Kinetics of copolymer localization at a selective liquid-liquid interface

The localization kinetics of a regular block-copolymer of total length $N$ and block size $M$ at a selective liquid-liquid interface is studied in the limit of strong segregation between hydrophobic and polar segments in the chain. We propose a simple analytic theory based on scaling arguments which describes the relaxation of the initial coil into a flat-shaped layer for the cases of both Rouse and Zimm dynamics. For Rouse dynamics the characteristic times for attaining equilibrium values of the gyration radius components perpendicular and parallel to the interface are predicted to scale with block length $M$ and chain length $N$ as $\tau_{\perp} \propto M^{1+2\nu}$ (here $\nu\approx 0.6$ is the Flory exponent) and as $\tau_{\parallel} \propto N^2$, although initially the characteristic coil flattening time is predicted to scale with block size as $\propto M$. Since typically $N\gg M$ for multiblock copolymers, our results suggest that the flattening dynamics proceeds faster perpendicular rather than parallel to the interface, in contrast to the case of Zimm dynamics where the two components relax with comparable rate, and proceed considerably slower than in the Rouse case. We also demonstrate that, in the case of Rouse dynamics, these scaling predictions agree well with the results of Monte Carlo simulations of the localization dynamics. A comparison to the localization dynamics of {\em random} copolymers is also carried out.Comment: 11 pages, 15 figure

Field - Driven Translocation of Regular Block Copolymers through a Selective Liquid - Liquid Interface

We propose a simple scaling theory describing the variation of the mean first passage time (MFPT) $\tau(N,M)$ of a regular block copolymer of chain length $N$ and block size $M$ which is dragged through a selective liquid-liquid interface by an external field $B$. The theory predicts a non-Arrhenian $\tau$ vs. $B$ relationship which depends strongly on the size of the blocks, $M$, and rather weakly on the total polymer length, $N$. The overall behavior is strongly influenced by the degree of selectivity between the two solvents $\chi$. The variation of $\tau(N,M)$ with $N$ and $M$ in the regimes of weak and strong selectivity of the interface is also studied by means of computer simulations using a dynamic Monte Carlo coarse-grained model. Good qualitative agreement with theoretical predictions is found. The MFPT distribution is found to be well described by a $\Gamma$ - distribution. Transition dynamics of ring- and telechelic polymers is also examined and compared to that of the linear chains. The strong sensitivity of the ``capture'' time $\tau(N,M)$ with respect to block length $M$ suggests a possible application as a new type of chromatography designed to separate and purify complex mixtures with different block sizes of the individual macromolecules.Comment: 20 pages, 10 figure

THE EFFECT OF BMP4 AND MECHANICAL STIMULATION ON MUSCLE-DERIVED STEM CELLS: IMPLICATIONS FOR BONE AND ARTICULAR CARTILAGE REGENERATION

The prevalence of bone and articular cartilage injuries is expected to increase with the aging population. As a possible therapeutic option, stem cell-based therapies are being investigated. It has previously been reported that muscle-derived stem cells (MDSCs) isolated from mouse skeletal muscle can undergo osteogenic and chondrogenic differentiation in vitro and in vivo when stimulated with bone morphogenetic protein 4 (BMP4). One goal of this project was to determine whether cell sex influences this differentiation potential. Using in vitro osteogenic assays, it was determined that male MDSCs (M-MDSCs) stimulated with BMP4 expressed osteogenic markers and displayed more mineralization than female MDSCs (F-MDSCs). In vivo, M-MDSCs expressing BMP4 and implanted into the hind limb of mice induced a more robust ectopic bone formation when compared to F-MDSCs. These results suggest that cell sex influences the osteogenic differentiation potential of MDSCs. In the second study, the signaling pathways involved during BMP4 stimulation were investigated to further characterize the osteogenic differentiation process. The phosphatidyl inositol 3-kinase and p38 MAPK pathways played a positive role in MDSC osteogenesis, while the extracellular signal-regulated kinase pathway was identified as a negative regulator of osteogenesis. These results suggest that the osteogenic differentiation of MDSCs could be manipulated by regulating these pathways. In the third study, the effect of BMP4 and transforming growth factor-b1 (TGF-b1) on the chondrogenic differentiation of F- and M-MDSCs in vitro was investigated. All MDSCs tested underwent chondrogenic differentiation, with no significant sex-related differences observed. However, addition of TGF-b1 synergistically enhanced BMP4-induced chondrogenic differentiation. In the final study, the effect of mechanical stimulation on the proliferation and osteogenic differentiation of MDSCs was investigated by using both biaxial and uniaxial strain. Mechanical stimulation affected cell orientation, but did not significantly affect the proliferation or osteogenic differentiation of MDSCs. In conclusion, the BMP4-induced osteogenic and chondrogenic differentiation of MDSCs can be influenced by several factors including cell sex and growth factors and can be guided through the manipulation of cell signaling pathways. The results from this project support the continued investigation of MDSCs as a potential cell source for bone and articular cartilage tissue engineering

Control and navigation problems for model bio-inspired microswimmers

Navigation problems for a model bio-inspired micro-swimmer, consisting of a cargo head and propelled by multiple rotating flagella or propellers and swimming at low Reynolds numbers, are formulated and solved. We consider both the direct problem, namely, predicting velocity and trajectories of the swimmer as a consequence of prescribed rotation rates of the propellers, and inverse problems, namely, find the rotation rates to best approximate desired translational and rotational velocities and, ultimately, target trajectories. The equations of motion of the swimmer express the balance of the forces and torques acting on the swimmer, and relate translational and rotational velocities of the cargo head to rotation rates of the propellers. The coefficients of these equations, representing hydrodynamic resistance coefficients, are evaluated numerically through a custom-built finite-element code to simulate the (Stokes) fluid flows generated by the movement of the swimmer and of its parts. Several designs of the propulsive rotors are considered: from helical flagella with different chirality to marine propellers, and their relative performance is assessed

