How to build better bones — and revolutionize joint replacements

Teaming up with two other Toronto researchers, Pilliar, now professor emeritus in the University of Toronto’s Faculty of Dentistry and Institute of Biomaterials and Biomedical Engineering, sought out natural ingredients to build the implant of the future. In order to replace artificial knees and hips, his components would have to be biodegradable, long-lasting and tailored specifically for each individual.

“Let’s not downplay it: metallic (implants) are one of the most successful surgeries around,” he said. “But they are not custom-sized for different people.”

The researchers ultimately found their secret ingredient in the form of calcium polyphosphate. The powder — composed of the same minerals found in human bone — caught the eye of researchers after they learned that Monsanto, a U.S.-based company that engineers new varieties of plant seeds, had abandoned its efforts working with the biodegradable biomaterial.

Several studies and patents later, Pilliar and his colleagues were convinced they found the right compound to create a bone substitute. Now all they needed was the right tool to build it.

A young mechatronics engineer (a field that combines computers, electronic and mechanical systems) by the name of Mihaela Vlasea answered the call. Today, the professor has been charged with manufacturing the custom-shaped joint implants, one tiny layer at a time.

The University of Waterloo expert is a whiz in the world of additive manufacturing, a fancy term scientists use for three-dimensional printing. While the trend is to use a machine to create solid objects based on a digital blueprint, her custom-built 3D printing press takes the process to a next-generation biological level.

The robotic system is the size of a two-door refrigerator. By using ultraviolet light to bind the calcium phosphate powder together, Vlasea is able to manufacture canals and cavities within the implant itself with pinpoint precision.

Like an anthill, tiny holes on the outside surface of the implant lead to an internal network of nutrient-carrying tubes. Once implanted, human bone cells spread and mechanically interlock with the skeletal structure.

“The way we arrange pores inside of the part essentially enables the natural bone to grow inside the implant at different rates,” she said, adding the method can potentially be expanded to design fuel cells and dental implants.

Over time, the calcium polyphosphate is absorbed within the body while the patient’s own tissues and cells retain the artificial implant’s shape.

“It’s a little short of Star Trek where you zap a person, and they’re fixed,” Pilliar said. “But it’s along the same lines.”

At least, that’s the idea.

“It is nice to think of replacing joints and getting rid of all these metals. But in the short term, we are looking at substituting small regions of bone,” he said. “If we’re successful, you can imagine trying to regenerate a larger region of a joint.”

Engineering on the inside

Pilliar is also working on developing replacements for human cartilage, a potentially huge advance for people with arthritis.

Contrary to popular opinion, arthritis isn’t limited to the urban elderly. The disease can arise as a result of trauma, a misshapen joint or a sport injury. Because cartilage cells do not regenerate, treatment options are limited.

“Right now, if you have a damaged joint, there is no real treatment that can stimulate its repair,” said Rita Kandel, chief of pathology and laboratory medicine at Mount Sinai Hospital. “Ultimately, you require a replacement that utilizes metal and plastics.”

As one of the bone project’s three principal investigators, she has worked in tandem with Pilliar and University of Toronto researcher Marc Grynpas for two decades.

According to her, the one-size-fits-all implants of today last between 20 to 30 years before more surgeries to replace the replacement are needed. Kandel hopes to bypass this defect with “biological joint replacements” built from a patient’s own tissue and cells.

The musculoskeletal marvel begins with extracting stem cells from a patient’s bone marrow. These are reprogrammed at Kandel’s lab into immature cartilage cells.

After the batch matures over the course of several weeks, this bioactive spread of sorts is then layered and grown on the calcium polyphosphate implant printed at the University of Waterloo. Once implanted in the body during surgery, the homegrown cells function naturally and can even heal themselves.

Called “biological resurfacing,” this process further reduces the chance of a body rejecting an implant after it’s installed.

“If you are using the individual’s own cells, they are not recognized by the body as foreign,” she said, adding the novel treatment could potentially prevent the progression of osteoarthritis.

“It will help people so they don’t experience as much pain,” she said. “For me, that’s a major contribution.”

While a potential price point per custom implant is not yet known, Kandel expects a commercial product will be cheaper in the future because the raw materials are relatively inexpensive.

Further, she estimates this new class of “bio-replacement” for articulating joints such as the knee, hip and finger will be widely available in roughly a decade.

Animal trials, meanwhile, are currently testing the viability of repairing small bone substitutes using this new method. They are expected to continue for the next couple of years.