Enzyme-induced mineralization of hydrogels with amorphous calcium carbonate for fast synthesis of ultrastiff, strong and tough organic–inorganic double networks

Hydrogels with good mechanical properties have great importance in biological and medical applications. Double-network (DN) hydrogels were found to be very tough materials. If one of the two network phases is an inorganic material, the DN hydrogels also become very stiff without losing their toughness. So far, the only example of such an organic–inorganic DN hydrogel is based on calcium phosphate, which takes about a week to be formed as an amorphous inorganic phase by enzyme-induced mineralization. An alternative organic–inorganic DN hydrogel, based on amorphous CaCO3, which can be formed as inorganic phase within hours, was designed in this study. The precipitation of CaCO3 within a hydrogel was induced by urease and a urea/CaCl2 calcification medium. The amorphous character of the CaCO3 was retained by using the previously reported crystallization inhibiting effects of N-(phosphonomethyl)glycine (PMGly). The connection between organic and inorganic phases via reversible bonds was realized by the introduction of ionic groups. The best results were obtained by copolymerization of acrylamide (AAm) and sodium acrylate (SA), which led to water-swollen organic–inorganic DN hydrogels with a high Young’s modulus (455 ± 80 MPa), remarkable tensile strength (3.4 ± 0.7 MPa) and fracture toughness (1.1 ± 0.2 kJ m−2)

The effects of phrasing on the answer likelihood in multiple choice based examinations : a case study in microbiology

Multiple choice (MC)-Klausuren sind im deutschen Medizinstudium trotz weitgehend fehlender Daten zur Validität dieser Prüfungsform zur Regelprüfung geworden. Darüber hinaus ist unklar, in welchem Ausmaß die Studierenden - auch solche mit guten Prüfungsergebnissen - den geprüften Lernstoff tatsächlich beherrschen. Am Fachbereich Medizin der Johann-Wolfgang-Goethe-Universität Frankfurt wurde am Ende des SS 2003 im Fach Mikrobiologie für die Studierenden des 2. klinischen Semesters eine MC-basierte Abschlussprüfung geschrieben. Die Studierenden des 1. klinischen Semesters hatten - bedingt durch Umstellungen des Curriculums - eine identische Ausbildung. Diese wurde durch eine inhaltlich weitgehend identische, im Format aber andere Klausur abgeschlossen, in der sowohl offene Fragen enthalten waren als auch Fragen, bei denen die Studierenden jede Aussage einzeln auf Korrektheit bewerten mussten. Der Vergleich der Ergebnisse für inhaltlich gleiche Fragen zeigt, dass die Studierenden im MC-Format eine hohe Quote richtiger Antworten erzielen, diese jedoch durch ein geändertes Fragenformat stark reduziert wird. So erreichten nur 20 - 30% der Studierenden ein vollständig richtiges Ergebnis, wenn jede Aussage einzeln bewertet werden musste, während die inhaltlich gleiche Frage im MC-Format 80 - 90% richtige Ergebnisse erzielte. In freien Fragen konnten nur 30 - 40% der Studierenden die richtige Antwort aktiv niederschreiben, während 90 -99% der Studierenden die richtige Lösung passiv erkannten. Wir interpretieren diese Ergebnisse dahin, dass der Entscheidungszwang in MC-basierten Fragen einen starken Einfluss auf die Quote richtiger Antworten hat, und die Prüfungsergebnisse damit wesentlich durch das Format beeinflusst werden, das Wissen dagegen nicht beherrscht wird. Die Ergebnisse dieser Studie legen nahe, Sorgfalt bei der Auswahl des Prüfungsverfahrens walten zu lassen und der Steuerung des studentischen Lernverhaltens durch das Prüfungsformat wesentlich mehr Aufmerksamkeit zu widmen als bisher.Multiple choice(MC) questions have become the mainstay medical examinations in Germany, although there are currently few data available to show their validity. It also remains unclear, whether or not students master the knowledge tested, even those students with good test results. Students of the second clinical semester at the Medical Faculty of the Johann Wolfgang Goethe-University in Frankfurt have written an MC-based examination in microbiology. Due to changes in their curriculum students of the first clinical semester took the identical class in microbiology. This class was concluded by an examination identical in content, however in a different format including open questions as well as questions consisting of statements that had to be judged individually whether or not they are true. A comparison of test results between these two groups showed that only 20 - 30% of the students were able to correctly assess five statements, whereas the identical question presented in MC-format yielded 80 - 90% correct answers. For open questions only 30 - 40% of the students were able to actively answer the question correctly whereas 90 - 99% of the students passively recognized the correct answer. These results indicate that the need to choose one among five options as it is inherent for MC-based questions has a strong influence on the ratio of correct answers, and examination results are strongly depended upon the format of the test, while the knowledge presumed to be tested is not necessarily available. Our results suggest that care should be taken when selecting the mode of an examination. Moreover, the faculty should be more aware of the impact of the test format on the students learning behaviour

Enzyme‐induced ferrification of hydrogels for toughening of functional inorganic compounds

