Supported lipid bilayers (SLBs) are popular models of cell membranes with potential biotechnological applications, yet the mechanism of SLB formation is only partially understood. In this study, the adsorption and subsequent conformational changes of sonicated unilamellar vesicles on silica supports were investigated by quartz crystal microbalance with dissipation monitoring and atomic force microscopy, using mixtures of zwitterionic, negatively charged, and positively charged lipids, both in the presence and in the absence of Ca 2 + ions. Four different pathways of vesicle deposition could be distinguished. Depending on their charge, vesicles i), did not adsorb; ii), formed a stable vesicular layer; or iii), decomposed into an SLB after adsorption at high critical coverage or iv), at low coverage. Calcium was shown to enhance the tendency of SLB formation for negatively charged and zwitterionic vesicles. The role of vesicle-support, interbilayer, and intrabilayer interactions in the formation of SLBs is discussed.

Pathways of lipid vesicle deposition on solid surfaces: A combined QCM-D and AFM study

In the field of bottom-up synthetic biology, lipid vesicles provide an important role in the construction of artificial cells. Giant unilamellar vesicles (GUVs), due to their membrane's similarity to natural biomembranes, have been widely used as cellular mimics. So far, several methods exist for the production of GUVs with the possibility to encapsulate biological macromolecules. The inverted emulsion-based method is one such technique, which has great potential for rapid production of GUVs with high encapsulation efficiencies for large biomolecules. However, the lack of understanding of various parameters that affect production yields has resulted in sparse adaptation within the membrane and bottom-up synthetic biology research communities. Here, we optimize various parameters of the inverted emulsion-based method to maximize the production of GUVs. We demonstrate that the density difference between the emulsion droplets, oil phase, and the outer aqueous phase plays a crucial role in vesicle formation. We also investigated the impact that centrifugation speed/time, lipid concentration, pH, temperature, and emulsion droplet volume has on vesicle yield and size. Compared to conventional electroformation, our preparation method was not found to significantly alter the membrane mechanical properties. Finally, we optimize the parameters to minimize the time from workbench to microscope and in this way open up the possibility of time-sensitive experiments. In conclusion, our findings will promote the usage of the inverted emulsion method for basic membrane biophysics studies as well as the development of GUVs for use as future artificial cells.

https://pure.mpg.de/pubman/item/item_3165377_2/component/file_3171607/Article.pdf

Optimization of the Inverted Emulsion Method for High-Yield Production of Biomimetic Giant Unilamellar Vesicles.

In this chapter, we review the principal astrocyte functions and the interactions between neurons and astrocytes. We then address how the experimentally observed functions have been verified in computational models and review recent experimental literature on astrocyte–neuron interactions. Benefits of computational neuroscience work are highlighted through selected studies with neurons and astrocytes by analyzing the existing models qualitatively and assessing the relevance of these models to experimental data. Common strategies to mathematical modeling and computer simulation in neuroscience are summarized for the nontechnical reader. The astrocyte–neuron interactions are then further illustrated by examples of some neurological and neurodegenerative diseases, where the miscommunication between glia and neurons is found to be increasingly important.

Astrocyte-neuron interactions: from experimental research-based models to translational medicine.

The human brain is an energy hungry organ. How that brain manages its energy consumption in maintaining its health and executing sensori-motor and cognitive functions is an important but overlooked research area in contemporary cognitive neuroscience. It is argued here that the principal method whereby the human brain manages its energy utilization is through maintaining a relatively elevated level of activity in what can be referred to as “resting state networks” (RSN). The elevated energy consumption in the human brain's varied RSNs is driven and maintained by a physiological mechanism we call the Frame-Formation Energy Cycle (FFEC). Running the FFEC cycle is metabolically expensive and therefore offers a mechanism to explain the increased energy consumption in human-brain RSNs as compared to regions not involved in such networks.

/pdf/resting-state-neural-networks-and-energy-metabolism-217lhnxnxc.pdf

Resting state neural networks and energy metabolism

The health state of concrete is deteriorating during its service. Nonlinear ultrasonic detection based on the amplitude of the fundamental and the second harmonic is considered to be a powerful tool for the discovery of the microcrack in concrete. However, the research on processing the nonlinear ultrasonic signal is still insufficient. In order to highlight the real frequency domain components in the nonlinear ultrasonic signal, wavelet and ensemble empirical mode decomposition (EEMD) were joined to denoise the numerical and measured signal. The optimal wavelet base and the decomposition level were determined by the signal-to-noise ratios (SNRs). Then, the wavelet threshold denoising signal was decomposed by EEMD, omitting the high-frequency components and ultimately achieving the desired denoising effect. The denoising result of the test signals demonstrates that this method is effective in denoising the details of the ultrasonic signal and improving the reliability and adaptability of the nonlinear ultrasonic testing. In this experiment, the concrete with the microcrack was tested by linear and nonlinear ultrasonic methods. Based on the variation regularity of the nonlinear ultrasonic coefficient and velocity , we can conclude that the nonlinear ultrasonic parameter is more sensitive to the microcrack in concrete than the traditional wave velocity . The nonlinear ultrasonic testing can be an important supplement to the current nondestructive testing technique of the concrete.

