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Artificial Limb Transitions Between Prosthetics and Bionics

Although prosthetic limbs have been around for thousands of years and have undergone myriad transformations and refinements, modern-day prosthetics still have a variety of notable drawbacks. Prosthetic legs, for example, are often so heavy that their use exhausts amputees, making walking a burdensome and unpleasant exercise. Dedicated to restoring natural movement for lower-limb amputees and improving their quality of life, iWalk (Bedford, MA) has created a system that the company claims is the world's first proven bionic intervention that utilizes robotics to replicate the function of the missing calf muscle and Achilles tendon.

For more than a hundred years, prosthetics simply replicated bone, providing wearers with a structure on which to stand, remarks Ryan Hixenbaugh, iWalk's marketing and strategic planning representative. Eventually, the introduction of microprocessors and carbon fiber marked the first attempt to provide better support for mobility. "But BiOM technology has dramatically changed the future of prosthetics," Hixenbaugh adds. "It introduced the idea of using robotics to replicate muscles and tendons, and it is the first device to actually provide power to lower-limb amputees."

Using a series of computers and sensors, the device responds to the human gait, providing a push-off mechanism that carries the weight of the leg and moves the person forward in response to the power needs of the chosen speed. Known as power plantar flexion, this technology enables the prosthetic device to function without depending on the wearer's energy. "Personal bionic devices are fundamentally redefining the standard of care for those with limb loss by not merely emulating human function but enhancing it," Hixenbaugh says. "The BiOM lower-leg system restores natural motion through personalized bionic technology."

By restoring natural walking function, the device drives the user, instead of the reverse, according to Hixenbaugh. As a result, BiOM-wearing amputees don't tire as easily as those that wear traditional prostheses, and they do not expend more metabolic energy to walk than that expended by nonamputees. "In general," Hixenbaugh adds, "amputees also tend to live with knee, hip, and back problems. By adapting their gait cycle to manage the weight of a traditional artificial limb, they add forces to their joints, initiating the process of degeneration." By removing this weight, the BiOM may also help to alleviate lower-back and knee pain resulting from osteoarthritis.

After it had developed the BiOM concept, iWalk turned to OnCore Manufacturing Services (Springfield, MA) to provide the boards to power the prosthetic limb. Offering design for manufacturability (DFM), design for cost, and verification/validation support, OnCore understood that because iWalk's device would be used for prosthetic applications, the major consideration was ensuring ruggedness, remarks Dave Busch, the company's vice president of corporate development. "We needed to ensure that the boards and the control device used to help the ankle move could withstand shocks." To design a rugged board, the company analyzed the underfills and the positional relationships among the components to prevent the formation of weak joints that could eventually fail.

iWalk chose OnCore because it preferred to work with a nearby company that had expertise in developing boards used in critical environments, such as military and medical device applications, according to Busch. The OEM was also looking for a company capable of performing rapid prototyping cycles of learning. "Normally, customers come to us with a hypothesis of a board layout that they think will work," Busch notes. "After we produce a prototype, they try it out in an actual setting and return to us to refine the board. Instead of spending huge amounts of time trying to work out all the details using board-layout software, we use rapid cycles of learning." OnCore fulfilled iWalk's engineering change orders within 24 to 48 hours, producing a working prototype.

With the completion of the prototyping phase, iWalk enlisted the services of Cogmedix (West Bolyston, MA) to manufacture the BiOM. "Our role is to perform assembly, test, and inspection; document the device-history record; package the device; and fulfill orders--all with rigorous adherence to FDA's Quality System Regulation," remarks Matt Giza, the company's vice president and general manager. "Our assembly process includes building multiple subassemblies and integrating them together with other purchased components and subassemblies to create the final device." These assemblies consist of high-precision machined components, advanced materials, various electronic components, printed circuit boards, sensors, advanced battery packs, and several other components. "We are effectively iWalk's manufacturing floor," Giza adds.

By managing all aspects of the manufacturing process and performing associated resource management tasks, Cogmedix enables iWalk to focus its resources on continued product innovation and marketing, Giza says. And it helps reduce iWalk's costs by removing the need for the medical device manufacturer to establish its own compliant manufacturing facility. In addition, during product launch and subsequent change cycles, Cogmedix's flexible model has proved capable of reacting effectively to demand fluctuations, enabling the company to increase and decrease production rapidly according to real-time demand. "The end result of this endeavor," according to iWalk's Hixenbaugh, "is an artificial limb that is really the transition point between prosthetics and bionics."

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