Der Mikrokavitäten-Array: Folien-basierte 3D-Zellkultursysteme

Die Geschichte der Zellkultur stützt sich seit jeher auf Systeme, die eine Kultivierung auf planaren Oberflächen, und damit in nur zwei Dimensionen (2D) zuläßt. Zu diesen Systemen gehören Petrischalen, Kulturflaschen und deren Derivate, wie Multiwellplatten. Die über hundertjährige Erfolgsgeschichte der 2D-Systeme ist auf die einfache Handhabbarkeit, die niedrigen Kosten und die Möglichkeit, die Zellen enorm expandieren zu können, zurückzuführen. Sobald jedoch organotypische Leistungen der kultivierten Zellen im Vordergrund stehen, können Versuche in 2D-Systemen nicht oder nur eingeschränkt durchgeführt werden, da häufig insbesondere primäre Zellen ihre organotypischen Leistungen aufgrund dieser sehr gewebsuntypischen Kulturform innerhalb weniger Tage verlieren

Advanced 3D Cell Culture Techniques in Micro-Bioreactors, Part I: A Systematic Analysis of the Literature Published between 2000 and 2020

Bioreactors have proven useful for a vast amount of applications. Besides classical large-scale bioreactors and fermenters for prokaryotic and eukaryotic organisms, micro-bioreactors, as specialized bioreactor systems, have become an invaluable tool for mammalian 3D cell cultures. In this systematic review we analyze the literature in the field of eukaryotic 3D cell culture in micro-bioreactors within the last 20 years. For this, we define complexity levels with regard to the cellular 3D microenvironment concerning cell–matrix-contact, cell–cell-contact and the number of different cell types present at the same time. Moreover, we examine the data with regard to the micro-bioreactor design including mode of cell stimulation/nutrient supply and materials used for the micro-bioreactors, the corresponding 3D cell culture techniques and the related cellular microenvironment, the cell types and in vitro models used. As a data source we used the National Library of Medicine and analyzed the studies published from 2000 to 202

Tracking Cellular Functions by Exploiting the Paramagnetic Properties of X‐Nuclei

The term X‐nuclei summarises all nuclei (except protons) that occur in biological systems carrying a non‐zero nuclear spin. Significant involvement in physiological processes such as maintaining the transmembrane potential of living cells and energy metabolism make these nuclei highly interesting for nuclear magnetic resonance (NMR) experiments. In this chapter, a discussion of the basic physics of nuclei with a nuclear spin >1/2 is presented. On this basis, pulse sequences for the detection of multi quantum coherences (MQCs) are presented and explained. Information contained in the obtained MQC signal is linked to biophysical processes. Applications to study energy metabolism, oxygen consumption, and to track brain metabolites by means of X‐nuclei NMR are discussed as well as the use of functional phantoms, which can bridge the gap between basic biological research and NMR data interpretation

Advanced 3D cell culture techniques in micro-bioreactors, Part II: Systems and applications

In this second part of our systematic review on the research area of 3D cell culture in micro-bioreactors we give a detailed description of the published work with regard to the existing micro-bioreactor types and their applications, and highlight important results gathered with the respective systems. As an interesting detail, we found that micro-bioreactors have already been used in SARS-CoV research prior to the SARS-CoV2 pandemic. As our literature research revealed a variety of 3D cell culture configurations in the examined bioreactor systems, we defined in review part one “complexity levels” by means of the corresponding 3D cell culture techniques applied in the systems. The definition of the complexity is thereby based on the knowledge that the spatial distribution of cell-extracellular matrix interactions and the spatial distribution of homologous and heterologous cell–cell contacts play an important role in modulating cell functions. Because at least one of these parameters can be assigned to the 3D cell culture techniques discussed in the present review, we structured the studies according to the complexity levels applied in the MBR systems

Leveling the Playing Field: Is It Time for a Legal Assistance Center for Developing Nations in Investment Treaty Arbitration?

