Confined compression experiments on bovine nucleus pulposus and annulus fibrosus: sensitivity of the experiment in the determination of compressive modulus and hydraulic permeability

The biphasic material properties for nucleus pulposus tissue in confined compression have not been reported previously, and are required for a better understanding of intervertebral disc function and to provide material properties for use in finite-element models. The aims of this study were to determine linear and non-linear material properties for nucleus pulposus and annulus fibrosus tissues in confined compression, to define the influence of swelling conditions on these properties, and to determine the changes in the compressive modulus and hydraulic permeability induced by the repetition of the stress-relaxation experiment after a return to swelling pressure equilibrium. Specimens from caudal bovine nucleus and annulus were tested in confined compression stress-relaxation experiments and analyzed to quantify the compressive modulus and hydraulic permeability using linear and non-linear biphasic models. Our results suggested the use of confined swelling pre-test condition and non-linear biphasic model, which provided the material parameters with lowest relative variance and water content most representative of physiological conditions. Smaller compressive modulus and higher hydraulic permeability were obtained for the nucleus (H(A0)=0.31+/-0.04 MPa, k(0)=0.67+/-0.09 x 10(-15)m(4)/Ns) than for the annulus (H(A0)=0.74+/-0.13 MPa, k(0)=0.23+/-0.19 x 10(-15)m(4)/Ns), with relatively weak non-linearities. Strains up to 20% resulted in material properties that were significantly altered upon retesting. These altered material properties are an effort to quantify non-recoverable damage that occurs in disc tissue and suggest that in vivo exposure of disc tissues to low strain-rate and high-deformation loading conditions which outpace biological repair may result in altered mechanical behaviors.     

Analysis of large compression loads on lumbar spine in flexion and in torsion using a novel wrapping element

Axial compression on the spine could reach large values especially in lifting tasks which also involve large rotations. Experimental and numerical investigations on the spinal multi motion segments in presence of physiological compression loads cannot adequately be carried out due to the structural instability and artefact loads. To circumvent these problems, a novel wrapping cable element is used in a nonlinear finite element model of the lumbosacral spine (L1-S1) to investigate the role of moderate to large compression loads on the lumbar stiffness in flexion and axial moments/rotations. The compression loads up to 2,700 N was applied with no instability or artefact loads. The lumbar stiffness substantially increased under compression force, flexion moment, and axial torque when applied alone. The presence of compression preloads significantly stiffened the load-displacement response under flexion and axial moments/rotations. This stiffening effect was much more pronounced under larger preloads and smaller moments/rotations. Compression preloads also increased intradiscal pressure, facet contact forces, and maximum disc fibre strain at different levels. Forces in posterior ligaments were, however, diminished with compression preload. The significant increase in spinal stiffness, hence, should be considered in biomechanical studies for accurate investigation of the load partitioning, system stability, and fixation systems/disc prostheses.     

Confined compression of a tissue-equivalent: collagen fibril and cell alignment in response to anisotropic strain

A method to impose and measure a one dimensional strain field via confined compression of a tissue-equivalent and measure the resulting cell and collagen fibril alignment was developed Strain was determined locally by the displacement of polystyrene beads dispersed and entrapped within the network of collagen fibrils along with the cells, and it was correlated to the spatial variation of collagen network birefringence and concentration. Alignment of fibroblasts and smooth muscle cells was determined based on the long axis of elongated cells. Cell and collagen network alignment were observed normal to the direction of compression after a step strain and increased monotonically up to 50% strain. These results were independent of time after straining over 24 hr despite continued cell motility after responding instantly to the step strain with a change in alignment by deforming/convecting with the strained network. Since the time course of cell alignment followed that of strain and not stress which, due to the viscoelastic fluid-like nature of the network relaxes completely within the observation period, these results imply cell alignment in a compacting tissue-equivalent is due to fibril alignment associated with anisotropic network strain. Estimation of a contact guidance sensitivity parameter indicates that both cell types align to a greater extent than the surrounding fibrils.     

Modeling biological variability in 2-D gel proteomic carcinogenesis experiments

We propose a statistical method to model the underlying distribution of protein spot volumes in 2-D gels using a generalized model (GM). We apply this approach to discover mechanisms of chemical carcinogenesis in a rodent model. We generated 247 protein spots that were common to all gels (n = 18). Traditional statistical methods found 6.5% (13 out of 247) significant protein spots, our GM approach yielded a total of 53 (22.5%) differentially expressed protein spots.     

