239 research outputs found
Development of a novel cell encapsulation system based on natural origin polymers for tissue engineering applications
Cells microencapsulated in biocompatible semi-permeable polymeric
membranes are effective as cell delivery systems while protecting the host
against immune responses. In this study, cell encapsulation membranes were
prepared based on carrageenan and alginate, two natural cationic polymers.
Different formulations/conditions were explored to optimize the microcapsules
which were characterized with respect to their morphology, mechanical stability,
and cytotoxicity. Spherical-shaped microcapsules were obtained from all the
polymeric systems. The iota-carrageenan/sodium alginate microcapsules exhibited
the best stability and permeability, and therefore, these were selected for
the cell encapsulation. These capsules provided an environment that supported
cell proliferation and have the potential for tissue engineering as well as other
cell-based therapy applications.One of the authors (SML) acknowledges the support of the Programme Alssan-the European Union Programme of High Level Scholarships for Latin America (scholarship no. E04M041362CO). This work was partially supported by the European STREP HIPPOCRATES (NMP3-CT-2003-505758) and by the Fundacao para a Ciencia e Tecnologia (project PTDC/QUI/68804/2006) and carried out under the scope of European NoE EXPERTISSUES (NMP3-CT-2004-500283)
Effects of starch/polycaprolactone-based blends for spinal cord injury regeneration in neurons/glial cells viability and proliferation
Spinal cord injury (SCI) leads to drastic alterations on the quality of life of afflicted individuals. With the advent of Tissue Engineering and Regenerative Medicine where approaches combining biomaterials, cells and growth factors are used, one can envisage novel strategies that can adequately tackle this problem. The objective of this study was to evaluate a blend of starch with poly(ε-caprolactone) (SPCL) aimed to be used for the development of scaffolds spinal cord injury (SCI) repair. SPCL linear parallel filaments were deposited on polystyrene coverslips and assays were carried out using primary cultures of hippocampal neurons and glial cells. Light and fluorescence microscopy observations revealed that both cell populations were not negatively affected by the SPCL-based biomaterial. MTS and total protein quantification indicated that both cell viability and proliferation rates were similar to controls. Both neurons and astrocytes occasionally contacted the surface of SPCL filaments through their dendrites and cytoplasmatic processes, respectively, while microglial cells were unable to do so. Using single cell [Ca2+ ]i imaging, hippocampal neurons were observed growing within the patterned channels and were functional as assessed by the response to a 30 mM KCl stimulus. The present data demonstrated that SPCL-based blends are potentially suitable for the development of scaffolds in SCI regenerative medicine.Portuguese Foundation for Science and Technology through funds from POCTI and/or FEDER programs (Funding to ICVS, 3B's Research Group and post doctoral fellowship to A.J. Salgado-SFRH/BPD/17595/2004)
Radiating black hole solutions in arbitrary dimensions
We prove a theorem that characterizes a large family of non-static solutions
to Einstein equations in -dimensional space-time, representing, in general,
spherically symmetric Type II fluid. It is shown that the best known
Vaidya-based (radiating) black hole solutions to Einstein equations, in both
four dimensions (4D) and higher dimensions (HD), are particular cases from this
family. The spherically symmetric static black hole solutions for Type I fluid
can also be retrieved. A brief discussion on the energy conditions,
singularities and horizons is provided.Comment: RevTeX 9 pages, no figure
Combinatorial activity of flavonoids with antibiotics against drug resistant Staphylococcus aureus
The use of resistance-modifying agents is a potential strategy that is used to prolong the effective life of antibiotics in the face of increasing antibiotic resistance. Since certain flavonoids are potent bacterial efflux pump inhibitors, we assessed morin, rutin, quercetin, hesperidin, and (+)-catechin for their combined activity with the antibiotics ciprofloxacin, tetracycline, erythromycin, oxacillin, and ampicillin against drug-resistant strains of Staphylococcus aureus, including methicillin-resistant S. aureus. Four established methods were used to determine the combined efficacy of each combination: microdilution checkerboard assays, time-kill determinations, the Etest, and dual disc-diffusion methods. The cytotoxicity of the flavonoids was additionally evaluated in a mouse fibroblast cell line. Quercetin and its isomer morin decreased by 3- to 16-fold the minimal inhibitory concentration of ciprofloxacin, tetracycline, and erythromycin against some S. aureus strains. Rutin, hesperidin, and (+)-catechin did not promote any potentiation of antibiotics. Despite the potential cytotoxicity of these phytochemicals at a high concentration (fibroblast IC50 of 41.8 and 67.5mg/L, respectively), quercetin is commonly used as a supplement for several therapeutic purposes. All the methods, with exception of the time-kill assay, presented a high degree of congruence without any apparent strain specificity.This work was supported by Operational Program for
Competitiveness Factors—COMPETE, FCT/MEC (PIDDAC),
and FEDER through Projects Bioresist—PTDC/EBB-EBI/
105085/2008; Phytodisinfectants—PTDC/DTP-SAP/1078/
2012 (COMPETE: FCOMP-01-0124-FEDER-028765) and
the PhD grants awarded to Ana Abreu (SFRH/BD/84393/
2012) and Anabela Borges (SFRH/BD/63398/2009). The
authors are very grateful to Professor Simon Gibbons (De-
partment of Pharmaceutical and Biological Chemistry, The
School of Pharmacy, UCL School of Pharmacy, London) for
providing the bacterial strains.info:eu-repo/semantics/publishedVersio
A novel enzymatically-mediated drug delivery carrier for bone tissue engineering applications: combining biodegradable starch-based microparticles and differentiation agents
In many biomedical applications, the performance
of biomaterials depends largely on their degradation
behavior. For instance, in drug delivery applications, the
polymeric carrier should degrade under physiological
conditions slowly releasing the encapsulated drug. The aim
of this work was, therefore, to develop an enzymaticmediated
degradation carrier system for the delivery of
