144 research outputs found
Citoesteatonecrose Abdominal Encapsulada
info:eu-repo/semantics/publishedVersio
Chitosan membranes exhibiting shape memory capability by the action of controlled hydration
Chitosan membranes can undergo a glass transition at room temperaturetriggered by hydration. The mechanical properties of the membranes were followed by atension test and dynamic mechanical analysis (DMA), with the sample in wet conditionsafter being immersed in varying compositions of water/ethanol mixtures. Results show thatwith the increasing of water content, the Young’s and storage modulus decreasesystematically. For water contents of ca. 35 vol%, chitosan (CHT) exhibits a glasstransition, showing an elastomeric plateau in the elastic modulus above this hydration leveland the occurrence of a peak in the loss factor. Due to the semi-crystalline nature of CHT,membranes of this biomaterial present a shape memory capability induced by water uptake.By fixation of the permanent shape by further covalent cross-linking, the membranes canhave different permanent shapes appropriate for different applications, including in thebiomedical area.This work was supported by the Portuguese Foundation for Science and Technology Foundation (FCT) through project PTDC/FIS/115048/2009
Participação escolar: representações dos alunos do 3º ciclo de Aveiro (Portugal)
Este artigo propõe uma reflexão sobre a relação intrínseca entre
democracia e educação, particularmente na vertente relacionada com
a participação dos discentes nas decisões da escola. Neste sentido e,
no quadro do regime de autonomia das escolas portuguesas, importa
identificar os espaços formais e informais que são proporcionados
aos jovens na tomada de decisões da vida organizativa da escola para
compreendermos o papel desta na promoção e capacitação dos jovens
para o exercício de uma cidadania ativa. O modo de vida democrático
constrói-se através de oportunidades de aprendizagem acerca do
mesmo, nomeadamente pela vivência de experiências participativas
no contexto escolar.
Em 2009, realizámos um estudo, no âmbito da dissertação de uma
dissertação de mestrado em Ciências da Educação da Universidade
de Aveiro, Portugal, em duas escolas públicas do ensino básico, do
Concelho de Aveiro, abrangendo uma população composta por 240
alunos do 8º e 9º ano de escolaridade e 14 delegados de turma.
Os resultados mostram que os alunos possuem uma débil participação
formal e informal, apesar de o Decreto-lei n. 115-A/98 prever a
possibilidade de cada escola, no âmbito da sua autonomia, poder
promover e criar espaços de efetiva participação dos alunos. A análise
dos instrumentos de autonomia das escolas estudadas revela que a
participação dos alunos é assumida, ainda, como um ideal e não já
como um efetivo projeto de concretização. Concluímos, pois, que as
escolas ainda mantêm uma centralização das decisões nos professores,
verificando-se, por parte dos alunos, uma participação formal, passiva
e ritualizad
Cell adhesion in free-standing multilayer films made of chitosan and alginate
The method for preparing multilayer ultrathin films by the consecu- tive deposition of oppositely charged polyelectrolytes has gained tre- mendous recognition due the user friendly preparation, capability of incorporating high loads of different types of biomolecules in the films, fine control over the materials’ structure, and robustness of the products under ambient and physiological conditions. However the preparation of such films needs the assembly on a substrate and, sometimes, cannot be detached from it, which has limited the appli- cation of such films in areas as tissue engineering and regenerative medicine (TERM).Thus, the production of free-standing films is of extreme importance once it allows the direct experimental determi- nation of many physical properties of fundamental significance such as ion permeation and mechanical properties that can be tuned for real-world applications. In this work, we investigated the elaboration of free-standing multilayer films made of chitosan (CHI) and alginate (ALG), by detaching a polyelectrolyte multilayer film from its under- lying substrate without any postprocessing step. The conditions for optimized film growth were investigated. The adhesion of C2C12 myoblast cells on the CHI/ALG membrane was assessed by cytoskele- tal and nuclear staining. A good cell adhesion and spreading was observed all over the surface. The results demonstrate the potential of such biocompatible free standing membranes made of CHI and ALG for applications in TERM
Effect of crosslinking in chitosan/aloe vera-based membranes for biomedical applications