Changes of the concentrations of chlorophyll and phaeopigment in grazing experiments

In grazing experiments, the changes in fluorometric determined concentrations of chlorophyll a and phaeopigment are probably less bothered by the interference of other chlorophyll pigments than in analysis of single seawater samples. Theoretically, phaeopigment recovery will be ca 100%, regardless the eventual presence of chlorophyllb. In shipboard experiments in the northern North Sea in May 1983 the chlorophyll consumption by zooplankton was compared with phaeophorbide egestion. Phaeophorbide recovery amounted on average to 67%, comparable with a previous estimate in laboratory experiments by SHUMAN & LORENZEN (1975). Because phaeophorbide concentrations are expressed in chlorophyll equivalents, one third of the chlorophyll consumed is apparently degraded further than phaeophorbide into non-fluorescent material. In grazing experiments withCalanus finmarchicus stages CIV, CV and CVI filtering rates were determined both with the chlorophyll method and with a particle counter. Values roughly doubled with stage and averages per stage did not differ systematically between both methods, suggesting that the natural algae food, dominated by the microflagellateCorymbellus aureus, was not preferred above other seston.     

Phytostabilization of a Pb-contaminated mine tailing by various tree species in pot and field trial experiments

The potential of 6 tree species (Leucaena leucocephala, Acacia mangium, Peltophorum pterocarpum, Pterocarpus macrocarpus, Lagerstroemia floribunda, Eucalyptus camaldulensis) for phytoremediation of Pb in sand tailings (total Pb >9850 mg kg(-1)) from KEMCO Pb mine in Kanchanaburi province, Thailand, were investigated employing a pot experiment (3 months) and field trial experiment (12 months). In pot study E. camaldulensis treated with Osmocote fertilizer attained the highest total biomass (15.3 g plant(-1)) followed by P. pterocarpum (12.6 g plant(-1)) and A. mangium (10.8 g plant(-1)) both treated with cow manure. Cow manure application resulted in the highest root Pb accumulation (>10000 mg kg(-1)) in L. floribunda and P. macrocarpus. These two species also exhibited the highest Pb uptake (85-88 mg plant(-1)). Results from field trial also showed that Osmocote promoted the best growth performance in E. camaldulensis (biomass 385.7 g plant(-1), height 141.7 cm) followed by A. mangium (biomass 215.9 g plant(-1), height 102.7 cm), and they also exhibited the highest Pb uptake (600-800 microg plant(-1)). A. mangium with the addition of organic fertilizer was the best option for phytostabilization of Pb-contaminated mine tailing because it retained higher Pb concentration in the roots.     

Three-dimensional bending,torsion and axial compression of the femoropopliteal artery during limb flexion

High failure rates of femoropopliteal artery reconstruction are commonly attributed to complex 3D arterial deformations that occur with limb movement. The purpose of this study was to develop a method for accurate assessment of these deformations. Custom-made stainless-steel markers were deployed into 5 in situ cadaveric femoropopliteal arteries using fluoroscopy. Thin-section CT images were acquired with each limb in the straight and acutely bent states. Image segmentation and 3D reconstruction allowed comparison of the relative locations of each intra-arterial marker position for determination of the artery’s bending, torsion and axial compression. After imaging, each artery was excised for histological analysis using Verhoeff–Van Gieson staining. Femoropopliteal arteries deformed non-uniformly with highly localized deformations in the proximal superficial femoral artery, and between the adductor hiatus and distal popliteal artery. The largest bending (11±3–6±1 mm radius of curvature), twisting (28±9–77±27°/cm) and axial compression (19±10–30±8%) were registered at the adductor hiatus and the below knee popliteal artery. These deformations were 3.7, 19 and 2.5 fold more severe than values currently reported in the literature. Histology demonstrated a distinct sub-adventitial layer of longitudinally oriented elastin fibers with intimal thickening in the segments with the largest deformations. This endovascular intra-arterial marker technique can quantify the non-uniform 3D deformations of the femoropopliteal artery during knee flexion without disturbing surrounding structures. We demonstrate that 3D arterial bending, torsion and compression in the flexed lower limb are highly localized and are substantially more severe than previously reported.     

Effects of various concentrations of erythropoietin on cultured erythroblast islands

Proliferative effects of increasing concentrations of erythropoietin were studied in vitro. The maximal amount of erythroblastic islands consisting of residual macrophages and erythroid cells was observed with the doses 0.5 to 1.5 ME/ml of erythropoietin. Smaller doses stimulated the reconstruction of erythroblastic islands.     

