A new multi-scale simulation model of the circulation: from cells to system

We developed a comprehensive cell model that simulates the sequential cellular events from membrane excitation to contraction in the human ventricle. By combining this ventricular cell model with a lumped circulation model, we examined how blood pressure dynamics in the ventricle and aorta are related to the cellular processes. To convert cell contraction into ventricular pressure using Laplace's law, we introduced a simple geometric model of a ventricle: one shaped like a thin-walled hemisphere. The force of contraction of a single cell induces tension in the hemispheric ventricular wall, which generates the ventricular and aortic pressures in the lumped circulation model. The time courses of the hemodynamic properties, as well as the volume-pressure trajectory of the left ventricle, were well reproduced. Our multi-scale cardiovascular model, which covers from cardiac cells to the circulatory system, simulates the typical characteristics of heart mechanics, such as the pressure-volume relationship, stroke volume and the effect of the increased maximum free calcium concentration on cardiovascular hemodynamics. To test the cell-circulation coupling characteristics of the model, we simulated the effects of a decrease in L-type calcium channel conductance (cell level) on left ventricular pressure (system level). The variation due to different pacing frequencies for myocyte excitation was also investigated to assess the effects of heart rate on cardiac cells and the circulatory system.     

Cell and molecular mechanics of biological materials

Living cells can sense mechanical forces and convert them into biological responses. Similarly, biological and biochemical signals are known to influence the abilities of cells to sense, generate and bear mechanical forces. Studies into the mechanics of single cells, subcellular components and biological molecules have rapidly evolved during the past decade with significant implications for biotechnology and human health. This progress has been facilitated by new capabilities for measuring forces and displacements with piconewton and nanometre resolutions, respectively, and by improvements in bio-imaging. Details of mechanical, chemical and biological interactions in cells remain elusive. However, the mechanical deformation of proteins and nucleic acids may provide key insights for understanding the changes in cellular structure, response and function under force, and offer new opportunities for the diagnosis and treatment of disease. This review discusses some basic features of the deformation of single cells and biomolecules, and examines opportunities for further research.     

Imaging of freeze-fractured cells with in situ fluorescence and time-of-flight secondary ion mass spectrometry

Bioanalytical imaging techniques have been employed to investigate cellular composition at the single-cell and subcellular regimes. Four imaging modes have been performed sequentially in situ to demonstrate the utility of a more integrated approach to imaging cells. The combination of bright-field, scanning ion, and fluorescence microscopy complements TOF-SIMS imaging of native biomolecules. Bright-field microscopy provides a blurred visualization of cells in frozen-hydrated samples, while scanning ion imaging provides a morphological view of freeze-fractured cells after TOF-SIMS analysis is completed. With the use of selective fluorescent labels, fluorescence microscopy allows single mammalian cells to be located in the complex ice matrix of freeze-fractured samples, a task that has not been routine with either bright-field or TOF-SIMS. A fluorescent label, DiI (m/z 834), that does not interfere with the mass spectra of membrane phosphatidylcholine, has been chosen for fluorescence and TOF-SIMS imaging of membrane phospholipids. In this paper, in situ fluorescence microscopy allows the distinction of single cells from ice and other sample debris, previously not possible with bright-field or scanning ion imaging. Once cells are located, TOF-SIMS imaging reveals the localization of membrane lipids, even in the membrane of a single 15-microm rat pheochromocytoma cell. The utility of mapping lipids in the membranes of single cells using this integrated approach will provide more understanding of the functional role of specific lipids in functions of cellular membranes.     

