Tyrosine phosphorylation of p130Cas is involved in actin organization in osteoclasts

Integrin-mediated interaction with the extracellular matrix plays a critical role in the function of osteoclasts, the bone-resorbing cells. This study examines the role of p130Cas (Crk-associated substrate (Cas)) in actin organization in osteoclasts. Multinucleated osteoclast-like cells (OCLs) were obtained in a co-culture of murine bone marrow cells and primary osteoblasts. After plating on culture dishes, OCLs formed a ringlike structure consisting of F-actin dots at cell periphery (actin ring). The percentage of OCLs with actin rings and its diameter increased with time and cell spreading. Tyrosine phosphorylation of a protein (p130) increased with actin ring formation. Treatment with cytochalasin D disrupted actin rings and reduced tyrosine phosphorylation of p130. Using specific antibodies, p130 was identified as Cas. By immunocytochemistry, Cas was localized to the peripheral regions of OCLs and its distribution overlapped that of F-actin. In OCLs derived from Src(-/-) mice, in which osteoclast activity is severely compromised, tyrosine phosphorylation of Cas was markedly reduced. Moreover, Cas was diffusely distributed in the cytoplasm and actin ring formation is not observed. These findings suggest that Src-dependent tyrosine phosphorylation of Cas is involved in the adhesion-induced actin organization associated with osteoclast activation.     

Mechanical behavior of injection molded β-crystalline phase polypropylene

High purity and a large amount of β-modification can be produced in polypropylene (PP) by adding a bicomponent β-nucleator consisting of equal amounts of pimelic acid and calcium stearate. Wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), static tensile tests, Izod impact tests, and instrumented drop weight impact testing were used to characterize the structure, morphology, and mechanical behavior of the β-phase PP. The WAXD patterns show that the relative content of the β-phase (K value) in the skin layer of the injection molded specimen is 0.54, whereas the K value in the core section is 0.92. SEM observations reveal that the β-spherulite exhibits a sheaf-like structure and there are no clear boundaries between the spherulites. Static tensile tests indicate that the elongation at break of pure PP is enhanced by the addition of a β-nucleator. The impact and drop weight tests also indicate that the impact resistance of PP is improved by adding the β-nucleating agent. The improvement in impact toughness is associated with the formation of microcrazes within the PP.     

Wear behaviour of an Al–12% Si alloy reinforced with a low volume fraction of SiC particles

Aluminium–silicon alloys reinforced with low volume fractions of SiC particles were prepared by the compocasting process. The wear behaviour of the unreinforced Al–12Si alloy and metal-matrix composites (MMCs) was investigated by using a block-on-ring test at room temperature under dry conditions. The results showed that the addition of a low volume fraction of SiC particles (2–8 vol%) is a very effective way of increasing the wear resistance of the matrix alloy. Metallographic examinations revealed that the wear zone of the Al–12Si alloy consists of both hardened and deformation layers. The depth of the hardened layer depended on the applied load and was in the vicinity of 10–50 μm. The formation of the hardened layer was related to the alignment and redistribution of fragmented eutectic phase to the surface region during sliding wear. Furthermore, the delamination of debris from the hardened layer was responsible for a higher wear loss observed in the Al–12Si alloy. The thickness of the hardened layer formed on the MMC specimens was reduced considerably by the incorporation of fragmented SiC particles. This layer exhibited higher hardness and wear resistance than that developed in the unreinforced alloy.     

Internal field emission and conductivity relaxation in carbon nanofiber filled polymer system

Conducting polymer nanocomposites based on high density polyethylene (HDPE) and carbon nanofiber (CNF) were fabricated by melt compounding. The conductivity of the nanocomposites was found to follow the percolation behavior. Effect of electric field on the electrical conduction behavior of such composites was investigated. The results revealed two competing processes in the composite: internal field emission and electrical conduction relaxation. The former is dominant at lower filler concentrations or under low electric field, while the latter is pronounced under the application of strong electric field. Further, the relaxation time is nearly independent on the electric field strength but decreased with increasing temperature.     

Value of MR cholangiopancreatography in evaluating choledochal cysts

OBJECTIVE: The aim of this retrospective study was to clarify whether MR cholangiopancreatography (MRCP) is a suitable replacement for ERCP in evaluation of the choledochal cyst. MATERIALS AND METHODS: Sixteen patients (six adult and 10 pediatric) with choledochal cysts underwent MRCP using a half-Fourier acquisition single-shot turbo spin-echo sequence. Extent of the cyst, defects within the biliary tree, and presence or absence of the anomalous junction of the pancreaticobiliary duct were evaluated. Findings were compared with those of ERCP. RESULTS: MRCP better defined the proximal biliary tree than did ERCP in two patients. Defects within the biliary tree were diagnosed correctly on MRCP in eight patients; however, two defects within the distal common bile duct were missed in pediatric patients. The presence of the anomalous junction of the pancreaticobiliary duct was revealed accurately by MRCP in all adult patients but was revealed accurately in only four of the 10 pediatric patients. CONCLUSION: MRCP appears to offer diagnostic information that is equivalent to that of ERCP for assessment of choledochal cysts in adults. In pediatric patients, MRCP should not replace ERCP; however, MRCP can play an important role as a noninvasive examination and should be considered a first-choice imaging technique for evaluation of choledochal cysts.