Photon transmission study on swelling of kappa-carrageenan gels prepared in various concentrations

κ-Carrageenan gels prepared with various carrageenan concentrations in pure water were completely dried and then swelled in pure water. Photon transmission measurements were performed using a UV-Vis (UVV) spectrometer during the swelling of κ-carrageenan gels. Transmitted photon intensity, I_tr, increased exponentially as swelling time is increased for all gel samples. The behaviour of I_tr was interpreted by Monte-Carlo Simulation. The increase in I_tr was quantified by employing Li-Tanaka equation, from which time constants τ₁ and collective diffusion coefficients, D_o were determined for the gels in various carrageenan concentrations. Gravimetric and volumetric measurements were also carried out during swelling of gels. It is observed that gel with high carrageenan content possess more double helices and more lattice dislocations and swell slower than gels with low carrageenan content which may contain less double helices and less lattice imperfections. Increase in I_tr was interpreted by the homogeneous distribution of double helices in the carrageenan gel system.     

Determination of concentrations of flecainide in human serum by high-performance liquid chromatography on a fluorocarbon-bonded silica gel column

An optimized method for the determination of flecainide in serum is presented. Extraction using a solid-phase C₁₈ column and chromatography on a stabilized fluorocarbon-bonded silica gel column effectively separate flecainide from an internal standard (a positional isomer of flecainide). The HPLC apparatus and conditions were as follows: analytical column, Fluofix 120N; sample solvent, 20 μl; column temperature, 40°C; detector, Shimadzu RF-5000 fluorescence spectrophotometer (excitation wavelength=300 nm, emission wavelength=370 nm); mobile phase, 0.06% phosphoric acid containing 0.1% tetra-n-butyl ammonium bromide–acetonitrile (75:25, v/v); flow-rate, 1.0 ml/min. The standard curves for flecainide were linear in the concentration range examined (10–2000 ng/ml). The regression equation was y=0.08+0.0078x (r=0.9998). The minimum detectable amount of flecainide was approximately 5 ng/ml. In the within-day study, the precision coefficients of variation were 2.66, 2.18, 2.54, 2.72, 2.88, 2.24, and 3.29% for the 10, 50, 100, 200, 500, 1000, and 1500 ng/ml standards, respectively. The absolute recovery rates of flecainide at each concentrations were 94–100%. The method described provides analytical sensitivity, specificity and reproducibility suitable for both biomedical research and therapeutic drug monitoring.     

Ubiquinone concentrations in Athiorhodaceae grown under various environmental conditions

1. The nature and concentration of ubiquinone in six species of Athiorhodaceae have been examined after growth under aerobic and photosynthetic conditions. 2. Increase in ubiquinone concentration during adaptive synthesis of photosynthetic pigments by Rhodopseudomonas spheroides incubated under low-aeration conditions was observed. 3. The nature of the carbon source was found to have a marked effect on ubiquinone, as well as bacteriochlorophyll, concentrations.     

Increased concentrations of various amino acids in schizophrenic patients

Summary The hypothesis is examined that heteroxygosity for amino acid disorders (AAD) is a genetic component of susceptibility for schizophrenic psychoses. To detect possible heterozygotes, urinary and blood amino acid levels were analyzed in a sample of subjects with a diagnosis of schizophrenia and in their biological parents and compared with those of a sample of healthy volunteers. The results showed increased blood and urinary levels of certain amino acid in those patients who have at least one parent with the same amino acid abnormality. This finding points to the possibility of heterozygosity for AAD in schizophrenic patients.     

Luteinizing hormone concentrations in anestrous ewes administered various estrogens

Twenty four anestrous ewes were evenly assigned to one of six groups and administered either sesame oil, estradiol-17β, estradiol-17α, estrone, estradiol benzoate or estradiol valerate. All estrogen treated ewes received 50 μg of the respective estrogen. Blood plasma was collected for 28 hours post-treatment and quantified for luteinizing hormone (LH) by radioimmunoassay. An estrogen induced LH surge was detected in at least three of the four ewes administered either estradiol-17β, estrone, estradiol benzoate or estradiol valerate whereas only one of the four estradiol-17α treated ewes and none of the ewes administered sesame oil had an LH surge. The interval from treatment to peak LH was similar for estradiol-17β (17.3±2.7 hours), estrone (18.5±1.0 hours) and estradiol benzoate (19.0±0.6 hours) treated ewes but delayed 7 to 9 hours for ewes administered estradiol valerate (26.0±1.2 hours).