Modelling biological gel contraction by cells: mechanocellular formulation and cell traction force quantification

Traction forces developed by most cell types play a significant role in the spatial organisation of biological tissues. However, due to the complexity of cell-extracellular matrix interactions, these forces are quantitatively difficult to estimate without explicitly considering cell properties and extracellular mechanical matrix responses. Recent experimental devices elaborated for measuring cell traction on extracellular matrix use cell deposits on a piece of gel placed between one fixed and one moving holder. We formulate here a mathematical model describing the dynamic behaviour of the cell-gel medium in such devices. This model is based on a mechanical force balance quantification of the gel visco-elastic response to the traction forces exerted by the diffusing cells. Thus, we theoretically analyzed and simulated the displacement of the free moving boundary of the system under various conditions for cells and gel concentrations. This model is then used as the theoretical basis of an experimental device where endothelial cells are seeded on a rectangular biogel of fibrin cast between two floating holders, one fixed and the other linked to a force sensor. From a comparison of displacement of the gel moving boundary simulated by the model and the experimental data recorded from the moving holder displacement, the magnitude of the traction forces exerted by the endothelial cell on the fibrin gel was estimated for different experimental situations. Different analytical expressions for the cell traction term are proposed and the corresponding force quantifications are compared to the traction force measurements reported for various kind of cells with the use of similar or different experimental devices.     

Current-mode A/D converter

The authors report the design of a new current-mode A/D converter, based on a modified successive-approximations model, in 1.2 μm CMOS technology. The proposed circuit is characterised by good accuracy and fast dynamic performance, low power consumption and small occupation area. SPICE simulations allow the design approach to be validated and the electrical performance of the ADC to be predicted     

Filter matrix estimation in automated DNA sequencing

In four-color fluorescence-based automated DNA sequencing, a 4×4 filter matrix parameterizes the relationship between the dye-intensity signals of interest and the data collected by an optical imaging system. The filter matrix is important because the estimated DNA sequence is based on the dye intensities that can only be recovered via inversion of the matrix. Here, the authors present a calibration method for the estimation of the columns of this matrix, using data generated through a special experiment in which DNA samples are labeled with only one fluorescent dye at a time. Simulations and applications of the method to real data are provided, with promising results     

Analysis of the deformation of polypropylene hot-tool butt welds

Thin microtomed samples from hot-tool butt welds of polypropylene pipes are subjected to uniaxial tensile stress using a specially built instrumented microtesting machine. The deformation of the interface between the weld and the bulk polymer is measured by an optical method. An analysis of these measurements is carried out using the finite element method, and contours of the effective stress are obtained. There is a steep stress gradient at the junction of the weld flash and the bulk polymer, although the stress concentration factor is relatively low. The stress is essentially constant in the bulk polymer apart from the region near the weld zone. Tests on samples without the weld flash show that the maximum stress occurs within the weld zone. This is consistent with long-term tests on larger samples, where the fracture is found to initiate within the weld. The method of analysis enables the stress-strain response of the weld material to be determined.     

Insulinomimetic effect on glucose transport by epidermal growth factor when combined with a major histocompatibility complex class I-derived peptide

