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Abstract: Poly(l-lactide) (PLLA) has actively been used as a biomaterial for resorbable bone fixation devices for use in orthopedic and oral surgeries. Recently, in order to improve the fracture properties of brittle PLLA, polymer blends of PLLA and a ductile bioabsorbable polymer, poly(ε-caprolactone) (PCL), have been developed. The aim of the present study is to elucidate details of the fracture behavior and toughening mechanisms of PLLA/PCL blends. PLLA/PCL blends with different PCL contents were developed, and the critical energy release rate at crack initiation, G in, was then measured to assess the effect of PCL content. It was shown that G in is dramatically improved by blending PCL with PLLA, and the maximum 51% of increase of G in is acheived with 5wt% of PCL. Polarizing optical microscopy (POM) and scanning electron microscopy (SEM) of crack growth behavior were also performed to characterize the fracture mechanism. PLLA/PCL showed multiple craze formation in the crack-tip region, and elongated fibrils and voids construct the crazes. SEM of fracture surface also indicated that stretched fibril structures are formed on the surface as a result of elongation of PCL spherulites under high tensile stress condition in the crack-tip region. Thus, these damage formations are considered to be the primary energy dissipation mechanisms that resulted in the improvement of fracture energy. [Copyright &y& Elsevier]

Objective: We previously showed that in asphyxiated fetal lambs the duration of hypotension correlated well with the severity of histologic damage to the brain, whereas the duration of bradycardia did not. This study compares fetal heart rate patterns with the degree of histologic damage to the brain.Study Design: Twelve chronically instrumented near-term fetal lambs were subjected to asphyxia by umbilical cord occlusion until fetal arterial pH was <6. 9 and base excess was <-20 mEq/L. An additional 4 fetuses served as sham-asphyxia controls. Fetal heart rate (from electrocardiogram), arterial blood pressure, fetal breathing movements, and electrocorticogram were continuously monitored before, during, and for 72 hours after asphyxia. Fetal brain histologic features were categorized as mild (group 1, n = 5), moderate (group 2, n = 4), and severe (group 3, n = 3). Long-term fetal heart rate variability expressed as amplitude range was assessed visually every 5 minutes from 30 minutes before asphyxia until 2 hours of recovery and at 6, 12, 24, 48, and 72 hours of recovery.Results: Long-term fetal heart rate variability amplitude decreased from 32 +/- 17 beats/min (mean +/- SEM) preocclusion to 4 +/- 13 beats/min at the end of occlusion (P <.001) without significant differences among the 3 groups. During 10 to 45 minutes of recovery, the long-term variability of group 1 was significantly greater than that of groups 2 and 3. At 24 to 72 hours of recovery, the long-term variability of groups 1 and 2 was significantly higher than that of group 3, which was almost 0. The "checkmark" and sinusoidal fetal heart rate patterns were observed during the recovery period in groups 2 and 3.Conclusions: Decreased long-term fetal heart rate variability and the "checkmark" and sinusoidal fetal heart rate patterns were indicators of the severity of asphyxial histologic damage in the fetal brain. [ABSTRACT FROM AUTHOR]

Objectives: The purpose of this study was to explain the role of oxidative stress in the pathogenesis of brain damage caused by intrauterine fetal asphyxia.Study Design: Six chronically instrumented near-term fetal lambs were subjected to asphyxia by partial umbilical cord occlusion for approximately 60 minutes until fetal arterial pH diminished to less than 6.9 and base excess to less than -20 mEq. Another six fetuses surgically prepared but not occluded were used as control. Fetuses were killed after 72 hours and eight different brain regions (frontal and parietal gray matter, frontal and parietal white matter, basal ganglia, thalamus, hippocampus, and cerebellum) were dissected and assayed for thiobarbituric acid reactive substances, glutathione, and superoxide dismutase.Results: Thiobarbituric acid reactive substance levels in asphyxiated animals were elevated in frontal and parietal white matter, basal ganglia, and thalamus compared with those in controls. The concentrations of superoxide dismutase in the asphyxiated group were also higher in frontal and parietal white matter, basal ganglia, and cerebellum compared with those in the control group. Between the two groups, however, glutathione concentrations did not differ significantly.Conclusion: These results suggest that oxidative stress may be a major contributing factor to the development of brain damage in intrauterine fetal asphyxia. [ABSTRACT FROM AUTHOR]

