Electropolymerization processing of side-chain engineered EDOT for high performance microelectrode arrays

Microelectrode Arrays (MEAs) are popular tools for in vitro extracellular recording. They are often optimized by surface engineering to improve affinity with neurons and guarantee higher recording quality and stability. Recently, PEDOT:PSS has been used to coat microelectrodes due to its good biocompatibility and low impedance, which enhances neural coupling. Herein, we investigate on electro-co-polymerization of EDOT with its triglymated derivative to control valence between monomer units and hydrophilic functions on a conducting polymer. Molecular packing, cation complexation, dopant stoichiometry are governed by the glycolation degree of the electro-active coating of the microelectrodes. Optimal monomer ratio allows fine-tuning the material hydrophilicity and biocompatibility without compromising the electrochemical impedance of microelectrodes nor their stability while interfaced with a neural cell culture. After incubation, sensing readout on the modified electrodes shows higher performances with respect to unmodified electropolymerized PEDOT, with higher signal-to-noise ratio (SNR) and higher spike counts on the same neural culture. Reported SNR values are superior to that of state-of-the-art PEDOT microelectrodes and close to that of state-of-the-art 3D microelectrodes, with a reduced fabrication complexity. Thanks to this versatile technique and its impact on the surface chemistry of the microelectrode, we show that electro-co-polymerization trades with many-compound properties to easily gather them into single macromolecular structures. Applied on sensor arrays, it holds great potential for the customization of neurosensors to adapt to environmental boundaries and to optimize extracted sensing features.

Surface tension of model tissues during malignant transformation and epithelial–mesenchymal transition

Epithelial–mesenchymal transition is associated with migration, invasion, and metastasis. The translation at the tissue scale of these changes has not yet been enlightened while being essential in the understanding of tumor progression. Thus, biophysical tools dedicated to measurements on model tumor systems are needed to reveal the impact of epithelial–mesenchymal transition at the collective cell scale. Herein, using an original biophysical approach based on magnetic nanoparticle insertion inside cells, we formed and flattened multicellular aggregates to explore the consequences of the loss of the metastasis suppressor NME1 on the mechanical properties at the tissue scale. Multicellular spheroids behave as viscoelastic fluids, and their equilibrium shape is driven by surface tension as measured by their deformation upon magnetic field application. In a model of breast tumor cells genetically modified for NME1, we correlated tumor invasion, migration, and adhesion modifications with shape maintenance properties by measuring surface tension and exploring both invasive and migratory potential as well as adhesion characteristics.

DHA-phospholipids control membrane fusion and transcellular tunnel dynamics

Metabolic studies and animal knockout models point to the critical role of polyunsaturated docosahexaenoic acid (22:6, DHA)-containing phospholipids (PLs) in physiology. Here, we investigated the impact of DHA-PLs on the dynamics of transendothelial cell macroapertures (TEMs) triggered by RhoA inhibition-associated cell spreading. Lipidomic analyses show that human umbilical vein endothelial cells (HUVECs) subjected to DHA-diet undergo a 6-fold enrichment in DHA-PLs at plasma membrane (PM) at the expense of monounsaturated OA-PLs. Consequently, DHA-PLs enrichment at the PM induces a reduction of cell thickness and shifts cellular membranes towards a permissive mode of membrane fusion for transcellular tunnel initiation. We provide evidence that a global homeostatic control of membrane tension and cell cortex rigidity minimizes overall changes of TEM area through a decrease of TEM size and lifetime. Conversely, low DHA-PL levels at the PM leads to the opening of unstable and wider TEMs. Together, this provides evidence that variations of DHA-PLs levels in membranes affect cell biomechanical properties.

Stiffness tomography of eukaryotic intracellular compartments by atomic force microscopy

Precise localization and biophysical characterization of cellular structures is a key to the understanding of biological processes happening both inside the cell and at the cell surface. Atomic force microscopy is a powerful tool to study the cell surface - topography, elasticity, viscosity, interactions - and also the viscoelastic behavior of the underlying cytoplasm, cytoskeleton or the nucleus. Here, we demonstrate the ability of atomic force microscopy to also map and characterize organelles and microorganisms inside cells, at the nanoscale, by combining stiffness tomography with super-resolution fluorescence and electron microscopy. By using this correlative approach, we could both identify and characterize intracellular compartments. The validation of this approach was performed by monitoring the stiffening effect according to the metabolic status of the mitochondria in living cells in real-time.

Blocking bacterial entry at the adhesion step reveals dynamic recruitment of membrane and cytosolic probes

BACKGROUND

Bacterial invasion covers two steps: adhesion and entry per se. The cell signalling response is triggered upon pathogen interaction at the cell surface. This response continues when the pathogen is internalised. It is likely that these two steps activate different molecular machineries. So far, it has not been possible to easily follow in physiological conditions these events separately. We thus developed an approach to uncouple adhesion from entry using atomic force microscopy (AFM)-driven force and fluorescence measurements.