Role of cell polarity dynamics and motility in pattern formation due to contact-dependent signalling

A key challenge in biology is to understand how spatio-temporal patterns and structures arise during the development of an organism. An initial aggregate of spatially uniform cells develops and forms the differentiated structures of a fully developed organism. On the one hand, contact-dependent cell–cell signalling is responsible for generating a large number of complex, self-organized, spatial patterns in the distribution of the signalling molecules. On the other hand, the motility of cells coupled with their polarity can independently lead to collective motion patterns that depend on mechanical parameters influencing tissue deformation, such as cellular elasticity, cell–cell adhesion and active forces generated by actin and myosin dynamics. Although modelling efforts have, thus far, treated cell motility and cell–cell signalling separately, experiments in recent years suggest that these processes could be tightly coupled. Hence, in this paper, we study how the dynamics of cell polarity and migration influence the spatiotemporal patterning of signalling molecules. Such signalling interactions can occur only between cells that are in physical contact, either directly at the junctions of adjacent cells or through cellular protrusional contacts. We present a vertex model which accounts for contact-dependent signalling between adjacent cells and between non-adjacent neighbours through long protrusional contacts that occur along the orientation of cell polarization. We observe a rich variety of spatiotemporal patterns of signalling molecules that is influenced by polarity dynamics of the cells, relative strengths of adjacent and non-adjacent signalling interactions, range of polarized interaction, signalling activation threshold, relative time scales of signalling and polarity orientation, and cell motility. Though our results are developed in the context of Delta–Notch signalling, they are sufficiently general and can be extended to other contact dependent morpho-mechanical dynamics.     

Gold-enhanced biomolecular surface imaging of cells and tissue by SIMS and MALDI mass spectrometry

Surface metallization by plasma coating enhances desorption/ionization of membrane components such as lipids and sterols in imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS) of tissues and cells. High-resolution images of cholesterol and other membrane components were obtained for neuroblastoma cells and revealed subcellular details (resolving power 1.5 mum). Alternatively, in matrix-enhanced SIMS, 2,5-dihydroxybenzoic acid electrosprayed on neuroblastoma cells allowed intact molecular ion imaging of phosphatidylcholine and sphingomyelin at the cellular level. Gold deposition on top of matrix-coated rat brain tissue sections strongly enhanced image quality and signal intensity in stigmatic matrix-assisted laser desorption/ionization imaging mass spectrometry. High-quality total ion count images were acquired, and the neuropeptide vasopressin was localized in the rat brain tissue section at the hypothalamic area around the third ventricle. Although the mechanism of signal enhancement by gold deposition is under debate, the results we have obtained for cells and tissue sections illustrate the potential of this sample preparation technique for biomolecular surface imaging by mass spectrometry.     

Lysosome‐Targeted Bioprobes for Sequential Cell Tracking from Macroscopic to Microscopic Scales

Longitudinal tracking of living cells is crucial to understanding the mechanism of action and toxicity of cell‐based therapeutics. To quantify the presence of administered cells in the host tissue without sacrifice of animals, labeling of the target cells with a nontoxic and stable contrast agent is a prerequisite. However, such long‐term live cell tracking is currently limited by the lack of fluorophores with steady optical and physicochemical properties in the near‐infrared (NIR) window. Herein, for the first time, the design of fixable cell‐tracking NIR fluorophores (CTNFs) with high optical properties, excellent cell permeation and retention, and high stability against chemical treatments is reported. Efficient cellular labeling and tracking of CTNFs using intraoperative optical fluorescence imaging by following the fate of NIR‐labeled cells from the time of injection into animals to ex vivo cellular analysis after resection of the target tissue is demonstrated. Due to the lipophilic cationicity and primary amine docking group, CTNF126 outperforms the other tested fluorophores with rapid diffusion into the cytoplasmic membrane and sequestration inside the lysosomes, which prevents cellular efflux and improves cellular retention. Thus, CTNF126 will be useful to track cells in living organisms for the mechanism of action at the single cell level.     

