Beta radiation excited thermoluminescence of solid-state synthesized SrZrO3 phosphors.

In this work, we report on the solid-state reaction synthesis of SrZrO3 phosphors, and their beta particle irradiation excited thermoluminescence (TL) characterization. X-ray diffraction data confirmed the obtention of the orthorhombic phase of SrZrO3. Through computational glow curve deconvolution, the whole glow curve was resolved into six individual first order kinetics peaks. This is the first report concerning the usefulness of SrZrO3 as TL dosimeter. The synthesized phosphors exhibit TL emission from below 100 °C up to above 300 °C, being the most intense TL between 200 and 300 °C, as well as a remarkable reproducibility of the TL response in repeated irradiation-TL readout cycles.

Beta radiation excited thermoluminescence of SrB4O7 phosphors synthesized through solid state reaction.

In this work, the synthesis of SrB4O7 through solid state reaction and its beta particle excited thermoluminescence (TL) are reported. The glow curves show maxima around 200 and 300 -considered suitable for TL dosimetry-, and a remarkable reproducibility in successive irradiation - TL readout cycles. The integrated TL exhibits a linear dependence upon the irradiation dose in the tested dose range (from 1.0 up to 8.0 Gy). The lower detection limit and the sensitivity relative to the TLD-100 dosimeter are 88 mGy and 0.49, respectively. From the results here presented, we conclude that SrB4O7 synthesized through solid state reaction can be considered a phosphor material interesting to develop TL dosimeters.

Optically stimulated luminescence dosimetry performance of novel MgO-La(OH)3 phosphors.

The aim of this work was to study the optically stimulated luminescence (OSL) properties of novel MgO co-doped with different lanthanides and lithium ions as well as to evaluate the feasibility of using the mentioned phosphors as OSL dosimeters. In this context, the OSL efficiency corresponding to different stimulation wavelengths and different filters was analyzed for all the samples. The properties of the most efficient material, namely, MgO-La(OH)3, were further studied. Moreover, the repeatability and linearity of the OSL response, the fading of the OSL signal and the minimum detectable dose were investigated. Finally, feasibility of using these compounds in OSL dosimetry was assessed.

Synthesis and thermoluminescence characterization of self-agglomerating CaSO4 exposed to beta radiation.

The synthesis and thermoluminescence (TL) characterization of self-agglomerating pellet-shaped CaSO4 phosphors, through a low cost and environmentally friendly method is reported. In order to investigate their TL features, some samples were exposed to beta particle irradiation in the dose range from 0.07 to 10 Gy. Characteristic TL glow curve consists of a single main maximum located at 216 °C, which is considered stable, hence, suitable for dosimetry applications. The dose-response was remarkable linear. Moreover, the lower detection limit was determined to be 6.0 µGy, and the relative TL sensitivity twice the one from the commercial TLD-100 dosimeter.

Effects of intervertebral disk degeneration on the flexibility of the human thoracolumbar spine.

The objective of this study was to investigate the effects of intervertebral disk degeneration on the flexibility of the thoracolumbar spine in flexion and extension, both experimentally and computationally. A seven-level biomechanically tested human cadaveric spine (T11-L5) and a 3D finite element model of the same thoracolumbar spine were used for this purpose. The anatomically accurate computer model was generated from detailed computed tomography images and included the vertebral shell, the trabecular centrum, cartilage endplates, intervertebral disks, seven spinal ligament groups, and the facet joints. The cadaveric spinal segment and the specimen-specific finite element model were subjected to various compressive loads ranging from 75 to 975 N using the follower load principle and an oscillating bending moment of +/-5 Nm applied in the sagittal plane. The biomechanical behavior of the finite element model of the spine was validated with the experimental mechanical test data for the corresponding physical thoracolumbar spine specimen. In addition, the effect of intervertebral disk material property variation within the thoracolumbar spinal column on the spinal flexibility was extensively studied. The results of this study provided significant insight into how mechanical properties of the intervertebral disk influence spinal flexibility along the thoracolumbar spinal column. It was found that in order to get comparable results between experimental and computed data, the material properties of the intervertebral disks had to vary along the spinal column. However, these effects are diminished with increasing axial compressive load. Because of the trend between disk properties and spinal level, we further concluded that there might be a mechanism at play that links endplate size, body weight fraction, and segmental flexibility. More studies are needed to further investigate that relationship.