RESULTS

We report nanometric-scale, high-resolution, functional dynamic measurements of bacterial interaction with the host cell surface using photonic and adhesion force analyses. We describe how to achieve a precise monitoring of iterative cell-bacterium interactions to analyse host cell signalling responses to infection. By applying this method to Yersinia pseudotuberculosis, we first unveil glycosylphosphatidylinositol-anchored protein domains recruitment to the bacterium cell surface binding site and concomitant cytoskeleton rearrangements using super-resolution fluorescence microscopy. Second, we demonstrate the feasibility of monitoring post-translationally modified proteins, for example, via ubiquitylation, during the first step of infection.

CONCLUSION

We provide an approach to discriminate between cellular signalling response activated at the plasma membrane during host-pathogen interaction and that is triggered during the internalisation of the pathogen within the cell.

SIGNIFICANCE

This approach adds to the technological arsenal to better understand and fight against pathogens and beyond the scope of microbiology to address conceptual issues of cell surface signalling.

CLAFEM: Correlative light atomic force electron microscopy

Atomic force microscopy (AFM) is becoming increasingly used in the biology field. It can give highly accurate topography and biomechanical quantitative data, such as adhesion, elasticity, and viscosity, on living samples. Nowadays, correlative light electron microscopy is a must-have tool in the biology field that combines different microscopy techniques to spatially and temporally analyze the structure and function of a single sample. Here, we describe the combination of AFM with superresolution light microscopy and electron microscopy. We named this technique correlative light atomic force electron microscopy (CLAFEM) in which AFM can be used on fixed and living cells in association with superresolution light microscopy and further processed for transmission or scanning electron microscopy. We herein illustrate this approach to observe cellular bacterial infection and cytoskeleton. We show that CLAFEM brings complementary information at the cellular level, from on the one hand protein distribution and topography at the nanometer scale and on the other hand elasticity at the piconewton scales to fine ultrastructural details.

Adhesiveness of opportunistic Staphylococcus aureus to materials used in dental office: In vitro study

Staphylococcus aureus (S. aureus) is one of several opportunistic microbial pathogens associated with many healthcare problems. In the present study, S. aureus was assessed for its biofilm-forming ability on materials routinely used in dental offices, including stainless steel (SS), polyethylene (PE), and polyvinyl chloride (PVC). Materials that were tested were characterized for roughness (Ra) and surface free energy (SFE). The adhesion forces exerted by S. aureus to each substratum were investigated using atomic force microscopy (AFM), and biofilm formation was quantitatively assessed by crystal violet staining assay. AFM measurements demonstrated that the strongest adhesion forces (20 nN) were exerted on the PE surfaces (P < 0.05) and depended more on Ra. In addition, the results of biofilm formation capability indicated that S. aureus exhibited more affinity to SS materials when compared to the other materials (P < 0.05). This ability of biofilm formation seems to be more correlated to SFE (R = 0.65). Hence, control of the surface properties of materials used in dental practices is of crucial importance for preventing biofilm formation on dental materials to be used for patients' dental care.

High potential of adhesion to biotic and abiotic surfaces by opportunistic Staphylococcus aureus strains isolated from orthodontic appliances

Orthodontic and other oral appliances act as reservoir of opportunistic pathogens that can easily become resistant to antibiotics and cause systemic infections. The aim of this study was to investigate the ability of Staphylococcus aureus strains isolated from healthy patients with orthodontic appliances, to adhere to biotic (HeLa cells) and abiotic surfaces (polystyrene and dental alloy). Adhesive ability to polystyrene was tested by crystal violet staining and quantitative biofilm production on dental alloy surfaces was evaluated by MTT reduction assay. In addition, the presence of icaA and icaD genes was achieved by polymerase chain reaction (PCR). Qualitative biofilm production revealed that 70.6% of strains were slime producers. The metabolic activity of S. aureus biofilms on dental alloy surfaces was high and did not differ between tested strains. Moreover, all the isolates were adhesive to HeLa cells and 94% of them harbor icaA and icaD genes. Considerable adhesion and internalization capacity to the epithelial HeLa cells and strong biofilm production abilities together, with a high genotypic expression of icaA/icaD genes are an important equipment of S. aureus to colonize orthodontic appliances and eventually to disseminate towards other body areas.

Interplay between troponin T phosphorylation and O-N-acetylglucosaminylation in ischaemic heart failure

AIMS

Previous studies have reported that decreased serine 208 phosphorylation of troponin T (TnTpSer208) is associated with ischaemic heart failure (HF), but the molecular mechanisms and functional consequences of these changes are unknown. The aim of this study was to characterize the balance between serine phosphorylation and O-N-acetylglucosaminylation (O-GlcNAcylation) of TnT in HF, its mechanisms, and the consequences of modulating these post-translational modifications.

