High-speed sensing of microliter-order whole-blood viscosity using laser-induced capillary wave

The present paper introduces an innovative contact-free optical viscosity measurement technique, laser-induced capillary wave (LiCW) using pulsed YAG laser as a heating source, to measure whole-blood viscosity with only a microliter-order sample volume and measurement time on the millisecond order. In this method, interfering pulsed laser beams heat a whole-blood sample and generate a capillary wave, the amplitude of which is less than 10 nm with wavelength of 80–100 μm in the present experiment, caused by a spatially sinusoidal temperature distribution. The damped oscillation of the capillary wave, which is detected by a diffracted probing laser beam at the heated area, provides information regarding the viscosity and surface tension of the whole blood. To demonstrate the validity of the present laser-induced capillary wave viscometer, the viscosity of human whole blood taken from two healthy donors having different hematocrit values was measured using 90 μl sample volumes at 37°C. To consider the feasibility of the present technique for blood rheological studies, we discuss the characteristics of LiCW regarding the non-Newtonian behavior of blood, the velocity boundary layer, the existence of a free surface, and the temperature increase of the blood, and also demonstrate the capability of the method to sense the temporal evolution of blood viscosity with sampling frequency of 0.25 Hz.     

New instrument for on-line viscosity measurement of fermentation media

In an attempt to resolve the difficult problem of on-line determination of the viscosity of non-Newtonian fermentation media, the authors have used a vibrating rod sensor mounted on a bioreactor. The sensor signal decreases nonlinearly with increased apparent viscosity. Electronic filtering of the signal damps the interfering effect of aeration and mechanical agitation. Sensor drift is very low (0.03% of measured value per hour).On the rheological level the sensor is primarily an empirical tool that must be specifically calibarated for each fermentation process. Once this is accomplished, it becomes possible to establish linear or second-degree correlations between the electrical signal from the sensor and the essential parameters of the ferementation process in question (pH of a feremented milk during acidification, concentration of extra cellular polysaccharide). In addition, by applying the power law to describe the rheological behavior of fermentation media, we observe a second-order polynomial correlation between the sensor signal and the behavior index (n).     

The effects of viscosity on gramicidin tryptophan rotational motion.

The rotational amplitude of gramicidin tryptophans was investigated as a function of temperature and viscosity in a variety of solvents using fluorescence spectroscopy. In 80% glycerol-ethanol, gramicidin behavior was similar to that of alpha helical globular proteins. In dioleoyl-phosphatidylcholine (DOPC) and egg-phosphatidylcholine bilayers, the rotational amplitude of the tryptophans remained constant from 5 degrees to 40 degrees C due to the large number of tryptophans participating in intermolecular aromatic ring stacking. In gel phase dimyristoyl-phosphatidylcholine (DMPC), the tryptophan rotations likewise do not respond to temperature and viscosity changes, presumably because of a combination of Trp 9 and 15 stacking and the high viscosity of the membrane. In fluid phase DMPC, stacking becomes disrupted as the temperature increases causing the change in tryptophan amplitude with temperature to be greater than allowed by the membrane. In n-octylglucoside micelles, ring interactions are also broken with heat. We conclude that membrane viscosity regulates both inter- and intramolecular gramicidin interactions but not in a straightforward manner.     

Microscopic viscosity and rotational diffusion of proteins in a macromolecular environment

The Stokes-Einstein-Debye equation is currently used to obtain information on protein size or on local viscosity from the measurement of the rotational correlation time. However, the implicit assumptions of a continuous and homogeneous solvent do not hold either in vivo, because of the high density of macromolecules, or in vitro, where viscosity is adjusted by adding viscous cosolvents of various size. To quantify the consequence of nonhomogeneity, we have measured the rotational Brownian motion of three globular proteins with molecular mass from 66 to 4000 kD in presence of 1.5 to 2000 kD dextrans as viscous cosolvents. Our results indicate that the linear viscosity dependence of the Stokes-Einstein relation must be replaced by a power law to describe the rotational Brownian motion of proteins in a macromolecular environment. The exponent of the power law expresses the fact that the protein experiences only a fraction of the hydrodynamic interactions of macromolecular cosolvents. An explicit expression of the exponent in terms of protein size and cosolvent's mass is obtained, permitting definition of a microscopic viscosity. Experimental data suggest that a similar effective microviscosity should be introduced in Kramers' equation describing protein reaction rates.     

