543 research outputs found
Drug complexation and physicochemical properties of vinylpyrrolidone-N, N′-dimethylacrylamide copolymers
Solid dispersions of the nonsteriodal antiin-flammatory drug (NSAID) 2′,4′-difluoro-4-hydroxy-(1,1′-biphenyl)-3-carboxylic acid (DIF) with the water-soluble random copolymer poly(N-vinyl-2-pyrrolidone-co-N, N′-dimethylacrylamide) (VP-co-DMAm) were prepared by the solvent method (coevaporates) and melting DIP/VP-co-DMAm (cofused) physical mixtures. Differential scanning calorimetry (DSC), infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were used to elucidate the possible interaction between the NSAID drug and VP-co-DMAm in cofused and coevaporated polymer-drug solid dispersions. The XRD and FTIR studies suggest the presence of physical interactions with formation of a charge transfer complex between DIF and the VP-co-DMAm copolymers as a consequence of the coevaporation or cofusion processes. In solution, dynamic and equilibrium solubility studies were determined to elucidate the mechanism of interaction between DIP and VP-co-DMAm copolymers. Thermodynamics data about the DIP: VP-co-DMAm dissolution process indicate that the coevaporated systems are more stable that the cofused systems. The dissolution of the cofused and coevaporated systems was diffusion controlled and the dissolution kinetics followed the Noyes-Whitney and the Levich equations. Molecular simulations using semiempirical quantum chemical calculations reinforce the experimental results, suggesting that the improvement in the DIF solubility could be attributed to the charge transfer complex formation between the drug and VP-co-DMAm copolymers.Fil: De Queiroz, Alvaro A.A.. Universidade Federal de Itajubá; BrasilFil: França, Écio J.. Universidade Federal de Itajubá; BrasilFil: Abraham, Gustavo Abel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales. Universidad Nacional de Mar del Plata. Facultad de IngenierĂa. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales; ArgentinaFil: Roman, Julio San. Instituto en Ciencia y TecnologĂa de PolĂmeros; Españ
Synthesis and characterization of sensitive hydrogels based on semi- interpenetrated networks of poly 2-ethyl-(2-pyrrolidone) methacrylate and hyaluronic acid
Sensitive hydrogels attract interest due to their soft wet appearance and shape response to environmental variations. The synthesis and characterization of semi-interpenetrated hydrogels obtained by radical-induced polymerization of 2-ethyl-(2-pyrrolidone)methacrylate (EPM) in the presence of different concentrations of hyaluronic acid (HA) using N,N′-methylene-bisacrylamide or triethylene glycol dimethacrylate as crosslinker, followed by freeze-drying, are described. Polymeric systems were characterized by NMR, FTIR, SEM, TGA, and DMA. PEPMHA hydrogels' mechanical properties and swelling were found to be intimately related to HA concentration and crosslinker. The swelling response was assessed for temperature and pH variation in order to study the behavior of the hydrogels. We found that the presence of HA in PEPM polymeric systems induced a sensitivity to pH variation rather than temperature. Finally, the biocompatibility profile of the hydrogels was evaluated, using mesenchymal stem cells. Cell adhesion and proliferation results revealed the non-cytotoxicity of the systems. We estimate that PEPMHA hydrogels can be used for applications in tissue engineering and for the controlled release of bioactive compounds.Contract grant sponsor: Marie Curie Early Stage Training Alea Jacta Est; contract grant number: MEST-CT-2004-8104The authors thank David Gomez, Sofia Caridade, and Justyna Chojnacka for their technical support and BIOIBERICA for the supply of hyaluronic acid. This work was carried out under the scope of the European NoE EXPERTISSUES, projects MAT 2007-63355, PTDC/QUI/68804/2006 (FCT), CIBER-BBN and Plan-E 2009-0144. In the memory of Prof. Roberto Sastre
Engineering cartilage like tissue using polymeric systems derived from 2-ethyl-2-pyrrolidone-methacrylate combined with hyaluronic acid
Hydrogels are potential candidates for Tissue engineering (TE), because of their water content, transport properties, and tissue like physical and chemical behaviour. This project was based on the production and characterization of implantable stimuli responsive scaffolds made of hyaluronic acid (HA) that presents a high water retention character, in combination with 2-ethyl (2-pyrrolidone) methacrylate (EPM), possessing temperature-dependent solubility in water, by bulk polymerization. [...]info:eu-repo/semantics/publishedVersio
