When Emma was 2, she wanted to play with blocks. But arthrogryposis meant she couldn't lift her arms. So researchers at a Delaware hospital 3D printed a custom assistive device that lets Emma color, hug and play. The 3D printed WREX is durable enough for everyday use, so Emma wears it at home, at preschool, and during occupational therapy. She calls them her "magic arms." And the design flexibility of 3D printing lets researchers continually improve upon the device — they've now made custom WREX arms for at least 15 kids.