hemocompatibility-testing-blood-contacting-implants-flow-loop-model

Hemocompatibility Testing of Blood-Contacting Implants in a Flow Loop Model Mimicking Human Blood Flow

The growing use of medical devices (e.g., vascular grafts, stents, and cardiac catheters) for temporary or permanent purposes that remain in the ...

ACANDIS GmbH

University of Stuttgart

In this work we evaluate the performance of a 40-mm diameter bore 0.2T desktop Halbach tomograph to obtain 2D and 3D velocity maps for studying intra-aneurismal flow in the presence or absence of nitinol meshed implants with the aim of optimizing the flow diverter efficacy. Phantoms with known spatial velocity distribution were used to determine the performance of the MRI system. Maximum velocities of about 200mm/s could be measured with a precision of 1% at a spatial resolution of 0.5×0.5×1mm(3). This accuracy is suitable to evaluate in vitro intra-aneurismal flow under different conditions such as variable flow rates, different vessel-aneurysm geometry, as well as the influence of metallic flow diverters on the intra-aneurismal flow distribution. The information obtained non-invasively with desktop tomographs can be used to complement in vivo studies in order to decide the optimum flow diverter. 

Desktop MRI as a promising tool for mapping intra-aneurismal flow.

Flow diverters are increasingly being used to treat intracranial aneurysms. This study evaluates occurring complications of flow-diverting devices in the treatment of experimental aneurysms, involving the use of micro-CT and small animal MRI at 9.4 T, in correlation to angiographic and histological findings.

Evaluation of occurring complications after flow diverter treatment of elastase-induced aneurysm in rabbits using micro-CT and MRI at 9.4 T.

Treatment of intracranial aneurysm with flow-diverting devices has become widespread in recent years. Despite that, intra-aneurysmal flow changes are yet not fully understood and can lead to different complications. Our aim was an in vitro contrast-based evaluation of the influence of flow diverter size and position on intra-aneurysmal flow dynamics.

In vitro, contrast agent-based evaluation of the influence of flow diverter size and position on intra-aneurysmal flow dynamics using syngo iFlow.

Particle image velocimetry (PIV) is a commonly used method for in vitro investigation of fluid dynamics in biomedical devices, such as flow diverters for intracranial aneurysm treatment. Since it is limited to transparent blood substituting fluids like water-glycerol mixture, the influence of coagulation and platelet aggregation is neglected. We aimed at the development and the application of a modified platelet rich plasma as a new PIV fluid with blood-like rheological and coagulation properties. In standardized intracranial aneurysm silicone models, the effect of this new PIV plasma on the fluid dynamics before and after flow diverter implantation was evaluated and compared with water-glycerol measurements. The flow diverting effect was strongly dependent on the used fluid, with considerably lower velocities achieved using PIV plasma, despite the same starting viscosity of both fluids. Moreover, triggering coagulation of PIV plasma allowed for intra-aneurysmal clot formation. We presented the first in vitro PIV investigation using a non-Newtonian, clottable PIV plasma, demonstrating a mismatch to a standard PIV fluid and allowing for thrombus formation.

A Novel Plasma-Based Fluid for Particle Image Velocimetry (PIV): In-Vitro Feasibility Study of Flow Diverter Effects in Aneurysm Model.

Braiding of Nitinol micro wires is an established technology for the manufacturing of fine-meshed neurovascular implants for tortuous vessel geometries. Electropolishing of wires before the braiding process has the potential to improve the in vitro behaviour in terms of thrombogenicity and endothelial cell proliferation. In this study, we present the first in vitro investigation of braided electropolished/blue oxide Nitinol samples in a blood flow loop, showing a significantly lower activation of the coagulation pathway (represented by the TAT III marker) and a tendency towards reduced platelet adhesion. Furthermore, we applied the same surface treatment on flat disks and measured protein adhesion as well as endothelial cell proliferation. We compared our results to non-electropolished samples with a native oxide surface. While platelet deposition was reduced on electropolished/blue oxide surface, a significant increase of endothelial cell seeding was observed. Investigation of inflammatory marker expression in endothelial cells provided divergent results depending on the marker tested, demanding closer investigation. Surface analysis using Auger electron spectroscopy revealed a thin layer mainly consisting of titanium oxynitride or titanium oxide + titanium nitride as a potential cause of the improved biological performance. Translated to the clinical field of intracranial aneurysm treatment, the improved biocompatibility has the potential to increase both safety (low thrombogenicity) and effectiveness (aneurysm neck reconstruction).

Article	Year
Desktop MRI as a promising tool for mapping intra-aneurismal flow. Magnetic resonance imaging\| PubMed ID: 25527392	2015
Evaluation of occurring complications after flow diverter treatment of elastase-induced aneurysm in rabbits using micro-CT and MRI at 9.4 T. Neuroradiology\| PubMed ID: 27457491	2016
In vitro, contrast agent-based evaluation of the influence of flow diverter size and position on intra-aneurysmal flow dynamics using syngo iFlow. Neuroradiology\| PubMed ID: 28842742	2017
A Novel Plasma-Based Fluid for Particle Image Velocimetry (PIV): In-Vitro Feasibility Study of Flow Diverter Effects in Aneurysm Model. Annals of biomedical engineering\| PubMed ID: 29488139	2018
In vitro investigation of chemical properties and biocompatibility of neurovascular braided implants. Journal of materials science. Materials in medicine\| PubMed ID: 31165278	2019

Giorgio Cattaneo

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