As part of an effort to encourage foreign direct investment, developing nations have signed over 1500 bilateral investment treaties (BITs) in just the last fifteen years. BITs grant foreign investors substantive rights, such as freedom from expropriation and the right to sue governments directly for a breach of the treaty in a process known as investment treaty arbitration. Over the last five years, the number of investment treaty arbitration claims filed against developing nations has more than tripled. The stakes are high: investor claims routinely seek damages in excess of $100,000,000 and challenge host state regulation of basic public services like water, energy, and waste disposal. Mounting an effective defense to these claims is essential for a developing nation, as even a single adverse award could wreak havoc on its economy, weaken its capacity to regulate in the public interest, and damage its reputation as a desirable investment location. However, due to financial and administrative barriers, many developing nations do not have the legal expertise within their government service to defend investment treaty claims. As a consequence, most are forced to hire one of a handful of international law firms who charge the same premium market rates that wealthy individual investors and corporations pay for their services. Meanwhile, developing nations who cannot hire outside counsel face scattered and incomplete sources of legal authority, uncertainty over the meaning of key BIT provisions, and no organized legal assistance from the international community. Unfortunately, these concerns are far from theoretical: in interviews done for this article, developing nation lawyers report not having access to fundamental sources of arbitration law, or having to go to extraordinary lengths to obtain it. Developing nations’ lack of access to affordable legal authority and expertise threatens the legitimacy of investment treaty arbitration by furthering the damaging perception that the arbitration process is unfairly tilted toward investors and wealthier States. The time is right for the establishment of a legal assistance center for developing nations facing actual or potential investment treaty arbitration claims. A legal assistance center would bolster the legitimacy of the investment treaty arbitration process by ensuring that developing nations have, at a minimum, access to fundamental legal authority and some basic level of legal expertise. A legal assistance center would not only promote fairness for developing nations, but also lead to a more efficient and effective arbitration process. Better informed developing nation counsel will make more cogent legal arguments, enhancing the quality and efficiency of the arbitration process as well as the ultimate result. By ensuring that developing nations have affordable access to legal authority and expertise, a legal assistance center will ensure that investment treaty arbitration more perfectly fulfills its vital mission of providing a truly neutral and just form of dispute settlement

O₂-sensitive microcavity arrays: A new platform for oxygen measurements in 3D cell cultures

Oxygen concentration plays a crucial role in (3D) cell culture. However, the oxygen content in vitro is usually not comparable to the in vivo situation, which is partly due to the fact that most experiments are performed under ambient atmosphere supplemented with 5% CO2, which can lead to hyperoxia. Cultivation under physiological conditions is necessary, but also fails to have suitable measurement methods, especially in 3D cell culture. Current oxygen measurement methods rely on global oxygen measurements (dish or well) and can only be performed in 2D cultures. In this paper, we describe a system that allows the determination of oxygen in 3D cell culture, especially in the microenvironment of single spheroids/organoids. For this purpose, microthermoforming was used to generate microcavity arrays from oxygensensitive polymer films. In these oxygen-sensitive microcavity arrays (sensor arrays), spheroids cannot only be generated but also cultivated further. In initial experiments we could show that the system is able to perform mitochondrial stress tests in spheroid cultures to characterize mitochondrial respiration in 3D. Thus, with the help of sensor arrays, it is possible to determine oxygen label-free and in real-time in the immediate microenvironment of spheroid cultures for the first time

Artificial Hematopoietic Stem Cell Niches-Dimensionality Matters

Hematopoietic stem cell niches are perhaps the best described niche system in mammals. The niches themselves, as well as their cellular and structural constituents and factors that play a role in maintaining the niche structure and function, are being refined on a more or less daily basis. Despite this, it seems as if the more we know the harder it gets to mimic the in vivo-situation using in vitro-systems. This is due to the fact that hematopoiesis is a multi step maturation process leading to HSC heterogeneity. Subpopulations of HSCs and niche supporting cells can be defined depending on characteristics such as their potency of leading to successful reconstitution of sub lethally irradiated mice in serial transplantation experiments or, with less scientific impact, clonogenic assays. Since the bone marrow obviously provides all necessary information to maintain the stem cell pool constant and to adapt the number of blood cells according to physiologic needs, it has been the goal to engineer artificial niches that display at least one or several of the major characteristics of the in vivo-situation to make use of these systems for not only fundamental research purposes but, moreover, also for clinical applications. This review will give an overview of approaches to engineering artificial hematopoietic niches with a focus on the complexity/dimensionality of the systems used

Light-induced magnetization reversal of high-anisotropy TbCo alloy films

Magnetization reversal using circularly polarized light provides a new way to control magnetization without any external magnetic field and has the potential to revolutionize magnetic data storage. However, in order to reach ultra-high density data storage, high anisotropy media providing thermal stability are needed. Here, we evidence all-optical magnetization switching for different TbxCo1-x ferrimagnetic alloy composition and demonstrate all-optical switching for films with anisotropy fields reaching 6 T corresponding to anisotropy constants of 3x106 ergs/cm3. Optical magnetization switching is observed only for alloys which compensation temperature can be reached through sample heating