Piezoelectric nanoribbons for monitoring cellular deformations

Methods for probing mechanical responses of mammalian cells to electrical excitations can improve our understanding of cellular physiology and function. The electrical response of neuronal cells to applied voltages has been studied in detail, but less is known about their mechanical response to electrical excitations. Studies using atomic force microscopes (AFMs) have shown that mammalian cells exhibit voltage-induced mechanical deflections at nanometre scales, but AFM measurements can be invasive and difficult to multiplex. Here we show that mechanical deformations of neuronal cells in response to electrical excitations can be measured using piezoelectric PbZr(x)Ti(1-)(x)O(3) (PZT) nanoribbons, and we find that cells deflect by 1?nm when 120?mV is applied to the cell membrane. The measured cellular forces agree with a theoretical model in which depolarization caused by an applied voltage induces a change in membrane tension, which results in the cell altering its radius so that the pressure remains constant across the membrane. We also transfer arrays of PZT nanoribbons onto a silicone elastomer and measure mechanical deformations on a cow lung that mimics respiration. The PZT nanoribbons offer a minimally invasive and scalable platform for electromechanical biosensing.     

Detection of kinase translocation using microfluidic electroporative flow cytometry

Directed localization of kinases within cells is important for their activation and involvement in signal transduction. Detection of these events has been largely carried out based on imaging of a low number of cells and subcellular fractionation/Western blotting. These conventional techniques either lack the high throughput desired for probing an entire cell population or provide only the average behaviors of cell populations without information from single cells. Here we demonstrate a new tool, referred to as microfluidic electroporative flow cytometry, to detect the translocation of an EGFP-tagged tyrosine kinase, Syk, to the plasma membrane in B cells at the level of the cell population. We combine electroporation with flow cytometry and observe the release of intracellular kinase out of the cells during electroporation. We found that the release of the kinase was strongly influenced by its subcellular localization. Cells stimulated through the antigen receptor have a fraction of the kinase at the plasma membrane and retain more kinase after electroporation than do cells without stimulation and translocation. We are able to differentiate a cell population with translocation from one without it with the information collected from individual cells of the entire population. This technique potentially allows detection of protein translocation at the single-cell level. Due to the frequent involvement of kinase translocations in disease processes such as oncogenesis, our approach will have utility for kinase-related drug discovery and tumor diagnosis and staging.     

Nanowire-based single-cell endoscopy

One-dimensional smart probes based on nanowires and nanotubes that can safely penetrate the plasma membrane and enter biological cells are potentially useful in high-resolution and high-throughput gene and drug delivery, biosensing and single-cell electrophysiology. However, using such probes for optical communication across the cellular membrane at the subwavelength level remains limited. Here, we show that a nanowire waveguide attached to the tapered tip of an optical fibre can guide visible light into intracellular compartments of a living mammalian cell, and can also detect optical signals from subcellular regions with high spatial resolution. Furthermore, we show that through light-activated mechanisms the endoscope can deliver payloads into cells with spatial and temporal specificity. Moreover, insertion of the endoscope into cells and illumination of the guided laser did not induce any significant toxicity in the cells.     

Characterisation of a collagen membrane for its potential use in cardiovascular tissue engineering applications

In this study, Biomend, a collagen membrane conventionally used in the regeneration of periodontal tissue, is investigated for its possible use in the field of cardiovascular tissue engineering. A key requirement of most potential tissue engineering scaffolds is that degradation occurs in tandem with tissue regeneration and extra cellular matrix remodelling. To this end, it is crucial to understand the degradation mechanics and mechanisms of the material and to investigate the practicability of using Biomend as a possible scaffold material. With this in mind, methodologies for the initial characterisation of the scaffold material were determined. The mechanical properties of Biomend samples, subjected to various degrees of hydration and enzymatic degradation, were examined primarily through tensile testing experiments. The effects of enzymatic degradation were monitored quantitatively, by observing weight loss, and visually, by studying micrographs. Cell adhesion and viability were of primary concern. Confocal laser scanning microscopy was employed to illustrate endothelialisation on the surface of this collagen membrane. Fluorescence microscopy was used to visualise cell viability on the membrane surface. These images, coupled with assays to measure cell activity, suggest that Biomend is not a suitable substrate to allow endothelialisation. In summary, this collagen membrane has suitable mechanical properties with the potential to control its degradation rate. However, since poor endothelial cell viability was observed on the membrane, it may not be suitable for use in cardiovascular tissue engineering applications.     