Enzyme-induced mineralization (EIM) has been shown to greatly enhance the mechanical properties of hydrogels by precipitation of calcium salts. Another feature of such hydrogels is their high toughness even when containing finely nanostructured mineral content of ≈75 wt%. This might be useful for bendable materials with high content of functional inorganic nanostructures. The present study demonstrates that EIM can form homogeneous nanostructures of water-insoluble iron salts within hydrogels. Crystalline iron(II) carbonate precipitates urease-induced within polyacrylate-based hydrogels and forms platelet structures that have the potential of forming self-organized nacre-like architectures. The platelet structure can be influenced by chemical composition of the hydrogel. Further, amorphous iron(II) phosphate precipitates within hydrogels with alkaline phosphatase, forming a nanostructured porous inorganic phase, homogeneously distributed within the double network hydrogel. The high amount of iron phosphate (more than 80 wt%) affords a stiffness of ≈100 MPa. The composite is still bendable with considerable toughness of 400 J m−2 and strength of 1 MPa. The high water content (>50%) may allow fast diffusion processes within the material. This makes the iron phosphate-based composite an interesting candidate for flexible electrodes and demonstrates that EIM can be used to deliberately soften ceramic materials, rendering them bendable

In vivo imaging of lymphocytes in the CNS reveals different behaviour of naïve T cells in health and autoimmunity

<p>Abstract</p> <p>Background</p> <p>Two-photon laser scanning microscopy (TPLSM) has become a powerful tool in the visualization of immune cell dynamics and cellular communication within the complex biological networks of the inflamed central nervous system (CNS). Whereas many previous studies mainly focused on the role of effector or effector memory T cells, the role of naïve T cells as possible key players in immune regulation directly in the CNS is still highly debated.</p> <p>Methods</p> <p>We applied <it>ex vivo </it>and intravital TPLSM to investigate migratory pathways of naïve T cells in the inflamed and non-inflamed CNS. MACS-sorted naïve CD4+ T cells were either applied on healthy CNS slices or intravenously injected into RAG1 -/- mice, which were affected by experimental autoimmune encephalomyelitis (EAE). We further checked for the generation of second harmonic generation (SHG) signals produced by extracellular matrix (ECM) structures.</p> <p>Results</p> <p>By applying TPLSM on living brain slices we could show that the migratory capacity of activated CD4+ T cells is not strongly influenced by antigen specificity and is independent of regulatory or effector T cell phenotype. Naïve T cells, however, cannot find sufficient migratory signals in healthy, non-inflamed CNS parenchyma since they only showed stationary behaviour in this context. This is in contrast to the high motility of naïve CD4+ T cells in lymphoid organs. We observed a highly motile migration pattern for naïve T cells as compared to effector CD4+ T cells in inflamed brain tissue of living EAE-affected mice. Interestingly, in the inflamed CNS we could detect reticular structures by their SHG signal which partially co-localises with naïve CD4+ T cell tracks.</p> <p>Conclusions</p> <p>The activation status rather than antigen specificity or regulatory phenotype is the central requirement for CD4+ T cell migration within healthy CNS tissue. However, under inflammatory conditions naïve CD4+ T cells can get access to CNS parenchyma and partially migrate along inflammation-induced extracellular SHG structures, which are similar to those seen in lymphoid organs. These SHG structures apparently provide essential migratory signals for naïve CD4+ T cells within the diseased CNS.</p

AJAM-A–tetraspanin–αvβ5 integrin complex regulates contact inhibition of locomotion

Contact inhibition of locomotion (CIL) is a process that regulates cell motility upon collision with other cells. Improper regulation of CIL has been implicated in cancer cell dissemination. Here, we identify the cell adhesion molecule JAM-A as a central regulator of CIL in tumor cells. JAM-A is part of a multimolecular signaling complex in which tetraspanins CD9 and CD81 link JAM-A to αvβ5 integrin. JAM-A binds Csk and inhibits the activity of αvβ5 integrin-associated Src. Loss of JAM-A results in increased activities of downstream effectors of Src, including Erk1/2, Abi1, and paxillin, as well as increased activity of Rac1 at cell–cell contact sites. As a consequence, JAM-A-depleted cells show increased motility, have a higher cell–matrix turnover, and fail to halt migration when colliding with other cells. We also find that proper regulation of CIL depends on αvβ5 integrin engagement. Our findings identify a molecular mechanism that regulates CIL in tumor cells and have implications on tumor cell dissemination.publishedVersio

The frontotemporal dementia mutation R406W blocks tau’s interaction with the membrane in an annexin A2–dependent manner

The R406W mutation prevents tau from functioning as a linker between the membrane and the microtubule cytoskeleton

High Power Electric Propulsion: MARS plus EUROPA – Already Beyond 2025!

It’s mid-term realization plus global strategic investments: the results of the European Russian DEMOCRITOS project (Horizon 2020) related to the MW class INPPS (International Nuclear Power and Propulsion System) flagship will be described. INPPS flagship includes high power electric thrusters cluster, supplied electric power by the nuclear reactor (successfully tested in Russia) and a solar power ring. Two INPPS versions were studied – the wide and arrow wing versions. Both versions have a futuristic design with standardized interfaces for several flagship subsystems. Especially the high payload mass of INPPS allows the transport of – for example – up to 12 t to JUPITER moon EUROPA and about 18 t to MARS – as a function of specific impulse of electric thrusters. INPPS flagship not only allows scientific, but especially commercial and communication payloads as well. This means industrial-scale production of space flight systems for robotic and human space exploration. International cooperation related to INPPS realization are necessary within an International High Power Space Transportation program to realize the DEMOCRITOS core, ground and space components until 2025. DEMOCRITOS project included partners from Europe, Russia and a Brazilian guest observer and received several inputs from NASA Cleveland and JAXA Tokyo

Functional Dissection of the Proton Pumping Modules of Mitochondrial Complex I

A catalytically active subcomplex of respiratory chain complex I lacks 14 of its 42 subunits yet retains half of its proton-pumping capacity, indicating that its membrane arm has two pump modules