Soft robotic heart pump
40 million people are affected worldwide by heart failure. This is where the heart muscle is diseased and cannot pump sufficient amounts of blood. It's very debilitating and it robs sufferers of their quality of life. At the moment, the only effective long-term solution is a transplant, but only a tiny minority of people are lucky enough to receive one. This prompted researchers to develop gadgets called ventricular assist devices that can be plumed into the heart to help it to pump, but they’re not without problems. Now Ellen Roche has designed a better one, which fits around the heart like a glove,m as she explained to Chris Smith...
Ellen - This is a sleeve made of rubber with embedded balloons that can contract and beat with the heart to help the heart to pump additional blood the body. The advantage of this type of technology is that the sleeve goes around the outside of the heart and it doesn’t contact the blood like the existing ventricular assisted devices.
Chris - Why is it a problem if these devices contact blood?
Ellen - Because blood is pumped through foreign materials and in contact with foreign components it can clot, and clotting can lead to events such as stroke. So patients who have these devices are on blood thinners and this medication can itself have complications.
Chris - Now tell us about the device then. How is it put in and how does it work?
Ellen - The device will be placed around the heart surgically. For the study in our preclinical models we open the chest through the sternum, which is a chest bone, and it is surgically placed around the heart. The device itself is made of silicon, and we’ve embedded artificial muscles that are small contractile elements and we oriented them in a way that mimicked the way the muscle of the heart is organised. So when they contracted you got squeezing motion as well as twisting motion and this is how the heart itself moves, so by mimicking the heart we improve the output.
Chris - How do power the device? How do you make it go through those shape changes?
Ellen - The elements work by pressurised air that comes from an external pressurised source. We have pressure regulators and valves and these are synchronised to open and close when the heart contracts and relaxes.
Chris - So you are effectively applying a pressure to the heart from outside squeezing the blood? It’s a bit like squeezing a cloth in your fist and wringing the water out - it’s sort of doing that to the heart and, therefore, helping it to eject enough blood to go around the body?
Ellen - Exactly. As you mentioned, squeezing but also wringing. This twisting really helps and that’s something that’s different to previously described research in this area.
Chris - Now, heart failure comes in lots of different flavours and can affect one side of the heart over the other because we have a left side and a right side to the heart which do slightly different jobs. So can your device accommodate all these ranges of heart failure types?
Ellen - Yeah, exactly. One of the nice things about our device is it’s quite modular so we can independently accurate or pressurise different sides of the device. We can programme it so that only the left side will contract. We can also adjust the timing and degree of assistance delivered to the heart and tailor it to specific patient needs.
Chris - What sort of performance can you get out of this? I know you’ve only done this preclinically and that means you’re working on things like pigs, doesn’t it? But what sort of performance will it generate?
Ellen - In our preclinical models, we used a drug to slow down the heart and to reduce contractility and the output from the main vessel coming from the heart - the flow in the aorta it’s called - reduced down to about 50 percent of healthy function. This simulated the reduction in function that you would typically see in a heart failure patient, and we were able to bring that back up to very close to the healthy baseline level.
Chris - How does the heart tolerate having one of these devices in contact with it - does it object to being squeezed from the outside in this way? Could it become bruised and damaged?
Ellen - Yeah, that’s a really good question and it’s one we looked at in the paper. At the interface between the device and the heart, there is a risk that you’ll have some friction and damage. So we looked at introducing a hydrogel, a jelly like layer that would sit at the interface of the heart device and reduce the trauma or friction that device could impart on the heart and protect it really.
Chris - Is there no alternative to doing this with an external compressed air source? Because, of course, one of the things people are going to find objectionable is having to trail around with tubes and leads coming out of themselves.
Ellen - Currently, there are devices that have portable pressurised fluid canisters that can be worn on a belt or a backpack. We used air for this proof of concept study but we could change it to helium which is a lower molecular weight, or we could use fluid like water. Ideally, we’d like to move to an implantable pump and so the less hardware that’s external to the body, as you mentioned, the better. Even in terms of power, eventually it would be nice to move to batteries that could be charged through the skin or transcutaneously… that’s in the future.