Chemical force microscopy of single live cells

Traditionally, cell surface properties have been difficult to study at the subcellular level, especially on hydrated, live cells. Here, we demonstrate the ability of chemical force microscopy to map the hydrophobicity of single live cells with nanoscale resolution. After validating the technique on reference surfaces with known chemistry, we probe the local hydrophobic character of two medically important microorganisms, Aspergillus fumigatus and Mycobacterium bovis, in relation with function. Applicable to a wide variety of cells, the chemically sensitive imaging method presented here provides new opportunities for studying the nanoscale surface properties of live cells and for understanding their roles in mediating cellular events.     

Spectroscopic probing of dynamic changes during stimulation and cell remodeling in the single cardiac myocyte

Optical microscopy, involving both fluorescence imaging and confocal Raman microspectroscopy, was used to visualize single, isolated, electrically active heart muscle cells. For example, short-term, dynamic changes in Raman bands during the contraction cycle, as well as persistent band changes during structural remodeling (microscopic rearrangements of cellular structures) in culture over longer periods of time, were obtained from the cellular content (sarcoplasm) of the heart cells. The results of the short-term studies, collected during electrical stimulation, showed dynamic changes in the Raman amide I band intensity, which occurred in phase with changes in cell length during cardiomyocyte contraction. The longer term studies of quiescent cardiomyocytes in culture over 3 days revealed a progressive and sustained increase in the intensity of the amide I band. Over the same period of culture, a decrease in the number of t-tubules (invaginations of the cell membrane, sarcolemma, which ensure the spreading of the action potential into the bulk of the sarcoplasm) was observed using confocal z-sections of the fluorescently labeled sarcolemma. The ability to measure both short-term dynamic changes associated with stimulated contraction and longer term persistent remodeling in the structure of intracellular macromolecules is valuable for assessing the physiological state of the cell, in real time.     

Capillary electrophoretic separation of nuclei released from single cells

We report here the first capillary electrophoresis analysis of intact nuclei released on-column from single cells. Expression of the nuclear-targeted protein nuDsRed2 and the plasma membrane-bound farnesylated enhanced green fluorescent protein in cultured human DeltaH2-1 cells allowed fluorescent monitoring of the fate of these subcellular compartments upon injection of a single cell into the separation capillary. On-column treatment with digitonin allowed for the separation of the plasma membrane from the nucleus as indicated by their selective laser-induced fluorescence detection in two separate spectral regions. The data suggest that less than 0.1% of the plasma membrane remains bound to individually detected nuclei. In digitonin-treated cells, the electropherograms consisted of a prominent fluorescent peak attributed to nuDsRed2 localized to the nucleus and a collection of weakly fluorescent events (barely distinguishable from scattering) that seem to indicate additional localization of this protein to other subcellular regions. Taken together, this report points to the feasibility of studying intact organelles released from a single mammalian cell by capillary electrophoresis, which is a prerequisite to understanding the relevance of subcellular heterogeneity in biological systems.     

A Difunctional Squarylium Indocyanine Dye Distinguishes Dead Cells through Diverse Staining of the Cell Nuclei/Membranes

Functionalized fluorescent dyes have attracted great interest for the specific staining of subcellular organelles in multicellular organisms. A novel nanometer‐sized water‐soluble multi‐functional squarylium indocyanine dye ( D1 ) that contains four primary amines is synthesized. The dye exhibits good photostability, non‐toxicity and biocompatibility. Isothermal titration calorimetry demonstrates that an affinity between D1 and DNA is higher than that between D1 and analogue of phospholipids. Analysis of circular dichroism spectra indicates that D1 targets to the DNA minor groove and aggregates to a helix. Because of the distinct affinity between the dye and subcellular organelles, the dye exhibits difunctional abilities to label the cell nuclei in fixed cells/tissue and the cell membranes in live cells/tissue. By combination of the two staining capabilities, the dye is further explored as a specific marker to distinguish apoptotic cells in live cells/tissue. The research opens a new way to design novel multifunctional dyes for life science applications.     

