In a small laboratory on the University of New Mexico campus, a 3-D printer is busy working its way back and forth, setting down material on something that looks like a microscope slide.
In fact, what the printer is doing is systematically and precisely placing thin layers of biopolymers containing bone, cartilage and ligament tissue on small scaffolds that biomechanics engineer Christina Salas believes will one day transform the way joints are replaced in the human body.
“We’re looking for something that can serve as a temporary replacement, but ultimately stimulate your body’s own immune system to start producing new cells in order to regenerate your own native tissue,” Salas said.
“So instead of plastics, metals or ceramic, this would be a degradable material that would be used to implant into the joint space, and over time it would degrade at the same rate your body would regenerate the native tissue — cartilage, bone, ligament— the whole thing. You’ll have your own tissue that’s regrown in its place.”
The scaffold could be inserted into the joint in a minimally invasive procedure and be anchored by bone screws or staples. The scaffold itself wouldn’t grow; rather it would degrade as the cells attached to it start to multiply and lay down tissue.
Salas also envisions how she and her team could conceivably one day use MRI or CT scans to create on their 3-D printer a scaffold containing the bone, cartilage and ligament material “that looks exactly anatomically like the arthritic end of bones that the surgeons remove.”
The goal is to make joint implants as we know them today unnecessary. How long it would take for the body to regrow the new material is not yet know. “It could take from a couple of months to a couple of years,” Salas said, depending on how much of the original joint the surgeons had to remove.
Salas said she anticipates that studies on mice or rats will begin within a year, but it could be 10 or more years before the scaffolds are implanted in people.
Salas, 40, has been on the UNM faculty for nearly six years, and has cross appointments in the UNM Health Sciences Center’s Department of Orthopedics, and in the School of Engineering. She has a doctorate in biomedical engineering, a master’s degree in mechanical engineering, did a fellowship in computational biomechanics at the Mayo Clinic in Minnesota and another one in experimental biomechanics at the University of California, San Francisco.
She already holds one patent on a mesh plate she designed for fixing more superficial bones, such as the patella in the knee, the olecranon bone in the elbow, and she has another seven patents pending.
As a child growing up in San Antonio, Salas thought she might like to become a computer engineer, but a teacher subsequently began taking to her about “engineers who are astronauts, and engineers who build bridges and buildings, and engineers who build cars,” she said.
That resonated with Salas, who became pretty good at fixing her own cars and said some of her first jobs were at auto parts stores.
“About six months ago I changed out the furnace in my house. I’ve always picked up a book and anytime I needed to do something it was more fun for me to learn how to do it myself, rather than pay somebody else to do it.”
That fancy 3-D printer in her lab was a do-it-yourself project cobbled together by Salas and her undergraduate and graduate research assistants from the UNM School of Engineering.
When Salas came to UNM to work on her master’s degree in mechanical engineering, she had a graduate adviser who was also a civil engineer.
“As a civil engineer, you’re working with structures, and the human body is a structure, so you’re just working with different materials,” she said.
The adviser, who had experience in biomechanics, was looking to do a research project with a graduate student in technical engineering, but who also had an interest in health care.
That set Salas on her current path.
In other labs at UNM, she and her research assistants are testing different configurations of spinal rods on synthetic spines that are placed in machines that simulate human motion and stresses.
“We’re trying to answer questions for surgeons if they need as much hardware in a patient in order to have a strong fixation, or can they have less hardware but still be able to hold the same load and stabilize the spine,” she said.
They are also testing an external, triangular configured fixation device using carbon fiber rods to stabilize a broken tibia bone.
“My role in orthopedics is to work with all our surgeons in every specialty, and help facilitate any development of new technologies and new surgical procedures,” Salas said. “If a new implant comes on the market, we test it to see if it’s as good as some of the impacts they’ve been using for many years.”
Salas, who is married and has two young children, acknowledges that she sometimes spends up to 60 hours a week doing research in her labs, mentoring students and teaching.
“All my research is focused on health care and patient care, but I wanted to be in the background,” she said. “I’m the typical introverted engineer. I do very well interacting with patients, but I do a better job making implants or devices that are used by those patients — and I can make just as big of an impact.”