A heartbeat for soft robots aiming to improve lives of millions of patients

The results obtained in this PhD research represent an important step towards more autonomous soft robots in general, and specifically towards the development of a fully implantable and biocompatible heart prosthesis that might one day provide a much-needed solution for millions of end-stage heart failure patients worldwide.

Soft, compressible, stretchable, bendable materials can be found everywhere in nature and this softness is essential for the survival of plants and animals. Think of an octopus that can squeeze through tiny openings, or an elephant trunk that is both flexible and very strong. Soft robotics is an emerging research field that aims to make robots safer and smarter by using deformable materials like rubber and fabrics, taking inspiration from nature. Applied to an artificial heart, soft robotics technology brings clear advantages, such as more gentle handling of blood, and a more natural fit in a patient’s chest. But the control systems that are necessary to activate soft robotic components are bulky, heavy, and rigid, undoing some of the advantages of the soft materials.

A ketchup bottle to the rescue

Enter Luuk van Laake’s project. His work focuses on the challenge of making the Hybrid Heart beat without any electronic components. This may sound unlikely at first, but it gets even more incredible when you hear what he uses to do it. He shows that something called a ‘soft hysteretic valve’ can be used to do exactly that. The valve is a little rubber membrane much like those we all know from ketchup, honey and shower gel containers. The secret of these well-known upside-down containers is the soft transparent membrane you see when you open the cap. That membrane helps to keep liquid from dripping out until you squeeze with sufficient force. But sometimes, when you squeeze with exactly the right – or wrong! – force the liquid starts to sputter in all directions. In his thesis, Van Laake uses an optimized version of that same sputtering effect to create a heartbeat for soft robots.

How does the soft heartbeat work?

“There is no magic here, just a smart use of materials and structure.” Luuk says, when asked to explain the mechanism behind the system. “First of all, a pump is still required to provide energy to the system. And designing a pump that can be safely implanted is a major hurdle before this technique can be applied. But once pressue is available, we do take care of all the rest, and we do it without any electronic or other rigid components. We make a loop in which the pump circulates air at a constant rate. The valve is inline in this loop and is initially closed. Therefore, pressure starts to builds up before the valve. Then suddenly, at a specifically designed pressure, the valve automatically opens because it can no longer support the pressure. When that happens, the compressed air bursts through the valve and into the pneumatic artificial muscles of the soft artificial heart, causing the heart to contract. During this event, the pressure before the valve quickly goes down, such that the valve closes and the cycle restarts.” Importantly, in such a system, the heart rate is not explicitly controlled by a computer  “An interesting finding is that the heart rate and stroke volume (blood volume pumped per beat) also depend on interactions with the patient’s blood circulation. That means that we need to take this effect into account in our simulations to ensure the heart will function in all circumstances. Excitingly, we also see beneficial effects of this interaction. For example, in some cases the artificial heart rate automatically goes up to compensate for lower stroke volume when the blood pressure rises.”

Intelligence of the body: other applications

In his thesis, Van Laake also identifies other applications. In a broader sense, the new concept enables soft robots in all kinds of situations to exhibit desired behavior in interaction with their environment, without the need for electronics or external control inputs. As an example, he built a soft robotic hand and a four-legged robot that can change its behavior in response to physical cues. Such robots may be applied in industry, or search- and rescue operations in the future. Intelligence of the body, or Embodied Intelligence (E.I.), is an upcoming discipline that Van Laake believes will complement purely computational A.I. in the future. “We can already see that A.I., for all its incredible achievements, also has some fundamental limitations, such as extreme energy use. I believe that studying the intelligence of the body will contribute to a better understanding of natural intelligence. This in turn, will enable more energy efficient A.I.”

The research of Luuk van Laake is part of the EU-funded project `Hybrid Heart’. In this project, a consortium of partners aims to develop a total artificial heart (TAH) based on soft robotics technology. The research was performed at AMOLF (Amsterdam, The Netherlands) and is part of the Dutch Research Council (NWO). This project received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 767195. Other main parties involved: Hybrid Heart consortium including Eindhoven University of Technology and Amsterdam UMC. For more information see: hybridheart.eu/publications/

Title of PhD thesis: A heartbeat for soft robots. Supervisors: Bas Overvelde and Carlijn Bouten.