The interplay of cell–cell and cell–substrate adhesion in collective cell migration

Collective cell migration often involves notable cell–cell and cell–substrate adhesions and highly coordinated motion of touching cells. We focus on the interplay between cell–substrate adhesion and cell–cell adhesion. We show that the loss of cell-surface contact does not significantly alter the dynamic pattern of protrusions and retractions of fast migrating amoeboid cells (Dictyostelium discoideum), but significantly changes their ability to adhere to other cells. Analysis of the dynamics of cell shapes reveals that cells that are adherent to a surface may coordinate their motion with neighbouring cells through protrusion waves that travel across cell–cell contacts. However, while shape waves exist if cells are detached from surfaces, they do not couple cell to cell. In addition, our investigation of actin polymerization indicates that loss of cell-surface adhesion changes actin polymerization at cell–cell contacts. To further investigate cell–cell/cell–substrate interactions, we used optical micromanipulation to form cell–substrate contact at controlled locations. We find that both cell-shape dynamics and cytoskeletal activity respond rapidly to the formation of cell–substrate contact.     

P-TlSe single crystal — based accumulating cell

Charging and discharging processes have been studied in an accumulating cell made on the basis of a p-TlSe single crystal and aqueous LiCl solution. The maximum e.m.f. of the cell was equal to 2.1 V, the short-circuit current density reached 100 mA/cm² for a fully charged cell, and the discharging depth amounted to 95%.     

Enhanced-fluorescence of europium–copper nanoclusters for cell imaging

Herein, a facile way to synthesize Cu nanoclusters (CuNCs) has been proposed while insulin played the role as a stabilizer. Specifically, this type of CuNCs existed in tunable diameters of 4–5 nm, and exhibited bright reddish-orange fluorescence with a quantum yield of 7.4 %. Interestingly, the fluorescence intensity of CuNCs could be obviously enhanced and more stable by introducing Eu³⁺. Moreover, this proposed Eu³⁺@CuNCs with low toxicity and near-infrared fluorescence may provide potential to broaden avenues for various applications in bioimaging and beyond.     

Bone cell–material interactions on metal-ion doped polarized hydroxyapatite

The objective of this work is to study the influence of Mg²⁺ and Sr²⁺ dopants on in vitro bone cell–material interactions of electrically polarized hydroxyapatite [HAp, Ca₁₀(PO₄)₆(OH)₂] ceramics with an aim to achieve additional advantage of matching bone chemistry along with the original benefits of electrical polarization treatment relevant to biomedical applications. To achieve our research objective, commercial phase pure HAp has been doped with MgO, and SrO in single, and binary compositions. All samples have been sintered at 1200 °C for 2 h and subsequently polarized using an external d.c. field (2.0 kV/cm) at 400 °C for 1 h. Combined addition of 1 wt.% MgO/1 wt.% SrO in HAp has been most beneficial in enhancing the polarizability in which stored charge was 4.19 μC/cm² compared to pure HAp of 2.23 μC/cm². Bone cell–material interaction has been studied by culturing with human fetal osteoblast cells (hFOB) for a maximum of 7 days. Scanning electron microscope (SEM) images of cell morphology reveal that favorable surface properties and dopant chemistry lead to good cellular adherence and spreading on negatively charged surfaces of both Sr²⁺ and Mg²⁺ doped HAp samples over undoped HAp. MTT assay results at 7 days show the highest viable cell densities on the negatively charged surfaces of binary doped HAp samples, while positive charged doped HAp surfaces exhibit limited cellular growth in comparison to neutral surfaces.     

AlPbOAg as a solid electrolyte cell

Thin film AlPbOAg sandwich solid electrolyte cells are obtained by vacuum evaporation on glass substrates; PbO is grown thermally by oxidizing vapour-deposited lead at 150 °C on the bottom aluminium electrode. A.c. and d.c. conductivity studies on symmetrical AlPbOAl sandwich cells indicate that PbO is an ionic conductor. The AlPbOAg sandwich cell is seen to generate a short-circuit current of few nanoampères and a dark voltage in the range 400–800 mV in air ambient, silver being the positive electrode. The discharge characteristics of the cells are studied and a cell reaction is proposed. The variation in cell voltage with temperature and white light illumination is also studied. The photovoltage of the cell is found to add to its dark voltage. The short-circuit current of the cell is also observed to increase with illumination.     

