167,838 research outputs found
Structure and dynamics of a thermoresponsive microgel around Its volume phase transition temperature
No full textSustained drug delivery requires the use of multifunctional devices with enhanced properties. These properties include responsiveness to external stimuli (such as temperature, pH, ionic strength), ability to deliver suitably designed ligands to specific receptors, enhanced bioadhesion to cells, and cytocompatibility. Microgels represent one of such multifunctional drug delivery devices. Recently, we described the fabrication of a stable colloidal aqueous suspension of cytocompatible microgel spheres based on a poly(vinyl alcohol)/poly(methacrylate-co-N-isopropylacrylamide) network ( Ghugare, S. Mozetic, P. Paradossi, G. Biomacromolecules 2009 , 10 , 1589 ). These microgel spheres undergo an entropy-driven volume phase transition around the physiological temperature, this phase transition being driven by the incorporation of NiPAAm residues in the network. In that study, the microgel was loaded with the anticancer drug doxorubicin. As the microgel shrank, a marked increase in the amount of doxorubicin released was noted. Indeed, dynamic light scattering measurements showed the diameter reduction to be about 50%. In the present paper, we focus on some fundamental issues regarding modifications of the hydrogel architecture at a nanoscopic level as well as of the diffusive behavior of water associated with the polymer network around the volume phase transition temperature (VPTT). Sieving and size exclusion effects were studied by laser scanning confocal microscopy with the microgel exposed to fluorescent probes with different molecular weights. Confocal microscopy observations at room temperature and at 40 degrees C (i.e., below and above the VPTT) provided an evaluation of the variation of the average pore size (from 5 nm to less than 3 nm). Using quasielastic neutron scattering (QENS) with the IRIS spectrometer at ISIS, UK, the diffusive behavior of water molecules closely associated to the polymer network around the VPTT was investigated. A clear change in the values of diffusion coefficient of bound water was observed at the transition temperature. In addition, the local dynamics of the polymer itself was probed using the QENS spectrometer SPHERES at FRM II, Germany. For this study, the microgel was swollen in D(2)O. An average characteristic distance of about 5 A for the localized chain motions was evaluated from the elastic incoherent structure factor (EISF) and from the Q-dependence of the Lorentzian width
Temperature-sensitive poly(vinyl alcohol)/poly(methacrylate-co-N-isopropyl acrylamide) microgels for doxorubicin delivery
No full textMicrogels based on poly(vinyl alcohol), PVA, grafted with methacrylate side chains, MA, incorporating N-isopropylacrylamide, NiPAAm, monomer, were prepared by water-in-water emulsion polymerization method. These systems exhibit a spherical shape and a volume-phase transition, that is, shrinking, below physiological temperature. The behavior of these microgels were studied with respect to their average size and size distribution, swelling, and release properties. It was observed that the stirring speed is a key parameter for controlling the amount of incorporated NiPAAm, the particle size and the sharpness of the volume-phase transition. The volume-phase transition temperature, VPPT, of the microgels was evaluated around 38 and 34 T for microgels with a NiPAAm/methacrylate molar ratio of 0.8 and 2.4, respectively. Water uptake increased with the amount of NiPAAm monomer present in the polymer network. In vitro biocompatibility of microgels was assessed with respect to NIH3T3 mouse fibroblasts. O-Succinoylated microgels were loaded with doxorubicin by exploiting the favorable electrostatic interaction between negatively charged microgel surface and positively charged doxorubicin. The drug release was influenced by the microgels surface/volume ratio. At physiological temperatures, above the VPTT exhibited by these systems, the release was enhanced by the specific area increase. This study provides the background for the design of an injectable device suitable for the controlled delivery of doxorubicin based on the volume-phase transition of microgels
Multiresponsive Hyaluronan-p(NiPAAm) click-linked Hydrogels
No full textCombined reversible addition-fragmentation chain transfer (RAFT) and chemoselective "click" chemistry are used for assembling two polymeric chains into a hybrid network capable to respond simultaneously or separately to different external stimuli. An azido-derivative of hyaluronate is clicked together with a new telechelic RAFT-generated p(NiPAAm), carrying a propargyl function at both ends, suitable as macromolecular "clickable" cross-linker with controlled molecular weight. This hybrid system displays a multiresponsive behavior versus temperature, pH, and ionic strength, maintaining cumulative as well as separate sensitivities to the external stimuli. Hyaluronidase catalyzed degradation of the hydrogels, mimicking the extracellular matrix degradation process, is an additional asset for the use of this class of hydrogels as scaffold. Tumor cells, HT-29, grow on the surface of these hybrid hydrogels more than the healthy ones, as NIH3T3. This finding opens a road to micro- and nano-devices based on hyaluronic acid as a promising biopolymer to pursue localized drug delivery
Structural Investigation on Thermoresponsive PVA/Poly(Methacrylate-co-N-isopropylacrylamide) Microgels across the Volume Phase Transition
No full textCharacterization of switchable microgels is a major task in drug delivery science. The study of soft polymeric devices requires a combined use of spectroscopy, microscopy, and scattering approaches enabling the characterization of nanostructured features across a volume phase transition. In this work the structural changes of poly(vinyl alcohol) based thermoreversible microgel particles which incorporate p(NiPAAm-co-methacrylate) chains across the transition temperature occurring at 33 °C have been addressed by utilizing reciprocal and direct space approaches such as small angle neutron scattering, SANS, dynamic light scattering, DLS, soft transmittance X-ray microscopy, STXM, and confocal laser scanning microscopy, CLSM, respectively. The comparison between the results obtained from those approaches allows an evaluation of the driving forces acting in the transition and reveals the changes in the microgel structure at nanoscale level. The structure of the poly(vinyl alcohol) based microgel particles, incorporating p(NiPAAm) sequences, consist of a hydrogel core and of a crown of polymer chains projected, at room temperature, in aqueous medium. An increase of the temperature above 33 °C causes a volume phase transition of the system characterized by the collapse of the particle core and of the chains grafted at the particle surface. This transition is accompanied by a massive release of water and an increase of the interface with the dispersing aqueous medium, causing the passage from a permeable to a semipermeable structure
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dr. Edward P. Wimberly, ITC, July 2011
No full textThis video is a conversation with Dr. Edward P. Wimberly. Dr. Wimberly talks about his book, "No Shame in Wesley's Gospel: A Twenty-First Century Pastoral Gospel". Brad Ost, AUC Woodruff Library, is the interviewer
Universal Statistical Properties of Inertial-particle Trajectories in Three-dimensional, Homogeneous, Isotropic, Fluid Turbulence
No full textWe obtain new universal statistical properties of heavy-particle trajectories in three-dimensional, statistically steady, homogeneous, and isotropic turbulent flows by direct numerical simulations. We show that the probability distribution functions (PDFs) P(Φ), of the angle Φ between the Eulerian velocity u and the particle velocity v, at a point and time, scales as P(Φ) ∼Φ−, with a new universal exponent ≃ 4
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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