Mending broken hearts with an injectable patch

The flexible tissue scaffold, emerging from a glass pipette with a one millimetre wide tip. (Image: Miles Montgomery and Rick Lu)

Physicians typically have to carry out an invasive open-heart surgery in order to repair the damaged heart tissue of a patient who has had a heart attack. Wouldn’t it be so much simpler if a micro repair patch could be injected into the damaged area?

University of Toronto Engineering researchers working on laboratory animals have proven that such an injectable lab-manufactured tissue, seeded with heart cells, can effectively patch-up a “broken heart.”

A team led by biomedical engineering Professor Milica Radisic worked for three years on the development of three-dimensional patches which can be injected rather than embedded.

What benefits does an injectable patch have over one that is put in place via surgery?

Following a heart attack, the functions of the heart are drastically reduced to a point where an invasive procedure such as an operation poses serious risks.

“If an implant requires open-heart surgery, it’s not going to be widely available to patients,” said Radisic in an interview with Tyler Irving of the U of T news website. “It’s just too dangerous.”

The minimally invasive technique has the potential to cut down patient recovery time, as well as, reduce scarring and other negative effects.

The project was supported by the Canadian Institutes of Health Research, National Sciences and Engineering Research Council of Canada, the University of Toronto, the Heart and Stroke Foundation, the Canada Foundation for Innovation, the Ontario Institute for Regenerative Medicine and the Ontario Research Fund.

The team’s research was published in Nature Material.

Radisic’s team worked on several solutions. One of those is the AngioChip – a platform for developing and tissues that can replace repair and perhaps even replace damaged organs. The AngioChip was developed by graduate student Boyang Zhang and other members of the team.

The AngioChip is a three-dimensional structure that has internal blood vessels. It serves as an environment for cells to attach to and grow. With this platform, the team is able to build model versions of heart and liver tissues which function just like their real counterparts.

Another member of the team, Miles Montgomery, a PhD candidate, created a patch which could be injected from a needle.

The patch has a “shape-memory behaviour” which enables the stamp-sized tissue to unfold as it comes out of a needle.

Because the shape memory is a physical property and not a chemical one, the unfolding process is not affected by conditions in the body. The patch is seeded with heart cells that are allowed to grow for a few days before the patch is injected into rats and pigs.

The method involved a biodegradable, elastic, and microfabricated scaffold delivering the tissue via injection. The scaffold’s shape memory was achieved using a microfabricated lattice design. Scaffolds and cardiac patches (1 cm × 1 cm) were delivered through an orifice as small as 1 mm. The scaffold and patches recovered their original shape following injection without affecting cardiomyocyte viability and function.

The scaffolds and cardiac patches (1 cm × 1 cm) were delivered through an orifice as small as 1 mm. The scaffolds and patches recovered their original shape following injection without affecting cardiomyocyte viability and function.

The biodegradable scaffolds naturally break down over time. What is left is the tissue which forms a patch over the damaged part of the organ.

Experiments carried out by the researchers showed that the injected patch unfolds to nearly the same size as implanted by more invasive methods. The heart cells also survive the procedure.

The patch injected into rat hears can also improve cardiac function. Ventricles damaged by a heart attack were able to pump more blood than those without the patch.

The team still has a long way to go before getting to clinical trials, but they have already applied for patents for their invention and are also looking at the possibilities of applying their methods on other organs.

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