A stability study of an opacity standard

Three procedures were adopted to increase the stability of the Chinese National Opacity Standard so that the change in opacity was within a range of +/- 5%.     

Relative Frequency Distribution of D125 C Values for Spore Isolates from the Mariner-Mars 1969 Spacecraft

Bacterial spore crops were prepared from 103 randomly selected aerobic mesophilic isolates collected during a spore assay of Mariner-Mars 1969 spacecraft conducted by the Jet Propulsion Laboratory. D_{125 c} values, which were determined by the fractional-replicate-unit-negative-most-probable number assay method using a forced air oven, ranged from less than 5 min to a maximum of 58 min. Subsequent identification of the 103 isolates indicated that there was no relationship between species and dry-heat resistance. A theoretical dry-heat survival curve of the “population” was nonlinear. The slope of this curve was determined almost exclusively by the more resistant organisms, although they represented only a small portion of the “population.”     

Relative frequency distribution of d(125 C) values for spore isolates from the mariner-Mars 1969 spacecraft

Bacterial spore crops were prepared from 103 randomly selected aerobic mesophilic isolates collected during a spore assay of Mariner-Mars 1969 spacecraft conducted by the Jet Propulsion Laboratory. D_{125 c} values, which were determined by the fractional-replicate-unit-negative-most-probable number assay method using a forced air oven, ranged from less than 5 min to a maximum of 58 min. Subsequent identification of the 103 isolates indicated that there was no relationship between species and dry-heat resistance. A theoretical dry-heat survival curve of the “population” was nonlinear. The slope of this curve was determined almost exclusively by the more resistant organisms, although they represented only a small portion of the “population.”     

An in vivo method for measuring the adsorption of plasma proteins to titanium in humans

A novel method of collecting in vivo plasma proteins of humans from osteotomies prepared during insertion of an oral implant is described. A rod containing a collecting portion with a predetermined surface is introduced into the osteomy, removed, and transferred for enzyme-linked immunosorbent assay analysis. Two experiments were used to examine the feasibility of the method. In the first, titanium (Ti) rods with different roughness were exposed for 10 min to the blood. Blasted and acid-etched surfaces adsorbed four times more and acid-etched surfaces adosorbed two times more plasma proteins as compared to machined surfaces. In the second experiment, blasted and acid-etched rods were wetted for 10 s prior to the insertion. The adsorption for fibronectin, albumin, fibrinogen, and IgG was enhanced significantly compared with nonwetted rods. These results are discussed in the light of previous methods used in studies on adsorption. Thus, use of the collecting instrument enables aspects of human plasma–implant interface to be studied in a more realistic manner.     

Cyclic GMP diffusion coefficient in rod photoreceptor outer segments.

Cyclic GMP (cGMP) is the intracellular messenger that mediates phototransduction in retinal rods. As photoisomerizations of rhodopsin molecules are local events, the longitudinal diffusion of cGMP in the rod outer segment should be a contributing factor to the response of the cell to light. We have employed the truncated rod outer segment preparation from bullfrog (Rana catesbeiana) and tiger salamander (Ambystoma tigrinum) to measure the cGMP diffusion coefficient. In this preparation, the distal portion of a rod outer segment was drawn into a suction pipette for measuring membrane current, and the rest of the cell was then sheared off with a glass probe, allowing bath cGMP to diffuse into the outer segment and activate the cGMP-gated channels on the surface membrane. Addition and removal of bath cGMP were fast enough to produce effectively step changes in cGMP concentration at the open end of the outer segment. When cGMP hydrolysis is inhibited by isobutylmethylxanthine (IBMX), the equation for the diffusion of cGMP inside the truncated rod outer segment has a simple analytical solution, which we have used to analyze the rise and decay kinetics of the cGMP-elicited currents. From these measurements we have obtained a cGMP diffusion coefficient of approximately 70 x 10(-8) cm2 s-1 for bullfrog rods and approximately 60 x 10(-8) cm2 s-1 for tiger salamander rods. These values are six to seven times lower than the expected value in aqueous solution. The estimated diffusion coefficient is the same at high (20-1000 microM) and low (5-10 microM) concentrations of cGMP, suggesting no significant effect from buffering over these concentration ranges.     