/pdf/application-of-wavelet-and-eemd-joint-denoising-in-nonlinear-3ia733kn08.pdf

Application of Wavelet and EEMD Joint Denoising in Nonlinear Ultrasonic Testing of Concrete

A planar lipid bilayer on a solid support serves as model system that explains fundamental aspects of membrane biology and enables us to characterize wide-range surface-sensitive techniques, including molecular engineering. The present study aims at understanding the process of single and multiple bilayer formation after the exposure of small unilamellar vesicles (SUVs) of dioleoyl phosphatidylcholine (DOPC) to mica substrate. Isolated single bilayer formation and co-existence of double and triple lipid bilayers in the aqueous medium have been quantitatively measured by atomic force microscopy and discussed the physicochemical mechanism. It has been observed that due to the strong adhesion of DOPC SUV to mica surface, vesicles of diluted solution rupture spontaneously and form isolated bilayer patches when they come in contact with the mica surface. No further lateral growth or movement of the bilayer patches has been observed upon increase of incubation time. However, the increase of vesicle number on the same surface area by successive deposition of DOPC solution of same concentration and increasing incubation time shows merging of the nearby patches as well as development of stacked second and third bilayers due to edge-guided rupture of adsorbed vesicles on first or second bilayer patches. Mechanisms of single and multi-bilayer formation and a theoretical interpretation of the process have been elucidated.

Supported Planar Single and Multiple Bilayer Formation by DOPC Vesicle Rupture on Mica Substrate: A Mechanism as Revealed by Atomic Force Microscopy Study

The tight coupling of regional neurometabolic activity with synaptic activity and regional cerebral blood perfusion constitutes a single functional unit, described generally as a neurovascular unit. This is central to any discussion of haemodynamic response linked to any neuronal activation. In normal as well as in pathologic conditions, neurons, astrocytes and endothelial cells of the vasculature interact to generate the complex activity-induced cerebral haemodynamic responses, with astrocytes not only partaking in the signaling but actually controlling it in many cases. Neurons and astrocytes have highly integrated signaling mechanisms, yet they form two separate networks. Bidirectional neuron-astrocyte interactions are crucial for the function and survival of the central nervous system. The primary purpose of such regulation is the homeostasis of the brain’s microenvironment. In the maintenance of such homeostasis, astrocytic calcium response is a crucial variable in determining neurovascular control. Future work will be directed towards resolving the nature and extent of astrocytic calcium-mediated mechanisms for gene transcription, in modelling neurovascular control, and in determining calcium sensitive imaging assays that can capture disease variables.

Calcium signaling in cerebral vasoregulation.

Giant Unilamellar Vesicles (GUV) and supported planar membranes are excellent model biological systems for studying the structure and functions of membranes. We have prepared GUV from Large Unilamellar Vesicles (LUV) using electroformation and Supported planar Lipid Bilayer (SLB) by vesicle fusion method. LUV was prepared using an extrusion method and was characterized using Dynamic Light Scattering (DLS) and zeta potential measurements. The techniques for obtaining GUV as well as SLB from LUV have been demonstrated. We have directly observed the formation of GUV under phase contrast microscopy. This study will provide some insights into the physico-chemical properties of both nano and micron size vesicles. We believe that this method could be extremely useful for reconstituting various bio-molecules in GUV. We have presented one example where an antimicrobial peptide NK-2 was reconstituted in GUV prepared from LUV. SLB formation was monitored and characterized using Atomic Force Microscopy (AFM).

Preparation of Giant Unilamellar Vesicles and Solid Supported Bilayer from Large Unilamellar Vesicles: Model Biological Membranes

Linearity extraction is complex higher level cognitive process. It involves non-linear and transient operations which can be best captured with signal analysis methods that assume non-linearity and non-stationarity in the data. In the present paper, we evaluate Ensemble Empirical Mode Decomposition (EEMD) in ERP data recorded during linearity abstraction task. EEMD as a datadriven denoising process, has a high signal retention percentage when compared to FIR denoising. On low SNR datasets, it shows fairly high degree of noise suppression as given by Noise Suppression Index (NSI). Time-frequency analysis of the EEMD denoised ERP data shows fairly high degree of signal retention.

Linearity Abstractions in Scene Perception: Evaluating EEMD for Maximizing Task-related Information in Event Related Potentials

We present a novel perception-driven approach to low-cost tele-presence systems, to support immersive experience in continuity between projected video and conferencing room.We use geometry and spectral correction to impart for perceptual continuity to the whole scene. The geometric correction comes from a learning-based approach to identifying horizontal and vertical surfaces. Our method redraws the projected video to match its vanishing point with that of the conference room in which it is projected. We quantify intuitive concepts such as the depth-of-field using a Gabor filter analysis of overall images of the conference room. We equalise spectral features across the projected video and the conference room, for spectral continuity between the two.

/pdf/perception-based-design-for-tele-presence-18ij2dy649.pdf

Amrita Basu

Papers

Supported Planar Single and Multiple Bilayer Formation by DOPC Vesicle Rupture on Mica Substrate: A Mechanism as Revealed by Atomic Force Microscopy Study

Calcium signaling in cerebral vasoregulation.

Preparation of Giant Unilamellar Vesicles and Solid Supported Bilayer from Large Unilamellar Vesicles: Model Biological Membranes

Linearity Abstractions in Scene Perception: Evaluating EEMD for Maximizing Task-related Information in Event Related Potentials

perception-based design for tele-presence