were of ferrocement 1 3/16" thick, their thinness made structurally feasible by their corrugated shapes."

"[B]y the end of 1943 Nervi's firm was at work on three 150-ton transport boats, their hulls completely of ferrocement, and one 400-ton vessel, largely of ferrocement. The first construction was interrupted by the war, and it was not until 1945 that Nervi's method resulted in... [t]he Irene... a motor boat with a 165-ton displacement. On a supporting frame of 1/4" steel rods spaced about 4" apart, Nervi spread eight layers of wire mesh, four on each side of the rods, which were tied tightly together and plastered by hand with a rich cement mortar. The resultant ferrocement was 1 3/8" thick (about the same thickness as Lambot's boat). Other than the rods sandwiched into the mesh, no formwork was needed."

"Although... two of the first patents for reinforced concrete of any type... were for ferrocement, that particular type of reinforced concrete was generally underutilized—in fact, forgotten—until 's work of the 1940s. ...The turning to ferrocement... was based on the logical use of a known fact: the structural behavior of reinforced concrete is most effective near the points of its reinforcement. ...Nervi was first to ask the question... why not distribute the metal reinforcement so evenly that all the concrete is in immediate proximity to it? On this theoretical foundation Nervi performed the experiments which led to his establishment of ferrocement building technique as we know it today."

"[B]efore... crude beginnings of work with conventional reinforced concrete, work with ferrocement had already begun. ...The ferrocement technique seems to have been first used by ... and, apparently... independently, by ...Jean-Louis Lambot. ...Lambot called his invention "ferciment" and used it to build boats... He constructed his first boat in 1848..."

"[B]ecause of its intrinsic hardening process which continues indefinitely, good concrete gets better and better, imperfect concrete (with flaws that invite erosion and corrosion) gets worse and worse."

"[A]t the new ... [the] famous sail-shaped roofs (built of conventional reinforced concrete) have been covered with tile-surfaced panels of ferrocement which serve as waterproofing..."

"[F]errocement... may eliminate the need for separate layers of waterproofing."

"Ferrocement... often acts more like steel than like a standard reinforced concrete. Hit with a hammer, it rings like a bell."

"The structural effectiveness of any reinforced concrete, including ferrocement, depends on the almost miraculously fortuitous fact (first discovered in 1870 by ) that steel and concrete have close to identical coefficients of expansion, swelling at exactly the same rate when heated, shrinking at exactly the same rate when cooled. Thus they may be permanently bonded together as a single material, utilizing the best structural characteristics of each: steel has the tensile strength... while concrete has the ..."

"[F]errocement ...uses wire mesh, rather than heavy rods or bars, as the primary part of its metal reinforcement and which uses sand [in a mortar mixture] rather than a mixture of sand and stone ...as the aggregate in its concrete mix. ...The resultant product can be a shell of surprising thinness, durability, resilience, and, when properly shaped, strength."

"[F]erroconcrete would be a more accurate term for our material, but that term is already in common use to describe... reinforced concrete work."

"All ferrocement can be said to be , but all types of reinforced concrete are not ferrocement."

"Ferrocement is used relatively little in the housing field because it is regarded as a labor-intensive... building technique. ...It is true that considerable labor is required to put together... sand, cement, and wire mesh... However, the elaborate temporary framework which consumes most of the labor in conventional work is often entirely eliminated... Even if we concede that ferrocement is impractical where labor is expensive... its use requires only time, not skill..."

"This highly specialized, but by no means highly complicated building technique had been almost forgotten after its first use... in the middle of the nineteenth century until it was virtually reinvented in the 1940s by... ."

"The purpose of this book is to match an existing resource with an existing need. The need is shelter... simpler structures... that can be assembled quickly in the wake of a hurricane or flood... that can be built economically in undeveloped countries... that... provides pleasure in the form of self-made personal retreats..."

"Chicken wire mesh was recommended because of its ductility. It shows no oxidation problems as it is made with galvanized wire. It has reliable properties and is low in cost."

"[A] dome of any shape will amply comply with safety requirements. Because of this it is believed that it is possible to build domes in situ without specifying the shape of the dome, which makes skilled labor unnecessary."

"[T]o increase the load capacity of the domes and to avoid excessive deformations, it is necessary to provide the best possible anchoring at the edges."

"[T]he ferrocement roofings are practically waterproof and that they do not need any special treatment."

"My invention shows a new product which helps to replace timber where it is endangered by wetness, as in wood flooring, water containers, plant pots, etc. The new substance consists of a metal net of wire or sticks which are connected or formed like a flexible woven mat. I give this net a form which looks in the best possible way, similar to the articles I want to create. Then I put in hydraulic cement or similar bitumen tar or mix, to fill up the joints."

"As eight of the shells tested failed as a result of the failure of the supporting concrete ties on the walls, it was decided to build samples which were very well reinforced... The ultimate load increased by 1.7 times for these shells..."

"The central part remains [bare wire] and will be completed after 72 hours. ...[T]he worker can [then] climb on the previously cast portion, carrying out the same process ...[S]upport the dome until the mortar has cured in order to avoid deformations caused by the weight of the mortar and to guarantee curvature of the shell."

"One worker on one of the supports... either manually or with a trowel distributes the mortar over the chicken wire... Simultaneously, another worker from within the room... holds the mortar which is applied from the outside with a metal float or trowel in order that the mortar does not fall. Once this operation is completed, the required finish is applied both from the outside and the inside."

"[T]he smaller the thickness of the cover, the better will be its quality, which is why at the time of pouring, the meshes of the wire should be well stretched. Care should be taken that only enough mortar to cover the reinforcement is used."

"The best solution found was to form a double curvature surface... The curvature does not necessarily follow a pre-determined law, so that it may be checked roughly "with the naked eye"."

"An alternative construction method was also developed which did not require the use of any type of mold or form."

"The curing of the shell is achieved by covering the surface with wet sand for a period of 72 hours."

"After a couple of hours, the desired finish is applied (polishing or brushing), with the object of sealing the cracks or faults that may appear on the surface of the dome."