Volume Changes In Response Research Articles

Unsaturated soil–geotextile interface behavior

The behavior of mechanically stabilized earth (MSE) structures under seasonal climatic variations, i.e. wetting and drying, is not well understood. Stability and serviceability of MSE walls and embankments can significantly depend on the soil-reinforcement (e.g., geosynthetics) interface shearing behavior in unsaturated conditions. This is especially true for reinforced soil slopes and embankments that have significant fines contents. This paper presents results of a laboratory study on the mechanical behavior of unsaturated soil-geotextile interfaces using a specially modified direct shear apparatus. Several suction-controlled laboratory tests were conducted to investigate the effect of soil suction on the soil-geotextile interface. Results of the study indicate that the peak shear strength of the soil-geotextile interface increases nonlinearly with the soil suction. On the other hand, while inconclusive, the effect of suction on the post-peak shear strength of the interface was negligible in some cases. An elastoplastic constitutive model was used to simulate the laboratory results. This study demonstrates that the constitutive model is capable of capturing the mechanical behavior of the unsaturated soil-geotextile interface subjected to constant suction. Both shearing and volume change responses were reasonably simulated by the model.

Fast response photonic crystal pH sensor based on templated photo-polymerized hydrogel inverse opal

Polymer hydrogels can exhibit large reversible volume changes in response to external stimuli, and thus are regarded as excellent materials for chemical sensors. In this report, we demonstrate a mechanically robust and fast response photonic crystal pH sensor fabricated by templated photo-polymerization of hydrogel monomers within the interstitial space of a self-assembled colloidal photonic crystal. Throughout a rigorous optimization of the photo-polymerization, pH sensors showing a response time of less than 10 s upon a pH change were fabricated. Repeated pH changes revealed that the sensor has a long lifetime (>6 months) without degradation of the response time or reproducibility in pH-driven color change.

Volume change behaviour of a compacted scaly clay during cyclic suction changes

The research presented in this paper focuses on the investigation and modelling of the volume change response of compacted tectonised clay samples subjected to several wetting and drying cycles in controlled-suction oedometers. Oedometer tests were carried out under different values of constant vertical net stress, and wetting and drying cycles were performed varying applied matric suction between 10 and 800 kPa. The investigation was complemented with a study of the material microstructure to support the interpretation of the overall mechanical response. At a microscopic level, the material is characterized by different types of particle assemblages, scales, and clay aggregates. One of these assemblages was also subjected to a relative humidity cycle in an environmental scanning electron microscope (ESEM) to investigate the reversibility of the mechanical response. Based on the experimental results, the clay volume change behaviour is discussed and interpreted within the context of a double structure elastoplastic model. The procedure used to derive elastic and plastic constitutive parameters is presented. Comparison of test results with model predictions shows a satisfactory agreement between measured and calculated strain evolution.

Polymer diffraction gratings on stimuli-responsive hydrogel surfaces: Soft-lithographic fabrication and optical sensing properties

In this work, a soft-lithographic contact printing approach was developed to fabricate polymer diffraction gratings on stimuli-responsive hydrogel surfaces. For the fabrication, azo polymer films with surface-relief-gratings (SRGs) on surfaces were used as masters, which were inscribed by irradiating solid films of BP-AZ-CA with interfering Ar + laser beams. Elastomeric stamps were prepared by replica molding of poly(dimethylsiloxane) (PDMS) prepolymer against the masters and curing properly. One-dimensional (1D) and two-dimensional (2D) gratings were fabricated on the surfaces of pH-sensitive hydrogel plates through soft-lithographic contact printing. Results show that the swellings of the hydrogel in buffer solutions are sensitively reflected by the variation of the gratings’ diffraction parameter. The pH of the buffer solutions shows a significant influence on the rate and degree of the diffraction parameter variation. Through the hydrogel volume change in response to external stimuli, the diffraction gratings can optically sense the variation of solution pH, which can be extended to sense the ionic strength and other analytes in solutions. Such a transduction mechanism is useful for optically detecting the external stimuli or molecular recognition events. The sensitive grating can also be used as the smart optical filters and other optical devices.

