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Hemocompatibility improvement and cost reduction of Ventricular Assist Devices by means of ceramization

Background

According to the world health organization, ischemic cardiovascular diseases are the most common causes of death worldwide. Several of these diseases result in terminal heart failure. In this state, the heart can only maintain the most essential functions of the body. For supporting the weakened heart, cardiac assist devices are used. In case of an implantable cardiac assist device, its hemocompatibility is the most crucial factor for a successful therapy. A lack of hemocompatibility leads to thrombus formation, which is one of the main complications. In order to prevent such thromboembolic events, patients undergo an anticoagulation therapy, which bears the risk of severe bleeding and thus reduces the quality of life of these patients even more.

According to the current state of the art, all foreign materials in blood contact should provide extremely smooth surfaces. Thus, the manufacturers of cardiac assist devices polish any blood-contacting part of their products extensively, even by hand, in the course of the finishing process. Nevertheless, component junctions and scratches caused during the transport of the assembled device still bear a high thrombus formation risk. In the last years, several researchers as well as the Department of Cardiovascular Engineering, in short CVE, proved that specific surface structuring reduces platelet adhesion and thrombogenicity compared to the flat surfaces. Based on these findings, the CVE investigates both the improvement of the hemocompatibility and the reduction of manufacturing costs by means of ceramization.

Objective

The focus of the CVE subproject “Prediction of the Hemocompatibility of Ceramized Surfaces” lies on the investigation of the relations between characteristics and hemocompatibility of metallic and ceramized surfaces. Therefore, we will examine various material samples with regard to both platelet activation and adhesion by static experiments followed by quasi-static and finally dynamic in-vitro experiments. All in vitro tests follow the DIN ISO 10993-4 standards.

Based on the obtained results, we will chose the most hemocompatible materials for the further proceeding of the project. For the dynamic in-vitro experiments, which simulate the flow conditions inside the final ventricular assist device, in short VAD, we will further develop an appropriate test setup. Finally, we manufacture VAD prototypes including the two best material modifications and analyze them in in-vitro pump experiments. As there is no standardized method for the in-vitro hemocompatibility evaluation of blood pumps available so far, we will establish a new analysis method. For this, we utilize the coagulation factor “von Willebrand-Factor”, as it loses its functionality due to mechanical destruction and/or high shear rates in blood pumps and therefore leads to the bleeding syndrome in patients. By means of the newly established detection method for the von Willebrand factor, we will evaluate the hemocompatibility of the modified and ceramized pump surfaces. Based on all results, CVE will develop a method for hemocompatibility prediction during the course of the project by correlating all various surface characteristics with the results of the hemocompatibility studies. This allows an incorporation of hemocompatibility prediction within the design process of blood carrying devices in the future, which is an enormous contribution to the effective and cost reduced development of medical products with blood contact. Above this, the insights of the subproject will contribute significantly to the development of an innovative heart assist device that represents a good alternative to current systems, both functionally and economically.

Methods

In various in-vitro blood experiments CVE will evaluate the hemocompatibility of different material samples. Initially, static experiments with platelet rich plasma, where we analyze the material samples optically by means of adsorbed thrombocytes, will enable us to choose a first preselection of materials. In a second step, the additional information and results obtained by quasi-static experiments with whole blood in a “bowry chamber” will result in the further reduction of the material matrix.

To investigate the influence of flow conditions occurring in VADs on their foreign surfaces, we will design a dynamic in-vitro test setup that is capable of simulating these flow conditions. Thus, we are able to investigate different ceramizations with regard to hemocompatibility under realistic conditions, similar to those in their later operating environment.

To investigate the aspect of mechanically and shear induced blood damage in VADs, we will examine both hemolysis and the destruction of the von Willebrand factor in in-vitro pump experiments. Therefore, an inexpensive and time efficient as well as reproducible analysis method that is applicable for in-vitro diagnostics of porcine blood based on the multimeric analysis method will be the result of this effort.

 
Funding: European Union and Land Nordrhein-Westfalen