In this paper a synthetic Poly(L‐lactic‐co‐ϵ‐caprolactone) [P(LLA‐CL)] (75:25) copolymer has been fabricated into a nanofibrous structure by electrospinning. The polymer crystal structure has been investigated by DSC and x‐ray diffraction method. During electrospinning at room temperature, a crystallization of LLA sequence in the P(LLA‐CL) copolymer could not form, while a relatively regular arrangement of CL sequence was observed. In order to obtain a tubular scaffold, a rotating mandrel was designed to collect the fiber, so that the tubular scaffold can be retrieved from the mandrel with an inner diameter same as that of the outer diameter of the mandrel. An auxiliary electrode with a sharp edge and a negative charge was set under the mandrel to guide the fiber deposition on the mandrel. When the sharp edge bar was vertical to the rotating axle of the mandrel and just beneath the spinning nozzle, nanofibers with circumferential alignment were obtained. With this method it is possible to obtain a tubular scaffold with suitable fiber alignment for blood vessel tissue engineering.
The number of candidates waiting for a heart valve replacement rises yearly. Even though there is a trend toward implantation of biological valves or reconstruction, the prosthetic heart valves (PHVs) are still commonly used for implantation or as a part of cardiac assist devices in many countries worldwide. However, the hemodynamic consequences of these valves are still not completely understood. Unfortunately, these devices currently do not perform sufficiently on a long-term basis and may lead to several complications, many of them are related to fluid mechanical aspects. A novel method, stereoscopic high-speed particle image velocimetry, was applied to quantify all three velocity components behind a PHV in detailed time domain. In this study, we compared clinically used bileaflet aortic prosthetic (ATS) valve and monoleaflet prototype of tilting disk PHV. The absolute velocities calculated out of two and three velocity components were compared to each other to estimate the overall difference in the desired region of interest. The most significant discrepancies between the two- and three-component absolute velocities were found at the regions of Valsalva sinuses and in a major jet stream of monoleaflet PHV.
The aim of this study was to validate the 2D computational fluid dynamics (CFD) results of a moving heart valve based on a fluid-structure interaction (FSI) algorithm with experimental measurements. Firstly, a pulsatile laminar flow through a monoleaflet valve model with a stiff leaflet was visualized by means of Particle Image Velocimetry (PIV). The inflow data sets were applied to a CFD simulation including blood-leaflet interaction. The measurement section with a fixed leaflet was enclosed into a standard mock loop in series with a Harvard Apparatus Pulsatile Blood Pump, a compliance chamber and a reservoir. Standard 2D PIV measurements were made at a frequency of 60 bpm. Average velocity magnitude results of 36 phase-locked measurements were evaluated at every 10° of the pump cycle. For the CFD flow simulation, a commercially available package from Fluent Inc. was used in combination with in-house developed FSI code based on the Arbitrary Lagrangian-Eulerian (ALE) method. Then the CFD code was applied to the leaflet to quantify the shear stress on it. Generally, the CFD results are in agreement with the PIV evaluated data in major flow regions, thereby validating the FSI simulation of a monoleaflet valve with a flexible leaflet. The applicability of the new CFD code for quantifying the shear stress on a flexible leaflet is thus demonstrated. (Int J Artif Organs 2007; 30: 640–8)
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