Volume-change response of precast concrete buildings

This paper summarizes the findings of the authors' recent study on the volume-change response of precast concrete buildings. The objective of this research was twofold: to develop a better understanding of volume-change movement and forces based on measured performance of precast concrete parking structures and calibration to analytical models and to recommend revised design procedures that reflect this understanding and account for the influence of flexible connections. The primary research tasks included field monitoring and finite-element analyses of actual structures as well as evaluation of the predictability of volume-change forces. The research revealed that deformations of flexible deck and spandrel connections change the deformation pattern and thereby substantially reduce volume-change movement and force at the lowest supported level, where volume-change forces are most significant. The study also developed new findings with respect to other volume-change parameters, including the thermal-expansion coefficient, the design temperature range, the degree of member softening due to creep and microcracking, and the load factor for volume-change effects. Design recommendations are provided for qualitative consideration of volume-change effects as well as quantitative analysis. Although the new research indicates that the procedures recommended in the PCI Design Handbook: Precast and Prestressed Concrete result in a conservative estimate of volume-change force, certain aspects of the PCI Design Handbook procedures were found to be unconservative. Therefore, the research findings should be considered in their entirety. The full research report is available from PCI.

Gender differences in plasma volume changes in response to arm & leg ergometer exercise

Plasma volume shift (PVS) in response to exercise is a well‐understood phenomenon that has not been investigated for gender differences. Ten healthy young subjects ‐ 5 men (mean age 24.8) and 5 women (mean age 24.4) ‐ each pedaled a cycle ergometer at 50 rpm starting at 0.5 kp and increasing by 0.5 kp every 2 min until heart rate (HR) reached 170. They continued for 8 min with work load adjusted to keep HR at 170±5 bpm. On a separate day, subjects turned an arm ergometer at 50 rpm starting at 0.25 kp and increasing by 0.25 kp every minute until HR reached 170, then continued for 8 min as above. Sessions were counterbalanced. Two‐mL blood samples (in EDTA) were drawn immediately before and after each exercise bout. Hematocrit (Hct) was measured using a microhematocrit reader. Hemoglobin (Hb) was measured using the cyanmethemoglobin method. PVS was calculated using the Dill & Costill equations. One‐way ANOVA revealed significant (p<0.05) pre‐ to post‐exercise increases in Hct and Hb and decreases in PV within both groups. Change in Hb was significant (p<0.05; F=18.366) between groups for arm ergometry. PVS was not significantly different between groups for either type of ergometry. Data suggest that, for a moderately high level of cardiovascular stress, upper and lower body aerobic exercise elicits similar PVS regardless of gender.This research was supported by the Department of Kinesiology and Health Studies, SLU.

Effect of flow rules and elastic strains on pressuremeter test results in dense sand

Simple numerical methods that allow to obtain stress and strain paths in sand during self-boring pressuremeter tests are presented in this paper. The material is considered to undergo deformation in drained and plane-strain conditions. The flow rules of Rowe, Cambridge-type (Cam clay and Nova) model, and the sawtooth model are used in the analysis. Elastic strains are also considered in relation with the flow rule of Rowe. The proposed approach has been evaluated using a reference pressuremeter test performed on Ticino sand in a calibration chamber. The results indicate that the stress–strain–volume change responses of the sand predicted by the various models are quite similar, with and without consideration of the elastic strain components.

Quantifying engineering parameters of expansive soils from their reflectance spectra

Occurrence of expansive soils in construction sites has serious implications on planning, design, construction, maintenance, and overall performance especially of lightweight engineering infrastructures. Such soils are particularly susceptible to large volume changes in response to moisture content fluctuations following seasonal climatic variations. This can lead to deformation of structures built up on them. For this study, soil samples were collected from the eastern part of Addis Ababa. Specific expansive soil engineering parameters namely; Atterberg limits (LL, PL and PI), free swell and cation exchange capacity were measured in a soil mechanics laboratory. Reflectance spectra of each soil sample were acquired in a remote sensing laboratory using ASD fieldspec full range spectrometer. A multivariate calibration method, partial least squares regression (PLSR) analysis, through simple wavelength approach, was used to construct empirical prediction models for estimating engineering parameters of expansive soils from their respective reflectance spectra. Correlation coefficients of 0.90, 0.87, 0.71, 0.81 and 0.71 for CEC, LL, PL, PI and FS respectively were obtained. The correlation coefficients showed that large portion of variations in engineering parameters of expansive soils could be accounted for by spectral parameters. Apart from these high correlation coefficients, small root mean square errors of calibration (RMSEC) and prediction (RMSEP), standard error of calibration (SEC) and prediction (SEP) and minimum bias were obtained. The results indicate potential of spectroscopy in deriving engineering parameters of expansive soils from their respective reflectance spectra and hence, its potential applicability in supporting geotechnical investigations of such soils.

