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Proposal: The Future of Prosthetics

Research Paper by Travis Pollen

Motivation for Project

I myself wear a prosthesis and am very interested in learning about the future of prosthetics as it pertains to myself as well as bioengineering. (Is there a code of ethics involved?) The situation over the summer involving the sprinter Oscar Pistorius really piqued my curiosity. Could artificial limbs really work better than human ones? Taking into consideration that I’m also missing my knee, could my artificial limb (with the flex foot and hydraulic knee) eventually be as good or better than my human leg? At what price? Also, after seeing I, Robot, I want to know if the technology exists now or is in the making for prosthetic limbs to look like human ones. I’m excited to utilize Swarthmore’s online resources such as science journals to get the newest information out there on this field.

Description of project

Five to six page paper that will include -- in technical as well as lay terms -- the history of prosthetics, current technology, and what the future may hold. I will also research who is doing the most state-of-the-art work, where the work is being done, how much it is costing, and who it is benefiting.

Time line

11/20 – Collect information from various sources and in various formats. 11/24 – Begin Wiki page, inputting information such as sources and notes. 11/25-12/8 – Create outline for final paper including source information. 12/9 – Present findings to class. 12/10 – Post final paper to Wiki.


Orthopedic Prosthetics and Orthotics in Rehabilitation. Bronzino, Joseph D. The Biomedical Engineering Handbook. Hartford: CRC Press, 1995.

Prosthesis - external devise that replaces lost parts or functions of neuroskeletomotor system (skeletal frame of body with muscles and nervous system which participate in movement and stabilization of body) -2055 Necessary after disease, trauma, or even birth Body has lost weight and is no longer symmetrical and balanced Engineers daunted by design requirements for prostheses In order for prosthesis to function like a human leg, it must provide structural support for upper body when standing and walking (complex joint articulations and muscular motor system), sensory feedback (pressure, length, force, position sensors) There's no foot on which to bear weight, load has to be transferred elsewhere, where depends on the individual's limb shape Strive to make limb of similar weight (ACTUALLY MUCH LIGHTER!!!) with powerful motors and sensors connected to patient's neuromuscular system OR accept loss and redefine optimal function of new unit of person+technology Interface between external environment and human body isn't natural, especially for use during all waking hours (often 16 continuous hours) and right up against skin Future of coupling: Direct transcutaneous fixation to bone leads to infection due to lack of materials biocompatibility, for now we use straps or suction-2056

THREE areas of consideration: function, structure, cosmetics FUNCTION: Kinematics, dynamics, energy Coupling: molded to contours of patient, but not an exact match, shape rectified (adjusted) to relieve areas of skin with low load tolerance Alignment: for determining moments and forces transmitted to interface when foot is flat on ground Check socket for changing alignment (can't be done once things have been connected) Components/mechanisms: hinges and dampers, motions can be driven from external power sources (gas, electric/computers) but are usually body-powered Adjustability for kids Durability - absorb repeated shock of walking and major shocks during sports of falls - 2057 Mode of failure (slow yielding to avoid injury) Life of limb, hygiene, ease of cleaning COSMETIC covers - 3-D computer-aided design, CNC machining to generate customized shapes to match remaining limb "It is possible to function fairly well with one arm, but try walking with one leg." -2058 Tryna line knees up

Materials: at first it was carved wood, shaped leather, or beaten sheet metal -2059 Now we have thermosetting fiber-reinforced pastics hand-shaped over a plaster cast of limb, substitution of thermoforming plastics that could be automatically vacuum-formed made a leap forward Polypropylene Flex foot - traditional anthropomorphic design with imitation ankle joint and metatarsal break abandoned for functional design adopted to optimize energy storage and return, based ontwo leaf springs joined together at ankle with one splaying down toward toes to form forefoot spring and other rearward to form heel spring, adaptable to rough ground and shock-absorption (athletes!) - 2060 Carbon fiber (flexible?)

Computer-aided engineering - design of customized components to match to body shape, ability to produce well-fitting socket in one visit What they do for me: cast residual limb in plaster of paris, pour positive mold, rectify manually, fabricate socket over rectified cast - takes weeks OR Use advanced technology to capture limbs shape on computer, rectify it with computer algorithms, and CNC machine to produce rectified cast in a matter of minutes, vacuum-form machinery pulls socket rapidly over cast, socket ready for trial fitting in single session, shape stored digitally in computer, can be reproduced or adjusted Difficult to measure limb/trunk because the rest of the body gets in the way (resists being orientated conveniently in machines and distorts with slightest pressure) Instrumentation for body shape scanning - contact probes measuring contours of paster casts, triangulation Use "an adapted lathe with a milling head to spiral down a large cylindrical plug of a material such as a plaster of paris mix" Rectification - two options - prosthetist uses own expertise on 3D model OR computer has rectification maps/templates -2061

Describe parts (PICTURE!): liner, hard socket - 2064

Phases of walking Control of artificial lower limb most problematic during swing phase (foot lifted off ground to be guided into contact ahead of walker) Prosthesis has to be lighter than it's real counterpart Carbon fiber (and other composite materials) makes it light, pneumatic/hydraulically controlled damping mechanisms enable adjustment of swing phase to suit individual walking pattern (gait) - 2065 Swing-phase control of knee: resistance to flexion at late stance during toe-off controls tendency to heel rise at early swing, extension assist after mid-swing ensures limb's fully extended and ready for heel strike, resistance before terminal impact at end of extension swing dampens out inertial forces allowing smooth transition form flexed to extended knee position Conventional limbs - parameters determined by fixed components (springs and valves) and set to optimum for normal gait (one speed - limb leeds if walking slowly or vice versa) With a computer, built-in intelligence adjusts swing-phase automatically for cadence variations

Potentiometers, touch sensors, contact force, slip sensors -2066 Electromyographic signals (touch, hold, squeeze, and release)

Knee doesn't have a fixed axis, but it's best represented by a polycentric joint

Goal of low cost, custom product very difficult "taxes the skills of most engineers, both to design the product at reasonable up-front costs and to manufacture it economically in low volume" - 2068

Intermediate technology for 3rd world Not mass production, either

Artificial Limb. Schlager, Neil. How Products are Made: an Illustrated Guide to Product Manufacturing. Detroit: Gale Research Inc., 1994.

We Have Always Been Bionic. Perkowitz, Sidney. Digital People: From Bionic Humans to Androids. Washington, D.C.: Joseph Henry Press, 2004.

Hin, Teoh Swee. Engineering Materials for Biomedical Applications. London: World Scientific, 2004.

Perspectives on How and Why Feet are Prescribed. Journal of Prosthetics and Orthotics > 2005 Vol. 17, Num. 4S > pp. 18-22

Terminology in Prosthetic Foot Design and Evaluation. Journal of Prosthetics and Orthotics > 2005 Vol. 17, Num. 4S > pp. 12-16

Enrique Ergas, "Prosthesis", in AccessScience@McGraw-Hill,, DOI 10.1036/1097-8542.YB990745