METHODS AND RESULTS

Decreased TnTpSer208 levels in the left ventricles of HF male Wistar rats were associated with reduced expression of PKCε but not of other cardiac PKC isoforms. In both isolated perfused rat hearts and cultured neonatal cardiomyocytes, the PKCε inhibitor εV1-2 decreased TnTpSer208 and simultaneously decreased cardiac contraction in isolated hearts and beating amplitude in neonatal cardiomyocytes (measured by atomic force microscopy). Down-regulating PKCε by silencing RNA (siRNA) also reduced TnTpSer208 in these cardiomyocytes, and PKCε-/- mice had lower TnTpSer208 levels than the wild-type. In parallel, HF increased TnT O-GlcNAcylation via both increased O-GlcNAc transferase and decreased O-GlcNAcase activity. Increasing O-GlcNAcylation (via O-GlcNAcase inhibition with Thiamet G) decreased TnTpSer208 in isolated hearts, while reducing O-GlcNAcylation (O-GlcNAc transferase siRNA) increased TnTpSer208 in neonatal cardiomyocytes. Mass spectrometry and NMR analysis identified O-GlcNAcylation of TnT on Ser190.

CONCLUSION

These data demonstrate interplay between Ser208 phosphorylation and Ser190 O-GlcNAcylation of TnT in ischaemic HF, linked to decreased activity of both PKCε and O-GlcNAcase and increased O-GlcNAc transferase activity. Modulation of these post-translational modifications of TnT may be a new therapeutic strategy in HF.

Quantifying bacterial adhesion on antifouling polymer brushes via single-cell force spectroscopy

The adhesion forces between a single bacterial cell and different polymer brushes were measured directly with an atomic force microscope and correlated with their resistance to fouling.

A role for septins in the interaction between the Listeria monocytogenes INVASION PROTEIN InlB and the Met receptor

Septins are conserved GTPases that form filaments and are required for cell division. During interphase, septin filaments associate with cellular membrane and cytoskeleton networks, yet the functional significance of these associations have, to our knowledge, remained unknown. We recently discovered that different septins, SEPT2 and SEPT11, regulate the InlB-mediated entry of Listeria monocytogenes into host cells. Here we address the role of SEPT2 and SEPT11 in the InlB-Met interactions underlying Listeria invasion to explore how septins modulate surface receptor function. We observed that differences in InlB-mediated Listeria entry correlated with differences in Met surface expression caused by septin depletion. Using atomic force microscopy on living cells, we show that septin depletion significantly reduced the unbinding force of InlB-Met interaction and the viscosity of membrane tethers at locations where the InlB-Met interaction occurs. Strikingly, the same order of difference was observed for cells in which the actin cytoskeleton was disrupted. Consistent with a proposed role of septins in association with the actin cytoskeleton, we show that cell elasticity is decreased upon septin or actin inactivation. Septins are therefore likely to participate in anchorage of the Met receptor to the actin cytoskeleton, and represent a critical determinant in surface receptor function.

Preparation of superhydrophobic silicon oxide nanowire surfaces

The paper reports on the preparation of superhydrophobic amorphous silicon oxide nanowires (a-SiONWs) on silicon substrates with a contact angle greater than 150 degrees by means of surface roughness and self-assembly. Nanowires with an average mean diameter in the range 20-150 nm and 15-20 microm in length were obtained by the so-called solid-liquid-solid (SLS) technique. The porous nature and the high roughness of the resulting surfaces were confirmed by AFM imaging. The superhydrophobicity resulted from the combined effects of surface roughness and chemical modification with fluorodecyl trichlorosilane.

Stability of the gold/silica thin film interface: electrochemical and surface plasmon resonance studies

This article reports chemical stability studies of a gold film electrode coated with thin silicon oxide (SiOx) layers using electrochemical, surface plasmon resonance (SPR) and atomic force microscopy (AFM) techniques. Silica films with different thicknesses (d = 6.4, 9.7, 14.5, and 18.5 nm) were deposited using a plasma-enhanced chemical vapor deposition technique (PECVD). For SiOx films with d >/= 18.5 nm, the electrochemical behavior is characteristic of a highly efficient barrier for a redox probe. SiOx films with thicknesses between 9.5 and 14.5 nm were found to be less efficient barriers for electron transfer. The Au/SiOx interface with 6.4 nm of SiOx, however, showed an enhanced steady-state current compared to that of the other films. The stability of this interface in solutions of different pH was investigated. Whereas a strongly basic solution led to a continuous dissolution of the SiOx interface, acidic treatment produced a more reticulated SiOx film and improved electrochemical behavior. The electrochemical results were corroborated by SPR measurements in real time and AFM studies.