UBC Reports | Vol. 51 | No. 4 | Apr. 7, 2005

Need a Joint Repair? Stick a Sponge in it

By Hilary Thomson

Tiny, full of holes, yet effective -- drug-filled implantable sponges may be a new way to promote bone growth in orthopedic surgeries, say a pair of UBC scientists.

Helen Burt, of the Faculty of Pharmaceutical Sciences, and Tim Durance, of the Faculty of Agricultural Sciences, have teamed up to create a biodegradable sponge that can be filled with microspheres full of growth factors (proteins), antibiotics and stem cells for use in joint repairs.

The research is part of a five-year project, funded by $1.5 million from the Canadian Institutes for Health Research, that sees a team of UBC scientists working together to create a new fixative material.

Small chips or beads of sponge could be inserted into spaces at the site of bone defects and repairs, or at hip replacement surgical sites. The sponge would release its contents at a controlled rate to stimulate cells to produce bone material. This bony matrix would help the prosthetic joint to fuse into surrounding bone and tissue.

The two scientists connected in what Burt -- an expert in drug delivery systems -- calls “a stunning piece of good fortune.”
She knew she needed a porous material and her research team was attempting, for the first time, to make sponges from a chemical recipe. It wasn’t going well.

Meanwhile, Durance was looking for new applications for a technique used to dehydrate food. The technique produces porous material such as sponge, and allows the organic structure of the material to be maintained, even though it is completely dehydrated.

A colleague, who knew the work of both scientists, realized they were destined to collaborate and made the introductions.
“I knew that the technique had more potential, especially in the medical materials field, so this collaborative opportunity really came at the right time,” says Durance, who directs the Food, Nutrition and Health program.

The technique evaporates liquids from biological materials via microwaves that are applied in a vacuum, which produces a boiling point of about 30 degrees Celsius, much lower than normal. The technique can create foams and sponges from all sorts of moist biological materials such as proteins, carbohydrates, gums and gels. However, the equipment was designed for batch sizes up to 10 lbs. The expense of the pharmaceutical materials Burt uses dictates an optimum batch size of less than a gram. Durance is now miniaturizing his equipment to handle the amounts required for the study.

“The ability to make sponge from almost any material has expanded our research ten-fold,” says Burt, who is associate dean, Research and Graduate Studies, in the Faculty of Pharmaceutical Sciences. “We now have a staggering array of possibilities to test different sponge materials and see how they work with different drug-carrying microspheres.”

Sponge offers a multitude of spaces and surface areas for chemical reactions to take place. The researchers will develop a sponge that will allow stem cells to attach, proliferate and migrate, as well as provide the open spaces needed for cell movement and new blood vessel growth. Sponges may also be useful for holding antibiotics, which could be released slowly to prevent infections at orthopedic surgical sites.

Other properties, such as being biodegradable, compatible with tissues and cells and having some mechanical strength make sponge an excellent material for this application, says Burt.

She says scientists know lots about microsphere release of drugs, but “absolutely zero” about how the release might work after microspheres are embedded in sponge. Research challenges include ensuring the molecular structural integrity of drugs that are encapsulated, confirming that stem cells can attach to sponge, and controlling the timed release of the drugs in the sponge environment.