Cell elongation and septation are two mutually exclusive processes in Escherichia coli

Bacterial rod morphogenesis was studied in synchronously growing cells of Escherichia coli C600 during the reshaping process that follows the removal of mecillinam, a β-lactam antibiotic that specifically inhibits lateral wall formation of gram-negative rods and causes transition to coccal shape. Removal of mecillinam after 30 min of action did not affect the timing of subsequent cell division, but removal after 50 min delayed resumption of cell division for approximately one generation time. In order to study the interplay between lateral wall elongation and septum formation in determining and maintaining the bacterial rod shape, we evaluated the effect of re-adding mecillinam or of adding aztreonam (a specific inhibitor of septum formation) at various stages of the reshaping process. We conclude that mecillinam was active only during the reshaping process, while aztreonam was active only later when the cells were close to dividing again. These results provide further evidence for our previous proposal according to which elongation and septation are two alternating and competing events of the cell cycle and are linked to each other to force bacterial rods to grow to a given length. Received: 23 January 1997 / Accepted: 2 May 1997     

Dry-heat resistance of bacterial spores recovered from mariner-Mars 1969 spacecraft

The dry-heat resistances of 70 bacterial spore isolates recovered from Mariner-Mars 1969 spacecraft were determined and expressed as D values (decimal reduction times). Fifty per cent of the spore isolates had D values of 60 min or less at 125 C. Of organisms with D values greater than 60 min, four were selected for a study of the effect of sporulation medium and suspension menstruum on dry-heat resistance. Both sporulation medium and suspension menstruum were found to affect significantly the dry-heat resistance of the bacterial spores tested.     

Protection of human induced pluripotent stem cells against shear stress in suspension culture by Bingham plastic fluid

Suspension culture is an important method used in the industrial preparation of pluripotent stem cells (PSCs), for regenerative therapy and drug screening. Generally, a suspension culture requires agitation to keep PSC aggregates suspended and to promote mass transfer, but agitation also causes cell damage. In this study, we investigated the use of a Bingham plastic fluid, supplemented with a polysaccharide-based polymer, to preserve PSCs from cell damage in suspension culture. Rheometric analysis showed that the culture medium gained yield stress and became a Bingham plastic fluid, after supplementation with the polymer FP003. A growth/death analysis revealed that 2 days of aggregate formation and 2 days of suspension in the Bingham plastic medium improved cell growth and prevented cell death. After the initial aggregation step, whereas strong agitation (120 rpm) of a conventional culture medium resulted in massive cell death, in the Bingham plastic fluid we obtained the same growth as the normal culture with optimal agitation (90 rpm). This indicates that Bingham plastic fluid protected cells from shear stress in suspension culture and could be used to enhance their robustness when developing a large-scale.     

The LSP test for determining oscillation resistance of spinal implants]

QUESTION: New spinal implants need to be tested for primary stability in vitro under standardized laboratory conditions. To ensure the reliability of the test procedures, quality assurance standards in accordance with ISO 9000 were introduced to standardize testing including experimental set ups, loading and test frequency. These standards, however, require a relatively long time to implement. METHOD: The LSP test was used to compare various surface treatments by different shot peening processes applied to spinal rods for dorsal spine implant systems. 6 rods made of two different cp-Titanium materials (Ti-2 and Ti-4) were tested. Dynamic tests were performed with the MTS 810 mono-axial servo-hydraulic test equipment. Beginning with a load of 200 N the rods were subjected to tensile and compressive loads, which were increased in steps of 100 N after every 50.000 cycles until rod failure. RESULTS: Results were available after one to two weeks. The best results (LSP 167 million) were achieved with Ti-4 rods shot peened with steel balls and glass beads. In comparison, the lowest LSP value of 81 million was found with Ti-2 rods shot peened with glass beads only. CONCLUSION: This high speed testing method has reduced the development time from two years to 6 months.     

The International Standard for Endotoxin: evaluation in an international collaborative study

An ampouled preparation of bacterial endotoxin, coded 84/650, was evaluated in 35 laboratories in 12 countries for its suitability to serve as the International Standard for Endotoxin. The ampouled preparation was calibrated in terms of the USA National Standard, EC5, in Limulus Amoebocyte Lysate gelation, turbidimetric and chromogenic tests and in rabbit pyrogen tests. On the basis of the results reported here, with the agreement of the participants in the study, and with the authorization of the Expert Committee on Biological Standardization of the World Health Organization, the preparation coded 84/650 was established in 1986 as the International Standard for Endotoxin for Limulus Gelation Tests with an assigned unitage of 14,000 IU of endotoxin per ampoule.     

Titanium as an implant material for rods of transpedicular instrumentation of the lumbar spine]

BACKGROUND AND AIM: Titanium alloys are increasingly being used as an implant material in orthopaedics and for spinal instrumentation. In this study a metallographic analysis and mechanical testing were performed to evaluate the resistance of rods of Ti-A16-V4 in particular to tensile forces. METHOD: The surface texture of unprepared Ti-A16-V4 and a rod of the same material for spinal instrumentation were evaluated in a metallographic analysis using light microscopy and electron microscopy. Tensile strength measurements were performed on 2 rods, and the strength of the connection between rod and pedicle screws was tested in 9 cases. An electron microscopic analysis of surface changes of the connections between rod and pedicle screws after loading was performed. RESULTS: The titanium alloy Ti-A16-V4 has a mill-annealed appearance, which has a high resistance to tearing under stress. Titanium rods show high tensile strength before failure under loading. The connection between rod and pedicle screws also as high resistance to tensile loads (> 27 kN) with only little deformation of the connecting surface and no tearing. CONCLUSION: The titanium alloy Ti-A16-V4 is an appropriate material for dorsal spinal instrumentation rods because of its low weight, high biocompability and high tensile strength.     