Conjugated Polymer Gels with Dendritic Hydrophilic Side Chains

This paper reports the synthesis and optical properties of poly(p-phenylene ethynylene) gels that features hydrophilic dendritic groups. The conjugated polymer gel particles with hydrophilic side chains have been prepared by a synthetic route that involves initial preparation of an analogue polymer gel having triester side chains through the modified Pd-catalyzed Sonogashira cross-coupling reaction in aqueous emulsion, and the following conversion of ester groups with tris(hydroxymethyl)aminomethane (Tris). The size distribution of the water-swollen particles is relatively narrow with an average diameter of 900 nm. The synthesized particles showed fluorescence and volume changes in response to various solvent compositions.

Effect of aldosterone on the regulation of the volume of principal cells of rat cortical collecting duct epithelium in early postnatal development

A rapid nongenomic regulatory effect of aldosterone on the volume of principal cells in the cortical segment of cortical collecting ducts (CCDs) of rat kidney was studied using the fluorescent dye calcein under hypoosmotic shock conditions (280‐140 mOsm/kg). In the presence of aldosterone (10 nM), the amplitude of cell volume growth significantly decreased ( p < 0.05) and the cell volume recovery time increased twice both in adult and ten-day-old animals. Age differences were detected when the time required for the cell volume recovery under hypoosmotic conditions was determined: in the adult animals, the cell volume recovered much more rapidly (by an order of magnitude) than in the ten-day-old animals both in the control and in the presence of aldosterone ( 0.09 ± 0.02 vs 2.8 ± 0.3 and 0.21 ± 0.03 vs 4.4 ± 0.5 , respectively, p < 0.001). This was the first study to demonstrate the involvement of aldosterone in the regulation of amplitude and dynamics of changes in the volume of CCD principal cells in early postnatal ontogeny. One of the key aspects of development of the osmoregulatory function of the kidney is the development of the molecular mechanisms of regulation of sodium transport in nephron epithelial cells by aldosterone. It is known that, in early ontogeny, kidneys of altricial animals including rats are insensitive to the antinatriuretic effect of aldosterone. Regulation of sodium transport in postnatal ontogeny of the rat is detected starting from the tenth day of life, when the transition from milk feeding to independent feeding is ended. The molecular mechanisms underlying the development of hormonal sensitivity of target cells of an immature kidney have been studied insufficiently well. It is known that the main proteins involved in the transmembrane sodium transport in the principal cells of the CCDs of rat nephron are the proteins of the apical epithelial of the sodium channel (ENaC) and the basolateral sodium pump ( Na + ,a + -ATPase) [6, 7]. The intracellular sodium concentration ([ ]) in principal cells is primarily determined by the dynamic equilibrium between the sodium influx through ENaC and its efflux form the cell into the intersticium against the concentration gradient by ATP-driven Na + ,a + -ATPase. Earlier, we showed that the expression of the genes encoding these proteins is suppressed and the intracellular sodium concentration in CCD principal cells is decreased in kidneys of tenday-old animals [1, 4]. At the same time, we discovered that aldosterone had a rapid nongenomic effect expressed in maintaining an increased [ ] in CCD principal cells at a low (14 mM) sodium concentration in the ambient medium both in adult and ten-day-old rats [4]. These data led us to assume that, along with the well-known mineralocorticoid effect, aldosterone is also involved in the regulation of the volume of CCD cells in rat nephron in hypoosmotic medium and that this mechanism functions even in the preweaning period. However, the rapid nongenomic effects of aldosterone on the regulation of the volume of CCD principal cells have been studied insufficiently comprehensively. In view of above, the goal of this study was to investigate the rapid nongenomic effect of aldosterone at a physiological concentration on the volume of CCD principal cells in kidneys of ten-day-old and adult rats under hypoosmotic shock conditions. Experiments were performed with CCDs of ten- and sixty-day-old Wistar rats, which were obtained by microdissection. The changes in the cell volume were assessed by the changes in the fluorescence intensity of the intracellular dye calcein and expressed in relative units. Fluorescence intensity was measured in the cells located at the open end of a CCD fragment; the basolateral and apical surfaces of these cells are in contact with the ambient solution. Continuous fluorescence recording during cell volume changes in response to osmotic shock was performed in our modification [11]. Renal tubule fragments contained in 100 µ l of suspension in aOa culture medium were loaded on a polylysinecoated slide and loaded with the fluorescent dye calcein

