An Anatomically Shaped Mitral Valve for Hemodynamic Testing.

In vitro modeling of the left heart relies on accurately replicating the physiological conditions of the native heart. The targeted physiological conditions include the complex fluid dynamics coming along with the opening and closing of the aortic and mitral valves. As the mitral valve possess a highly sophisticated apparatus, thence, accurately modeling it remained a missing piece in the perfect heart duplicator puzzle. In this study, we explore using a hydrogel-based mitral valve that offers a full representation of the mitral valve apparatus. The valve is tested using a custom-made mock circulatory loop to replicate the left heart. The flow analysis includes performing particle image velocimetry measurements in both left atrium and ventricle. The results showed the ability of the new mitral valve to replicate the real interventricular and atrial flow patterns during the whole cardiac cycle. Moreover, the investigated valve has a ventricular vortex formation time of 5.2, while the peak e- and a-wave ventricular velocities was 0.9 m/s and 0.4 m/s respectively.

Impact of Mitral Regurgitation on the Flow in a Model of a Left Ventricle.

PURPOSE: Mitral regurgitation (MR) is the second most common valve disease in industrialized countries. Despite its high prevalence, little is known about its impact on the flow dynamics in the left ventricle (LV). Because of the interdependence between valvular function and hemodynamics in the heart chambers, an exploration of the dynamics in the LV could lead to a diagnosis of MR. This in vitro study aimed to develop an advanced left heart simulator capable of reproducing several conditions of MR and to evaluate their impact on the LV flow dynamics in terms of flow structures and viscous energy dissipation (VED). METHODS: A simulator, previously developed to test mechanical and biological valves, was upgraded with an original anatomically-shaped mitral valve made from a hydrogel. The valve can be used in healthy or pathological configurations. The nature and severity of the disease was controlled by applying specific strain to the chordae. In this study, in addition to a healthy condition, two different severities of MR were investigated: moderate MR and severe MR. Planar time-resolved particle image velocimetry measurements were performed in order to evaluate the velocity field in the LV and the VED induced by each condition. RESULTS: Our results showed that MR led to flow disturbances in the LV that were characterized by an increase in mitral inflow velocity and by elevated values of VED. Interestingly VED increased in proportion to the severity of MR and with a dissipation predominating during systole. CONCLUSION: Considering these results, the introduction of new parameters based on LV VED could provide crucial information regarding the coupling between the mitral valve and the LV and allow for a better stratification of patients with MR.

In Vitro Quantification of Mitral Regurgitation of Complex Geometry by the Modified Proximal Isovelocity Surface Area Method.

BACKGROUND: Doppler echocardiographic methods, such as the proximal isovelocity surface area (PISA) method, are used to quantify mitral regurgitations (MRs). However, their accuracy and reproducibility are still being discussed, especially in the case of MR of complex geometry. The aim of this study was to evaluate the accuracy of the PISA method depending on the shape and number of regurgitant flows. METHODS: First, various MR shapes and severities (central, oblong, and multiple-jet MR) were mimicked in a left heart simulator. The effective regurgitant orifice area (EROA) was calculated using the standard and modified PISA methods and was compared to a reference value obtained from an electromagnetic flowmeter. Second, in order to clinically validate the in vitro findings, 16 patients were examined with two-dimensional (2D) echocardiography. The results were analyzed by comparing the PISA method and the echocardiographic 2D quantitative volumetric method. RESULTS: Both hemicylindrical and hemiellipsoidal PISA assumptions improved the quantification of the EROA for oblong MR compared with the traditional PISA method (hemispherical PISA assumption: 11 ± 4.6 mm2, P < .01; hemicylindrical PISA assumption: 2 ± 0.8 mm2, P = .83; hemiellipsoidal PISA assumption: 6 ± 3.7 mm2, P = .05). In the case of multiple jets of different sizes, an improved EROA calculation was measured when both jets were considered (single hemispherical PISA assumption: 4.5 ± 0.7 mm2, P < .01; double hemispherical PISA assumption: 2 ± 1.1 mm2, P = .64). CONCLUSION: For a correct diagnosis of MR, the PISA geometry must be considered. A measurement of both PISA radius and PISA width is necessary for an accurate quantification of an oblong MR. In the case of a double-jet MR, a measurement of the two radii is recommended.

A comparative investigation of Bombyx mori silk fibroin hydrogels generated by chemical and enzymatic cross-linking.

Fibroin, the major proteinaceous component of the silk fiber produced by larvae of the domesticated silk moth (Bombyx mori), has been widely investigated as a biomaterial for potential applications in tissue engineering and regenerative medicine. Following sol-gel transition, silk fibroin solutions can generate hydrogels that present certain advantages when employed as biomaterials, especially if they are cross-linked. The subject of this study was the self-cross-linking of silk fibroin through a process induced by the enzyme horseradish peroxidase (HRP) in the presence of hydrogen peroxide, a method only recently proposed and scarcely reported. The hydrogels were prepared either by physical cross-linking, by cross-linking with a natural compound (genipin), or by enzymatic cross-linking. The products were comparatively characterized in regard to their synthesis and background chemical aspects, physical and optical properties, mechanical properties, secondary structure, swelling/deswelling behavior, enzymatic degradation, and compatibility as substrates for cell adhesion and proliferation. The study confirmed the advantages of the HRP-induced cross-linking, which included considerably shorter gelation times, enhanced elasticity of the resulting hydrogels, and improved cytocompatibility. Discrepancies between certain results of this investigation and those reported previously were discussed in detail.