Polymer brush collapse under shear flow

Shear responsive surfaces offer potential advances in a number of applications. Surface functionalisation using polymer brushes is one route to such properties, particularly in the case of entangled polymers. We report on neutron reflectometry measurements of polymer brushes in entangled polymer solutions performed under controlled shear, as well as coarse-grained computer simulations corresponding to these interfaces. Here we show a reversible and reproducible collapse of the brushes, increasing with the shear rate. Using two brushes of greatly different chain lengths and grafting densities, we demonstrate that the dynamics responsible for the structural change of the brush are governed by the free chains in solution rather than the brush itself, within the range of parameters examined. The phenomenon of the brush collapse could find applications in the tailoring of nanosensors, and as a way to dynamically control surface friction and adhesion

Tackling the Root Cause of Surface-Induced Coagulation: Inhibition of FXII Activation to Mitigate Coagulation Propagation and Prevent Clotting

Factor XII (FXII) is a zymogen present in blood that tends to adsorb onto the surfaces of blood-contacting medical devices. Once adsorbed, it becomes activated, initiating a cascade of enzymatic reactions that lead to surface-induced coagulation. This process is characterized by multiple redundancies, making it extremely challenging to prevent clot formation and preserve the properties of the surface. In this study, a novel modulatory coating system based on C1-esterase inhibitor (C1INH) functionalized polymer brushes, which effectively regulates the activation of FXII is proposed. Using surface plasmon resonance it is demonstrated that this coating system effectively repels blood plasma proteins, including FXII, while exhibiting high activity against activated FXII and plasma kallikrein under physiological conditions. This unique property enables the modulation of FXII activation without interfering with the overall hemostasis process. Furthermore, through dynamic Chandler loop studies, it is shown that this coating significantly improves the hemocompatibility of polymeric surfaces commonly used in medical devices. By addressing the root cause of contact activation, the synergistic interplay between the antifouling polymer brushes and the modulatory C1INH is expected to lay the foundation to enhance the hemocompatibility of medical device surfaces.© 2023 The Authors. Macromolecular Bioscience published by Wiley-VCH GmbH

Clock-dependent chromatin topology modulates circadian transcription and behavior.

The circadian clock in animals orchestrates widespread oscillatory gene expression programs, which underlie 24-h rhythms in behavior and physiology. Several studies have shown the possible roles of transcription factors and chromatin marks in controlling cyclic gene expression. However, how daily active enhancers modulate rhythmic gene transcription in mammalian tissues is not known. Using circular chromosome conformation capture (4C) combined with sequencing (4C-seq), we discovered oscillatory promoter-enhancer interactions along the 24-h cycle in the mouse liver and kidney. Rhythms in chromatin interactions were abolished in arrhythmic <i>Bmal1</i> knockout mice. Deleting a contacted intronic enhancer element in the <i>Cryptochrome 1</i> ( <i>Cry1</i> ) gene was sufficient to compromise the rhythmic chromatin contacts in tissues. Moreover, the deletion reduced the daily dynamics of <i>Cry1</i> transcriptional burst frequency and, remarkably, shortened the circadian period of locomotor activity rhythms. Our results establish oscillating and clock-controlled promoter-enhancer looping as a regulatory layer underlying circadian transcription and behavior

Seasonal and diurnal characteristics of water soluble inorganic compounds in the gas and aerosol phase in the Zurich area

Gas and aerosol samples were taken using a wet effluent diffusion denuder/aerosol collector (WEDD/AC) coupled to ion chromatography (IC) in the city of Zurich, Switzerland from August to September 2002 and in March 2003. Major water soluble inorganic ions; nitrate, sulfate, and nitrite were analyzed online with a time resolution of two hours for the gas and aerosol phase. The fraction of water soluble inorganic anions in PM10 varied from 15% in August to about 38% in March. Seasonal and diurnal variations of nitrate in the gas and aerosol phase were observed with more than 50% of the total nitrate in the gas phase during August and more than 80% of nitrate in the aerosol phase during March exceeding the concentration of sulfate by a factor of 2. Aerosol sulfate, on the other hand, did not show significant variability with season. However, in the gas phase, the SO₂ concentration was 6.5 times higher in winter than in summer. Nitrous acid (HONO) also showed a diurnal variation in both the gas and aerosol phase with the lowest concentration (0.2–0.6 µg/m³) in the afternoon. The primary pollutants, NO, CO and SO₂ mixing ratios were often at their highest between 04:00–10:00 local time due to the build up of fresh vehicle emission under a nocturnal inversion