The positive interaction between polysaccharides with active phytochemicals found in medicinal plants may represent a strategy to create active wound dressing materials useful for skin repair. In the present work, blended membranes composed of chitosan (Cht) and Aloe vera gel were prepared through the solvent casting, and were crosslinked with genipin to improve their properties. Topography, swelling, wettability, mechanical properties and in vitro cellular response of the membranes were investigated. With the incorporation of aloe vera gel into chitosan solution, the developed chitosan/aloe-based membranes displayed increased roughness and wettability; while the genipin crosslinking promoted the formation of stiffer membranes in comparison to those of the non-modified membranes. Moreover, in vitro cell culture studies evidenced that the L929 cells have high cell viability, confirmed by MTS test and calcein-AM staining. The findings suggested that both blend compositions and crosslinking affected the physico-chemical properties and cellular behavior of the developed membranes.The authors acknowledge financial support from Portuguese Foundation for Science and Technology - FCT (Grant SFRH/BPD/45307/2008; SFRH/BD/64601/2009), "Fundo Social Europeu" - FSE, and "Programa Diferencial de Potencial Humano - POPH". This work was partially supported by the FEDER through POCTEP 0330_IBEROMARE_1_P
Biomineralization in chitosan/Bioglass® composite membranes under different dynamic mechanical conditions
Fundamental aspects of biomineralization may be important in order to understand and improve calcification
onto the surface of biomaterials. The biomineralization process is mainly followed in vitro by assessing the
evolution of the apatite layer that is formed upon immersion of the material in Simulated Body Fluid (SBF).
In this work we propose an innovative methodology to monitor apatite deposition by looking at the evolution
of the mechanical/viscoelastic properties of the sample while immersed in SBF, using non-conventional dynamic
mechanical analysis (DMA) performed under distinct displacement amplitudes (d). The biomimetic
biomineralization process in composite membranes of chitosan (CTS) with Bioglass® (BG) was followed by
measuring the change of the storage modulus, E′, and the loss factor, tan δ, at 37 °C and in SBF, both online
(d = 10 μm and d = 30 μm) and offline (d = 0 μm). The online experiments revealed that the E′ decreased
continuously up in the first hours of immersion in SBF that should be related to the dissolution of BG particles.
After that, an increase of the stiffness was verified due to the apatite deposition. SEM/EDS observations upon
24 h of immersion in SBF showed higher development of apatite deposition with increasing displacement
amplitude.This work was financially supported by Foundation for Science and Technology (FCT) by the projects PTDC/QUI/69263/2006, PTDC/CTM-BPC/112774/2009 and, through the scholarship SFRH/BD/64601/2009 granted to Sofia G. Caridade
Dynamics Study of the HO(v‘=0) + O2(v‘ ‘) Branching Atmospheric Reaction. 1. Formation of Hydroperoxyl Radical
We report a theoretical study of the title four-atom atmospheric reaction for a range of translational energies 0.1 ≤ Etr/kcal mol-1 ≤ 40 and the range 13 ≤ v‘ ‘ ≤ 27 of vibrational quantum numbers of the oxygen molecule. All calculations have employed the quasiclassical trajectory method, and a realistic potential energy surface obtained by using the double many-body expansion (DMBE) method for ground-state HO3
Processing of novel bioactive polymeric matrixes for tissue engineering using supercritical fluid technology
The aim of this study was to develop a new process for the production of bioactive 3D scaffolds using a clean
and environmentally friendly technology. The possibility of preparing composite scaffolds of Bioglass® and a
polymeric blend of starch and poly(L-lactic acid) (SPLA50) was evaluated. Supercritical phase-inversion
technique was used to prepare inorganic particles loaded starch-based porous composite matrixes in a onestep
process for bone tissue engineering purposes.
Due to their osteoconductive properties some glasses and ceramics are interesting materials to be used for
bone tissue engineering purposes; however their poor mechanical properties create the need of a polymeric
support where the inorganic fraction can be dispersed. Samples impregnated with different concentrations of
Bioglass® (10 and 15% wt/wt polymer) were prepared at 200 bar and 55 °C. The presence of Bioglass® did not
affect the porosity or interconnectivity of the polymeric matrixes. Dynamic mechanical analysis has proven
that the modulus of the SPLA50 scaffolds increases when glass particles are impregnated within the matrix.
