Prosthetic Progress

Material developments in artificial limbs

Estelle Martin, Senior Staff Writer

The Prosthetics Lab at the Palo Alto Veterans Affairs Hospital is a stark contrast to the surrounding building. Outside the doors of the lab, ordinary, sterile waiting rooms bustle with patients and family members. Inside the Prosthetics Lab, however, many of the rooms resemble a machine shop, including one caked with cream white plaster from floor to ceiling. It seems that everywhere, spare plastic limbs are tucked into shelves.

Showing me around is Chris Chandler, a certified prosthetist and orthotist at the VA Hospital. He is quick to show me various artificial limbs and devices perched on window sills and leaning against walls as we walk towards the main room of the lab. In my hand is a black upper portion of a prosthetic leg. The outside shell is hard, and seems unbreakable, but my fingertips sink into the soft silicone lining on the inside — a testament to the diverse types of materials in a single prosthetic.

Career of Service

According to Chandler, he began working for his uncle’s prosthetics business at age 15, motivated by the prospects of buying video games with the money he earned. Quickly, Chandler realized his natural skill in the field and continued to study prosthetics — artificial devices that replace missing limbs — and orthotics, artificial devices to help structure or support the body, in school.

Chandler says many amputations are a result of diabetes. The disease often causes the constriction of blood vessels in the lower extremities, according to Mayo Clinic. This, in combination with reduced nerve sensation, can lead to infections of wounds that go unnoticed. Since blood cannot reach the wound, it is unable to heal and the affected limb must be amputated to avoid risk of spreading infection.

More than 100 millions adults in the United States suffer from diabetes, according to a 2017 report by the Center for Disease Control and Prevention. With increasing prevalence of diabetes, their are increasing efforts to advance the field.

A Materialistic Evolution

After 28 years of work experience, Chandler has witnessed a rapid evolution in prosthetics and orthotics; the field is often years ahead of other industries when it comes to the use of new materials.

“We were one of the first industries to adopt carbon fiber when it was still pretty much an aerospace-only technology,” Chandler says. “When the rest of the country had only just heard of carbon fiber, the prosthetics field was already using it regularly.”

Increasingly, the field has been using S-Glass, a fiberglass found in helicopter blades. Fiberglass is a type of plastic that utilizes glass fiber for reinforcement. This material is known for its strength and ability to withstand breaking under high tension, while being more flexible in comparison to carbon fiber, according to Chandler.

Chandler emphasizes that the materials of different parts of an artificial limb are dependent on the point it touches on the body. There are pressure-sensitive areas, which require softer materials, like silicone, while pressure-tolerant areas can withstand firmer plastics.

An even newer material used in prosthetics and orthotics is magnetic fluid, which can only be currently found in two prosthetic products, according to Chandler.

“It [magnetic fluid] is a hydraulic fluid [liquid that operates machinery through movement], filled with a bunch of metal shavings inside of it. When you apply a magnet to the fluid, it becomes hard as a rock. When you take the magnet away, it turns into a fluid again,” Chandler says.

According to him, the fluid is used globally, from shock absorbers in tall skyscrapers to the suspension in high end sports cars. The outlying advantage to the material is that it can be fine tuned instantaneously with a magnetic field.

Magnetic fluid is now used in electronic knees, which features a cylinder containing many disks with the fluid floating in between.

“This proven MR [Magnetorheological Fluid] technology utilizes electromagnetic force to rapidly alter the viscosity of magnetic fluid in the knee.” states the website of Össur, a prominent prosthetics manufacturer. “Thus, RHEO KNEE 3 is capable of shifting almost instantaneously from the high resistance required for stability in stance phase to the low resistance needed for a dynamic, free swing phase.”

When the rest of the country had only just heard of carbon fiber, the prosthetics field was already using it regularly.

— Chris Chandler, Certified Prosthetist

Computerization

Chandler says an increase in prosthetic computerization has transformed the field and will continue doing so.

Before integrating electronics into artificial limbs, Chandler says that the industry had been unable to make much substantial progress, since mechanical methods are limited.

“We were kind of hitting that point in prosthetics where we needed more of a computer controlled system that could do more functions,” Chandler says. “Prior to that, we hit pretty much every body function you could do [without it].”

Now, with computerized limbs, a person can walk backwards without the fear of their knees buckling — a common concern with mechanical limbs. Rather than using methods such as loaded springs, these limbs contain sensors and personalized motors. These devices can then process incoming external stimuli and adapt its response movement.

Upper limb extremities are also experiencing new breakthroughs: better grasping patterns and individual finger motors. Previously, artificial hands could only slightly open and close, limiting task performance. As a result, those who required a prosthetic hand often chose to use hooks instead.

Looking Ahead

Chandler says the field has yet to fully incorporate everything that computerization has to offer. Studies are currently being conducted on neural surgical implants that process impulses from the brain, and then transfer that information to an artificial limb. This could potentially allow many paraplegics and quadriplegics regaining their ability to walk, or those with lost limbs being able to have robotic limbs that match the full function of their original appendage.

While the industry is taking great strides with the use of computerization and complex materials like S-Glass and Magnetic Fluid, Chandler emphasizes the importance of continuing research in the field. For now, you can find Chandler working away every day in his workshop at the VA, helping people get back on their feet.

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