Emma Lavelle was born with arthrogryposis multiplex congenita (AMC), which means she does not normally have the strength to lift or use her arms. The WREX system is an exoskeleton that aids in supporting the weight of the limbs, and enabled Emma to do things she she couldn't before. But it wasn't small enough to be of much use to a 2-year-old. Engineer Tariq Rahman and research designer Whitney Sample of the Nemours/Alfred I. duPont Hospital for Children used a 3D printer to custom-make a WREX in Emma's size, and you can see in the video how much that means. Link -via Metafilter
Stratasys 3D printers are unique in that the parts they print are very durable, which is why NASA uses them for their Mars Rover and why they worked well for Emma's WREX.
Everytime I've seen an object printed in 3-D, I've thought it looks accurate but too fragile to be of much use. I'd be interested in knowing more about how much stress 3-D printed devices can handle.