Prospects for Additive Manufacturing and Hemolysis Testing in Blood Pump Development
Open access
Autor(in)
Datum
2021Typ
- Doctoral Thesis
ETH Bibliographie
yes
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Abstract
The treatment of heart failure with a ventricular assist device (VAD) is subject to various severe complications. Many of these complications originate in the VAD design, which in turn is a consequence of the VAD development process. Although additive manufacturing (AM), colloquially known as 3D printing, generally holds excellent potential for design and process improvements in engineering processes, the use of AM in VAD development is currently limited only to the very early prototyping stages and therefore, is not being used to its full poten- tial. With AM technologies becoming increasingly mature, the key challenge for using AM in VAD design and development is to identify value-adding applications and overcome application-specific manufac- turability and manufacturing quality challenges.
This thesis reports applications for AM in VAD development that enable design improvements through design integration as well as through the possibility of rapid design iterations. As a prerequisite for rapid design iterations, it furthermore reports anchor points for improving the hemolysis testing as the bottleneck testing procedure.
Firstly, the design integration potential of AM was investigated by embedding sensing functionality into a VAD. An inflow cannula of a commercial VAD was redesigned to integrate a sensing concept that enabled the measurement of total pressure and flow rate at an accu- racy (±0.6 mmHg, ±0.14 L/min) and resolution (100 Hz) required for continuous monitoring and future automatic adaption of the VAD to the patients’ need. The use of AM for the fabrication of measurement channels enabled a miniaturized integration into the thin cannula wall.
Secondly, the limits of design integration with AM were investi- gated by developing and testing a functional pump prototype that was additively manufactured in a single production step. To enable the simultaneous integration of rotor and bearing magnets, a print- able magnetic polymer compound was developed that could be used in combination with other polymers on a multi-material printer. The printed magnets had a remanence of 353 mT, which is about a third of sintered NdFeB magnets used in current VADs. Despite the in- sufficient manufacturing quality for medical use, the prototype could be operated at 1000 rpm and was able to deliver a low flow rate of 3 L/min, however, at a very low pressure head of 6 mmHg.
Thirdly, the potential of AM to enable rapid design iterations was investigated by replacing the original impeller of a commercial VAD with AM impellers and then comparing their hydraulic characteristics and the hemolysis induced. AM impellers were manufactured using four different AM processes. While hydraulic test results were only slightly influenced by the use of AM parts, a significant increase in hemolysis was observed depending on the surface roughness of the AM parts. Only impellers manufactured by stereolithography were comparable to the injection-molded original impeller regarding low surface roughness and hemolysis levels. The results indicate a thresh- old level of surface roughness that depends on the local level of wall shear stress and above which the surface contributes significantly to hemolysis.
In addition, the potential of accelerating the hemolysis testing pro- cedures was investigated, as they represent a bottleneck of a rapid and iterative development process that AM can enable. The follow- ing three critical factors of a standard hemolysis test protocol for VAD development were identified: difficulty of obtaining blood, the high ex- perimental workload, and the poor reproducibility of the results. To experimentally investigate the source of poor reproducibility, blood from 23 bovine donors was used for hemolysis testing in combina- tion with a comprehensive blood analysis. The results showed that differences in the susceptibility to hemolysis between blood samples from different donors were the primary cause of poor reproducibility. Another result was that the adjustment of hematocrit to a standard level, as required by the standard protocol, might introduce addi- tional between-donor variations. Additionally, potential approaches to reduce the complexity and workload of VAD hemolysis testing were reviewed, including the replacement of blood with standardized shear- sensitive fluids and the use of novel sensors for a simplified measure- ment of hemoglobin concentrations.
In conclusion, both design improvements through integration and process improvements through rapid design iterations can be achieved by AM of VAD components. However, the use of AM is restricted by low manufacturing quality, especially regarding surface roughness. To enable large-scale testing and iterative development with AM proto- types, bottlenecks in the in vitro validation of hemolysis have to be solved. Mehr anzeigen
Persistenter Link
https://doi.org/10.3929/ethz-b-000511064Publikationsstatus
publishedExterne Links
Printexemplar via ETH-Bibliothek suchen
Verlag
ETH ZurichOrganisationseinheit
03943 - Meboldt, Mirko / Meboldt, Mirko
ETH Bibliographie
yes
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