Objectives: Our purpose was to characterize the histologic changes in the asphyxiated fetal lamb brain and to correlate the severity of these changes with fetal physiologic parameters during and after asphyxia.Study Design: Seventeen near-term fetuses were used for analysis: control group without manipulation (n = 4, 132 +/- 1.1 days of gestation at autopsy, mean +/- SEM), sham-asphyxia control group (n = 3, 132 +/- 1.3 days), and asphyxiated group, which successfully survived 72 hours after asphyxia (n = 10, 130 +/- 1.0 days). Asphyxia was produced by umbilical cord occlusion lasting for approximately 60 minutes until fetal arterial pH diminished to < 6.9 and base excess to < -20 mEq/L. Fetal heart rate, blood pressure, and electrocorticographic activity were continuously monitored. The fetuses were killed 72 hours after asphyxia, and the brains were fixed in formalin and processed for histologic and immunocytochemical studies.Results: Neuropathologic changes varied from case to case, ranging from almost total infarction of cortical and subcortical structures to extremely subtle and patchy white matter alterations characterized by slight vacuolization of the white matter or slight to moderate increases in cellularity confined to the junction of cerebral cortex and white matter. Even fetuses that showed full recovery of all physiologic parameters, including electrocorticographic activity, demonstrated subtle but distinct white matter lesions. The gray matter, including the hippocampal neurons, was generally spared in these cases. Electrocorticographic parameters, duration of hypotension during asphyxia, and delayed recovery of blood lactate concentrations correlated well with the histologic grading of brain damage.Conclusions: Asphyxia by partial umbilical cord occlusion in near-term fetal lambs produces variable neuropathologic changes. The mildest change is a white matter lesion characterized by vacuolization and loss of myelin or by increased cellularity in the damaged regions. [ABSTRACT FROM AUTHOR]

Abstract: To understand the effect of Y2BaCuO5 (Y211)/YBa2Cu3O7− y (Y123) interfaces on the oxygen diffusion in single grain YBa2Cu3O7− y superconductors, single grain Y123 superconductors with 0.05 and 0.3moles of Y2O3 additions were fabricated by a top-seeded melt growth (TSMG) process. Y123 compacts with Y2O3 additions were subjected to melt growth heating cycles with a cooling rate of 1°C/h through a peritectic temperature (1015°C) and then annealed at 450°C for 200h in flowing oxygen. The superconducting temperature (T c) and critical current density (J c) were estimated for the three different regions (top surface (s), intermediate (i) and center (c)) of samples. The amount of Y211/Y123 interface area in single grain Y123 superconductors was successfully controlled by Y2O3 additions. The T c values of s regions were higher than those of i and c regions, which indicates the presence of more oxygen at the sample surfaces. In addition, the T c values of i and c regions of the Y123 sample with 0.3mole Y2O3 addition were higher than those of the same regions of the Y123 sample with 0.05mole Y2O3 addition due to the promoted oxygen diffusion through Y211/Y123 interfaces and other related defects. In spite of the promoted oxygen diffusion by Y2O3 addition, the large Tc difference among the regions still existed, which suggests sluggish oxygen diffusion into single Y123 grains. [Copyright &y& Elsevier]

Highlights: [•] Spherical pores form during the formation reaction of MgB2. [•] The pore formation is remarkable at the temperature where a liquid forms. [•] The pore formation accompanies by pellet expansion and weight loss of MgB2. [•] The critical current density (Jc ) of MgB2 depends on a reaction temperature. [Copyright &y& Elsevier]

Highlights: [•] Corner or edge seeding modifies top surface morphologies of YBCO superconductors. [•] Numbers and a shape of facet lines on top surfaces depend on seeding technique. [•] Facet lines are straight but often have a curvature. [•] Unreacted regions form on top surfaces owing to a low growth rate of a 〈100〉 direction. [•] Magnetic flux density and levitation forces are dependent on top surface morphology. [Copyright &y& Elsevier]