Endothelial cell response to biomechanical forces under simulated vascular loading conditions.

In vivo, endothelial cells (EC) are constantly exposed to the haemodynamic forces (HF) of pressure, wall shear stress and hoop stress. The main aim of this study was to design, create and validate a novel perfusion bioreactor capable of delivering shear stress and intravascular pressure to EC in vitro and to characterise their morphology, orientation and gene expression. Here we report the creation and validation of such a simulator and the dual application of pressure (120/60 mmHg) and low shear stress (5 dyn/cm(2)) to a monolayer of EC established on a non-compliant silicone tube. Under these conditions, EC elongated and realigned obliquely to the direction of applied shear stress in a time-dependent manner. Furthermore, randomly distributed F-actin microfilaments reorganised into long, dense stress fibres crossing the cells in a direction perpendicular to that of flow. Finally, combinatorial biomechanical conditioning of EC induced the expression of the inflammatory-associated E-selectin gene.

Evaluation of Cartilage Repair by Mesenchymal Stem Cells Seeded on a PEOT/PBT Scaffold in an Osteochondral Defect.

The main objective of this study was to evaluate the effectiveness of a mesenchymal stem cell (MSC)-seeded polyethylene-oxide-terephthalate/polybutylene-terephthalate (PEOT/PBT) scaffold for cartilage tissue repair in an osteochondral defect using a rabbit model. Material characterisation using scanning electron microscopy indicated that the scaffold had a 3D architecture characteristic of the additive manufacturing fabrication method, with a strut diameter of 296 ± 52 µm and a pore size of 512 ± 22 µm × 476 ± 25 µm × 180 ± 30 µm. In vitro optimisation revealed that the scaffold did not generate an adverse cell response, optimal cell loading conditions were achieved using 50 µg/ml fibronectin and a cell seeding density of 25 × 10(6) cells/ml and glycosaminoglycan (GAG) accumulation after 28 days culture in the presence of TGFß3 indicated positive chondrogenesis. Cell-seeded scaffolds were implanted in osteochondral defects for 12 weeks, with cell-free scaffolds and empty defects employed as controls. On examination of toluidine blue staining for chondrogenesis and GAG accumulation, both the empty defect and the cell-seeded scaffold appeared to promote repair. However, the empty defect and the cell-free scaffold stained positive for collagen type I or fibrocartilage, while the cell-seeded scaffold stained positive for collagen type II indicative of hyaline cartilage and was statistically better than the cell-free scaffold in the blinded histological evaluation. In summary, MSCs in combination with a 3D PEOT/PBT scaffold created a reparative environment for cartilage repair.

Generation of a finite element model of the thoracolumbar spine.

The goal of this study was to generate a realistic 3D FE model of the seven level thoracolumbar spine. This research focused on the development of a robust and efficient procedure for generating anatomical 3D FE models, directly from a series of medical images, i.e., CT data. A complex model of the spine was created by combining two different modelling approaches, namely the CAD and STL-CAD methods. In addition, the entire meshing procedure for the vertebrae was significantly speeded up by combining 3D tetrahedral elements with brick elements, relative to conventional mapped mesh generation procedures. The resulting model generation method allowed for flexibility in element choice and in element type combinations. The model was subjected to various compressive loads to asses the overall behaviour of the spine. This case study was performed to illustrate the usefulness of the FE model. In the authors' opinion, the model presented is an important tool in computational spine research as it can provide general information on spinal behaviour under various loading conditions whether healthy, diseased or damaged.

Characterisation of a collagen membrane for its potential use in cardiovascular tissue engineering applications.

