New Central Fabrication Technology Steps Onstage

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By Miki Fairley

"There's a way to do it better-find it." -Thomas Edison (1847-1931)


When one of the world's fastest amputees, Jerome Singleton, Irmo, South Carolina, competes in the upcoming 2012 Paralympics in London, United Kingdom, his prosthesis will feature an extrastrong, extra-light socket fabricated using an innovative braided carbon-fiber technology.

POMI Project Receives Recognition

The POMI project has been receiving accolades. In 2011 it received a DoD Manufacturing Technology Program Defense Manufacturing Achievement Award, and in May it was awarded a Przirembel Prize for Collaboration in Technology and Product Development, which recognizes collaborations across diverse organizations in the southeastern United States with significance outside the region.

To date, the POMI has resulted in the commercialization of two of the technologies: the automated carbon-braided socket manufacturing method from Mentis Sciences and the SensorTech Zebra™, a high-resolution, threedimensional pressure-mapping sensor system that measures pressures exerted by patients on prosthetic systems during all phases of use.

The carbon-fiber braiding technology was developed in 2008 with U.S. Department of Defense (DoD) funding through public-private collaboration under the auspices of the Columbia, South Carolina-based SCRA Applied R&D sector Prosthetics and Orthotics Manufacturing Initiative (POMI). The sockets produced with this technology are up to 50 percent lighter, cost 40 percent less to manufacture, are produced quicker, and have longer lifecycles than traditionally fabricated sockets, according to SCRA.

Project collaborators include Friddle's Orthopedic Appliances, Honea Path, South Carolina; Mentis Sciences, Manchester, New Hampshire; SensorTech Corporation, Greenville, South Carolina; Georgia Institute of Technology (Georgia Tech), Atlanta; Clemson University, South Carolina; and other federal and state government agencies, private companies, and charitable organizations.

Developed through U.S. Department of Defense funding, the braiding machine from Mentis Sciences, Manchester, New Hampshire, automatically braids carbon fibers individually to the patient's residual limb shape, producing significantly lighter sockets that are tested to exceed ISO strength standards. Spyder Technologies plans to demonstrate the machine during the upcoming American Orthotic & Prosthetic Association (AOPA) National Assembly in Boston, Massachusetts. Photographs courtesy of Spyder Technologies.

Dennis Clark, CPO, founder and president of O&P1, Waterloo, Iowa, who uses this new technology, provides some examples of how light the sockets can be. "We made a prosthetic forearm socket with a wrist connection- no terminal device-and the wrist connection was more than 50 percent of the weight of the socket." Clark says. "And the socket is incredibly strong!" In another example, he says that the new sockets reduced the overall weight of the prostheses used by a young soldier with bilateral transtibial amputations by 2.6 pounds-1.3 pounds apiece. "That's a significant reduction in weight and increase in functionality for someone walking a tremendous number of steps per day; you're saving them from lifting an additional ton or more each day." The soldier also reported improved proprioception. "He could feel the ground, the gas pedal, the brake pedal better," Clark says. "He still used the same prostheses as he had before; the only change was the sockets."

Led by SCRA Program Manager Chris Norfolk, PhD, on behalf of the Office of the Secretary of Defense, POMI was initiated to aid in the care of wounded warriors returning to combat; however, the technology is now being used in the private sector by Spyder Technologies, a company incorporated in 2011 by Clark and Frank Friddle Jr., CO, owner and president of Friddle's Orthopedic Appliances.

WillowWood Tests Direct Manufacturing

Another innovative central fabrication technology may be waiting its turn to step into the spotlight.

WillowWood, Mt. Sterling, Ohio, has been testing selective laser sintering (SLS) technology, a direct manufacturing system that fabricates products from CAD files by sintering powder material into the desired shape, according to WillowWood Director of Engineering Jim Colvin, MSBME. "To improve our ability to design and fabricate prosthetic sockets with SLS, we further developed our OMEGA® Tracer® CAD System by adding direct manufacturing functionality," Colvin says. "We are now able to custom-design sockets with variable wall thickness on a computer and then output the socket shapes directly to the SLS machine for direct fabrication, automating the entire process up to the point that the socket is removed from the SLS machine. Direct manufacturing is a precise, automated fabrication method that offers the ability to customize sockets, control design dimensions, and incorporate unique features not previously attainable with other fabrication methods."