Observing single cell NF-κB dynamics under stimulant concentration gradient

Study of cell signaling often requires examination of the cellular dynamics under variation in the stimulant concentration. Such variation has typically been conducted by dispensing cell populations in a number of chambers or wells containing discrete concentrations. Such practice adds to the complexity associated with experimental or device design and requires substantial labor for implementation. Furthermore, there is also potential risk of missing important results due to the often arbitrary selection of discrete concentration values for testing. In this Letter, we study NF-κB activation and translocation at the single cell level using a microfluidic device that generates continuously varying concentration gradient. We use only three device settings to cover stimulant (interleukin-1β) concentrations of 4 orders of magnitude (0.001-10 ng/mL). Such device allows us to study temporal dynamics of NF-κB in single cells under different stimulant concentrations by real-time imaging. Interestingly, our results reveal that, while the percent of cells with NF-κB translocation decreases with lower stimulant concentration in the range of 0.1-0.001 ng/mL, the response time of such translocation remains constant, reflected by the single cell data.     

Quasi‐static analysis of electric and magnetic fields in tem cell

Abstract

A method is presented whereby the electric and magnetic fields within a rectangular coaxial transmission line (TEM cell) can easily be obtained. The analysis is based on the variational technique in the space domain combined with the Green's function method. Numerical data are presented for the characteristic impedance and for the field distributions within the cell. The results calculated by the present method are found to be in good agreement with those in open literature.     

Nanofibrous membrane of collagen–polycaprolactone for cell growth and tissue regeneration

Nanofibrous substrates of synthetic polymers including polycaprolactone (PCL) have shown considerable potential in tissue regeneration. This paper reports the use of PCL/collagen nanofibers to improve the in vitro osteoblastic responses for the applications in bone regeneration area. Collagen and PCL were dissolved in a co-solvent, and the resulting solution was electrospun into a nanofibrous web. Nonwoven fibrous matrices were successfully produced at various compositional ratios (PCL/collagen = 1/3, 1 and 3 by weight). Although the PCL nanofiber was hydrophobic, the presence of collagen significantly improved the water affinity, such as the water contact angle and water uptake capacity. Tensile mechanical tests showed that the collagen–PCL nanofiber had a significantly higher extension rate (approximately 2.8-fold) than the PCL while maintaining the maximum tensile load in a similar range. The osteoblastic cells cultured on the collagen–PCL nanofibrous substrate showed better initial adhesion and a higher level of growth than those cultured on the PCL nanofiber. Furthermore, real-time RT-PCR revealed the expression of a series of bone-associated genes, including osteopontin, collagen type I and alkaline phosphatase. The expression of these genes was significantly higher on the collagen–PCL nanofiber than on the PCL nanofiber. When subcutaneously implanted in mouse the collagen–PCL membrane facilitated tissue cells to well penetrate into the nanofibrous structure at day 7, whilst no such cell penetration was noticed in the pure PCL nanofiber. Overall, the presence of collagen within the PCL nanofiber improves the water affinity, tensile extension rate, and the tissue cell responses, such as initial adhesion, growth, penetration and the expression of bone-associated genes. Therefore, the collagen–PCL nanofibrous membrane may have potential applications in the cell growth and bone tissue regeneration.     

Osteoclastic cell behaviors affected by the α-tricalcium phosphate based bone cements

Calcium phosphate cements (CPCs) have recently gained great interest as injectable bone substitutes for use in dentistry and orthopedics. α-tricalcium phosphate (α-TCP) is a popularly used precursor powder for CPCs. When mixed with appropriate content of liquid and kept under aqueous conditions, α-TCP dissolves to form a calcium-deficient hydroxyapatite and then hardens to cement. In this study, α-TCP based cement (CP) and its composite cement with chitosan (Ch-CP) were prepared and the osteoclastic responses to the cements and their elution products were evaluated. Preliminary evaluation of the cements revealed that the CP and Ch-CP hardened within ~10 min at an appropriate powder-to-liquid ratio (PL) of 3.0. In addition, CP and Ch-CP were transformed into an apatite phase following immersion in a saline solution. Moreover, the osteoblastic cells were viable on the cements for up to 10 days. Mouse-derived bone marrow cells were isolated and activated with osteoclastic differentiation medium, and the effects of the CP and Ch-CP substrates and their ionic eluants on the osteoclastic activity were investigated. Osteoclastic cells were viable for up to 14 days on both types of cements, maintaining a higher cell growth level than the control culture dish. Multi-nucleated osteoclastic cells that were tartrate-resistant acid phosphatase (TRAP)-positive were clearly observed when cultured on the cement substrates as well as treated with the cement eluants. The TRAP activity was found to be significantly higher in cells influenced by the cement substrates and their eluants with respect to the control culture dish (Ch-CP > CP ≫ control). Overall, the osteoclastic differentiation was highly stimulated by the α-TCP based experimental cements in terms of both the substrate interaction and their elution products.     

