Dynamic in vitro hemocompatibility testing – improving the signal to noise ratio

Assigning the hemocompatibility of small vascular implants is one of the great challenges in biomedical engineering. Due to the fact, that there are no widely approved test setups1, we decided to developed a modified CHANDLER-Loop system for dynamic in vitro hemocompatibility tests. The setup allows simultaneous testing of about 30 tube rings with an inner diameter of 2,4 mm. Cardiovascular implants can be placed into these tube rings. After filling them with anticoagulated blood and closing them to loops, they were placed on a rotating disc. While the loop is rotating, the blood remains in the lower part of the loop. The relative movement between the foreign surface and the blood sample induces a blood flow without the need of mechanical pumping. A first test series with the new test setup had been conducted to achieve a highly hemocompatible tube material. The results were compared to hemocompatibility tests done by LEMM, mentioned in the ISO 10993-42,3. We could prove, that Tygon S50HL® and Polyurethane achieve similar hemocompatibility values. In addition, we did in vitro tests of bare metal stents. We recorded a difference in the index of thrombocytes of about 17 % between the loops with three stents and the control. During further experiments the difference decreases to 8 %, which might be due to adhesion processes. The ability to measure these processes demonstrates the high sensitivity and very low background activation of the test setup. This can be assured by the recorded index of hemolysis, which had been less than 0,8 % in all our experiments. By developing and improving our modified CHANDLER-Loop system, we were able to establish a dynamic in vitro test setup for the hemocompatibility testing of small vascular implants. Because of its extremely low background activation and a high variability, the system serves as a benchmark for upcoming test setups.SFB-TR37 – Q2SFB-TR37 – B

Dynamische In-Vitro-Studie zur Strömungsabhängigkeit der Degradationsrate von Magnesium

Zur Schaffung eines standardisierten Versuchsablaufs für Studien zur Magnesiumdegradation im Rahmen der Entwicklung eines biodegradablen Implantatwerkstoffs, wurde eine Steuerung für einen Prüfstand zur dynamischen in-vitro-Testung programmiert und deren Funktionsfähigkeit mit einer Testreihe bestätigt. Durch die Ergebnisse dieser Versuchsreihe konnte zudem die Strömungsabhängigkeit der Degradationsrate von Magnesium nachgewiesen werden

Antioxidantien als Strategie zur Optimierung der Kryokonservierung von Stammzellen für das Tissue Engineering

Kontrolliertes Einfrieren in den Temperaturbereich zwischen – 80 °C und – 196 °C erlaubt es Zellen, bei gleichzeitigem Erhalt ihrer Vitalität nach dem Auftauprozess, langfristig zu lagern. Durch die Verwendung von Antioxidantien sollte in der vorliegenden Arbeit eine Steigerung der Rekultivierbarkeit von mesenchymalen Stammzellen nach der Kryokonservierung erzielt werden. Der Zusatz von 100 μM α–Tocopherol steigerte die Rekultivierungseffzienz der Stammzellen um 117,5 % gegenüber der Kontrolle ohne Antioxidans. Darüber hinaus konnte gezeigt werden, dass eine Reduzierung der DMSO-Konzentration möglich ist, da Versuche mit 200 μM α–Tocopherol und 2,5 % bzw. 5 % DMSO vergleichbare Resultate von ca. 164 % bzw. 170 % Rekultivierbarkeit erzielten.EXC/62/

Correlation development for jet impingement heat transfer and force on a moving curved surface

The effect of jet Reynolds number, jet exit angle, the nozzle to surface distance, jet to jet spacing on the heat transfer, and pressure force performance from multiple impinging round jets on a moving curved surface have been numerically evaluated. Two correlations are developed and validated for the average Nu number and the pressure force coefficient and the agreement between the CFD and correlations was reasonable. The surface motion effect becomes more pronounced on the Nu number distribution for low jet Re number, high jet to jet spacing, large jet to surface distance, and angled jets. The pressure force coefficient is highly dependent on the jet to surface distance and jet angle but relatively insensitive to jet Re number and jet to jet spacing. © 2022, International Scientific Information, Inc.. All rights reserved

Entwicklung von schichtweise ausgerichteten Faserverbundstrukturen

Jedes Jahr müssen tausende defekte Herzklappen ersetzt werden. Die Verwendung von biologischen oder mechanischen Prothesen macht aufgrund der Tatsache, dass diese nicht mitwachsen, gerade bei Heranwachsenden regelmäßige Reimplantationen erforderlich. Eine mögliche Alternative sind Klappenprothesen bestehend aus einer Gerüststruktur, welche mit körpereigenen Zellen besiedelt wird. Das Gerüst wird im Laufe der Zeit vollständig durch lebendes Gewebe ersetzt. Ziel dieser Diplomarbeit ist die Herstellung von schichtweise ausgerichteten Faserverbundstrukturen, um zukünftig den aus mehreren Gewebeschichten bestehenden Aufbau der menschlichen Herzklappen nachahmen zu können und den Zellen so eine optimale Trägerstruktur bereit zu stellen

Numerical study of jet impingement force and heat transfer on a moving curved suface

