Media Of Different Viscosities Research Articles

Influences of viscosity on the osteogenic and adipogenic differentiation of mesenchymal stem cells with controlled morphology.

Matrix viscoelastic properties have been shown to have important effects on cell functions. However, the conventional culture methods for investigating the influences of viscoelastic properties on cell functions cannot exclude the influence of cell morphology. Therefore, in this study, cell morphology was well-controlled by using micropatterns, and the influences of the viscosity of the cell culture medium on cell functions under controlled cell morphology were investigated. Human bone marrow-derived mesenchymal stem cells (hMSCs) were cultured on circular micropatterns of different sizes and elliptic micropatterns of different aspect ratios to control cell size and elongation. The cells were cultured in viscous media of different viscosities, and their osteogenic and adipogenic differentiation were compared. Viscosity could affect the osteogenic and adipogenic differentiation of hMSCs, and the effect was dependent on cell morphology. High viscosity induced a promotive effect on the osteogenic differentiation and an inhibitory effect on the adipogenic differentiation of large and elongated hMSCs. However, viscosity did not affect the osteogenic or adipogenic differentiation of small hMSCs. The effects were correlated with its influence on the actin filament organization of the hMSCs on the micropatterns. The results provide useful information for controlling stem cell functions and tissue engineering.

Active Brownian particle in homogeneous media of different viscosities: numerical simulations.

Self-propelled colloids, active polymers and membranes, driven (vibrated) granular layers and hybrid synthetic-biological systems are striking examples of systems containing synthetic active Brownian particles. Such particles autonomously convert the available energy of the environment into their own directed mechanical motion. In most studies the self-propelled Brownian particles move in overdamped media. Recently, experiments with Janus particles in a low-pressure plasma have appeared. A distinctive feature of such a medium is an extremely low viscosity at which the inertial effects play a significant role, resulting in underdamped Brownian motion. At present, there is a lack of statistical theory describing the underdamped Brownian motion of self-propelled particles at all time scales. This paper presents the numerical simulation results of active Brownian motion in homogeneous media of different viscosities. The calculations are performed using a mathematical model of a self-propelled Brownian sphere with translational and rotational inertia. The time-dependent mean square displacement and mean linear displacement (the noise-averaged trajectory) of the particle are investigated as a function of medium viscosity, self-propulsion velocity and moment of inertia. Our simulation reveals that the dynamics of a self-propelled spherical particle significantly depends on two independent dimensionless parameters of the particle: the ratio of the self-propulsion velocity to the characteristic thermal velocity and the ratio of the friction coefficient to the rotational diffusion coefficient. The obtained statistical characteristics of active Brownian motion are compared with the known theoretical models in a wide range of medium viscosities. We propose simple corrections to the basic theory of overdamped active Brownian motion, which allow one to calculate the effective diffusion coefficient and the persistence length of a self-propelled Brownian particle in a medium with any dynamic viscosity. The results obtained are discussed in relation to active particles in a colloidal plasma and superfluid helium.

Sperm velocity in a promiscuous bird across experimental media of different viscosities.

In species with internal fertilization, the female genital tract appears challenging to sperm, possibly resulting from selection on for example ovarian fluid to control sperm behaviour and, ultimately, fertilization. Few studies, however, have examined the effects of swimming media viscosities on sperm performance. We quantified effects of media viscosities on sperm velocity in promiscuous willow warblers Phylloscopus trochilus. We used both a reaction norm and a character-state approach to model phenotypic plasticity of sperm behaviour across three experimental media of different viscosities. Compared with a standard medium (Dulbecco's Modified Eagle Medium, DMEM), media enriched with 1% or 2% w/v methyl cellulose decreased sperm velocity by up to about 50%. Spermatozoa from experimental ejaculates of different males responded similarly to different viscosities, and a lack of covariance between elevations and slopes of individual velocity-by-viscosity reaction norms indicated that spermatozoa from high- and low-velocity ejaculates were slowed down by a similar degree when confronted with high-viscosity environments. Positive cross-environment (1% versus 2% cellulose) covariances of sperm velocity under the character-state approach suggested that sperm performance represents a transitive trait, with rank order of individual ejaculates maintained when expressed against different environmental backgrounds. Importantly, however, a lack of significant covariances in sperm velocity involving a cellulose concentration of 0% indicated that pure DMEM represented a qualitatively different environment, questioning the validity of this widely used standard medium for assaying sperm performance. Enriching sperm environments along ecologically relevant gradients prior to assessing sperm performance will strengthen explanatory power of in vitro studies of sperm behaviour.