Peptides derived from the alpha 1-region of the murine H-2Dk molecule enhance glucose uptake in rat adipose cells above the maximum obtained with insulin stimulation alone (Stagsted, J., Reaven, G. M., Hansen, T., Goldstein, A., and Olsson, L. (1990) Cell 62, 297-307). We now describe that epidermal growth factor (EGF) in combination with the same peptides, Dk-(61-85) and Dk-(62-85), stimulates cellular glucose uptake 5-7 times over the basal level, i.e. to 30-50% of the maximal insulin effect. EGF alone increased glucose uptake by only approximately 50% above basal and the peptide alone by 100% above basal. Maximal effect of EGF and peptide was reached in 10-20 min with 30 microM peptide (EC50 10-15 microM) and 50 nM EGF (EC50 1-2 nM). The effect of EGF and peptide on glucose uptake was additive to that of insulin and peptide until the maximal level attained with insulin and peptide was reached. The combined effect of EGF plus peptide on glucose transport was associated with a recruitment of GLUT4 molecules to the plasma membrane. However, the phosphatidylinositol (PI) kinase which is activated by insulin was not activated by EGF plus peptide. Thus, the effect of EGF plus peptide on glucose uptake seems independent of the activity status of the insulin receptor. 125I-Labeled EGF bound specifically to rat adipose cells with an apparent affinity of approximately 2 nM and Bmax approximately 5 x 10(3). However, the major histocompatibility complex (MHC) peptides did not affect EGF-stimulated internalization of EGF receptor, in contrast to their effect on the insulin receptors. Transforming growth factor alpha had an effect similar to EGF on glucose uptake. Three other peptides derived from other parts of murine MHC class I had no effect on glucose uptake in combination with EGF. Thus, EGF in combination with certain MHC class I-derived peptides is insulinomimetic concerning glucose transport and this effect is independent of the insulin receptor activity.     

The pharmacokinetics of pancuronium bromide in infants, children and adults

Laparoscopic retroperitoneal lymph node dissection is a new surgical procedure used to enhance staging in men with clinical stage I nonseminomatous germ cell tumors of the testis. The procedure has been performed in a limited number of patients at several centers with extensive laparoscopic experience. Laparoscopic retroperitoneal lymphadenectomy is a technically demanding procedure which can be successfully completed in the majority of patients. However, the risk of complications is greater than in patients who undergo standard open retroperitoneal lymph node dissection. The primary advantage of a laparoscopic approach is shortened hospitalization and rapid return to normal activity. The role of laparoscopy in the management of patients with testis malignancy has not been defined. The use of this staging procedure may help minimize the need for surveillance studies following surgery and may be best utilized in men with a lower likelihood of nodal metastases. Ultimately, prospective study in large groups of patients will be necessary to determine the role of laparoscopic retroperitoneal lymph node dissection in patients with testis cancer.     

Efficient diode-pumped single-frequency erbium:ytterbium fiberlaser

We report a 7.6-mW single-frequency fiber laser operating at 1545 nm, using for the first time an Er³⁺:Yb³⁺ doped fiber and a fiber grating output coupler. The laser did not exhibit self-pulsation, which is a typical problem in short three-level fiber lasers, and had a relative intensity noise (RIN) level below -145.5 dB/Hz at frequencies above 10 MHz. The linewidth of the laser was limited by the relaxation oscillation sidebands in the optical spectrum and was typically less than 1 MHz     

The effects of cholecystokinin A and B receptor antagonists, devazepide and L 365260, on citalopram-induced decrease of exploratory behaviour in rat

The present study has been divided into two sets. In the first set, the aim of the experiments was to investigate the dose-response effect of selective serotonin re-uptake inhibitor (SSRI) citalopram on rat exploratory behaviour in the elevated plus-maze. In the second set of experiments, the effect of cholecystokinin (CCK) CCKA and CCKB receptor antagonists, devazepide and L 365260, on citalopram-induced decrease of exploratory behaviour in the elevated plus-maze was studied. Citalopram (5 and 10 mg/kg) decreased the number of open and total arm entries, line crossings on open arms, and percentage of time spent exploring in open arm. Dose 15 mg/kg was without any effect on rat exploratory behaviour. Devazepide (0.01 and 1.0 mg/kg) failed to modify any of the citalopram-induced changes observed. L 365260 (1.0 mg/kg) reversed most of the effects of citalopram: the numbers of open and total arm entries, the number of line crossings, and the percentage of time spent exploring in open arms. L 365260 at dose level 0.01 mg/kg was ineffective. These results support the involvement of the CCKB receptor subtype in SSRI-induced anxiogenic-like effects in rodents.