Submitted by Administrator on Thu, 02/08/2018 - 13:54
For heart valve replacement there are currently only two options - mechanical and animal-derived. A mechanical heart valve lasts for 15-25 years but requires lifelong anti-clotting (anticoagulation) drug therapy. An animal-derived valve circumvents the need for therapeutic treatment but only lasts for around 10 years.
There is a need in cardiovascular surgery for a durable artificial valve that removes the need for life-long drug treatment. Previous attempts to combine these two ideals have failed, but Prof Geoff Moggridge from the Department of Chemical Engineering and Biotechnology may have found the answer.
Prof Moggridge is a BHF-funded chemical engineer, who along with Dr Maria Laura Costantino from the Politecnico di Milano, conceived the idea of using a copolymer – a material designed over forty years ago that has now proven itself to be a vital piece of kit - to design a new generation of heart valves.
The material is a colourless, semi-transparent sheet and - most importantly - is anisotropic: “This means it can be stretched in one direction, but is very rigid in the other” explains Prof Moggridge. “Its structure mimics that of tissue fibres found in the valves of humans making this polymer an ideal material to recapitulate a human valve structure”.
In order to create the ideal size and shape of a heart valve, the polymer is first injected into bespoke metal moulds that were designed in collaboration with Dr James Taylor, an aerospace engineer in the Department of Engineering.
Once they had perfected the structure, Prof Moggridge and postdoctoral scientists Dr Joanna Stasiak and Dr Marta Serrani put the newly created valves through their paces, subjecting them to rigorous international testing guidelines to assess their durability and haemodynamic properties.
Using computational modelling and an artificial pulse duplicator (using a water and glycerol mixture to recapitulate blood viscosity), Prof Moggridge's research group has found that the new heart valves can last for 330 million cycles, which equals 6-7 years, a durability which is comparable to that of an animal-derived valve.
The polymer heart valve has the distinct advantage of mimicking the structure of a human valve to the extent that blood flow over the valve reflects the natural flow in humans. This reduces the risk of blood clot formation and potentially eliminates the need for life-long anti-clotting drug therapy. The valves are also coated in heparin, thus further diminishing the risk of clotting. BHF-funded Prof Azfar Zaman at Newcastle university has tested the likelihood of blood clot formation for the new valves and has shown that the clotting risk is comparable to that of the animal-derived valves.
Prof Moggridge is also working on a removable transcatheter heart valve. Using a variation of the polymer material, Prof Moggridge is working on a low melting point valve that can be delivered into a patient without becoming damaged, and that can be removed when it fails by simply melting it. “When a heart valve fails it is either taken out by open heart surgery or another valve is delivered by a catheter to push out the existing one” explains Prof Moggridge. The new design removes the need for either of these procedures.
These exciting results could revolutionise future aortic and heart valve replacements. Prof Moggridge is now turning his attention to testing the valves in animals. He collaborates with Prof Raimondo Ascione and Mr Saadeh Suleiman in Bristol to assess heart valves in large mammals. If successful, the polymer may become the go-to approach for human heart valve replacements in a matter of years.
The artificial valve polymer is funded by a BHF special project grant.
The removable transcatheter valve is funded by a BHF translational grant.
