One of Bickley’s early patients was Leo, a miniature collie whose front leg was lost to amputation and whose owner was determined to see him run again. Bickley obtained a CFRP limb from an overseas supplier and trimmed the piece to fit Leo. No one was sure how Leo would respond when the prosthesis was applied. “Animals are not picky, they just notice that they have their leg back,” says Bickley. Leo took off running, and the CFRP piece snapped. This particular construction didn’t work, so Bickley was back to the drawing board.
Realizing he needed a custom solution using woven CFRP, Bickley forwarded an aluminum prototype to deBot, who produced a group of CFRP samples for Bickley, which worked for Leo right out of the gate. Leo’s owner was thrilled. “The owner has a new puppy, and the prosthesis is the only thing that enables Leo to keep up with his young friend,” says deBot.
The success of the CFRP prosthesis lies in the high strength and stiffness-to-weight ratios and good fatigue behavior, which better simulate what the arm or leg does for the animal. Reinforcing the layup where the prosthetic will be mounted and varying the stiffness throughout the length accommodates changes in the animal’s activity. “You could not achieve the same mechanics from steel or other materials,” says deBot.
The prosthetic limb is made from aerospace-grade, ISO-certified prepreg carbon fiber with epoxy resin from Cytec Solvay Group. “Prepreg is tailorable to the design and provides us with a more consistent outcome,” notes deBot. Both unidirectional and multidirectional fiber orientations are deployed, with a combination of long-axis fibers at 0 and 90 degrees along the length of the member. “Each design varies the fiber orientation and number of layers to handle the size of the animal, front versus rear leg and specifics of the medical case,” says deBot. “Bill Bickley has gotten to be quite an expert in knowing which layup type to select based on his patients’ needs.”
The material is layed up, then vacuum-bagged and placed in an autoclave to cure. After demolding the blade, deBot trims the part and sends it to Bickley. Since they are still in the development stage, Bickley provides feedback, requesting increased stiffness or more flexibility in certain areas of the blade. Their most challenging case to date was a double front amputee Chihuahua named Cowboy. After receiving two carefully aligned blades, Cowboy is off and running in his hometown of Las Vegas. “Each animal is different and we are still in the trial and error phase, but we have been able to successfully accommodate each patient,” says deBot.