differentiation agents to be used in bone tissue engineering
applications. For that, a polymeric blend of starch with
polycaprolactone (SPCL) was used to produce a microparticle
carrier for the controlled release of dexamethasone
(DEX). In order to investigate the effect of enzymes on the
degradation behavior of the developed system and release
profile of the encapsulated osteogenic agent (DEX), the
microparticles were incubated in phosphate buffer solution
in the presence of a-amylase and/or lipase enzymes (at
physiological concentrations), at 37 C for different periods
of time. The degradation was followed by gravimetric
measurements, scanning electron microscopy (SEM) and
Fourier transformed infrared (FTIR) spectroscopy and the
release of DEX was monitored by high performance liquid
chromatography (HPLC). The developed microparticles
were shown to be susceptible to enzymatic degradation, as observed by an increase in weight loss and porosity with
degradation time when compared with control samples
(incubation in buffer only). For longer degradation times,
the diameter of the microparticles decreased significantly
and a highly porous matrix was obtained. The in vitro
release studies showed a sustained release pattern with
48% of the encapsulated drug being released for a period of
30 days. As the degradation proceeds, it is expected that
the remaining encapsulated drug will be completely
released as a consequence of an increasingly permeable
matrix and faster diffusion of the drug. Cytocompatibility
results indicated the possibility of the developed microparticles
to be used as biomaterial due to their reduced
cytotoxic effects
Biodegradable foams based on starch, polyvinyl alcohol, chitosan and sugarcane fibers obtained by extrusion
Nucleation and growth of biomimetic apatite layers on 3D plotted biodegradable polymeric scaffolds : effect of static and dynamic coating conditions
Apatite layers were grown on the surface of newly developed starch/polycaprolactone (SPCL)-based scaffolds by a 3D plotting technology.
To produce the biomimetic coatings, a sodium silicate gel was used as nucleating agent, followed by immersion in a simulated
body fluid (SBF) solution. After growing a stable apatite layer for 7 days, the scaffolds were placed in SBF under static, agitated (80 strokes
min!1) and circulating flow perfusion (Q = 4 ml min!1; tR = 15 s) for up to 14 days. The materials were characterized by scanning
electron microscopy/energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and thin-film X-ray diffraction.
Cross-sections were obtained and the coating thickness was measured. The elemental composition of solution and coatings was monitored
by inductively coupled plasma spectroscopy. After only 6 h of immersion in SBF it was possible to observe the formation of small
nuclei of an amorphous calcium phosphate (ACP) layer. After subsequent SBF immersion from 7 to 14 days under static, agitated and
circulating flow perfusion conditions, these layers grew into bone-like nanocrystalline carbonated apatites covering each scaffold fiber
without compromising its initial morphology. No differences in the apatite composition/chemical structure were detectable between
the coating conditions. In case of flow perfusion, the coating thickness was significantly higher. This condition, besides mimicking better
the biological milieu, allowed for the coating of complex architectures at higher rates, which can greatly reduce the coating step.The authors acknowledge the Portuguese Foundation for Science and Technology (PhD grant to A.L.O., SFRH/BD/10956/2002 and post-doctoral Grant to R.A.S., SFRH/BPD/17151/2004, under the POCTI Program). This work was partially supported by FCT through POCTI and/or FEDER programmes and also partially supported by the EU Project HIPPOCRATES (NMP3-CT-2003-505758) and EXPERTISSUES (NMP-CT-2004-500283)
Deep exclusive electroproduction off the proton at CLAS
The exclusive electroproduction of above the resonance region was
studied using the Large Acceptance Spectrometer () at
Jefferson Laboratory by scattering a 6 GeV continuous electron beam off a
hydrogen target. The large acceptance and good resolution of ,
together with the high luminosity, allowed us to measure the cross section for
the process in 140 (, , ) bins:
, 1.6 GeV GeV and 0.1 GeV
GeV. For most bins, the statistical accuracy is on the order of a few
percent. Differential cross sections are compared to two theoretical models,
based either on hadronic (Regge phenomenology) or on partonic (handbag diagram)
degrees of freedom. Both can describe the gross features of the data reasonably
well, but differ strongly in their ingredients. If the handbag approach can be
validated in this kinematical region, our data contain the interesting
potential to experimentally access transversity Generalized Parton
Distributions.Comment: 18pages, 21figures,2table
Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions
We review the most important experimental results from the first three years
of nucleus-nucleus collision studies at RHIC, with emphasis on results from the
STAR experiment, and we assess their interpretation and comparison to theory.
The theory-experiment comparison suggests that central Au+Au collisions at RHIC
produce dense, rapidly thermalizing matter characterized by: (1) initial energy
densities above the critical values predicted by lattice QCD for establishment
of a Quark-Gluon Plasma (QGP); (2) nearly ideal fluid flow, marked by
constituent interactions of very short mean free path, established most
probably at a stage preceding hadron formation; and (3) opacity to jets. Many
of the observations are consistent with models incorporating QGP formation in
the early collision stages, and have not found ready explanation in a hadronic
framework. However, the measurements themselves do not yet establish
unequivocal evidence for a transition to this new form of matter. The
theoretical treatment of the collision evolution, despite impressive successes,
invokes a suite of distinct models, degrees of freedom and assumptions of as
yet unknown quantitative consequence. We pose a set of important open
questions, and suggest additional measurements, at least some of which should
be addressed in order to establish a compelling basis to conclude definitively
that thermalized, deconfined quark-gluon matter has been produced at RHIC.Comment: 101 pages, 37 figures; revised version to Nucl. Phys.
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