The research and development project was an initial exploration of the use of direct manufacturing technology to fabricate prosthetic sockets and was funded by a contract grant awarded and administered by the U.S. Army Medical Research & Materiel Command (USAMRMC) and the Telemedicine & Advanced Technology Research Center (TATRC) under contract number W81XWH-08-10700. "We have successfully demonstrated the feasibility of the SLS system and that direct manufacturing can complement our CAD technology," Colvin says. "We currently have patients comfortably wearing SLS sockets as their primary prosthesis."

Colvin and Maria J. Gerschutz, PhD, an applied research engineer at WillowWood, presented results of the study in a paper, "Mechanical Evaluation of Direct Manufactured Prosthetic Sockets," during the 2012 American Academy of Orthotists and Prosthetists Annual Meeting & Scientific Syposium. (To read the paper, visit www.oandp.com/link/165.) The authors pointed out that traditional plaster-casting fabrication methods have several negative aspects including an inconsistent manual process, production of material waste, excessive process time, and the destruction of original shape data. They noted that CAD technology offered improvements; however, a positive model is still required for fabrication. "The SLS fabricated sockets produced sufficient strength and desirable fatigue resistance demonstrating it [direct manufacturing] as a viable option for prosthetic sockets. The static strengths of the SLS sockets were superior to the conventional carbon laminated sockets. In addition, the SLS direct manufacturing technology provided a more consistent process with minimal variability between sockets." The SLS sockets used Nylon 12, a material noted for strength including impact strength, abrasion resistance, fatigue resistance, and resistance to cracking under stress.

Another WillowWood research study found that SLS was superior to another direct manufacturing technology, fused deposition modeling (FDM). WillowWood design engineer Lonnie Nolt presented a paper, "Comparison of Direct Manufacturing Technologies for the Application of Prosthetic Sockets," during the 2012 ORTHOPÄDIE + REHA-TECHNIK World Congress and Trade Show May 13-16. Nolt and colleagues concluded, "FDM strengths and fatigue resistance were inferior to current technology, and therefore not a viable option. In contrast, the SLS fabricated sockets produced superior static strengths and desirable fatigue resistance." To read the abstract, visit www.oandp.com/link/166

Although promising, the direct manufacturing technology "is not ready for commercialization and still needs to be optimized before becoming a viable commercial option," Colvin says.

The custom sockets are manufactured exclusively at their respective central fabrication facilities, Clark says, adding that the system has been used to manufacture sockets for hip disarticulation, transfemoral, transtibial, transradial, and transhumeral levels.

"Practitioners can use any socket design they choose," Clark says. "What the individual practitioners do in their clinical practice- in terms of shape, liner, whatever they normally do-they can still do it. We have the standard, techniques, and technology in place where customers know exactly what they are getting. The technology produces consistent, clinically engineered results; we have a quality-assured standards checklist that is identical in both locations."

Exceeding the ISO Strength Standard

Mentis Sciences developed the carbon-fiber braiding machine that Friddle's received and began using in March 2010; O&P1 began using the technology about six months later. Clark says the sockets produced using this technology exceed the International Organization for Standardization (ISO) strength standards by twice as much or more.

"We have been developing the process and have had all the different socket variations we fabricate tested for strength against the ISO standard," Clark says. "Each socket is clinically engineered based on the patient's K-level and weight up to 500 pounds. Thus we know that each person's prosthetic socket is appropriate for his or her K-level and weight, and that it exceeds the ISO standard for strength."