Activation of Stretch-Activated Channels and Maxi-K+Channels by Membrane Stress of Human Lamina Cribrosa Cells

The lamina cribrosa (LC) region of the optic nerve head is considered the primary site of damage in glaucomatous optic neuropathy. Resident LC cells have a profibrotic potential when exposed to cyclical stretch. However, the mechanosensitive mechanisms of these cells remain unknown. Here the authors investigated the effects of membrane stretch on cell volume change and ion channel activity and examined the associated changes in intracellular calcium ([Ca(2+)](i)). The authors used primary LC cells obtained from normal human donor eyes. Confocal microscopy was used to investigate the effect of hypotonic cell membrane stretch on cell volume changes. Whole-cell patch-clamp and calcium imaging techniques were used to investigate the effect of hypotonicity on ion channel(s) activity and [Ca(2+)](i) changes, respectively. RT-PCR was used to examine for the maxi-K(+) signature in LC cells. In this study, LC cells showed significant volume changes in response to hypotonic cell swelling. The authors characterized a large conductance K(+) channel (maxi-K(+)) in LC cells and demonstrated its increased activity during cell membrane hypotonic stretch. RT-PCR revealed the presence of maxi-K(+) signature in LC cells. The authors showed the [Ca(2+)](i) and maxi-K(+) channels to be dependent on extracellular Ca(2+) and inhibited by gadolinium, which blocks stretch-activated channels (SACs). Pretreatment with thapsigargin, which blocks the release of Ca(2+) from endoplasmic reticulum stores, showed no significant difference in [Ca(2+)](i) concentration on hypotonic swelling. The results show that hypotonic stress of human LC cells activates SAC and Ca(2+)-dependent maxi-K(+) channels and that the increase in [Ca(2+)](i) during cell swelling was predominantly from extracellular sources (or intracellular stores other than the endoplasmic reticulum). These findings improve the understanding of how LC cells respond to cell membrane stretch. Further experiments in this area may reveal future targets for novel therapeutic intervention in the management of glaucoma.

Role of AQP2 in activation of calcium entry by hypotonicity: implications in cell volume regulation

We previously reported in a rat cortical collecting duct cell line (RCCD(1)) that the presence of aquaporin 2 (AQP2) in the cell membrane is critical for the rapid activation of regulatory volume decrease mechanisms (RVD) (Ford et al. Biol Cell 97: 687-697, 2005). The aim of our present work was to investigate the signaling pathway that links AQP2 to this rapid RVD activation. Since it has been previously described that hypotonic conditions induce intracellular calcium ([Ca(2+)](i)) increases in different cell types, we tested the hypothesis that AQP2 could have a role in activation of calcium entry by hypotonicity and its implication in cell volume regulation. Using a fluorescent probe technique, we studied [Ca(2+)](i) and cell volume changes in response to a hypotonic shock in WT-RCCD(1) (not expressing aquaporins) and in AQP2-RCCD(1) (transfected with AQP2) cells. We found that after a hypotonic shock only AQP2-RCCD(1) cells exhibit a substantial increase in [Ca(2+)](i). This [Ca(2+)](i) increase is strongly dependent on extracellular Ca(2+) and is partially inhibited by thapsigargin (1 muM) indicating that the rise in [Ca(2+)](i) reflects both influx from the extracellular medium and release from intracellular stores. Exposure of AQP2-RCCD(1) cells to 100 muM gadolinium reduced the increase in [Ca(2+)](i) suggesting the involvement of a mechanosensitive calcium channel. Furthermore, exposure of cells to all of the above described conditions impaired rapid RVD. We conclude that the expression of AQP2 in the cell membrane is critical to produce the increase in [Ca(2+)](i) which is necessary to activate RVD in RCCD(1) cells.

