Medical Device Daily Contributing Writer

VICTORIA, British Columbia – Researchers at the University of British Columbia (UBC; Vancouver) say they may have found a way to eliminate the risk of post-operative infection in patients who have undergone revision hip surgery.

Dr. Helen Burt is one of five researchers developing a sponge made of biodegradable materials that she hopes will be used eventually as a scaffold to support the growth of new bone in seriously deteriorated arthritic hips. The work at UBC, Burt told Medical Device Daily, is driven in part by recent applications of the scaffold concept to arthroscopic surgery.

“There are things on the market, for example, made of collagen and of biodegradable polymers,” she said, “but we didn’t want to buy some company’s material. We wanted to come up with our own material so that we could load our own growth factors into the scaffold.”

Hip implants typically break down after 20 years. As they deteriorate, wear debris from the implant inflames the tissue around the bone, loosening the implant. The inflamed tissue is normally removed in a second operation at this point and the area packed with bone chips from a cadaver. Bone chips are the “gold standard” in revision hip operations.

But bone chips are also limited in supply and can cause infection. The challenge, said Burt, is to come up with a different kind of material strong enough to bear the weight of the implant while providing an environment in which mesenchymal stem cells can thrive and new bone tissue grow without risk of infection.

“These stem cells have the ability to lay down bone matrix under the influence of growth factors,” she said. “The thing is, how do you get these cells into some environment where they can be packed into a bone cavity?”

Finding the answer involved an unusual collaboration between Burt, who is Angiotech professor of drug delivery at UBC, and Dr. Tim Durance in UBC’s food sciences division.

Durance has patented a microwave vacuum drying process that lowers the pressure and boiling point of water to produce a crispier, puffier fat-free potato chip. His microwave vacuum drying process also is in trials at the New York Blood Center, where it is being used to create a microbial prophylactic sponge to prevent AIDS in women.

In one of those “freak pieces of good fortune,” said Burt, a mutual friend heard about her search for a biodegradable material to be used in revision hip surgery and suggested that Durance contact Burt. E-mails quickly followed.

“So he and I got together, and I realized as soon as I saw this stuff that this potentially was exactly what we were looking for,” Burt said.

In the New York trials, 30 % of the sponge created using Durance’s technology is made of bioactive anti-viral compounds intended to combat the AIDS virus.

To make the sponge porous enough to absorb mesenchymal stem cells, the two researchers are using naturally occurring biodegradable materials such as hyaluronic acids, alginates, starch, gelatin and collagen. The sponge also will be embedded with micro beads made of biodegradable polymer and saturated with protein growth factors. The hope is that as the microspheres break down the stem cells will divide and proliferate under the influence of the growth factors.

“And as the stem cells are creating bone matrix,” said Burt, “the scaffold will disappear slowly over time. You won’t need it anymore.”

Before any of this can occur, however, Durance must build a microwave vacuum processor small enough to accommodate the production of Burt’s prototype sponge. It’s one thing to apply his technology to potatoes measured in kilograms, Burt said, quite another to apply it to expensive biomedical materials.

“I said we can’t possibly use your equipment and start making kilos of the stuff. We need to work with less than a gram. So currently he’s building a miniature version of the vacuum microwave devices.”

“We want it to be able to make a sponge out of just a few grams of material,” agreed Durance. “But on the other hand we want the approach to be expandable to a larger scale where you could do kilos of product if you wanted to.”

That equipment should be ready to begin producing the first prototype sponge by the end of May, added Durance. “The biggest hurdle” is not the equipment, however, but whether the sponge that is produced will actually permit the stem cells to live. The cells “will have to attach to the scaffold of the sponge,” Burt said. “They’ll have to live and grow and divide.”

“Will the sponge release something that just causes the cells to die? What if the growth factors come out too quickly or too slowly? What if the stem cells don’t attach to the sponge? There are a zillion potential problems.”

The sponge must also bear the weight of an implant, a feature Burt admits won’t exist in the prototype created this spring. That’s where UBC’s research engineers come in, she says.

“We’re thinking this will be a composite material – that is, the sponge will be one component, and there will be other materials added that will bear the mechanical weight characteristics, perhaps some kind of ceramic material.”

Funded by the Canadian Institutes for Health Research (Ottawa, Ontario), the Natural Sciences and Engineering Research Council of Canada (also Ottawa) and Enwave Energy Corp. (Toronto, Ontario), the project is still five years away from clinical trials. It could take another 10 years before a sponge is in commercial use.

None of this troubles Burt, who points out that the main candidates for this device will be older people whose hip implants have deteriorated. She predicts baby boomers will begin to need devices like hers at about the same time her sponge is ready to go to market.

Meantime, she remains buoyant about what her team has managed to accomplish even at this very early stage.

“I’m incredibly excited, especially now that we’ve figured out one of the hurdles, which is how to make this sponge. I think it’s really exciting.”