Clark notes that the issue of socket strength standards has been addressed in Thranhardt lectures and papers presented at the Annual Meeting & Scientific Symposium of the American Academy of Orthotists and Prosthetists (the Academy) and the American Orthotic & Prosthetic Association (AOPA) National Assembly. He cites a paper presented at the 2012 Academy meeting, "Industry Wide Evaluation of Prosthetic Socket Strength," by Maria J. Gerschutz, PhD, et al., which describes the testing of 98 sockets against the ISO strength standard. (Author's note: An abstract of Gerschutz's 2012 Academy presentation can be viewed at www.oandp.com/link/163. For expanded reading on this subject, see "Strength Evaluation of Prosthetic Check Sockets, Copolymer Sockets, and Definitive Laminated Sockets," Journal of Rehabilitation Research & Development vol. 49 no. 3 (2012), Maria J. Gerschutz, PhD, et al., which can be accessed at www.oandp.com/link/164)

The sockets tested in the study were provided by three central fabrication facilities, three private practice facilities, and three military/U.S. Department of Veterans Affairs (VA) hospital facilities. Thirty-four diagnostic sockets, 31 copolymer sockets, and 33 definitive laminated sockets were included. "A majority of the sockets, regardless of type, failed to pass the same strength standard other prosthetic components are required to pass [for the given geometry tested in the study]," the authors noted. "Socket strengths also varied significantly. Potential sources of variability for diagnostic and copolymer sockets included thickness and fabrication method. Diagnostic sockets also varied by material type. In contrast, definitive laminated sockets were influenced more by construction material and technique." The study suggests several areas for improvement in socket fabrication: (1) the development of industry-wide best practices; (2) the optimization of practices to reduce variability; and (3) the evaluation of new materials and practices with improved strength properties.

Clark says, "That is exactly what Spyder Technologies is working toward. When we work with patients, they want to know what they are getting, and when we work with payers, they want to know what they're buying." Because the sockets have been tested against ISO standards, Clark says they are "able to guarantee the strength and durability of our product for patients, providers, and payers alike."

Friddle adds that there is no additional cost over traditionally fabricated carbon-fiber sockets to manufacture sockets using the carbon-fiber braiding system.

Creating Carbon-Fiber Braided Sockets

The carbon-fiber braiding machine weaves the fiber directly onto a positive plaster mold or foam carving.

The machine adds a second layer of braided carbon fiber to the socket. The technician is able control the braid while it is being woven.

To create the sockets, carbon fibers are braided individually to the patient's shape rather than the socket being laminated with manufactured carbon stockinette, Clark explains. "The practitioner sends us an aligned diagnostic socket, and we send back a finished socket or completely finished prosthesis with the socket fabricated with Spyder technology. The definitive sockets are braided automatically on a machine developed by Mentis Sciences. The technician is able control the braid while it is being woven directly on the positive plaster mold or foam carving. Similar to traditional methods, resin is bagged and infused using vacuum pressure." (Editor's note: To view the braider in operation, visit www.oandp1.com/ and click on the Spyder Technologies video).

According to SCRA, the braider is capable of achieving fiber densities that are unobtainable using traditional fabrication methods and materials, producing substantially lighter sockets. "The braider is capable of triaxial braiding, which aligns fibers directly along the socket's main axis," SCRA noted in its POMI Przirembel Prize Application. "Studies of socket failure indicate that fibers aligned in this direction are important for overall socket strength. Further, the braiding of the metallic attachment point into the composite structure results in superior strength. The braider allows for the selective reinforcement of the structure at highly loaded areas, allowing tailoring of properties." Friddle adds, "Being able to control fiber orientation and density at any transverse level of the socket is the key to the entire process."

Shape-memory composite materials used in the application are "activated" by heat and can easily be influenced to assume other shapes, including changes that positively affect socket fit. This ability allows for easier adaptation to changes in socket volume and other anticipated changes, thus increasing the life of the socket, according to SCRA. "These materials are supplied as both resins and foam inserts, which can be positioned in areas anticipated to require change in the future."

The braiding machine was exhibited at the Academy Meeting in March and will also be on display during the AOPA National Assembly in September, Clark says.

"The patient feedback we have received from the new technology has been nothing less than phenomenal," Friddle says. "We are seeing more advantages than we had originally anticipated."

What's Next?

"Innovation is the process of turning ideas into manufacturable and marketable form," observed noted software engineer Watts Humphrey (1927-2010). The O&P industry, including central fabrication, seems well on the way to following Humphrey's dictum. One wonders what other new technologies and adaptations of existing technologies to O&P are in planning or rehearsal, just waiting their turn to step onto the stage.


Miki Fairley is a freelance writer based in southwest Colorado. She can be reached at