The eel retina. Receptor classes and spectral mechanisms

Light and electron microscopy revealed that there are both rods and cones in the retina of the eel Anguilla rostrata. The rods predominate with a rod to cone ratio of 150:1. The spectral sensitivity of the dark-adapted eyecup ERG had a peak at about 520 nm and was well fit by a vitamin A2 nomogram pigment with a lambdamax = 520 nm. This agrees with the eel photopigment measurements of other investigators. This result implies that a single spectral mechanism--the rods--provides the input for the dark-adapted ERG. The spectral sensitivity of the ERG to flicker in the light-adapted eyecup preparation was shifted to longer wavelengths; it peaked at around 550 nm. However, there was evidence that this technique might not have completely eliminated rod intrusion. Rod responses were abolished in a bleached isolated retina preparation, in which it was shown that there were two classes of cone-like mechanisms, one with lambdamax of 550 nm and the other with lambdamax of less than 450 nm. Ganglion cell recording provided preliminary evidence for opponent-color processing. Horizontal cells were only of the L type with both rod and cone inputs.     

A Genetically Encoded Reporter for Real-Time Imaging of Cofilin-Actin Rods in Living Neurons

Filament bundles (rods) of cofilin and actin (1:1) form in neurites of stressed neurons where they inhibit synaptic function. Live-cell imaging of rod formation is hampered by the fact that overexpression of a chimera of wild type cofilin with a fluorescent protein causes formation of spontaneous and persistent rods, which is exacerbated by the photostress of imaging. The study of rod induction in living cells calls for a rod reporter that does not cause spontaneous rods. From a study in which single cofilin surface residues were mutated, we identified a mutant, cofilinR21Q, which when fused with monomeric Red Fluorescent Protein (mRFP) and expressed several fold above endogenous cofilin, does not induce spontaneous rods even during the photostress of imaging. CofilinR21Q-mRFP only incorporates into rods when they form from endogenous proteins in stressed cells. In neurons, cofilinR21Q-mRFP reports on rods formed from endogenous cofilin and induced by all modes tested thus far. Rods have a half-life of 30–60 min upon removal of the inducer. Vesicle transport in neurites is arrested upon treatments that form rods and recovers as rods disappear. CofilinR21Q-mRFP is a genetically encoded rod reporter that is useful in live cell imaging studies of induced rod formation, including rod dynamics, and kinetics of rod elimination.     

Transducin GTPase provides for rapid quenching of the cGMP cascade in rod outer segments

The role of transducin GTPase in rapid cGMP phosphodiesterase quenching was studied by simultaneous registration of GTP hydrolysis and phosphodiesterase activity in the same rod outer segments (ROS) preparation. The results thus obtained allow the conclusion that: (i) phosphodiesterase quenching coincides with transducin-bound GTP hydrolysis independently of ROS concentration; (ii) an increase in the ROS concentration results in the acceleration of cascade quenching due to the existence of a GTPase accelerating mechanism in ROS; (iii) approximation to physiological conditions (protein concentration, temperature) provides a transducin GTPase rate equal to 1–2 turnovers per second i.e., sufficiently high for satisfying the real rate of photoresponse reversion in dark-adapted rods.     

Separation of Epoxy-Embedded Cell Cultures from Plastic Flasks for Electron Microscopy

Monolayers of cells grown in ordinary plastic flasks are fixed and embedded “in situ” into Epon. When polymerized at 40 C for 4 days instead of the usual 60 C., the Epon sheet containing the cells is easily detached from the bottom of the plastic container. The Epon sheet is observed by light microscopy as a histological preparation. Ultrathin sectioning of preselected areas can then be carried out in a horizontal plane.     

