The system modification track of Zurich Heart investigates new technologies that are required to improve the performance of existing ventricular assist devices (VADs). Based on clinical experience, a number of key weaknesses inherent to contemporary VADs were identified. Their elimination based on implementation of superior new technology will significantly advance handling and performance of future more cost-effictive VADs. Patients will benefit from improved life expectancy and comfort.
The system modification track currently addresses three challenges: Energy supply and information transfer, thrombosis and haemolysis, and dynamic and adaptive operation.
ENERGY SUPPLY AND COMMUNICATION
Transcutaneous Energy and Information Transfer
Prof. Johann W. Kolar (ETH)
One of the main challenges with the use of current VADs is the energy supply. Implanted devices are powered by an external energy source via a driveline penetrating the skin. To reduce the associated risk of infection and to improve patients’ comfort, wireless transcutaneous energy transfer and storage is needed. The main goal of this subproject is to develop a closed loop controlled VAD that is linked wirelessly to an external control unit to transfer energy and exchange information.
THROMBOSIS AND HAEMOLYSIS
Surface Material Modification
The contact of blood with artificial surfaces inside the pump activates blood coagulation. To avoid thrombus formation, aggressive anticoagulation measures and platelet inhibition is required which, in turn, increases the risk of bleeding complications. Thromboembolic complications could be markedly reduced if the inner pump surface was modified and coated with biocompatible materials.
The influence of surface properties on blood coagulation will be investigated. In particular, the question of blood coagulation on atomically smooth and on topographically modified surfaces will be addressed.
Topographic Surface Modifications and Flow Bioreactor
Prof. Dimos Poulikakos (ETH) and Dr. Aldo Ferrari (ETH)
The use of topographic surface modifications to promote healing and demote infection is among the expertise of the Laboratory of Thermodynamics in Emerging Technologies. The available library of surface geometries as well as new customized topographies will be used for the optimization of cell ingrowth up to the formation of a confluent and functional endothelium on the target surfaces (i.e. the process of endothelialization).
Blood/Surface contact area of housings: The group additionally exploits an original flow bioreactor reproducing physiological (1-5 Pa) and supra-physiological WSS conditions, to investigate the combined effect of wall shear stress (WSS) and substrate topography on the adhesion and migration of primary human endothelial cells. In particular, the efficiency of specific topographical modifications of the surface in inducing endothelialization is assessed as a function of the local WSS. Another part of the project is represented by the development of an anti-fibrotic envelope composed of an ultrapure, micro-structured, cellulose matrix that aims at protecting the external surface of the proposed pumping device.
Biocompatible Metallic Glasses
Prof. Jörg F. Löffler (ETH)
The aim of this project is to develop biocompatible metallic glasses, which, due to their excellent mechanical, electrochemical and surface properties, may be deployed as implant material in heart support systems. Metallic glasses have no crystalline structure and volume shrinkage through crystallization does not occur. Therefore the smooth surfaces of a metallic glass can be structured with great dimensional accuracy, i.e. down to the micro- or nanometer scale.
Prof. Vartan Kurtcuoglu (UZH) and Dr. Oliver Speer (UZH/Kispi)
The biophysical interaction between ventricular assist devices (VAD) and blood is critically influenced by fluid dynamics: Areas of stagnating flow harbor the risk of increased thrombogenesis, while regions of high shear stress can lead to blood damage.
The primary aim of this project is to optimize haemodynamics in the VAD for the reduction of haemolysis and thrombosis. To this end, we developed a computational framework to probe the local hemodynamics in VADs under operating conditions. At the same time, we are conducting in vitro studies to further elucidate the relationship between blood damage and mechanical stress. Ultimately, such experimental data can be used to refine existing or establish new blood damage models and, once integrated into our computational framework, to accurately predict blood damage associated with a given VAD design.
DYNAMIC AND ADAPTIVE OPERATION
Control Systems, Sensor Concepts and Testing
Prof. Christofer Hierold (ETH), Prof. Mirko Meboldt (ETH), Dr. Marianne Schmid Daners (ETH)
Today, VAD's do typically not adapt to the situation and the activity of a patient. Control systems that adjust the pump’s operating point according to the patient’s need are highly desirable as they would allow for more physiological operation.
In this subproject innovative sensor concepts are developed to measure ventricular volume and blood pressure. Based on these parameters, physiological control algorithms and systems could be implemented to control the status of the patient. As a first step, a novel mock circulation for the evaluation of ventricular assist devices has been designed which is based on a hardware-in-the-loop concept. A numerical model of the human blood circulation runs in real-time and computes instantaneous pressure, volume, and flow rate values. The VAD to be tested is connected to a numerical-hydraulic interface, which allows the interaction between the VAD and the numerical model of the circulation and thus the evaluation of the performance of the VAD. The setup is a valuable tool for researchers involved in the design and development of mechanical circulatory support devices.