Spin-label techniques for monitoring macromolecular rotational motion: empirical calibration under nonideal conditions.

Practical techniques are demonstrated for determining rotational correlation times of macromolecules from the first harmonic absorption electron spin reasonance spectra of tightly bound spin labels. The techniques are developed to compensate for such nonideal conditions as residual label motion, temperature dependence of rigid limit spectral parameters, and the presence of inhomogeneous line broadening. These effects are all shown to be of importance in monitoring the rotational motion of carbonmonoxyhemoglobin which is spin labeled with the tightly bound nitroxide label, 4-maleimido-2,2,6,6-tetramethylpiperidinyl-1-oxy. Spin-label interactions with other paramagnetic agents are also shown to produce spectral changes which are qualitatively similar to, but quantitatively different from, those resulting from increases in the rate of rotational motion.     

Readily synthesized calibration compounds for quadrupole and magnetic instruments for use over the mass range to 2000 daltons

Volatile mass calibration standards have been prepared by esterifying beta-cellobiose (4-beta-D-glucopyranosyl-D-glucose) with a mixture of heptafluorobutyric (HFB) anhydride and pentafluoropropionic (PFP) anhydride. The mixed esters produce spectra that are useful for mass spectrometer calibration with positive or negative ion methane chemical ionization and electron impact over the mass range 300-2000. The spectra contain prominent ions spaced at m/z 20 and m/z 50 intervals. Using the mixed ester with direct insertion probe introduction gives intense spectra that persist for tens of minutes. All signals above m/z 194 derived from these substances disappear rapidly upon withdrawal of the probe. The composition and exact masses are given for the positive and negative ion spectra of a mixed HFB/PFP ester of beta-cellobiose. Two other calibrants are described: one made from beta-cellobiose using a mixture of HFB, PFP and trifluoroacetic anhydrides, and another the HFB/PFP mixed ester of perseitol. These are examples of the flexibility of this approach with respect to mass range and ion composition.     

The static accuracy and calibration of inertial measurement units for 3D orientation

Inertial measurement units (IMUs) are integrated electronic devices that contain accelerometers, magnetometers and gyroscopes. Wearable motion capture systems based on IMUs have been advertised as alternatives to optical motion capture. In this paper, the accuracy of five different IMUs of the same type in measuring 3D orientation in static situations, as well as the calibration of the accelerometers and magnetometers within the IMUs, has been investigated. The maximum absolute static orientation error was 5.2 degrees , higher than the 1 degrees claimed by the vendor. If the IMUs are re-calibrated at the time of measurement with the re-calibration procedure described in this paper, it is possible to obtain an error of less than 1 degrees , in agreement with the vendor's specifications (XSens Technologies B.V. 2005. Motion tracker technical documentation Mtx-B. Version 1.03. Available from: www.xsens.com). The new calibration appears to be valid for at least 22 days providing the sensor is not exposed to high impacts. However, if several sensors are 'daisy chained' together changes to the magnetometer bias can cause heading errors of up to 15 degrees . The results demonstrate the non-linear relationship between the vendor's orthogonality claim of < 0.1 degrees and the accuracy of 3D orientation obtained from factory calibrated IMUs in static situations. The authors hypothesise that the high magnetic dip (64 degrees ) in our laboratory may have exacerbated the errors reported. For biomechanical research, small relative movements of a body segment from a calibrated position are likely to be more accurate than large scale global motion that may have an error of up to 9.8 degrees .     

Residual motion of hemoglobin-bound spin labels and protein dynamics: viscosity dependence of the rotational correlation times

The residual motion of spin labels bound to cysteine 93 and to lysines of methemoglobin has been studied by electron paramagnetic resonance spectroscopy. To separate the influences of the solvent and the protein environment of the label fluctuations, the correlation times, , were analyzed as a function of temperature for fixed solvent viscosities, . Results show that over a wide range of viscosity the dependence of on may be empirically described by a power law ^k . The exponent k depends strongly on the location of the label on the protein surface. If one regards the spin labels as artificial amino acid side chains, characteristic values of correlation times and amplitudes of the rotational motion at the surface can be given. For =1 cP and T=297 K the correlation time of the labels bound to lysines is found to be =9 · 10^–10 s and the rotational diffusion is nearly isotropic. The spin label bound to cysteine 93 occupies a protein pocket, its rotational motion is therefore restricted. The correlation time of the label motion within a limited motion cone of semi angle =30° ± 3° is found to be =1.3 · 10^–9 s for =1 cP and T=297 K.     