Modeling the Volumetric Change of Head and Neck Tumor in Response to Radiation Therapy

A large fraction of head-n-neck (HN) cancer patients experience tumor or lymph node volume change during the course of radiation therapy. Modeling the volumetric tumor kinetics is an essential step to better understand the therapeutic process and to compute the cumulative dose for offline/online adaptive radiation therapy. In this work we develop a novel method to model the tumor shrinkage and illustrate the performance by applying the technique to five clinical HN cases. Tumor shrinkage or growth cannot be described solely by an elasticity or similarity based deformable model because of the non-conservation of the tissue. The underlying hypothesis here is that, when a tumor grows or shrinks, some of the tissue features in the tumor volume or at the boundary region are preserved, despite of possible scale changes. Our algorithm focuses on auto-detecting the homologous tissue features shared by the planning CT and subsequent on-treatment CBCT images (typically, 3∼5 CBCT scans for each patient). Once the tissue features are identified, a voxel-to-voxel correspondence between two images for the rest of points can be established by basis spline interpolation. The tissue feature at a point of interest in an image is described by the local information using the Scale Invariance Feature Transformation (SIFT) method, which includes scale-space extrema detection, control point localization, orientation assignment and control point descriptor. If a feature region in the fixed image is mapped correctly to the moving image, it will necessarily be mapped back to the original region in the fixed image when we apply the inverse map to the corresponding region in the moving image. The bi-directional mapping procedure was included in our algorithm to increase the precision of tissue feature correspondence. The proposed method is applied to a number of synthetic cases and five clinical HN cases. A novel model describing the kinetics of tumor volume change in response to radiation therapy has been established. The identification of tissue features shared by the images acquired at different time points plays an essential role in the modeling process. Our bi-directional SIFT method further warrants the reliable association of the tissue features. In the testing cases based on synthetic images with artificially introduced “tumor” volume changes, the bi-directional SIFT was able to correctly identify majority of the features appeared before the introduction of artificial volumetric changes. Because the number of identifiable feature points are generally large in HN cases, the voxel-to-voxel correspondence resulted from the subsequent basis spline interpolation almost reproduced the “ground truth” solution provided that the tumor volume change is less than 15%∼20%. Generally, the model works well for a small or modest volume change and suggests that the time span between two consequent imaging sessions should not be unreasonably far away in order for the model to function properly. Tumor change kinetics can be derived reliably from consecutive imaging data by using the proposed SIFT-based model. The model is valuable to better understand the tumor response to radiation therapy, and to compute the cumulative dose distribution during the treatment. The latter makes adaptive therapy with consideration of dose delivery history practically feasible.

Variable‐Focus Liquid Microlenses and Microlens Arrays Actuated by Thermoresponsive Hydrogels

Traditional optical systems utilize mechanical parts (e.g., gears, motors, and drivers) to allow adjustable focusing and magnification. Emerging variable-focus microlenses have exhibited the potential to miniaturize and advance optical systems without the need for mechanical parts, impacting significantly on a multitude of fields, such as cameras, biomedical instruments, and lab-on-a-chip systems. A variety of variable-focus liquid microlenses have been demonstrated based on different mechanisms, including reorientation of liquid crystals, electrowetting of a liquid droplet, and mechanical actuation of polymeric materials. These microlens technologies rely on external controls and power supplies; for example, additional electric fields are necessary to drive both electrowetting liquid microlenses and liquid-crystal microlenses, and external actuation devices are required to control the pressure in flexible polymer microlenses. The requirement for additional discrete components increases the complexity and makes integration, especially in lab-on-a-chip applications, challenging. We are interested in taking advantage of smart materials to realize variable-focus liquid microlenses without requiring external controls and power supplies. Responsive hydrogels are smart materials that undergo significant and reversible volume change in response to environmental stimuli by absorbing and releasing water through the network interstitials of the hydrogels. The ability to convert chemical energy directly into mechanical work means that the hydrogels can function as sensors, actuators, and power sources in specific conditions (e.g., the human body) where most external controls and power supplies are limited or difficult to obtain. By taking advantage of responsive hydrogels, we previously reported an innovative approach for realizing smart-liquid microlenses responsive to environmental changes. The liquid microlens extends the concept of pinned liquid/liquid interfaces to apertures to form a liquid microlens. A hydrogel ring located within a microfluidic channel responds to an environmental change by expanding and contracting, which regulates the shape of a water/oil interface (i.e., a liquid microlens), thus, tuning the focal length of the microlens. In this paper, we demonstrate thermoresponsive variable-focus cylindrical microlenses and spherical microlens arrays formed using liquid/liquid interfaces. Thermoresponsive reversible N-isopropylacrylamide (NIPAAm) hydrogels were employed; unconstrained NIPAAm hydrogels swell by as much as a factor of ten when the temperature decreases from above to below the hydrogel’s lower critical solution temperature (LCST). First, arbitrary shapes of microlenses (e.g., cylindrical and spherical) can be realized by patterning apertures that have corresponding shapes (e.g., rectangular and circular, respectively). This benefits the implementation of various microlenses with different shapes, among which variable-focus cylindrical lenses are of strong interest for a multitude of optical applications such as stretching an image, focusing light into a slit, and correcting low-order aberration. Second, we extended single variable-focus spherical microlenses to microlens arrays, allowing the devices not only to have wide-angle observation and parallel optical signal acquisition, but also to implement combinatorial interrogation of complicated environments in microfluidics by individually regulating the focal lengths of the microlens elements. In a typical variable-focus cylindrical microlens (Fig. 1a), a rectangular window was photopatterned in a 250 lm thick polymer slip to form an aperture. The sidewall of the aperture was treated to be hydrophilic (water contact angle of 29°) through an oxygen plasma treatment; the top-side surface of the aperture was rendered hydrophobic (water contact angle of 118°) by coating it with an octadecyltrichlorosilane solution. Thus, a hydrophobic/hydrophilic contact line coincided at the boundary between the sidewall and top-side surface of the aperture. A thermoresponsive NIPAAm hydrogel (LCST = 32 °C) ring was photopatterned in a 750 lm deep microfluidic channel. When the hydrogel ring was filled with deionized water through the aperture, a water meniscus emerged from the rectangular aperture, and the peripheral boundary of the meniscus was pinned stably at the hydrophobic/hydrophilic contact line. Mineral oil was stored within a C O M M U N IC A IO N

