The silk road to recovery
The need
Bypassing blocked coronary arteries can help prevent heart attacks, but the surgical options currently available to the patients most in need are limited, and vulnerable to failure.
The solution
Blood vessels engineered from silk are emerging as a feasible and reliable alternative for use in bypasses, and may even be able to trigger the growth of new tissue, over time.
Cardiovascular disease is , and a factor in . A significant contributor to that high mortality rate is coronary heart disease, a condition which occurs when coronary arteries are clogged with a fatty build-up, reducing the flow of blood to the heart, and typically resulting in life-threatening events such as heart attacks.
The conventional surgical response is to bypass the blockage with a healthy vein, grafted from elsewhere in the body, usually the leg or the wall of the chest. But this approach has limitations, as Associate Professor Jelena Rnjak-Kovacina explains.
“If you think about who actually suffers from cardiovascular disease, these are people that are often elderly by the time they need this sort of intervention, often Type 2 diabetic, sometimes obese. And that means you don't have that many healthy blood vessels available to use – or you can only have this surgery once or twice, before you run out of healthy blood vessels.”
Synthetic blood vessels made from plastics have been explored as an alternative for bypass surgery, but while they can be effective in other parts of the body, they are generally too unwieldy for the small diameter of coronary arteries, and prone to rejection.
Against this background, Jelena and her colleagues are exploring the transformative possibilities of a biomaterial that promises to be easy to source, easy to use, and may even be able to trigger the regeneration of blood vessels over time–a biomaterial based on silk.
“It’s the same silk that your shirts and ties are made from,” says Jelena, who trained in a ‘silk lab’ in Boston’s Tufts University before joining the School of Biomedical Engineering in 2014.
I really like this idea that we can go into a lab, and mimic some of some of the complexity that has evolved over millennia, and ultimately contribute to something that has a tangible impact on a patient’s health. I think that's really exciting.
The fact that silk is a protein (although not a human protein) makes it a good candidate for grafts, given that most of the structures in the body are built from proteins. Blood vessels, in particular, are largely made of collagen and elastin, and while there have been very successful attempts to engineer blood vessels out of those components, the complexities associated with isolating and extracting them for use as base materials renders the solution impractical.
Silk, meanwhile, is far more accessible, says Jelena.
“It's abundantly available. We use the silk that comes from silkworms, already scaled up for the textile industry.”
Silk-based grafts also have the potential to be engineered in such a way that they send signals to the body to start producing new tissue. The focus of Jelena’s work now is on developing a product which can be implanted in the body to bypass the blocked artery in the short term, but which in the long term can act as scaffolding for the regenerated tissue, ultimately biodegrading and leaving in its place all new blood vessels to promote the healthy flow of blood to and from the heart.
The same thinking is also being applied by Jelena and her colleagues to the development of silk-based heart valve leaflets for the treatment of aortic stenosis, the most common heart valve disease which, if untreated, has a three-year survival rate of less than 30 percent.
These, and a raft of associated projects, require input from a wide range of collaborators.
“We get input from the clinical and patient perspective, of course,” says Jelena, “We also collaborate with material scientists. We collaborate with mechanical engineers for the testing of blood flow and fluid dynamics side of things. We also want to know if we can learn from the design of the silk and make better silks in the lab, so we are even working with non-medical biologists who understand how silk is produced.”
The success of these projects will mean longer-lasting solutions for patients living with cardiovascular diseases, and less exposure to invasive surgical procedures.
“I love research, generally. I love the idea of discovering something no one else has discovered. And I really like this idea that we can go into a lab, and mimic some of some of the complexity that has evolved over millennia, and ultimately contribute to something that has a tangible impact on a patient’s health. I think that's really exciting.”