In this study, Biomend, a collagen membrane conventionally used in the regeneration of periodontal tissue, is investigated for its possible use in the field of cardiovascular tissue engineering. A key requirement of most potential tissue engineering scaffolds is that degradation occurs in tandem with tissue regeneration and extra cellular matrix remodelling. To this end, it is crucial to understand the degradation mechanics and mechanisms of the material and to investigate the practicability of using Biomend as a possible scaffold material. With this in mind, methodologies for the initial characterisation of the scaffold material were determined. The mechanical properties of Biomend samples, subjected to various degrees of hydration and enzymatic degradation, were examined primarily through tensile testing experiments. The effects of enzymatic degradation were monitored quantitatively, by observing weight loss, and visually, by studying micrographs. Cell adhesion and viability were of primary concern. Confocal laser scanning microscopy was employed to illustrate endothelialisation on the surface of this collagen membrane. Fluorescence microscopy was used to visualise cell viability on the membrane surface. These images, coupled with assays to measure cell activity, suggest that Biomend is not a suitable substrate to allow endothelialisation. In summary, this collagen membrane has suitable mechanical properties with the potential to control its degradation rate. However, since poor endothelial cell viability was observed on the membrane, it may not be suitable for use in cardiovascular tissue engineering applications.

Biomodels of bone: a review.

In this paper, a definition of a biomodel is presented, based on which different specific types of biomodels are identified, viz., virtual biomodels, computational biomodels, and physical biomodels. The paper then focuses on both physical and virtual biomodels of bone, and presents a review of model generation methodologies, giving examples of typical biomodel applications. The use of macroscale biomodels for such issues as the design and preclinical testing of surgical implants and preoperative planning is discussed. At the microscale, biomodels of trabecular bone are examined and the link with scaffolds for tissue engineering is established. Conclusions are drawn on the state of the art, and the major developments necessary for the continued expansion of the field are identified. Finally, arguments are given on the benefits of integrating the use of the different types of biomodels reviewed in this paper, for the benefit of future research in biomechanics and biomaterials.

Texaco mortality study: III. A cohort study of producing and pipeline workers.

While there have been numerous epidemiology studies of refinery workers, no studies have been done on producing and pipeline workers. This is a retrospective follow-up study of all persons who were employed for at least 6 months at a Texaco producing or pipeline location and who worked at some time during the period 1946-1980. Of the 11,098 white men in the cohort, 8,964 were alive, 1,886 were known to be dead, and the vital status of the remaining 248 as of December 31, 1980 was unknown. The standardized mortality ratio (SMR) of 63 for all causes was significantly low, on the basis of 2,976 expected deaths. Statistically significant deficits also were seen for all major causes of death. Mortality patterns were also examined for the major job categories in these departments. Similar patterns of mortality were seen, although there was a significant excess of thyroid cancer in those employed as pumper-gaugers. However, it was based on only four cases.

Texaco Mortality Study: II. Patterns of mortality among white males by specific job groups.

While an earlier report on the Texaco Mortality Study cohort showed no statistically significant elevations for any cause of death for the white males, it did not preclude any excess risk of mortality within subgroups of workers. In this study, an employee's complete job history was used to determine his work categories, and patterns of mortality were examined for the more common job categories. All of the job categories examined showed deficits for mortality overall, and the patterns seen were similar to those for the entire cohort. Significant elevations were seen in pancreas cancer mortality for office and managerial people and in leukemia mortality for pipefitters and boilermakers. Other elevations of particular interest based on five or more deaths were brain cancer for laboratory workers and benign neoplasms in pipefitters and boilermakers. These associations were examined by latency and years worked, and no consistently positive associations were seen. It was not possible to take into account calendar time of exposure in this type of analysis, nor could any specific chemicals or levels of exposure be associated with the job categories where the standardized mortality ratios were elevated.

Reversible encephalopathy possibly associated with bismuth subgallate ingestion.

Four patients who had undergone abdominoperineal resection for carcinoma of the colon and who had been taking oral bismuth subgallate developed a stereotyped recurrent and reversible neurological syndrome. This was characterized by confusion, tremulousness, clumsiness, myoclonic jerks, and an inability to walk. All patients were extensively investigated and no cause could be found, but symptoms regressed when the intake of bismuth was stopped. Postmortem examination in one patient failed to show any appreciable abnormality apart from a loss of Purkinje cells in the cerebellum. In the other three patients amino-acid chromatography performed on urine showed the presence of an abnormal unidentified constituent. It is thought that these four patients developed an encephalopathy associated with their bismuth subgallate ingestion.

Texaco mortality study. I. Mortality among refinery, petrochemical, and research workers.