Sperm‐Driven Micromotors Moving in Oviduct Fluid and Viscoelastic Media

Biohybrid micromotors propelled by motile cells are fascinating entities for autonomous biomedical operations on the microscale. Their operation under physiological conditions, including highly viscous environments, is an essential prerequisite to be translated to in vivo settings. In this work, a sperm-driven microswimmer, referred to as a spermbot, is demonstrated to operate in oviduct fluid in vitro. The viscoelastic properties of bovine oviduct fluid (BOF), one of the fluids that sperm cells encounter on their way to the oocyte, are first characterized using passive microrheology. This allows to design an artificial oviduct fluid to match the rheological properties of oviduct fluid for further experiments. Sperm motion is analyzed and it is confirmed that kinetic parameters match in real and artificial oviduct fluids, respectively. It is demonstrated that sperm cells can efficiently couple to magnetic microtubes and propel them forward in media of different viscosities and in BOF. The flagellar beat pattern of coupled as well as of free sperm cells is investigated, revealing an alteration on the regular flagellar beat, presenting an on-off behavior caused by the additional load of the microtube. Finally, a new microcap design is proposed to improve the overall performance of the spermbot in complex biofluids.

A diffusion NMR method for the prediction of the weight-average molecular weight of globular proteins in aqueous media of different viscosities

We have introduced for the first time, a non-viscosity dependent universal calibration curve (UCC) for the successful prediction of the weight-average molecular weights of globular proteins in the range of 8.5–66.2 kDa with no dependence on the solvent viscosity.

Large variability in the motility of spiroplasmas in media of different viscosities

Spiroplasmas are bacteria that do not possess flagella and their motility is linked to kink propagation coupled to changes in the cell body helicity. While the motility of bacteria with flagellar motion has been studied extensively, less work has been devoted to the motility of spiroplasmas. We first show that the motility of such bacteria has large variability from individual to individual as well as large fluctuations in time. The Brownian motion of such bacteria both in orientation and translation is also highlighted. We propose a simple model to disentangle the different components of this motility by examining trajectories of single bacteria in different viscosity solvents. The mean velocity of the bacteria turns out to depend on the viscosity of the medium as it increases with viscosity. Further, the temporal fluctuations of the bacteria motility turn out to be very strong with a direct link to tumbling events particular to this bacteria.

Studying the Dynamics of Miniature in-Pipe Vibration Type Robots

Actual problem is the study of oscillation acting on functional characteristics of miniature robots based on frequency modulation and changing of pulse recurrence frequency. Such robots are the systems with electromagnetic action, investigation of which is performing in many scientific centers of the world. Study of oscillation processes satisfy the receiving of relationships between functional and frequency characteristics, determine conformity working and required parameters and to extend robot's possibilities. Miniature robots with electromagnetic drive system and technological on board sensors are intended mainly for direct or inverse motion inside of pipes with small diameter (5-20 mm) and analyze of the quality internal surfaces of the pipes, for nondestructive testing and other inspection operations in energy, nuclear power stations for example, in aviation and space technologies. In this paper the motion equations of electromagnetic in-pipe robot are presented, as so as nomographs and characteristics, those may use under design of miniature robots for the purposes of target applications. The results of investigations of oscillatory processes in miniature in-pipe robots of the electromagnetic principle of action are presented. Robots are equipped with coupling devices with internal surfaces of small diameter pipes. Dependences of the robot's parameters on the frequency, length and duration of the control pulses are given. The oscillations effects for a different frequency on the characteristics of the robot with the possibility of reversible motion when moving in media of different viscosities are analyzed.

