(CNN) - A child throwing a ball. On the face of it, a simple act, but for four-year old Hannah Mohn this is a milestone.
Hannah was born with the neuromuscular disease arthrogryposis, which makes her joints curve and muscles extremely weak. She can't lift her arms very high without help.
Hannah survived, but with severe challenges and a long road ahead.
Hannah's chance at a normal life came aged 18 months, when she visited the Dupont Children's Hospital in Wilmington, Del., a leading hospital in the United States. She began using a device the hospital designed, called the "WREX", robotic arms made from 3-D printing.
"WREX stands for Wilmington Robotic Exoskeleton," explains Whitney Sample, a research design engineer at the hospital. "Most of the kids that we deal with have neuromuscular issues that affect their ability to raise their arms. So they have a lot of difficulty getting their hand to their mouth, doing typical activities of daily living, combing their hair, scratching their nose, so it allows their arm to pretty much float."
The WREX uses special elastic bands to give a child's arm a weightless feeling. "The mechanism is similar to how a luxo lamp works to make it 'effortless' to move and position the head of the lamp," says Sample.
It's a life-changing device, and one that's benefited hugely from 3-D printing. Producing components on site by printing them layer by layer greatly reduces the time it takes to create a WREX.
Even after 25 years designing devices for those with disabilities, Sample still gets emotional when children he has helped thank him for the difference he's making.
When one child was given a school assignment to write a story about their personal hero, they chose to write about Sample.
Arthrogryposis is a condition that affects one in 3,000 children born in the United States, according to the American Association of Neuromuscular and Electrodiagnostic Medicine. The Dupont Children's Hospital says it sees a little more than 30 new cases each year.
The device has helped improve Hannah's movements, even when she is not using it.
Teaching her, and opening up a future that knows no limits.