The Wilmington Robotic Exoskeleton (WREX) is a body-powered exoskeleton designed to assist children with neuromuscular diseases perform simple activities, such as feeding themselves or giving a hug. The device was originally intended for older children, typically in wheelchairs, who could handle the weight of the metal frame, but researchers discovered that a 3-D printer could fabricate a lighter device, so the technology could reach a larger, more ambulatory patient population.

“The flexibility that it offers us is mindboggling,” said Whitney Sample, BFA, research design engineer at Nemours/Alfred I. DuPont Hospital for Children in Wilmington, Del., where the WREX was developed. “You are really only limited by your imagination.”

WREX

The WREX is a body-powered arm orthosis that is mounted on a wheelchair or body jacket. The exoskeleton uses rubber bands to activate the arms and move in 3-D space, assisting with voluntary movements. The WREX allows for full passive range of motion and is intended for children with little to no strength in their arms, typically caused by muscular dystrophy, spinal muscular atrophy or cerebral palsy.

“The arm orthosis basically does its best to cancel out gravity for kids with limited muscle strength,” Sample told O&P Business News. “It’s a very simple device that uses rubber bands and allows kids to move their arms where they would normally not be able to.”

While wearing the WREX, children can feed themselves, write, color and perform other tasks necessary for daily living.

“They wear it for as long as they can tolerate it,” Sample said. “Some of our kids just wear it for certain activities, and some of them wear it for as long as they are awake.”

 

Emma demonstrates her range of motion while wearing the WREX orthosis.

Images: Karen Bengston, Nemours/Alfred I. DuPont Hospital for Children

Metal vs. plastic

The original WREX is constructed out of metal parts and intended for older children for whom weight is not an issue. It was designed to be mounted onto a wheelchair. Sample and his colleagues began to look for ways to expand the availability of this technology when they met Emma, a toddler affected by arthrogryposis multiplex congenita, a congenital disorder that can cause joint contractures and muscle weakness.

Emma was younger and smaller than the typical WREX user and did not use a wheelchair, but the severe muscle weakness in her arms made her an ideal candidate for the device.

Sample used a 3-D printer to fabricate a smaller, lightweight version of the WREX out of plastic, which he secured to a plastic vest. Although Sample originally intended to use this version only as a prototype, he found that the plastic version worked just as well as the metal for these tiny patients.

“I don’t think we ever intended or envisioned using plastic parts as an end-use item, but with lighter kids like Emma, we demoed it on her and it worked well and held up,” Sample said. “So we just kind of ran with it, and for these smaller kids, it works great.”

With a few more modifications, Sample was able to create a fully-functional WREX for Emma, which she refers to as her “magic arms.”

 

Whitney Sample, BFA, fabricates the plastic WREX device in-house.

 

Fabrication benefits

The original WREX device is fabricated using a CNC milling machine, so any design changes or modifications could take weeks or months to generate. However, with a 3-D printer, changes can be made in a matter of days.

“It has really changed our whole process,” Sample said. “The ability to make changes on the fly or try out new concepts or fix something that is broken or didn’t work can be done so much faster now.”

This is especially important for children, who grow quickly and require continued device modifications. The plastic material will also help control the cost of the WREX, because it is much cheaper to fabricate than the metal device and reduces the need to maintain a large supply of premade parts.

“Typically in regular manufacturing, you have to keep lots of parts on hand, because the lead time that it takes to machine a part would hold up the entire supply chain,” Sample said. “But now, if you need new parts, you can just make them.”

Although the plastic can be less durable than metal, according to Sample, the other benefits far outweigh this concern.

“There’s always a trade-off with any material,” he said. “If you go lighter, you tend to sacrifice a certain amount of durability and strength, but it’s certainly something we can work around. Stratasys, the 3-D printer company that makes our printer, has been fantastic in this regard, and their engineers have been working closely with us to find new and better ways to get stronger, lighter parts.”

The original metal WREX is currently manufactured and distributed by JAECO Orthopedic, who purchased the patent rights for the WREX design, but the plastic version is fabricated by Sample and his colleagues in the hospital. They are continuing to research new innovations to improve the WREX and hope to create a motorized version in the 
future. — by Megan Gilbride