Oriented immobilization of Pep19-2.5 on antifouling brushes suppresses the development of Staphylococcus aureus biofilms

Bacterial colonization of indwelling medical devices poses a danger to the patient and is a tremendous economic burden that costs billions of dollars to the healthcare system. Thus, it is essential to develop an effective mechanism that prevents the attachment of bacteria to the surface in combination with bactericidal strategies to kill them in direct contact. In this work, we combine the repellent/antifouling properties of polymer brushes with the antimicrobial activity of the synthetic peptide Pep19-2.5 and test its efficacy to inhibit Staphylococcus aureus biofilm formation. To tackle this, we utilized hierarchical polymer brushes, where the bottom block provides an effective barrier against adhesion while the top block provides functional groups for the immobilization of active molecules. Further, these polymer brushes were decorated with dibenzocyclooctine (DBCO)-functionalized Pep19-2.5 using strain-promoted alkyne-azide cycloaddition (SPAAC). This click chemistry proceeds very fast and does not require any catalyst, which is crucial for biomedical applications. The obtained coating was not only able to decrease the number of freely planktonic bacteria in the surrounding media (by 52.5%) but also inhibit the development of S. aureus biofilm by reducing the number of total, viable, and viable but non-culturable (VBNC) cells (up to 58%, 66%, and 70% respectively) and reduce the biovolume and thickness. Conversely, this coating does not exert any cytotoxic effect on Normal Human Dermal Fibroblasts (NHDF) cells. Thus, the combination of hierarchical polymer brushes with Pep19-2.5 is a promising approach to fight medical biofilms without affecting surrounding tissues

Cortical miR-709 links glutamatergic signaling to NREM sleep EEG slow waves in an activity-dependent manner.

MicroRNAs (miRNAs) are key post-transcriptional regulators of gene expression that have been implicated in a plethora of neuronal processes. Nevertheless, their role in regulating brain activity in the context of sleep has so far received little attention. To test their involvement, we deleted mature miRNAs in post-mitotic neurons at two developmental ages, i.e., in early adulthood using conditional Dicer knockout (cKO) mice and in adult mice using an inducible conditional Dicer cKO (icKO) line. In both models, electroencephalographic (EEG) activity was affected and the response to sleep deprivation (SD) altered; while the rapid-eye-movement sleep (REMS) rebound was compromised in both, the increase in EEG delta (1 to 4 Hz) power during non-REMS (NREMS) was smaller in cKO mice and larger in icKO mice compared to controls. We subsequently investigated the effects of SD on the forebrain miRNA transcriptome and found that the expression of 48 miRNAs was affected, and in particular that of the activity-dependent miR-709. In vivo inhibition of miR-709 in the brain increased EEG power during NREMS in the slow-delta (0.75 to 1.75 Hz) range, particularly after periods of prolonged wakefulness. Transcriptome analysis of primary cortical neurons in vitro revealed that miR-709 regulates genes involved in glutamatergic neurotransmission. A subset of these genes was also affected in the cortices of sleep-deprived, miR-709-inhibited mice. Our data implicate miRNAs in the regulation of EEG activity and indicate that miR-709 links neuronal activity during wakefulness to brain synchrony during sleep through the regulation of glutamatergic signaling

Assessment of recent advances in measurement techniques for atmospheric carbon dioxide and methane observations

This is the final version. Available from European Geosciences Union via the DOI in this record. Until recently, atmospheric carbon dioxide (CO2) and methane (CH4) measurements were made almost exclusively using nondispersive infrared (NDIR) absorption and gas chromatography with flame ionisation detection (GC/FID) techniques, respectively. Recently, commercially available instruments based on spectroscopic techniques such as cavity ring-down spectroscopy (CRDS), off-axis integrated cavity output spectroscopy (OA-ICOS) and Fourier transform infrared (FTIR) spectroscopy have become more widely available and affordable. This resulted in a widespread use of these techniques at many measurement stations. This paper is focused on the comparison between a CRDS "travelling instrument" that has been used during performance audits within the Global Atmosphere Watch (GAW) programme of the World Meteorological Organization (WMO) with instruments incorporating other, more traditional techniques for measuring CO2 and CH4 (NDIR and GC/FID). We demonstrate that CRDS instruments and likely other spectroscopic techniques are suitable for WMO/GAW stations and allow a smooth continuation of historic CO2 and CH4 time series. Moreover, the analysis of the audit results indicates that the spectroscopic techniques have a number of advantages over the traditional methods which will lead to the improved accuracy of atmospheric CO2 and CH4 measurements