Selenization of electrodeposited copper–indium alloy thin films for solar cell applications

Copper–Indium (Cu–In) alloys with sulfur and selenium have technological importance in the development of thin film solar cell technology. We have used potentiostatic electrochemical technique with three-electrode geometry for the deposition of Cu–In alloy thin films in an aqueous electrolyte. Cathodic voltammetry (CV) was thoroughly studied to optimize the electrodeposition parameters. The deposition potential for Cu–In alloy was found to be in the range ?0.70 to ?0.85 V versus Ag/AgCl reference electrode. Polycrystalline Cu_xIn_y thin films were electrodeposited from aqueous bath at room temperature and 45 °C. Effect of concentration of citric acid was extensively studied by CV measurements. The as-deposited Cu–In films were characterized with a range of characterization techniques to study the structural, morphological, compositional and electrical properties. Thin layers of Cu–In were selenized in a homemade tubular furnace at 400 ^°C, which reveals the formation of polycrystalline CuInSe₂ (CISe) thin films with tetragonal structure. The band gap of CISe thin film was estimated ~1.05 eV by optical absorption spectroscopy. Nearly stoichiometric CISe thin film, Cu = 25.25 %, In = 26.48 % and Se = 48.27 % was obtained after selenization. The linear behavior of current density–voltage (J–V) was observed for Cu–In alloy thin films whereas, the selenized Cu–In alloy films (CISe) possess rectifying properties.     

Investigations of a wedge-shaped nematic liquid crystal cell using Mach–Zehnder interferometer

We report optical interferometric studies of a wedge-shaped nematic liquid crystal cell. Interference fringes were observed when a nematic liquid crystal cell was placed in one of the arms of Mach–Zehnder interferometer. In the case of homogenous gap cell, the fringe contrast remained unaffected on applying voltage. However, in the case of wedge-shaped cell, the fringe contrast was found to degrade under an applied electric (DC) field and it became poorer at higher voltages. At higher voltages the fringe contrast improved where complete switching occurred. The degradation in fringe contrast due to wedge-shaped cell structure might find applications for speckle reduction in future laser-based rear projection displays.     

Compressive properties of closed cell Al alloy–fly ash particle composite foams

Abstract

The closed cell aluminium alloy–fly ash particle composite (Al/FA) foams containing 1·5 wt-% fly ash were manufactured by molten body transitional foaming process. The quasi-static compressive properties of Al/FA have been investigated. Results show the compressive stress–strain curves of Al/FA foams exhibit three regions, i.e. the elastic region, the plastic plateau region and the densification region. A linear relationship between the densification strain and the relative density was obtained. The relation between the plastic collapse stress and the relative density can be described with Gibson and Ashby’s model. The energy absorption capacities of the Al/FA foams gradually increase with increasing strain and relative density.     

Biocompatible fluorescence-enhanced ZrO₂-CdTe quantum dot nanocomposite for in vitro cell imaging

With advances of quantum dots (QDs) in bioimaging applications, various materials have been used to coat QDs to reduce their nanotoxicity; however, the coating could introduce new toxic sources and quench the fluorescence in bioimaging applications. In this work, ZrO?, an excellent ceramic material with low extinction coefficient and good biocompatibility, is utilized to coat CdTe QDs for the first time. Experimental results show that ZrO?-QD nanocomposites with the size of ~30 nm possess enhanced fluorescence emission, lower nanotoxicity and gradually increased fluorescence under 350 nm light illumination. After functionalization with folic acid, they were applied to label cultured HeLa cells effectively. Therefore, the ZrO?-QD nanocomposites could be promising biocompatible nanomaterials with strong fluorescence emission to replace or complement QDs in biomedical applications.     

Dilute nitride based III–V alloys for laser and solar cell applications

The dilute nitrogen alloy GaAs_1−xN_x is of recent technological importance for high efficiency solar cells and vertical cavity surface emitting diode lasers used in fiber optic communications. The giant band gap lowering and the abnormal effective mass phenomena observed in this material have been extensively researched. There exist many inconsistencies between the results of various theoretical models and experimental techniques used to probe the above phenomena. It appears that these arise because GaAs_1−xN_x should be viewed not as an abnormal alloy but rather as a heavy isoelectronically doped semiconductor.     