A survey of cherry leaf roll virus in intensively managed grafted english (Persian) walnut trees in Italy

Blackline disease, caused by Cherry leaf roll virus (CLRV), is considered a serious threat limiting English walnut (Juglans regia) production in Italy and the EU if walnut species other than J. regia e.g. \u2018Paradox\u2019 hybrid (J. regia 7 J. hindsii), French hybrid (J. regia 7 J. major or J. regia 7 J. nigra) or northern California black walnut (J. hindsii) are used as the rootstock. The virus transmissibility by pollen as well as latent infections can result in the spread of CLRVcontaminated propagative material, which is a major means of the virus dispersal by human activities. In 2014 and 2015 to ascertain the presence and the distribution of blackline symptoms in commercial orchards and to provide a description of the symptomatology, visual inspections and double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) analyses were carried out on 1,684 walnut trees in four different intensively managed grafted English walnut orchards in northeast Italy (Veneto Region). Trees with clear blackline symptoms at the scion-rootstock junction, often associated with general decline of the plant, were found only in one commercial orchard in northeast Italy on trees older than ten years of cvs. \u2018Tulare\u2019 and \u2018Chandler\u2019, grafted onto \u2018Paradox\u2019 rootstock. To our knowledge this is the first report of CLRV (blackline) decline and death in a commercial walnut orchard in Italy

Glutamate Receptors and Glioblastoma Multiforme: An Old "Route" for New Perspectives

Glioblastoma multiforme (GBM) is the most aggressive malignant tumor of the central nervous system, with poor survival in both treated and untreated patients. Recent studies began to explain the molecular pathway, comprising the dynamic structural and mechanical changes involved in GBM. In this context, some studies showed that the human glioblastoma cells release high levels of glutamate, which regulates the proliferation and survival of neuronal progenitor cells. Considering that cancer cells possess properties in common with neural progenitor cells, it is likely that the functions of glutamate receptors may affect the growth of cancer cells and, therefore, open the road to new and more targeted therapies

XRF 050406 late-time flattening: an inverse Compton component?

We investigate for possible evidence of inverse Compton (IC) emission in the X-ray afterglow of XRF 050406. In the framework of the standard fireball model, we show how the late-time flattening observed in the X-ray light curve between \~10^{4} s and ~10^{6} s can be explained in a synchrotron-plus-IC scenario, when the IC peak frequency crosses the X-ray band. We thus conclude that the appearance of an IC component above the synchrotron one at late times successfully accounts for these X-ray observations.Comment: 9 pages, 7 figures, 1 table, accepted for publication in A&A. Version accepted by A&A, minor changes in the title, contents and conclusions unchanged, language corrections include

Sinonasal angioleiomyoma with adipocyte differentiation: clinicopathologic study of 2 cases and review of the literature

Angioleiomyoma (ALM) is a benign tumor of the skin and soft tissues composed of well differentiated smooth muscle cells arranged around and among many vascular channels. Few cases have been reported in the sinonasal region, where ALM may show a variable amount of mature adipose tissue that may make hard the distinction from angiomyolipoma. We report here two cases that presented with a three- and six-month history of left nasal obstruction respectively. In both patients, clinical examination and imaging studies failed to reveal features of tuberous sclerosis complex and demonstrated a mass obliterating the nasal cavity arising from the inferior turbinate. Both masses were endoscopically excised. Pathologic analysis revealed highly vascularized tumors composed of well differentiated smooth muscle cells intermingled with a variable number of mature adipocytes. Immunostaining for melanocytic markers was negative. Based on these findings, both tumors were diagnosed as sinonasal-ALM with adipocytic differentiation. These two cases indicate that both clinical data (i.e. absence of features of tuberous sclerosis complex) and immunohistochemistry (i.e. absence of melanocytic markers) are mandatory for the recognition of sinonasal-ALM with adipocytic differentiation. The term angiomyolipoma to identify these lesions is confusing and should be abandoned

Copolymer adsorption kinetics at a selective liquid-liquid interface: Scaling theory and computer experiment

We consider the adsorption kinetics of a regular block-copolymer of total length $N$ and block size $M$ at a selective liquid-liquid interface in the limit of strong localization. We propose a simple analytic theory based on scaling considerations which describes the relaxation of the initial coil into a flat-shaped layer. The characteristic times for attaining equilibrium values of the gyration radius components perpendicular and parallel to the interface are predicted to scale with chain length $N$ and block length $M$ as $\tau_{\perp} \propto M^{1+2\nu}$ (here $\nu\approx 0.6$ is the Flory exponent) and as $\tau_{\parallel} \propto N^2$, although initially the rate of coil flattening is expected to decrease with block size as $\propto M^{-1}$. Since typically $N\gg M$ for multiblock copolymers, our results suggest that the flattening dynamics proceeds faster perpendicular rather than parallel to the interface. We also demonstrate that these scaling predictions agree well with the results of extensive Monte Carlo simulations of the localization dynamics.Comment: 4 pages, 4 figures, submited to Europhys. Let