Development of a Butterfly-type Artificial Atrioventricular Valve—Influence of Mechanical Design of Valve Cusps on Performance—

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  • バタフライ型人工房室弁の開発―弁膜の寸法，構造等の力学設計が性能におよぼす影響―
  • バタフライガタジン コウボウシツベン ノ カイハツ : ベンマク ノ スンポウ,コウゾウ トウ ノ リキガク セッケイ ガ セイノウ ニ オヨボス エイキョウ

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Abstract

<p>In our previous study, we developed heart valve-like tissue (Biovalve), which was fabricated by employing the technique of in-body tissue architecture (iBTA). We fabricated Biovalve so that it can closely mimic the functionalities of the native mitral valve, papillary muscles, and chordae tendineae. However, owing to its complex structure, Biovalve has not yet been implemented. Hence, the objective of this study is to develop a novel artificial atrioventricular valve by incorporating a sheet of autologous tissue (Biosheet) through iBTA. Since a period of approximately two months is required for obtaining Biosheet, it is unsuited for developing the aforementioned artificial valve. Hence, we fabricated an experimental model by employing a polyurethane sheet, which has comparable mechanical properties as Biosheet. To validate the experimental model, the valve functions of the actual model and experimental model were compared by using Biosheet and the polyurethane sheet, respectively. Furthermore, to determine the optimal shape of the valve cusps, the amount of sheet overhanging from the stent, sheet suture angle, and sheet thickness were varied as experimental parameters. A model of the valve cusps with mechanical anisotropy was fabricated by sandwiching Ni-Ti alloy wires between two polyurethane sheets and thermally welding them. Subsequently, an isotropic model and the fabricated anisotropic model were compared. The experiment was conducted by incorporating our fabricated in-vitro simulator under the physiological conditions of a healthy adult human. The valve function was evaluated on the basis of the ISO 5840-1 and ISO 5840-2 international standards for artificial valves. The obtained results indicate that the valve functions of the actual model and experimental model are nearly identical, which confirms the validity of the experimental model. Furthermore, in the case of the anisotropic model, it is found that when the sheet thickness is 200µm, sheet overhang is 3mm, and suture angle is 0 deg. , the pressure drop reduces by approximately 25%and the regurgitant fraction decreases by approximately 90%, as compared to the isotropic model of the same shape. These results suggest that anisotropic valve cusps can improve both valve opening and closing functionalities.</p>

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