Cassidy, a tuxedo kitten with a white mustache and socks, lost his hind limbs from below the knee at birth. When he was found starving after nine weeks, his wounds infected with E. coli, the emergency vet recommended euthanasia. But Shelly Roche refused to give up on him. She runs the TinyKittens rescue operated out of Fort Langley, B.C., Canada, that specializes in lost causes. She nursed him back to health, with the Internet cheering him on.

This video shows Cassidy walking with a leash and harness to hold up his rear end, then getting a little wheelchair and finally running around and bounding off his rear leg stumps.

Two local high school students made him a wheelchair using their school’s 3D printer. This was not the last time 3D printing would help Cassidy. Handicapped Pets Canada also provided one that he used up until recently. Now that Cassidy has outgrown his wheelchairs, he gets around riding Roche’s Roomba.

But the Roomba is only a temporary solution. Cassidy is being fitted for prosthetic leg extensions. Last week, in the first step toward receiving prosthetics, Cassidy got Botox injections to relax the muscles of his rear legs, for ongoing physical therapy.

Roche said of Cassidy’s prosthetics, "I'm not sure if they use titanium or carbon fiber. I'm not sure what the end-point will be. I tell people he's going to get fancy new bionic legs."

That will be up to Dr. Denis Marcellin-Little and the team at North Carolina State University working on Cassidy’s prosthetics. Marcellin-Little is an expert in custom prosthetics and physical therapy. Like a real-life Dr. House for dogs and cats, Dr. Marcellin-Little gets the most challenging cases, where existing methods cannot provide treatment, so he and an international team of collaborators develop new ones.

The process for building a custom implant starts with a CT scan. Then, 3D-printed models of bones may be made. Marcellin-Little has over a decade-long collaboration with Dr. Ola Harrysson of the department of Industrial Systems and Engineering building implants. Marcellin-Little and Harrysson have invented a technique called osseointegration, where a titanium implant gets attached directly to bone via a honeycombed surface the bone grows to fill. The implant itself is made using a type of metal 3D printing called electron beam melting (EBM) where titanium powder is melted in successive layers to make the object.

Several news articles have mentioned the cost of Cassidy’s care. $10,000 has been spent on Cassidy already. The implant procedures can cost up to $20,000 per leg.

The procedure does not only benefit a single animal. Marcellin-Little talks of translating the technique to human patients “All the progress we make in free-form fabrication very quickly gets translated to human prosthetic research. Free-form transdermal osseointegration will cross over at some point to human patients.”