Biomechanical assessment of a PEEK rod system for semi-rigid fixation of lumbar fusion constructs

The concept of semi-rigid fixation (SRF) has driven the development of spinal implants that utilize nonmetallic materials and novel rod geometries in an effort to promote fusion via a balance of stability, intra- and inter-level load sharing, and durability. The purpose of this study was to characterize the mechanical and biomechanical properties of a pedicle screw-based polyetheretherketone (PEEK) SRF system for the lumbar spine to compare its kinematic, structural, and durability performance profile against that of traditional lumbar fusion systems. Performance of the SRF system was characterized using a validated spectrum of experimental, computational, and in vitro testing. Finite element models were first used to optimize the size and shape of the polymeric rods and bound their performance parameters. Subsequently, benchtop tests determined the static and dynamic performance threshold of PEEK rods in relevant loading modes (flexion-extension (F/E), axial rotation (AR), and lateral bending (LB)). Numerical analyses evaluated the amount of anteroposterior column load sharing provided by both metallic and PEEK rods. Finally, a cadaveric spine simulator was used to determine the level of stability that PEEK rods provide. Under physiological loading conditions, a 6.35 mm nominal diameter oval PEEK rod construct unloads the bone-screw interface and increases anterior column load (approx. 75% anterior, 25% posterior) when compared to titanium (Ti) rod constructs. The PEEK construct's stiffness demonstrated a value lower than that of all the metallic rod systems, regardless of diameter or metallic composition (78%??80% reduction in F/E, p??70% reduction in LB, p??54% reduction in AR, p?相似文献   

A simple method for in vivo measurement of implant rod three-dimensional geometry during scoliosis surgery

Scoliosis is defined as a spinal pathology characterized as a three-dimensional deformity of the spine combined with vertebral rotation. Treatment for severe scoliosis is achieved when the scoliotic spine is surgically corrected and fixed using implanted rods and screws. Several studies performed biomechanical modeling and corrective forces measurements of scoliosis correction. These studies were able to predict the clinical outcome and measured the corrective forces acting on screws, however, they were not able to measure the intraoperative three-dimensional geometry of the spinal rod. In effect, the results of biomechanical modeling might not be so realistic and the corrective forces during the surgical correction procedure were intra-operatively difficult to measure. Projective geometry has been shown to be successful in the reconstruction of a three-dimensional structure using a series of images obtained from different views. In this study, we propose a new method to measure the three-dimensional geometry of an implant rod using two cameras. The reconstruction method requires only a few parameters, the included angle θ between the two cameras, the actual length of the rod in mm, and the location of points for curve fitting. The implant rod utilized in spine surgery was used to evaluate the accuracy of the current method. The three-dimensional geometry of the rod was measured from the image obtained by a scanner and compared to the proposed method using two cameras. The mean error in the reconstruction measurements ranged from 0.32 to 0.45 mm. The method presented here demonstrated the possibility of intra-operatively measuring the three-dimensional geometry of spinal rod. The proposed method could be used in surgical procedures to better understand the biomechanics of scoliosis correction through real-time measurement of three-dimensional implant rod geometry in vivo.     

Nonlinear signal transfer from mouse rods to bipolar cells and implications for visual sensitivity

We investigated the impact of rod-bipolar signal transfer on visual sensitivity. Two observations indicate that rod-rod bipolar signal transfer is nonlinear. First, responses of rods increased linearly with flash strength, while those of rod bipolars increased supralinearly. Second, fluctuations in the responses of rod bipolars were larger than expected from linear summation of the rod inputs. Rod-OFF bipolar signal transfer did not share this strong nonlinearity. Surprisingly, nonlinear rod-rod bipolar signal transfer eliminated many of the rod's single-photon responses. The impact on sensitivity, however, was more than compensated for by rejection of noise from rods that did not absorb photons. As a consequence, rod bipolars provide a near-optimal readout of rod signals at light levels near visual threshold.     

The preparation and characterization of chitosan rods modified with Fe3+ by a chelation mechanism

Chitosan composite rods (CS-Fe(3+)) were prepared via an in situ precipitation method. The relationships among the preparation, structures, and properties of the CS-Fe(3+) composite rods have been investigated. The results of Fourier-transform infrared spectroscopy (FTIR) and core electron X-ray photoelectron spectroscopy (XPS) indicate that the CS and Fe(3+) are coordinated via a chelation mechanism. The content of Fe(3+) in the complex was determined by atomic absorption spectrometry (AAS) and elemental analysis (EA), the results of which suggested that the content of Fe(3+) in the complex can be controlled by the concentration of the ferric salts during coordination. The changes in thermal stability and crystallization properties were measured by thermogravimetric analysis (TGA) and X-ray diffraction (XRD) patterns, respectively. Scanning electron microscopy (SEM) was used to observe the morphological change of the CS-Fe(3+) complex rod. After coordination with Fe(3+), the CS rod had a denser, layered structure. However, the layered structure cannot remain intact when the ratios of -NH(2)/Fe(3+) are 100/15 and 100/20. Moreover, its thermal stability decreased, and its bending strength was improved significantly (from 86 MPa to more than 210 MPa), despite the remarkable decrease in the degree of crystallinity.