The combination of the viscosity increment with the harmonic mean rotational relaxation time for determining the conformation of biological macromolecules in solution.

A new hydrodynamic shape function, lambda, is derived for determining the conformation of biological macromolecules in solution, adding to the increasing number of shape parameters whose experimental determination does not require a knowledge of the particle swelling due to solvation in solution. lambda can be found from a knowledge of the molecular weight, intrinsic viscosity and the harmonic mean rotational relaxation time. A table of values and a plot of lambda as a function of axial ratio for both oblate and prolate ellipsoids of revolution are given.     

In vivo measurement of leukocyte viscosity during capillary plugging.

Leukocyte plugging of capillaries in vivo was measured in rat spinotrapezius muscle. The plug durations, leukocyte and capillary dimensions, and arteriolar pressure at the plug sites were applied to the mechanical model of Needham and Hochmuth (1990) to estimate the leukocyte viscosities. The viscosity distribution of 389 cells was lognormal with a median value of 232 Poise. 3.1 percent of the cells were apparently activated and displayed viscosities greater than 3000 Poise. The median viscosity suggests that inactivated leukocytes have a minimal effect on blood flow, but that leukocyte activation may result in significant increases in microvascular flow resistance.     

Intracellular viscosity: Methods of measurement and role in metabolism

This review is devoted to the study of intracellular viscosity. Methods of intracellular viscosity measurement in cell populations and single cells are characterized and critically evaluated. Examples of intracellular viscosity assessment in a number of various cell types and intracellular organelles are presented. The main results of the in vitro and in vivo studies on the role of viscosity in metabolism are discussed.     

On the rotational operators in protein structure simulations

The reduction of the computational complexity of the algorithms dealing with protein structure analysis and conformation predictions is of prime importance. One common element in most of these algorithms is the process of transforming geometrical information between dihedral angles and Cartesian coordinates of the atoms in the protein using rotational operators. In the literature, the operators used in protein structures are rotation matrices, quaternions in vector and matrix forms and the Rodrigues-Gibbs formula. In the protein structure-related literature, the most widely promoted rotational operator is the quaternions operator. In this work, we studied the computational efficiency of the mathematical operations of the above rotational operators applied to protein structures. A similar study applied to protein structures has not been reported previously. We concluded that the computational efficiency of these rotational operators applied to protein chains is different from those reported for other applications (such as mechanical machinery) and the conclusions are not analogous. Rotation matrices are the most efficient mathematical operators in the protein chains. We examined our findings in two protein molecules: Ab1 tyrosine kinase and heparin-binding growth factor 2. We found that the rotation matrix operator has between 2 and 187% fewer mathematical operations than the other rotational operators.     

A new calibration method for 3-D position measurement in biomedical applications.

Aim of the study was to determine practicality and to test accuracy of a new calibration technique firstly introduced in 1998 by Schmid and Bess for biomechanical human tests. This technique enables three-dimensional calibration of camera positions as well as the calculation of internal and external camera parameters. It can be performed unlike other three-dimensional calibration techniques as the first with a planar calibration grid and only one single video image (of each camera) to calculate all 3-D reconstruction parameters. The tests were performed using two albavision ACAM G-Cameras with a resolution of 480 (h) by 420 (v) pixels. The achievable accuracy of distance measurements in recent commercially available motion measurement systems usually ranges from about 0.09% to 1.77% and higher. Accuracy of 0.0373% was determined with the new calibration technique. The 95% confidence interval ranged at +/- 0.02322 mm, the RMS (root mean square) error at 0.18776 mm. Better accuracy, easier and faster calibration are features of this new calibration technique. Required time for complete calibration ranged below one minute. Anticipating this new method will have good practicality in gait analysis or in research and industry due to increased accuracy and ease of use.     

A simple capillary viscosity meter for the on-line measurement and control of the biomass concentration in high-density cultures

A capillary viscosity meter was used for the on-line determination of the biomass concentration in a fermentation broth. At high cell densities the viscosity of the broth increases, which can be measured as the pressure drop over a capillary. Calibration aspects of this viscosity meter are presented, and the use of the device for the control of the biomass concentration in a membrane recycle fermentor is demonstrated.