Newly Identified Star Clusters in M33. III. Structural Parameters
We present the morphological properties of 161 star clusters in M33 using the
Advanced Camera For Surveys Wide Field Channel onboard the Hubble Space
Telescope using observations with the F606W and F814W filters. We obtain, for
the first time, ellipticities, position angles, and surface brightness profiles
for a significant number of clusters. On average, M33 clusters are more
flattened than those of the Milky Way and M31, and more similar to clusters in
the Small Magellanic Cloud. The ellipticities do not show any correlation with
age or mass, suggesting that rotation is not the main cause of elongation in
the M33 clusters. The position angles of the clusters show a bimodality with a
strong peak perpendicular to the position angle of the galaxy major axis. These
results support the notion that tidal forces are the reason for the cluster
flattening. We fit King and EFF models to the surface brightness profiles and
derive structural parameters including core radii, concentration, half-light
radii and central surface brightness for both filters. The surface brightness
profiles of a significant number of clusters show irregularities such as bumps
and dips. Young clusters (Log age < 8) are notably better fitted by models with
no radial truncation (EFF models), while older clusters show no significant
differences between King or EFF fits. M33 star clusters seem to have smaller
sizes, smaller concentrations, and smaller central surface brightness as
compared to clusters in the MW, M31, LMC and SMC. Analysis of the structural
parameters presents a age-radius relation also detected in other star cluster
systems. The overall analysis shows differences in the structural evolution
between the M33 cluster system and cluster systems in nearby galaxies. These
differences could have been caused by the strong differences in these various
environments.Comment: 30 pages, 12 figures, accepted for publication in MNRA
Biomimetic Ca-P coatings Incorporating bisphosphonates produced on starch-based degradable biomaterials
In this study, sodium clodronate, a well-known therapeutic agent from the family
of bisphosphonates (BPs), is incorporated in a biomimetic calcium phosphate (CaP) coating,
previously formed on the surface of a starch-based biomaterial by a sodium silicate
methodology, as a strategy to develop a site-specific drug delivery system for bone tissue
regeneration applications. The effects on the resulting CaP coatings were evaluated in terms of
morphology, chemistry, and structure. The dissolution of Ca and P from the coating and the
release profiles of sodium clodronate was also assessed. As a preliminary approach, this first
study also aimed at evaluating the effects of this BP on the viability of a human osteoblastic
cell line since there is still little information available on the interaction between BPs and this
type of cells. Sodium clodronate was successfully incorporated, at different doses, in the
structure of a biomimetic CaP layer previously formed by a sodium silicate process. This
type of BPs had a stimulatory effect on osteoblastic activity, particularly at the specific
concentration of 0.32 mg/mL. It is foreseen that these coatings can, for instances, be
produced on the surface of degradable polymers and then used for regulating the
equilibrium on osteoblastic/osteoclastic activity, leading to a controlled regenerative effect
at the interface between the biomaterial and bone
Total Degree Formula for the Generic Offset to a Parametric Surface
We provide a resultant-based formula for the total degree w.r.t. the spatial
variables of the generic offset to a parametric surface. The parametrization of
the surface is not assumed to be proper.Comment: Preprint of an article to be published at the International Journal
of Algebra and Computation, World Scientific Publishing,
DOI:10.1142/S021819671100680
Testing the chemical tagging technique with open clusters
Context. Stars are born together from giant molecular clouds and, if we
assume that the priors were chemically homogeneous and well-mixed, we expect
them to share the same chemical composition. Most of the stellar aggregates are
disrupted while orbiting the Galaxy and most of the dynamic information is
lost, thus the only possibility of reconstructing the stellar formation history
is to analyze the chemical abundances that we observe today.