Beat Frequency is Reduced but Waveform Shape is Conserved in Chlamydomonas Flagella at High Viscosity

Motivation: Cilia and flagella are thin subcellular organelles that produce fluid movement and cell motility. Coordinated activity of the motor protein dynein causes sliding between adjacent microtubule doublets and subsequent bending of the cilium. Here, the role of mechanical feedback in dynein regulation is investigated by studying the effects of increased viscosity on the flagellar waveform.Methods: Flagellar waveforms of the unicellular green alga Chlamydomonas reinhardtii were measured in media of different viscosities. Genetic mutants missing inner dynein arms (ida1) or outer dynein arms (oda2) were used to investigate the force-dependent contributions of these molecular motors to the flagellar waveform. Media viscosity was increased from 1.5 cP to 4.7 cP using Ficoll 10% w/v. High speed videos (350 fps) of periodically-beating uniflagellate cells were processed in MATLAB to extract waveform parameters sensitive to external viscosity, and to compare mutant cells to wild-type cells.Results: Beat frequency decreased with increasing viscosity in wild-type (59.5±7.0 Hz to 31.7±9.1 Hz) and mutant cells (ida1: 50.4±6.1 Hz to 27.3±11.1 Hz; oda2: 24.9 ±4.0 Hz to 7.2±1.8 Hz). Both wild-type and oda2 cells exhibited greater maximum curvature at the higher viscosity (wild-type: 0.212±0.042 rad/μm to 0.287±0.025 rad/μm; oda2: 0.163±0.033 rad/μm to 0.230±0.014 rad/μm). Curvature differences were smaller in the ida1 mutant (0.266±0.024 rad/μm to 0.288±0.089 rad/μm). Shear rate and bend propagation speed decreased with viscosity, and the amplitude of shear was reduced slightly. Notably the qualitative shape of the waveform and relative differences between wild-type, ida1, and oda2 were maintained at the higher viscosity.Discussion: At higher viscosity, beat frequency decreases to maintain viscous force amplitudes and flagellar waveforms similar to baseline, which supports the role of mechanical feedback in dynein coordination.

Gassed and ungassed power draw in a pilot scale 550 litre fermentor retrofitted with up-pumping hydrofoil B2 impellers in media of different viscosity and with very high power draw

A number of modern impellers have been designed in the pursuit of an alternative to the traditional Rushton turbine, which has a number of well recognized deficiencies. A dual up-pumping combination of the Hayward Tyler B2 (former APV-B2 or simply B2), a high solidity ratio hydrofoil impeller, was retrofitted using traditional methods to a pilot scale fermentor based on cited reference studies of the impeller performance. Using water as a media and comparatively low power draws, the B2 impeller has previously been shown to have good gas handling properties and a low ungassed power number allowing for use at high impeller-to-tank diameter ratio. In the present study a power characterization of the B2 impeller was undertaken in order to extend the available data to viscous media resembling fermentation broths and to very high power draws. Power characterizations were carried out with specific energy input rates up to 12.9 kW/m 3 using different shear-thinning media. The ungassed power number of the B2 impeller was determined (3.3 for power draws in the range 0–11.6 kW/m 3) and our findings confirm those of previous studies and extend the trends to media of high viscosity. Upon aeration the B2 impellers loose little power compared to the traditional impeller even when applying a very high power draw (10–20% power loss at 450 rpm and 1.28 vvm corresponding to 11.6 kW/m 3). Torque fluctuations are found to be small (<5%) for this impeller at high power draw and high viscosity media. Finally it is shown that the B2 impeller can be retrofitted to pilot scale fermentors using traditional methods with a high degree of confidence.

Mineralized matrix deposition by marrow stromal osteoblasts in 3D perfusion culture increases with increasing fluid shear forces.

In this study we report on direct involvement of fluid shear stresses on the osteoblastic differentiation of marrow stromal cells. Rat bone marrow stromal cells were seeded in 3D porous titanium fiber mesh scaffolds and cultured for 16 days in a flow perfusion bioreactor with perfusing culture media of different viscosities while maintaining the fluid flow rate constant. This methodology allowed exposure of the cultured cells to increasing levels of mechanical stimulation, in the form of fluid shear stress, whereas chemotransport conditions for nutrient delivery and waste removal remained essentially constant. Under similar chemotransport for the cultured cells in the 3D porous scaffolds, increasing fluid shear forces led to increased mineral deposition, suggesting that the mechanical stimulation provided by fluid shear forces in 3D flow perfusion culture can indeed enhance the expression of the osteoblastic phenotype. Increased fluid shear forces also resulted in the generation of a better spatially distributed extracellular matrix inside the porosity of the 3D titanium fiber mesh scaffolds. The combined effect of fluid shear forces on the mineralized extracellular matrix production and distribution emphasizes the importance of mechanosensation on osteoblastic cell function in a 3D environment.

