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Papers by Hans-Joachim Weber

International Journal of Artificial Organs, Jul 1, 2007

The aim of this study was to validate the 2D computational fluid dynamics (CFD) results of a movi... more 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 inhouse 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.

Interactive CardioVascular and Thoracic Surgery, 2018

OBJECTIVES: The first aim was the development of a human blood miniature mock-loop system consist... more OBJECTIVES: The first aim was the development of a human blood miniature mock-loop system consisting of 2 identical extracorporeal circuits, which enable systematic head-to-head comparisons of test substances. In a second step, we evaluated the suitability of the mockloop system, by comparing 2 different brands of heparin (ROTEXMEDICA vs B.BRAUN), which have showed different anticoagulation capacities in the clinic. METHODS: For 1 experiment (18 in total), blood of the same healthy human donor was divided into 2 portions (2 Â 50 ml), heparinized with 37.5 IUÁml-1 of the competing test substances and diluted to a haematocrit value of 20-25%. Each mock loop was filled with 70 ml, and in vivo heparin degradation was simulated in 3 different groups by protamine application, representing 0%, 50% and 100% heparin antagonization. At baseline, 5, 60, 120, 240 and 360 min, blood samples were taken to perform thromboelastometry, flow cytometry, haemolysis and general haemostasis analysis.

Critical Care Nephrology, 1998

Intensive care monitoring and therapy is nowadays usually associated with measurement, control an... more Intensive care monitoring and therapy is nowadays usually associated with measurement, control and monitoring techniques using complex medical equipment. Fundamental knowledge of the measurement units, measurement techniques and their physiological relationships forms the basis for a correct interpretation of the biological signal. Therefore, the basics of the physics of pressure in fluids and gases are pointed out, and examples of application are given.

Journal of Dermatological Science, 2009

After skin tissue injury, multipotent progenitor cells like mesenchymal stem cells (MSCs) are mob... more After skin tissue injury, multipotent progenitor cells like mesenchymal stem cells (MSCs) are mobilized from bone marrow into the pool of circulating cells. These cells then home to the sites of injury, where they differentiate into keratinocytes (KERs) and regulate the proliferation and migration of cutaneous cells to reconstitute epidermis and facilitate wound healing during the early inflammatory phase [1-3]. Previous works suggest that there are several mechanisms in which BM-MSCs could participate in cutaneous wound healing of the epidermis. They could either differentiate into phenotypes of various damaged cells [4] and/or enhance repair by creating a microenvironment that promotes the local regeneration of cells endogenous to the tissue [5]. In recent studies, it was found that after homing to the injury sites, BM-MSCs are incorporated in the epidermis especially in the region of hair follicle suggesting they may be involved in skin repair and regeneration [6], and it was demonstrated that BM-MSCs are able to trans-differentiate into epithelia lineage cells [7,8]. Another important fact is that in response to injury, BM-MSCs are stimulated to increase the

Artificial Organs, 2007

The number of candidates waiting for a heart valve replacement rises yearly. Even though there is... more 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 highspeed 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.