Injectable tissue patch may help repair damaged organs

Researchers have developed a technique that lets them use a small needle to inject a repair patch, without the need to open the chest cavity.

The research team at the University of Toronto are experts in using polymer scaffolds to grow realistic 3D slices of human tissue in the lab. Such lab-grown tissues are already being used to test potential drug candidates for side effects, but the long-term goal is to implant them back into the body to repair damage.

Researchers in Prof Radisic’s lab, have spent nearly three years developing a patch that could be injected, rather than implanted."At the beginning, it was a real challenge; there was no template to base my design on and nothing I tried was working," says Miles Montgomery Researcher at the University of Toronto. "But I took these failures as an indication that I was working on a problem worth solving,"he added.

After dozens of attempts, Mr Montgomery found a design that matched the mechanical properties of the target tissue, and had the required shape-memory behaviour: as it emerges from the needle, the patch unfolds itself into a bandage-like shape.

"The shape-memory effect is based on physical properties, not chemical ones," says Prof Radisic. This means that the unfolding process doesn’t require additional injections, and won’t be affected by the local conditions within the body.

The next step was to seed the patch with real heart cells. After letting them grow for a few days, they injected the patch into rats and pigs. Not only does the injected patch unfold to nearly the same size as a patch implanted by more invasive methods, the heart cells survive the procedure well."When we saw that the lab-grown cardiac tissue was functional and not affected by the injection process, that was very exciting," said Mr Montgomery. "Heart cells are extremely sensitive, so if we can do it with them, we can likely do it with other tissues as well."

The team also showed that injecting the patch into rat hearts can improve cardiac function after a heart attack: damaged ventricles pumped more blood than they did without the patch.

"It can’t restore the heart back to full health, but if it could be done in a human, we think it would significantly improve quality of life," said Prof Radisic.

There is still a long way to go before the material is ready for clinical trials, to assess the long-term stability of the patches, Prof Radisic and her team are collaborating with researchers at the Hospital for Sick Children to assess the long-term stability of the patches, as well as whether the improved cardiac function can be maintained.