Intramolecular formation of excimers in model compounds for polymers of 2,6-naphthalene dicarboxylic acid and five glycols in media of different viscosity

Steady-state fluorescence has been used to study the dependence of the intramolecular formation of excimers in media of differing viscosity, η, for model compounds of polyesters containing naphthalene groups. The model compounds are derived from 2-naphthalene carboxylic acid as rigid units and glycols, HO (SINGLEBOND) (CH2)m (SINGLEBOND) OH, m = 2(SINGLEBOND) 6, as flexible spacers. The ratio of the intensity of excimer and monomer emissions, ID/IM, exhibits two regimes: a regime at high η where ID/IM shows an odd(SINGLEBOND) even effect with m, with maxima at odd m, and a regime at low η where the odd-even effect is lost, and the maximum values are obtained for m = 3 and 6. Calculations performed for the equilibrium state using the rotational isomeric state model and Molecular Dynamics (MD) simulations allow the rationalization of the behavior of ID/IM with m in the media of high and low η, respectively. © 1996 John Wiley & Sons, Inc.

Intramolecular energy transfer in compounds with two 1-pyrenoate groups separated by methylene spacers

Steady-state fluorescence anisotropy (r) and fluorescence lifetime (τ) measurements have been used to study the efficiency of nonradiative singlet energy transfer as a function of alkane size in 1-pyrenecarboxylic acid alkanediyl esters (as a function ofm in Py-COO-(CH2) m -OOC-Py, where Py denotes pyrene substituted in the 1-position, andm=2-6). Experiments were performed in media of different viscosity, η, obtained by changing the temperature (from -20 to 40°C) of dilute solutions in ethylene glycol and by examination of the compounds in a solid matrix of poly(methyl methacrylate) (PMMA) at ambient temperature. The Py-COO-(CH2)m-OOC-Py exhibit intramolecular excimer emission in ethylene glycol at these temperatures, but the intensity of this emission is much lower than when these compounds are placed in common solvents of lower η. The values of τ indicate that excitation hopping or intramolecular energy transfer takes place between the chromophores attached to the ends of the alkane bridges. Values ofr obtained by the extrapolationsT/η→0 orτT/η→0 in ethylene glycol, as well as the values obtained in the rigid matrix of PMMA, show very little dependence onm. A theoretical conformational analysis, using the rotational isomeric state (RIS) model, was also performed. The combination of the experimental results forr in the media of high η with the theoretical (RIS) analysis produces an estimated value of 21 ±2 Å for the Förster radius in Py-COO-(CH2)m-OOC-Py.

Viscosity‐dependent locomotion of oral spirochetes

Spirochetes are thought to remain motile in environments (such as intercellular spaces) that immobilize extracellularly flagellated eubacteria. This attribute suggests that the viscosity of the milieu is of importance to locomotion. We sought to determine the interdependence of oral spirochete locomotion with media viscosity. Video time-lapse microscopy using darkfield optics was used. The motility of the spirochetes in media of different viscosities (various concentrations of Noble agar) was measured. Treponema denticola exhibited the fastest speed (18.7 +/- 4.4 microns/min) at a viscosity of 30 mPa.s. The highest speeds for Treponema vincentii and Treponema socranskii were 41.9 +/- 14.9 and 33.4 +/- 13.2 microns/min, respectively, at 88 mPa.s. These data show that optimal migration of spirochetes is viscosity-dependent. The results support the hypothesis that such viscosity-dependent locomotion could be a virulence factor that enables oral spirochetes to initiate and sustain periodontal disease.

Application of diffractometry and a linear image sensor to measurement of erythrocyte deformability.

We applied laser diffractometry and a linear image sensor to measurement of erythrocyte deformability to detect the light intensity pattern of the diffraction image. Deformability was evaluated as the deformability index (DI), calculated from the width and length of the diffraction pattern ellipse, estimated by the linear image sensor. With the erythrocytes under various shear stresses, the DI was linearly related to results by the geometric method (r = 0.996, p < 0.01). The coefficient of variance of DI at a shear stress of 236 dynes/cm2 was 0.2% (seven human blood samples), which was satisfactory for practical use. The DI was independent of the erythrocyte concentration in the range of 1.5 x 10(7)-5.0 x 10(7) cells/ml of suspension. Correlation between the DI and the logarithm of shear stress was linear in the range of 5 to 350 dynes/cm2 of shear stress in suspension media of different viscosities. Heat-treatment, which decreased membrane flexibility, caused parallel reduction of the DI plotted against the logarithm of shear stress. The method was sensitive and gave reproducible results. It may be useful for clinical applications.