Dynamic ductile crack growth and transition to cleavage – a cell model approach

The fracture behavior of ferritic steel in the transition regime is controlled by the competition between ductile tearing and cleavage. Many test specimens that failed by catastrophic cleavage showed significant amounts of ductile tearing prior to cleavage fracture. The transition from ductile tearing to cleavage has been attributed to the increase in constraint and sampling volume associated with ductile crack growth. This work examines the role of dynamic ductile crack growth on the fracture mode transition by way of a cell model of the material. The cell model incorporates the effects of stress triaxiality and strain rate on material failure characteristics of hole growth and coalescence. Loading rate and microstructure effects on the stress fields that evolve with rapid (ductile) crack growth are systematically studied. The stress fields are employed to compute the Weibull stress which provides probability estimates for the susceptibility to cleavage fracture. A center-cracked panel subjected to remote tension is the model problem under study. The computational model uses an elastic-viscoplastic constitutive relation which incorporates enhanced strain rate hardening at high strain rates. Adiabatic heating due to plastic dissipation and the resulting thermal softening are also accounted for. Under dynamically high loading rate, our model shows the crack speed achieves its peak value soon after crack initiation and quickly falls off to slower speeds with further crack growth. Remarkably, the Weibull stress follows a similar pattern which suggests that the transition to the cleavage fracture is most likely to occur, if at all, at the peak speed of ductile crack growth. Key words: Dynamic fracture, ductile tearing, crack growth, transition regime, cleavage fracture, cell model, finite element.     

Poly-dl-lactic acid coated Bioglass? scaffolds: toughening effects and osteosarcoma cell proliferation

The fabrication and in vitro characterisation of 45S5 Bioglass^?-derived scaffolds coated with poly-dl-lactic acid (PDLLA) are presented. Two types of scaffolds with different porosities were studied. The scaffold microstructure was analysed by scanning electron microscopy before and after polymer coating. Compressive strength tests were performed in as-fabricated condition and after 28?days of immersion in simulated body fluid. It was found that PDLLA-coated samples have higher compression strength compared with the uncoated samples. Human osteosarcoma cell line (HOS-TE85) was used to determine the biocompatibility of the scaffolds. Cell proliferation and differentiated functions were investigated by AlamarBlue^?, alkaline phosphatase and osteocalcin assays. The scaffolds were maintained in cell culture for periods of up to 14?days. The combined effects of the scaffold microstructure (porosity, surface roughness and bioreactivity) and the polymeric coating induce favourable HOS cell behaviour. The results confirmed the biocompatibility of Bioglass^?/PDLLA composite scaffolds for HOS cell culture and contribute to the understanding of the characteristics of these scaffolds for potential applications in bone tissue engineering.     

System integration design in MEMS — A case study of micromachined load cell

One of the critical issues in large scale commercial exploitation of MEMS technology is its system integration. In MEMS, a system design approach requires integration of varied and disparate subsystems with one of a kind interface. The physical scales as well as the magnitude of signals of various subsystems vary widely. Known and proven integration techniques often lead to considerable loss in advantages the tiny MEMS sensors have to offer. Therefore, it becomes imperative to think of the entire system at the outset, at least in terms of the concept design. Such design entails various aspects of the system ranging from selection of material, transduction mechanism, structural configuration, interface electronics, and packaging. One way of handling this problem is the system-in-package approach that uses optimized technology for each function using the concurrent hybrid engineering approach. The main strength of this design approach is the fast time to prototype development. In the present work, we pursue this approach for a MEMS load cell to complete the process of system integration for high capacity load sensing. The system includes; a micromachined sensing gauge, interface electronics and a packaging module representing a system-in-package ready for end characterization. The various subsystems are presented in a modular stacked form using hybrid technologies. The micromachined sensing subsystem works on principles of piezo-resistive sensing and is fabricated using CMOS compatible processes. The structural configuration of the sensing layer is designed to reduce the offset, temperature drift, and residual stress effects of the piezo-resistive sensor. ANSYS simulations are carried out to study the effect of substrate coupling on sensor structure and its sensitivity. The load cell system has built-in electronics for signal conditioning, processing, and communication, taking into consideration the issues associated with resolution of minimum detectable signal. The packaged system represents a compact and low cost solution for high capacity load sensing in the category of compressive type load sensor.