DEARBORN, MICH. - When Douglas A. Taylor molds parts in his Indiana plant, he thinks of the people who use them and how individual needs vary. Taylor's customers are patients, and his products are artificial limbs. So he also thinks about stress, as in the case of the 200-pound patient who routinely carries 100-pound bags of cement on his shoulders.
Taylor, a certified prosthetist and owner of O&P Associates in Indianapolis, spoke at the Advanced Composites Conference and Exposition in Dearborn, sponsored by the Engineering Society of Detroit and the Society of Automotive Engineers, based in Warrendale, Pa.
The market for prosthetic devices is moving steadily upward these days as the world's population ages and as circulatory diseases and conditions like diabetes take their toll in amputated feet and legs.
A prosthesis is an expensive item. For example, a full-length, high-performance artificial leg made with up-to-date technology costs about $7,000, Taylor said. A high-performance, spring-like foot of carbon fiber can cost about $2,000. Geriatric feet tend to be lower in cost because they are not designed for high-performance applications.
Taylor gave his audience a look at the impressive variety of materials and forming techniques he and his suppliers use in making a typical leg.
``I call it potpourri prosthetics,'' he said.
He made it clear that his route to a safe finished product and a comfortable, mobile customer is not static. It changes continuously as processes and materials are developed, he said. There is a proposed ISO standard calling for cycling prosthetic devices through such modes as compression, torsion, bending and tension. But, as of now, no standards exist and materials and forming technique variety is widespread.
``We need to do our science better in testing so we know where, how and why something works under what conditions. We need guidelines - standards we can go by,'' Taylor said.
Carbon fiber is being used more frequently for artificial feet and to replace aluminum that has been widely used for the femur-like shafts of legs.
Blade-like feet are common. But at least one more anatomic arrangement looks something like a foot and provides a good example of the diversity of materials being used in prosthetics.
``It has a forefoot section of compression molded carbon fiber and nylon heel and ankle bones with urethane bumpers at the instep and forefoot. The bumpers come in a variety of stiffness so we can adjust the amount of stiffness in the heel and toe and the axial rotation in tuning-in the patient's gait. The ankle bone has a rotational axle bushing that also is compliant. The foot acts very much like a human foot does,'' Taylor said.
``Every prosthetic socket that's made has to be custom-molded to the patient. Every one is a prototype off one-off tooling. We can't mass produce them. We've tried to manufacture adjustable sockets but they've fallen by the wayside.''
For sockets, Taylor prefers a cloth-like carbon material hand laid over a plaster mold that is cast from the patient. He said the material is stable and costs about $40 a yard.
``We have to make sure these things are incredibly strong, that they perform and are light enough that the patient isn't worn out at the end of the day,'' he said.
Despite higher labor costs, use of carbon fiber material instead of the fiberglass and nylon stockinette often used in prosthetics probably does not increase part costs.
``When you increase the strength of the unit by an incredible amount and lighten it by a pound and a half, you can't argue,'' he added.