Fluorescence properties of some coumarin dyes and their analytical implication

Fluorescence characteristics of two substituted coumarin dyes have been investigated. The effect of solvent polarity and viscosity on the fluorescence properties of these dyes was examined. It was found that the fluorescence quantum yield (φf) is a steep function of the viscosity. The dependence of φf on viscosity is successfully explained on the basis of the free volume theory of viscosity. Moreover, fluorescence depolarization measurements in media of different viscosities assist in the establishment of an analytical method for microviscosity determination in the interior of some micellar assemblies.

Pressure gradients in catheters during digital subtraction angiography

The F4 and F5 catheters used for digital subtraction angiography are subjected to high pressure gradients. The paper analyses the pressure gradients resulting from contrast media of different viscosities in catheters of varying internal diameters and related to the rate of injection. These are demonstrated diagrammatically. The pressure sequences which occur in F4 and F5 sequences can be demonstrated on an oscillograph. The usual high pressure injections also result in turbulent flow conditions.

MOLECULAR PROBES: PHOTOISOMERIZATION OF OPTICALLY ACTIVE AZO COMPOUNDS

Abstract— The azo group may be used as a probe to gain information about the molecular surroundings. The circular dichroism (CD) spectra of two azo steroids have been investigated in media of different viscosity and polarity. The CD spectra of the trans‐compounds are only slightly affected by the environment while those of the cis‐compounds are strongly dependent on the environment. Photoisomerization is analysed by absorption and ellipticity diagrams as tests for chromophoric and conformeric uniformity. Our results support an inversion mechanism of the photoisomerization of azo compounds.

The lateral diffusion coefficient of lecithin molecules in single bilayer vesicles studied by 14N NMR

The 14N nuclear relaxation times T 1 and T 2 in egg yolk phosphatidylcholine have been observed in single bilayer vesicles dispersed in the media of different viscosities, 1H 2O and 2H 2O. The lateral diffusion coefficient of lipid molecule D has been calculated according to the method reported earlier: D = 2.2 × 10 −8cm 2s −1 in 1H 2O and 2.1 × 10 −8cm 2s −1 in 2H 2O at 20°C. They are in excellent agreement. This result gives a strong basis of usefulness of 14N NMR method in the evaluation of D without introducing any system perturbation.

Translational movements of macrophages through media of different viscosities.

The extent of the migration of guinea-pig peritoneal macrophages from capillary tubes over the surfaces of plastic Petri dishes, was quantitated by planimetry. It was observed that the amount of migration decreased as the viscosity of the medium was increased by the addition of agarose. An essential component of translational movement is the formation of adhesions between cells and their substrata. It is suggested on the basis of the present migration and adhesion experiments, that the increased viscosity reduces migration by retarding the formation of adhesions between the cells and their substrata. The experiments do not support the suggestion that agarose adsorbed to the dish surface affects the adhesion-dependent arm of migration or that viscous 'drag' on whole cells (over the viscosity range of 0.71 to 3.9 x 10(-3) N s m-2) reduces their movements.

Ionic diffusion delays in the transverse tubules of frog twitch muscle fibres.

1. The possibility of retarding the diffusional processes in the transverse tubules of frog single muscle fibres was explored by increasing the viscosity of the bathing medium. The viscosity was increased by adding Dextran 15 to the experimental solutions.2. The criterion used to test this possibility was the speed of repolarization of muscle fibre membranes produced by sudden reduction in [K](o) in media of different viscosity.3. In fibres equilibrated in media containing 15% Dextran 15, and that had been depolarized with 80 mM-K for more than 5 sec, the repolarization caused by lowering the [K](o) to 40 mM proceeded more slowly than in fibres in Dextran-free media.4. On the basis of the above results, it was deduced that high viscosity solutions would delay the diffusion of Na ions in the transverse tubules. Thus the effect of sudden changes in [Na](o) on the twitch tension of single fibres could be studied.5. The recovery of twitches when the fibres were exposed from a solution containing no Na, to one that contained 46 mM-Na, occurred more slowly in high viscosity media.6. This result can be explained assuming that a Na regenerative process occurs at the level of the membrane of the transverse tubules.