The new artificial heart valve that could change lives

Thousands of people in the UK have heart valve surgery every year, either to replace or repair a damaged heart valve. Heart valves control the way blood flows through your heart, so in order for your heart to work properly, it’s vital that they do their job well. Without treatment, a faulty valve can cause breathlessness, tiredness and can even lead to heart failure.

Replacement valves can be mechanical (usually made from carbon or titanium flaps attached to a Teflon or polyester ring) or tissue (usually from a cow or pig). Both types help people with heart valve disease, but neither are perfect, and complications can occur with time.

How can heart valve replacements be improved?

People with mechanical valves usually take warfarin or another anticoagulant for life, as there is an increased risk of blood clots. Tissue valves have a lower risk of clots, but tend not to last as long, in particular because they can begin to calcify. This means calcium builds up on the valve, causing it to stiffen and not function as well as it should.

Scientists are searching for a new type of valve that lasts longer and is less likely to calcify or cause blood clots. But that’s no easy feat. Heart valves are in constant motion and play a crucial role in helping blood flow in and out of the heart, so need to withstand a lot of pressure. Professor Geoff Moggridge, in collaboration with Professor Raimondo Ascione, has developed and tested a prototype, made from a material not previously used for heart valves.

Four years ago, we reported on Professor Geoff Moggridge’s artificial heart valve research, and now, things are looking more promising than ever.

What are the new heart valves made from?

Professor Moggridge, a chemical engineer at the University of Cambridge, is an expert on the properties and function of soft materials. He says: “I’ve been working with materials called polymers – specifically block co-polymers, which are two polymers that are chemically bonded together.”

A chance meeting led to Professor Moggridge’s heart valve research. His team were working on an exciting material which is anisotropic – meaning it can stretch in some directions while staying rigid in others. A visiting researcher said a colleague in Milan was looking for an anisotropic material that could be used to make replacement heart valves. Professor Moggridge says: “That was it. Our teams started to talk, and we thought, let’s give this a try!”

Professor Moggridge started working on this valve in 2011 and we’ve funded this work ever since. Since 2015 he’s been working with Professor Ascione at Bristol, a heart surgeon and medical researcher.

How long can the heart valve replacements last?

An important question was whether it was strong and long-lasting enough. After years of detailed testing and modelling, much of it carried out by Dr Joanna Stasiak and Dr Marta Serrani, they have completed the first round of their lab work and have published their findings so far.

“A really exciting development for us since we last spoke to Heart Matters, is getting the valve’s durability to an excellent place,” says Professor Moggridge. “Testing four valves, we averaged over a billion cycles – in fact, 1.2 billion, mimicking 1.2 billion pumps of the heart, or roughly 30 years of your heart beating. It obviously takes a very long time to carry out an experiment like that, but it’s such an important experiment to do. “These are the best durability results reported for any polymer valve. We’re on a mission to improve even further.”

The team also carried out measurements in the lab to see how fluids flow through the valve. They found that the valve is able to withstand high levels of pressure and can open and close with ease. Professor Moggridge says: “We wanted to be able to match the performance of our valve on key measures, such as regurgitation (how much ‘leakage’ or backwards flow there is through the valve) and pressure gradient (the difference in pressure on each side of the valve).

“These are important areas of performance that tell us whether the valve will function well in the body. We’ve found that our valve matches one of the leading tissue valves currently available in these measures.”

Stopping blood clots from forming

Clotting is a risk with mechanical valves. Because of this, patients with these valves have to take anticoagulant drugs for life. Anticoagulants stop clotting but carry a risk of bleeding and, in the case of warfarin, require regular monitoring and blood tests.

Professor Moggridge thinks it is the shape of mechanical valves and the way they open that causes blood to flow and swirl differently, increasing the risk of clots. That’s why the team have designed their valve to resemble a healthy human valve and have studied how blood would flow through the heart. A coating of heparin (a drug designed to help stop clots from forming), on the valve can reduce the risk of clots even further.

The hope is that this valve won’t require lifelong anticoagulant drugs. But the team can’t know for sure until animal studies prove successful, paving the way for clinical trials in humans.

The team are also looking at whether calcium build-up could happen on their new valve. “Our tests in the lab look promising,” says Professor Moggridge. “But it’s difficult to mimic what happens in the body. It’s vital that we now test our valves in animals so we get a better understanding of how they would work in humans.”

What’s next?

BHF-funded Professor Raimondo Ascione at the University of Bristol is co-leader of the team. He’s testing the valve in a small number of sheep. Although there were some delays due to Covid-19, the team have now started a six-month trial with BHF support.

With their latest prototype showing great promise, the team hope that the material could be used for more products in future, such as heart patches for people with heart muscle damage, or other medical devices.

Professor Moggridge says: “It’s clear the opportunities are endless with a material like this. We’re excited for where our work takes us next.”

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