Effect of the initiator on thermosensitive rate of poly(N-isopropylacrylamide) hydrogels

As the main of thermosensitive polymeric materials, poly(N-isopropylacrylamide) (PNIPAM) undergoes volume changes in response to external temperature changes. While in some potential applications, a fast response rate is needed. In this article, effect of the initiator on thermosensitivity of PNIPAM hydrogels was carried out. The characterization of the resulting hydrogels was gravimetrically measured, and the result displays that with increasing the initiator dosage, much faster deswelling rate and much faster shrinking/swelling dynamic response are obtained.

Pore-Scale Analysis of Bulk Volume Change from Crystalline Interlayer Swelling in Na+- and Ca2+-Smectite

AbstractWater-vapor sorption experiments were conducted to quantify bulk volume change of compacted expansive clay specimens resulting from interlayer hydration and dehydration in the crystalline swelling regime. Effects of interlayer cation type and pore fabric are examined by comparing results for natural Na+-smectite and Ca2+-smectite specimens compacted over a range of initial bulk densities. Transitions in interlayer hydration states are reflected in the general shape of the sorption isotherms and corresponding relationships between humidity and volume change. Hysteresis is observed in both the sorption and volume-change response. Volume change for Ca2+-smectite specimens is significantly greater than for Na+-smectite over the entire range of packing densities considered. Loosely compacted specimens result in less volume change for both clays. Results are interpreted in light of a conceptual framework based on previous SEM and TEM observations of particle and pore fabric for Na+ and Ca2+ smectite at high suctions. A pore-scale microstructural model is developed to quantitatively assess changes in interlayer and interparticle void volume during hydration. Modeling suggests that the relatively small volume changes observed for Na+-smectite are attributable to a reduction of interparticle void volume as expanding quasicrystals encroach into surrounding larger-scale pores. Volume change hysteresis is attributed to unrecovered alterations in interparticle fabric required to accommodate the swelling process. The results provide new insight to address volume change upscaling, hysteresis, and the general evolution of bi-modal pore fabric during crystalline swelling.