Spatial control of cellular measurements with the laser micropipet

Continued progress in understanding cellular physiology requires new strategies for biochemical measurements in solitary cells, multiple cells, and subcompartments of cells. Large spatial gradients in the concentrations of molecules and presumably the activities of enzymes can occur in cells. Consequently, there is a critical need for measurement techniques for mammalian cells with control over the numbers or regions of cells interrogated. In the present work, we developed a strategy to rapidly load the cytoplasmic contents of either multiple cells or a subregion of a single cell into a capillary. A single, focused pulse from a laser created a mechanical shock wave which disrupted a group of cells or a portion of a cell in the path of the shock wave. Simultaneously, the cytoplasm was loaded into a capillary for electrophoretic separation. The size of the region of cellular disruption (and therefore the volume of cytoplasm collected) was controlled by the amount of energy in the laser pulse. Higher energies could be used to sample groups of cells while much lower energies could be utilized to selectively sample the tip of a neuronal process. The feasibility of performing measurements on subcellular compartments was also demonstrated by targeting reporter molecules to these compartments. A reporter localized to the nucleus was detected on the electropherogram following laser-mediated disruption of the cell and the nucleus. Finally, we demonstrate that this method terminated cellular reactions with sufficient rapidity that cellular membrane repair mechanisms were not activated during cytoplasmic collection. The combined ability to preselect a spatial region of a cell or cells and to rapidly load that region into a capillary will greatly enhance the utility of CE in the biochemical analysis of cells.     

Bottom‐Up Assembly of Functional Intracellular Synthetic Organelles by Droplet‐Based Microfluidics

Bottom‐up synthetic biology has directed most efforts toward the construction of artificial compartmentalized systems that recreate living cell functions in their mechanical, morphological, or metabolic characteristics. However, bottom‐up synthetic biology also offers great potential to study subcellular structures like organelles. Because of their intricate and complex structure, these key elements of eukaryotic life forms remain poorly understood. Here, the controlled assembly of lipid enclosed, organelle‐like architectures is explored by droplet‐based microfluidics. Three types of giant unilamellar vesicles (GUVs)‐based synthetic organelles (SOs) functioning within natural living cells are procedured: (A) synthetic peroxisomes supporting cellular stress‐management, mimicking an organelle innate to the host cell by using analogous enzymatic modules; (B) synthetic endoplasmic reticulum (ER) as intracellular light‐responsive calcium stores involved in intercellular calcium signalling, mimicking an organelle innate to the host cell but utilizing a fundamentally different mechanism; and (C) synthetic magnetosomes providing eukaryotic cells with a magnetotactic sense, mimicking an organelle that is not natural to the host cell but transplanting its functionality from other branches of the phylogenetic tree. Microfluidic assembly of functional SOs paves the way for high‐throughput generation of versatile intracellular structures implantable into living cells. This in‐droplet SO design may support or expand cellular functionalities in translational nanomedicine.     

Evaluating the effect of green synthesised copper oxide nanoparticles on oxidative stress and mitochondrial function using murine model

