Up to now, serious heart damage from attacks or disease can be treated only by heart transplants. While the procedure has saved thousands of lives over the past half century, the main drawbacks are a lack of enough donors, rejection rates, and high costs.
If it were possible to transplant just parts of the heart muscle to replace damaged sections, that would be a promising alternative. But researchers have yet to figure out how to get the replacement tissue, called a cardiac patch, to conduct electricity or to be accepted by the recipient’s immune system.
In a forward-looking study published in the journal Nano Letters in September, the Israeli researchers tested a cardiac patch they engineered using a new technique and enhanced with gold nanoparticles. The gold nanoparticles appeared to improve the cardiac patch’s electrical conductivity. Heartbeat is controlled by electrical impulses generated by the heart tissue itself.
Prof. Tal Dvir, a bioengineer at Tel Aviv University, who led the study, at work in his lab. (photo credit: Courtesy)
While they used animal tissues in the study, the researchers say that in the future, the same kind of cardiac patch could be made from the tissues of a human transplant recipient. In this form, the patch could be personalized to also avoid immune system rejection. Clinical trials are several years away.
A golden opportunity
A heart attack blocks blood supply to the heart, damaging or killing affected tissue. Because heart cells cannot multiply, and because heart muscles contain few stem cells, the tissue is unable to repair itself. Along with other technologies, cardiac patches are being developed to repair the heart without replacing it.
If the kinks are worked out, the impact could be significant.
Heart disease is the leading cause of death in Western countries. The only treatment for advanced heart disease today is heart transplant. But almost half of the people on donation lists today have been waiting for more than a year, and about the same percentage of people die within five years of their first heart attack, according to the Centers for Disease Control and Prevention.
‘The patches we made using the gold are much superior’
Dvir has been engineering heart tissue in his lab since 2011, using various materials like animal tissues, collagen springs, and gold nanoparticles. In the latest study, he and his students engineered the first cardiac patch made with animal tissues and with gold nanoparticles. Dvir introduced the engineering technique in a study published this summer.
Cardiac patches are engineered by allowing heart cells to grow on a 3-D scaffold, similar to the extracellular matrix that naturally supports the cells in the heart. In the study, the researchers derived the extracellular matrix for their cardiac patch from a membrane taken from a pig’s abdomen, a biomaterial also found in humans.
Because foreign bodies can trigger an immune system response in a recipient, they removed all the pig cells and antigens from the membrane. They then coated the remaining cocktail-napkin-sized scaffold with gold nanoparticles.
To turn the gold-coated scaffold into a cardiac patch, the researchers “seeded” it with stem cells taken from rat hearts. Over time, the cells came together to form a tissue that generated its own electrical impulses and expanded and contracted spontaneously.
With microscopic imaging and chemical and electrical tests, the researchers found that the cardiac patch looked more like natural heart tissue and contracted more forcefully with less electrical stimulation than did a cardiac patch without a golden sheen.
“The results we got were very nice,” said Dvir. “We saw good electrical signaling, which is extremely important to the heart. The patches we made using the gold are much superior.”
Making it personal
The researchers say the heart cells grown in cardiac patches need time to develop the proteins that enable them to conduct electricity — time someone with heart damage may not have. With their cardiac patch, they say, the gold nanoparticles do the job until the proteins can.
Since finishing the study, the researchers have been transplanting the cardiac patch into rats with damaged hearts. Preliminary results suggest that the gold-coating greatly improves the cardiac patches’ capacity to conduct electricity from the healthy part of the heart, they say.
The next step is to try making the cardiac patches with tissue from the rats receiving them.
From there, it’s on to larger animals, and eventually to clinical trials.