The effect of surface curvature, number of jets, number of jet rows, jet arrangement, crossflow, and surface motion on the heat transfer and pressure force performance from multiple impinging round jets on the moving flat and curved surface have been numerically evaluated. The more number of jets (more than three jets) has no significant effect on the average heat transfer rate. The more number of jet rows increases the strength of wall jets interference and crossflow effects and degrade the average heat transfer rates. There is a minor difference between inline and staggered arrangements on both moving flat and curved surfaces. The surface motion has a stronger effect on the impinging jets in the intermediate crossflow scheme than in the minimum crossflow scheme. The total average Nu on both moving flat and curved surfaces reduces with an increase in the velocity ratio and surface curvature. The pressure force is relatively insensitive to the surface motion on both moving flat and curved surfaces. © 2022, International Scientific Information, Inc.. All rights reserved

Effect of cryopreservation on the integrity of coaxial alginate capsules

Encapsulation of clinically relevant cells, such as multipotent stromal cells (MSCs), in three-dimensional (3D) core-shell alginate structures is a promising method for the treatment of various diseases as well as drug testing and development. By utilizing the alginate capsules, drugs and active substances can be delivered specifically to the desired place within the patients’ body. The aim of this work was to investigate the effect of cryopreservation on the integrity of cell-free coaxial alginate capsules after thawing using slow freezing to ensure their long-term storage. Alginate capsules were produced by electro-spraying and cryopreserved using different cryoprotective agents (CPAs), incubation time and thawing temperature. The results suggest that the capsules loaded with 10% (v/v) dimethyl sulfoxide (DMSO) and 0.3 M sucrose and using high thawing rates demonstrated a beneficial effect on the integrity of capsules, as compared to 10% (v/v) DMSO alone and applying low thawing rates. This study is a further development towards the application of cryopreservation for long-term storage and the emerging cell-based medicine

Assuring Quality of Scaffolds in Musculoskeletal Tissue Engineering Mueller Matrix Polarimetry and Transillumination Imaging

In order to achieve the high quality required in medical products, reliable characterization methods and quality management systems are necessary. In the field of musculoskeletal Tissue Engineering (mTE), electrospinning is utilized to manufacture fibre scaffolds as implant material. Depending on the application, in this case the regeneration of tendon-bone junctions, properties like the degree of fibre orientation, homogeneity of fibre throughout the scaffold and reaction to external mechanical load are of particular importance. Currently, destructive methods, like scanning electron microscopy (SEM), are widely used to determine these properties. In addition to the destruction of the samples, these methods often only allow the investigation of very small sections. In this study, we present two new methods for the fast, non-destructive and contactless characterization of electrospun fibre scaffolds for mTE. These methods are based on Transillumination Imaging (TI) and Mueller Matrix Polarimetry (MMP), utilizing low-power laser sources or LED light sources, respectively, to determine the relative homogeneity (TI) and the degree of fibre orientation (MMP) in electrospun fibre scaffolds

Optimization of a test setup for examining blood damage caused by high shear forces

If blood pumps are applied in the human body or extracorporeal, blood damage can be caused by shear forces that act on the blood during the delivery. For an accelerated development of blood pumps with help of simulations there is a need for reliable limit values for shear forces. To determine these limit values a shear force test setup was built at the Institute for Multiphase Processes. In the context of the presented master thesis the former test setup peripheral devices were evaluated, possible blood damage mechanisms were considered, blood analysis in different experiments to identify the blood damage caused by different elements were made and peripheral devices were replaced. At the same time the shear chamber was constructional reengineered in a project thesis [1]. We were able to show, that in former works the blood damage caused by test setup peripheral devices had heterodyned the results. Finally the test setup was rebuilt with the results and a test was made. Two findings of the thesis are a reduction of about 60% of the number of components in the blood-conveying tube system and an application of a new fluid seal.SFB-TR37 - Q2SFB-TR37 - B4EXC 62/

Automation of a test bench for accessing the bendability of electrospun vascular grafts

One of the greatest challenges in cardiovascular tissue engineering is to develop vascular grafts with properties similar to autologous vessels. A promising approach is the fabrication of scaffolds from biodegradable polymers by electrospinning. Unstructured vascular subs possess a weak dimensional stability resulting in lumen collapse when subjected to bending stress. In order to examine different structured grafts, a standardised test method is required. A manual test method, designed in a former study, was adopted in terms of standardisation and automation. Therefore, a control system was programmed to regulate the required electronics. The electronic circuit was then developed and put into service. To fix samples into the test bench a new sample holder and a new collector for electrospinning were designed. Subsequently, a validation showed the new systems' improved functionality compared to the former test bench. The samples were manufactured with the new collector. They could be fixed to the sample holder with high repeatability. The demand for vascular grafts with biological and mechanical properties similar to autologous vessels requires a standardised test method to examine bendability. The new test system enables the scaffolds to be examined regarding bendability with low personal expense and a simultaneously high degree of reproducibility. In addition, the new collector geometry can be easily adapted to higher or lower inner diameters. Hence, a new sample geometry was developed within this work