The Texaco mortality study is a retrospective follow-up study of all persons who were employed for at least five years in a refining, petrochemical, or research facility and who worked at some time during the period 1947 through 1977. Of the 19,077 white men in the cohort, 14,609 were alive, 4,024 were known to be dead, and the vital status of the remaining 444 was unknown as of Dec. 31, 1977. The standardized mortality ratio (SMR) of 75 for all causes was significantly low, on the basis of 5,332 expected deaths. Statistically significant deficits also were seen for all major causes of death and for cancer of many sites, including lung, stomach, bladder, and colon. The SMR was greater than 100 for six causes of death: pancreas cancer, brain cancer, leukemia, Hodgkin's disease, other lymphatic cancer, and benign neoplasms. However, none of these increases was statistically significant, and all SMRs except that for benign neoplasms (SMR = 148) were under 119.

Endothelial cell alignment on cyclically-stretched silicone surfaces.

Endothelial cells at the interface between the bloodstream and the vessel wall are continuously subjected to mechanical stimulation in vivo, and it widely recognised that such stimulation plays an important role in cardiovascular physiology. Cell deformation is induced by mechanical forces such as cyclic stretch, fluid shear stress, and transmural pressure. Although much of the work in this field has dealt with the effect of fluid shear stress, very little is known about how cyclic forces modulate and alter the morphology of single endothelial cells, and thereafter, how they effect the confluent layer of endothelial cells lining the vessel wall. The aim of this study is to investigate the response of endothelial cells when subjected to substrate deformation of similar magnitude to those experienced in vivo. Human umbilical vein endothelial cells (HUVEC) were cultured on plasma-treated silicone strips and uni-axially cyclically stretched using a custom made mechanical device. Results showed that endothelial cells subject to 10% deformation for as little as 4 h reoriented perpendicular to the stretch direction. In addition, although no integrin coating was applied to the substrate, it was found that plasma-treated silicone provided a cell adhesion substrate comparable to the commonly used collagen type I. Thus the results show that the stretch stimulus alone affects the morphology of endothelial cells. Further studies are required to establish the relative importance of substrate strain vs. fluid flow stimuli.

Bioreactors for cardiovascular cell and tissue growth: a review.

Heart disease is a major cause of death in the Western world. In the past three decades there has been a number of improvements in artificial devices and surgical techniques for cardiovascular disease; however, there is still a need for novel devices, especially for those individuals who cannot receive conventional therapy. The major disadvantage of current artificial devices lies in the fact that they cannot grow, remodel, or repair in vivo. Tissue engineering offers the possibility of developing a biological substitute material in vitro with the inherent mechanical, chemical, biological, and morphological properties required in vivo, on an individual patient basis. In order to develop a true biological cardiovascular device a dynamic physiological environment needs to be created. One approach that employs the use of a simulated biological environment is a bioreactor in which the in vivo biomechanical and biochemical conditions are created in vitro for functional tissue development. A review of the current state of the art bioreactors for the generation of tissue engineered cardiovascular devices is presented in this study. The effect of the simulated physiological environment of the bioreactor on tissue development is examined with respect to the materials properties of vascular grafts, heart valves, and cardiac muscles developed in these bioreactors.

Aptitudes, opiniones y tendencias de los medicos residentes de Pediatria en Hospitales de tercer nivel del MPS y SP 1992 Santa Cruz / Aptitudes, opinions and tendences of Pediatric residents at the third level hospitals at Santa Cruz

Se realiza una encuesta a 18 residentes de Pediatria en dos hospitales de tercer nivel del sistema, investigando sus actitudes, opiniones y tendencias; las misma que muestran un grado de insatisfaccion en el 66 por ciento con ausencia de interes de los medicos de planta hacia los residentes, falta de programas y material didactico y ademas de otros problemas. Sus relaciones de trabajo son aparentemente buenas en las mayorias de los casos, aunque tambien se reporta un porcenatje menor con ausencia de relacion entre el personal del hospital. La calidad de atencion y la calidad de ensenanza de servicios nos muestra diferencia importante, senalando sin embargo que la practica medica, predominatemente en los hospitales es estimulante, humanitaria de alta calidad y progresista. Asi mismo la calidad de atencion no se deja influir con la parte economica e influencia personal.