Gemma Downey

What Is It?Prosthetic Technology is used when people

have lost limbs, and can regain the use by means of these artificial limbs

Vocabulary To KnowMeasurand – physical quantity that a system

measures. The accessibility is important because it could be internal, external, etc. In this case, its an external because its an electric pulse on the end of a limb. The book calls this “electrocardiogram potential.”

Sensor – a sensor converts a physical measurand to an electric output. It responds to only the form of energy present in the measurand and it ignores all other kinds to prevent interference.

John, Webster G. Medical Instrumentation. Danvers, MA: John Wiley and Sons, 1997.

New technologyExisting prosthetic arms are so clunky that many amputees

do not even bother with them. By flexing a back muscle, cables and pulleys bend the arm. Flexing the bicep can close the hand.

Motions are slow and limited (usually only 3 motions)

However: In contrast, the new prosthetic arm, is electrically

operated and has as many as 10 motions. The problem has been controlling the motions.

So How Can Engineers Fix This?Nerves from the arm are attached to chest

muscles, whose movements amplify the nerve signal. The patient can control prosthetics with only their thoughts.

Sensors placed over the new locations on the chest

pick up impulses from the brain and transmit them to

the prosthetic arms, a process called ‘targeted muscle reinnervation’

Likewise…

Cricket Car!Cricket Car!Using stainless steel insect pins as electrodes, the

cricket is attached to the circuit by using a socket. One electrode in each hind leg is used to get the signals.

http://www.ele.uri.edu/~diceccoj/cricket_car_NEBC.pdf

What Differences Has This Made?Aside from facilitation of these limbs, and addition of

motions, the new technology has improved response time and reflexes:

Flexing or rotating the wrist took about 0.22 second for the amputees

vs.

0.16 second for the controls. Completing a task took

1.29 seconds for amputeesvs.

1.08 seconds for controls.

…Conventional prosthetic arms require much longer times.

Material ImprovementsMaterials such as carbon fiber have allowed

artificial limbs to be stronger and lighter reducing the energy needed to operate the limb.

Additional materials have allowed artificial limbs to look much more realistic

MedGadget, April 27, 2007

Biomaterials and the Construction of Prosthetics…Specific materials are important for the

fabrication and creation of these limbs for two reasons:1. Comfort of the socket2. Strength

There is no one universal material that suits all amputees. Their lifestyle and physical characteristics need to be evaluated first.

Biomaterials and the Construction of Prosthetics…Plastic Polymer LaminatesThese laminates begin as a liquid and are mixed

with a catalyst. This combination, which is put under vacuum pressure to make it lightweight and strong, creates a lamination. By adjusting the amount of resin in it, you can make it more flexible or more rigid.

Examples: acrylic, epoxy, and polyesterBenefits- designer can easily control strength and thicknessDisadvantages- difficult to remold if uncomfortable

Biomaterials and the Construction of Prosthetics…Reinforcement Textiles are fabrics used in

the laminate for strength.Examples- fiberglass, nylon, dacron, carbon,

kevlarDisadvantages- Some laminations (for example, carbon fiber) are thin, which means you cannot grind a relief area into the material. Carbon fiber is brittle, as opposed to materials like kevlar or fiberglass which will bend rather than break.

Biomaterials and the Construction of Prosthetics…Lamination Process: How Its Done

Basically, you need to saturate the reinforcement textiles with a plastic polymer resin and put the combination under vacuum pressure (as previously mentioned).

But in more detail…

Biomaterials and the Construction of Prosthetics…The custom designed socket is put over the

residual limb and is made out of plastic laminate, but besides strength, it needs to connect the body to the artificial limb via the electrodes.

Electrode dummies and screw anchors will be incorporated in the socket so that this can happen.

Biomaterials and the Construction of Prosthetics…Then…After making a plaster cast of the limb, a

polyvinyl alcohol film is applied to separate from the plastic resin.

The vacuum is applied to the polyvinyl alcohol film. The aforementioned textiles are applied along with whatever is going to connect the socket and the electrical components.

Biomaterials and the Construction of Prosthetics…There are many varieties of available materials:

1. Casting listed over 20 different types of plaster bandages. The way these bandages differed depended on how long it took for the materials to set.2. Under the lamination subheading, there were resins ranging from flexible to firm, and even additives for the resins were listed.3. To line and finish the prosthetics, hides and leathers (coming from skins of horse, cow, goat, etc.), padding materials, textiles, and cork was used.

Who is Behind It All?BIOENGINEERS!

An team led by the Johns Hopkins University Applied Physics Laboratory developed the first fully integrated prosthetic arm that can be controlled naturally and allows for eight degrees of freedom. It was developed for the Defense Advanced Research Projects Agency Revolutionizing Prosthetics Program, is a complete limb system that also includes a virtual environment used for patient training.

APL is already hard at work on a second prototype that will have more than 25 degrees of freedom and the strength and speed of movement approaching the capabilities of the human limb.

The End!