Aims. The chemical tagging technique aims to recover disrupted stellar
clusters based merely on their chemical composition. We evaluate the viability
of this technique to recover co-natal stars that are no longer gravitationally
bound.
Methods. Open clusters are co-natal aggregates that have managed to survive
together. We compiled stellar spectra from 31 old and intermediate-age open
clusters, homogeneously derived atmospheric parameters, and 17 abundance
species, and applied machine learning algorithms to group the stars based on
their chemical composition. This approach allows us to evaluate the viability
and efficiency of the chemical tagging technique.
Results. We found that stars at different evolutionary stages have distinct
chemical patterns that may be due to NLTE effects, atomic diffusion, mixing,
and biases. When separating stars into dwarfs and giants, we observed that a
few open clusters show distinct chemical signatures while the majority show a
high degree of overlap. This limits the recovery of co-natal aggregates by
applying the chemical tagging technique. Nevertheless, there is room for
improvement if more elements are included and models are improved.Comment: accepted for publication in Astronomy and Astrophysics. Corrected
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The M33 Globular Cluster System with PAndAS Data: The Last Outer Halo Cluster?
We use CFHT/MegaCam data to search for outer halo star clusters in M33 as
part of the Pan-Andromeda Archaeological Survey (PAndAS). This work extends
previous studies out to a projected radius of 50 kpc and covers over 40 square
degrees. We find only one new unambiguous star cluster in addition to the five
previously known in the M33 outer halo (10 kpc <= r <= 50 kpc). Although we
identify 2440 cluster candidates of various degrees of confidence from our
objective image search procedure, almost all of these are likely background
contaminants, mostly faint unresolved galaxies. We measure the luminosity,
color and structural parameters of the new cluster in addition to the five
previously-known outer halo clusters. At a projected radius of 22 kpc, the new
cluster is slightly smaller, fainter and redder than all but one of the other
outer halo clusters, and has g' ~ 19.9, (g'-i') ~ 0.6, concentration parameter
c ~ 1.0, a core radius r_c ~ 3.5 pc, and a half-light radius r_h ~ 5.5 pc. For
M33 to have so few outer halo clusters compared to M31 suggests either tidal
stripping of M33's outer halo clusters by M31, or a very different, much calmer
accretion history of M33.Comment: 37 pages, 9 figures. Accepted by the Astrophysical Journa
Comparison of Figulla Flex® and Amplatzer™ devices for atrial septal defect closure: A meta-analysis
Background: Atrial septal defect (ASD) is one of the most common congenital heart diseases. Percutaneousclosure is the preferred treatment, but certain complications remain a concern. The most common devices are AMPLATZER™ (ASO) (St. Jude Medical, St. Paul, MN, USA) and Figulla Flex® septal occluders (FSO) (Occlutech GmbH, Jena, Germany). The present study aimed to assess main differences in outcomes.Methods: A systematic search in Pubmed and Google scholarship was performed by two independent reviewers for any study comparing ASO and FSO. Searched terms were “Figulla”, “Amplatzer”, and “atrial septal defect”. A random-effects model was used.Results: A total of 11 studies including 1770 patients (897 ASO; 873 FSO) were gathered. Baseline clinical and echocardiographic characteristics were comparable although septal aneurysm was more often reported in patients treated with ASO (32% vs. 25%; p = 0.061). Success rate (94% vs. 95%; OR: 0.81; 95% CI: 0.38–1.71; p = 0.58) and peri-procedural complications were comparable. Procedures were shorter, requiring less fluoroscopy time with an FSO device (OR: 0.59; 95% CI: 0.20–0.97; p = 0.003). Although the global rate of complications in long-term was similar, the ASO device was associated with a higher rate of supraventricular arrhythmias (14.7% vs. 7.8%, p = 0.009).Conclusions: Percutaneous closure of ASD is a safe and effective, irrespective of the type of device. No differences exist regarding procedural success between the ASO and FSO devices but the last was associated to shorter procedure time, less radiation, and lower rate of supraventricular arrhythmias in follow-up. Late cardiac perforation did not occur and death in the follow-up was exceptional
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