Green synthesis of metal nanoparticles (NPs) has now received the attention of researchers due to ease of preparation and its potential to overcome hazards of these chemicals for an eco‐friendly milieu. In this study, copper oxide (CuO) NPs were synthesised via Desmodium gangeticum aqueous root extract and standard chemical method, further characterised by UV–visible spectroscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, Thermogravimetric analysis and scanning electron microscopy. The nephrotoxicity of the NP obtained from two routes were compared and evaluated at subcellular level in Wistar rat, renal proximal epithelial cells (LLC PK1 cell lines) and isolated renal mitochondria. CuO NP synthesised by chemical route showed prominent nephrotoxicity measured via adverse cytotoxicity to LLC PK1 cells, elevated renal oxidative stress and damage to renal tissue (determined by impaired alanine transaminase, aspartate transaminase, urea, uric acid and creatinine in the blood). However, at the level of cell organelle, CuO NP from both routes are non‐toxic to mitochondrial functional activity. The authors’ finding suggests that CuO NP synthesised by chemical route may induce nephrotoxicity, but may be overcome by co‐administration of antioxidants, as it is not mito‐toxic.Inspec keywords: cellular biophysics, scanning electron microscopy, toxicology, nanomedicine, oxidation, nanoparticles, enzymes, blood, visible spectra, X‐ray diffraction, biochemistry, nanofabrication, antibacterial activity, ultraviolet spectra, copper compounds, Fourier transform infrared spectra, molecular biophysics, thermal analysis, biological tissuesOther keywords: green synthesised copper oxide nanoparticles, murine model, metal nanoparticles, chemicals, eco‐friendly milieu, copper oxide NPs, standard chemical method, X‐ray diffraction, scanning electron microscopy, subcellular level, renal proximal epithelial cells, LLC PK1 cell lines, renal mitochondria, renal tissue, cell organelle, mitochondrial functional activity, UV‐visible spectroscopy, Fourier transform infrared spectroscopy, nephrotoxicity, renal oxidative stress, Desmodium gangeticum aqueous root extract, thermogravimetric analysis, Wistar rat, cytotoxicity, impaired alanine transaminase, aspartate transaminase, urea, uric acid, creatinine, blood, CuO     

Microfluidic selection and retention of a single cardiac myocyte, on-chip dye loading, cell contraction by chemical stimulation, and quantitative fluorescent analysis of intracellular calcium

A microfluidic method to study the contraction of a single cardiac myocyte (heart muscle cell) has been developed. This method integrates various single-cell operations as well as on-chip dye loading, and quantitative analysis of intracellular calcium concentration, [Ca2+]i. After the channel enlargement by on-chip etching to accommodate large-sized cardiac myocytes, a single cell is selected and retained at a V-shaped cell retention structure within the microchip. Owing to the fragile property of the cardiac myocytes that could easily be damaged by centrifugation, the calcium-sensitive fluorescent dye was loaded in the cell by on-chip dye loading. This on-chip method minimized the damage to the cells from the use of a centrifuge in the conventional method and provided a way of cellular analysis of fragile cells. Subsequently, quantitative analysis of [Ca2+]i of a single cardiac myocyte by fluorescence measurement was achieved for the first time in a microfluidic chip, thanks to the intracellular calcium stimulant of ionomycin. The resting [Ca2+]i of the cardiomyocyte determined was consistent with the literature value. From the spontaneous contraction study, it was found that fluorescence intensity cannot represent the [Ca2+]i variation accurately, which implied the importance of the quantitative analysis of [Ca2+]i.     

Magnetic Tweezers‐Based 3D Microchannel Electroporation for High‐Throughput Gene Transfection in Living Cells

A novel high‐throughput magnetic tweezers‐based 3D microchannel electroporation system capable of transfecting 40 000 cells/cm² on a single chip for gene therapy, regenerative medicine, and intracellular detection of target mRNA for screening cellular heterogeneity is reported. A single cell or an ordered array of individual cells are remotely guided by programmable magnetic fields to poration sites with high (>90%) cell alignment efficiency to enable various transfection reagents to be delivered simultaneously into the cells. The present technique, in contrast to the conventional vacuum‐based approach, is significantly gentler on the cellular membrane yielding >90% cell viability and, moreover, allows transfected cells to be transported for further analysis. Illustrating the versatility of the system, the GATA2 molecular beacon is delivered into leukemia cells to detect the regulation level of the GATA2 gene that is associated with the initiation of leukemia. The uniform delivery and a sharp contrast of fluorescence intensity between GATA2 positive and negative cells demonstrate key aspects of the platform for gene transfer, screening and detection of targeted intracellular markers in living cells.