In vitro bioactivity studies were carried out using simulated body fluid and the results show that a calciumphosphate
layer started to be formed after only 1 day of immersion. Chemical analysis of the apatite layer
formed on the surface of the scaffold was performed by different techniques, namely EDS and FTIR
spectroscopy and X-ray diffraction (XRD). The ion concentration in the simulated body fluid was also carried
out by ICP analysis. Results suggest that a bone-like apatite layer was formed.
This study reports the feasibility of using supercritical fluid technology to process, in one step, a porous
matrix loaded with a bioactive material for tissue engineering purposes.Ana Rita C. Duarte is grateful for financial support from Funda go para a Ciencia e Tecnologia through the grant SFRH/BPD/34994/2007. The authors also acknowledge the financial support from FCT through the project PTDC/QUI/69263/2006
Effect of solvent-dependent viscoelastic properties of chitosan membranes on the permeation of low molecular weight drugs
Chitosan (CTS), a widely used biopolymer in different biomedical applications, is a derivative of chitin, the most abundant polysaccharide found in the marine world. This work aimed at providing relevant information about the use of CTS membranes in separation applications or in sustained release systems of therapeutic molecules. Moreover, the mechanical characterization may be also very important in such kind of applications, especially if the materials are tested in adequate physiological conditions.
Chitosan membranes, both non-crosslinked and crosslinked with genipin, were characterized by dynamic mechanical analysis, swelling and permeability experiments using a model molecule. The membranes were tested immersed in different mixtures of water/ethanol. The swelling equilibrium varied linearly with the volumetric composition of the solvent mixture. The mechanical properties of CTS increased with the enhancement of the crosslinking density. A peak of the loss factor appeared at 24.5% of water attributed to the α-relaxation of chitosan and simultaneously a reduction of the storage modulus was observed. This was the first time that the glass transition (Tg) dynamics was monitored in a polymer in immersion conditions, where the plasticizer composition in the bath changed in a controlled way. Permeability decreased sharply until it reached very small values around the Tg.
We hypothesise that conformational mobility of the polymeric chains may play an important role in the diffusion properties of molecules through polymer matrices. Results may elucidate some aspects regarding to relationships between glass transition and transport properties that may be important in the use of CTS in TE strategies.info:eu-repo/semantics/publishedVersio
Effect of solvent-dependent viscoelastic properties of chitosan membranes on the permeation of 2-phenylethanol
The viscoelastic behaviour of chitosan was followed by dynamic mechanical analysis (DMA) while the
sample was immersed in gradient compositions of water/ethanol mixtures. The swelling equilibrium
of chitosan membranes, both crosslinked with genipin or not, increased linearly with the water content.
Increasing the water content, it was simultaneously observed a peak in the loss factor (around 25 vol.%)
and a reduction of the storage modulus, which was attributed to the a-relaxation of chitosan. This was
the first time that the glass transition dynamics in a polymer was monitored in immersion conditions
where the composition of the plasticizer in the bath is changed in a controlled way. The water content
at which tan d presented a maximum increased with both increasing frequency and increasing crosslinking
density. The permeability decreased steadily with the ethanol content, reaching very low values
around the glass transition. Therefore we hypothesize that conformational mobility of the polymeric
chains may play an important role in the diffusion properties of molecules trough polymeric matrices.This work was partially supported by the Portuguese Foundation for Science and Technology (FCT), through funds from the POCTI and/or FEDER programmes and through the scholarship SFRH/BPD/34545/2007 granted to Ricardo M.P. da Silva. This work was carried out under the scope of the European NoE EXPERTISSUES (NMP3-CT-2004-500283) and also partially supported by the EU funded projects HIPPOCRATES (STREP - NMP3-CT-2003-505758) and PROTEUS (INTERREG III A - SP1.P151/03). The technical assistance of Ana Pinheiro in the execution of the DMA experiments is also acknowledged
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