A new noninvasive method to determine central venous pressure

Knowledge of central venous pressure (CVP) is considered valuable in the assessment and treatment of various states of critical illness and injury. We tested a noninvasive means of determining CVP (NICVP), by monitoring forearm volume changes in response to externally applied circumferential pressure to the upper arm veins. Sixteen patients who were undergoing CVP monitoring as a part of their care had NICVP determined and compared with CVP. Volume changes were measured in the forearm with mercury-in-silastic strain gauge plethysmography. A pressure cuff is placed in the upper extremity. The cuff is inflated over 5s to a pressure above CVP but below diastolic arterial pressure (40 mmHg). This allows blood into the forearm but prevents venous return. After 45-60 s the cuff is rapidly deflated. NICVP was determined as the cuff pressure noted at the maximum derivative of the forearm volume decrease during deflation. NICVP was then compared to invasively measured CVP taken during the same period. A total of 48 trials (three per subject) were performed on 16 patients. The range of CVP recorded was 0-22 mmHg. The correlation between CVP and NICVP was 0.98 (95% CI: 0.95-0.98) (p<0.001). The bias between methods was 0.26 mmHg with the limits of agreement being 3.4 to -2.89 mmHg. When the average of three trials per patients was analysed the bias stayed at 0.26 mmHg but the limits of agreement improved to 2.54 and -2.03 mmHg. NICVP as determined in this study may be a clinically useful substitute for traditional CVP measurement and may offer a valid tool for early diagnosis and treatment of acute states in which knowledge of CVP would be helpful.

Ultraslow Thermoresponse in Hydrogels Synthesized with Radiation Technique

Hydrogels, which were synthesized by simultaneously occurring processes of radiation-induced polymerization and cross-linked reactions of acryloyl-l-proline methyl ester (APM) at 0 °C in aqueous alcohol solutions, exhibit an ultraslow volume change in response to variations in external temperature. The shrinking speed of the hydrogels prepared in aqueous alcohol is 1000 times slower than that of the hydrogel prepared in pure water; e.g., the hydrogel prepared in aqueous 1-propanol solution shrunk in 6 months. It is revealed that the ultraslow thermoresponse consists of quick- and slow-shrinking periods; the ratio between the two periods depends on the alcohol molecules in the solution. The generation of a hydroxyl group in the polymer network by the coupling reaction between α-hydroxyalkyl radical of alcohols and α-radical of proline moiety was confirmed by GC/MS analysis of the radiation products. The hydrogen bonding domain containing the hydroxyl groups is proposed to be responsible for the ultraslow r...

Rapid depletion of mutant eukaryotic initiation factor 5A at restrictive temperature reveals connections to actin cytoskeleton and cell cycle progression

Eukaryotic initiation factor 5A (eIF5A) is the only protein in nature that contains hypusine, an unusual amino acid derived from the modification of lysine by spermidine. Two genes, TIF51A and TIF51B, encode eIF5A in the yeast Saccharomyces cerevisiae. In an effort to understand the structure-function relationship of eIF5A, we have generated yeast mutants by introducing plasmid-borne tif51A into a double null strain where both TIF51A and TIF51B have been disrupted. One of the mutants, tsL102A strain (tif51A L102A tif51aDelta tif51bDelta) exhibits a strong temperature-sensitive growth phenotype. At the restrictive temperature, tsL102A strain also exhibits a cell shape change, a lack of volume change in response to temperature increase and becomes more sensitive to ethanol, a hallmark of defects in the PKC/WSC cell wall integrity pathway. In addition, a striking change in actin dynamics and a complete cell cycle arrest at G1 phase occur in tsL102A cells at restrictive temperature. The temperature-sensitivity of tsL102A strain is due to a rapid loss of mutant eIF5A with the half-life reduced from 6 h at permissive temperature to 20 min at restrictive temperature. Phenylmethyl sulfonylfluoride (PMSF), an irreversible inhibitor of serine protease, inhibited the degradation of mutant eIF5A and suppressed the temperature-sensitive growth arrest. Sorbitol, an osmotic stabilizer that complement defects in PKC/WSC pathways, stabilizes the mutant eIF5A and suppresses all the observed temperature-sensitive phenotypes.

Surprising shrinkage of expanding gels under an external load

Hydrogels are fascinating and useful in that they can show large volume changes in response to various stimuli, such as temperature or chemical environment. Here we report the peculiar observation that chemically crosslinked hydrogels that normally expand owing to a change in electrolyte pH can be made to shrink in certain circumstances. Specifically, these hydrogels contract when tested at a constant compressive force and subjected to a pH change that causes expansion in the absence of the applied load. When tested under tension, the gels always expand. Although the effects of external stress on the swelling of gels is known, the concomitant change in gel mechanical properties during pH switching was found to be a more dominant effect in our studies. However, existing mechanical models used to predict dimensional changes in actuator materials could not explain both the tensile and compression results. In addition, we show that the friction between metal plates of the apparatus and the gel is a key factor in explaining the contractile actuation under compressive loads. The observations reported in this paper are important for the successful design and use of hydrogel actuators in devices such as valves for microfluidics.