Showing papers by "University of Minho published in 2003"

Effect of flow perfusion on the osteogenic differentiation of bone marrow stromal cells cultured on starch-based three-dimensional scaffolds.

Abstract: This study aims to investigate the effect of culturing conditions (static and flow perfusion) on the proliferation and osteogenic differentiation of rat bone marrow stromal cells seeded on two novel scaffolds exhibiting distinct porous structures. Specifically, scaffolds based on SEVA-C (a blend of starch with ethylene vinyl alcohol) and SPCL (a blend of starch with polycaprolactone) were examined in static and flow perfusion culture. SEVA-C scaffolds were formed using an extrusion process, whereas SPCL scaffolds were obtained by a fiber bonding process. For this purpose, these scaffolds were seeded with marrow stromal cells harvested from femoras and tibias of Wistar rats and cultured in a flow perfusion bioreactor and in 6-well plates for 3, 7, and 15 days. The proliferation and alkaline phosphatase activity patterns were similar for both types of scaffolds and for both culture conditions. However, calcium content analysis revealed a significant enhancement of calcium deposition on both scaffold types cultured under flow perfusion. This observation was confirmed by Von Kossa-stained sections and tetracycline fluorescence. Histological analysis and confocal images of the cultured scaffolds showed a much better distribution of cells within the SPCL scaffolds than the SEVA-C scaffolds, which had limited pore interconnectivity, under flow perfusion conditions. In the scaffolds cultured under static conditions, only a surface layer of cells was observed. These results suggest that flow perfusion culture enhances the osteogenic differentiation of marrow stromal cells and improves their distribution in three-dimensional, starch-based scaffolds. They also indicate that scaffold architecture and especially pore interconnectivity affect the homogeneity of the formed tissue.

Thermal properties of thermoplastic starch/synthetic polymer blends with potential biomedical applicability.

Abstract: Previous studies shown that thermoplastic blends of corn starch with some biodegradable synthetic polymers (poly(e-caprolactone), cellulose acetate, poly(lactic acid) and ethylene-vinyl alcohol copolymer) have good potential to be used in a series of biomedical applications. In this work the thermal behavior of these structurally complex materials is investigated by differential scanning calorimetry (DSC) and by thermogravimetric analysis (TGA). In addition, Fourier-transform infrared (FTIR) spectroscopy was used to investigate the chemical interactions between the different components. The endothermic gelatinization process (or water evaporation) observed by DSC in starch is also observed in the blends. Special attention was paid to the structural relaxation that can occur in the blends with poly(lactic acid) at body temperature that may change the physical properties of the material during its application as a biomaterial. At least three degradation mechanisms were identified in the blends by means of using TGA, being assigned to the mass loss due to the plasticizer leaching, and to the degradation of the starch and the synthetic polymer fractions. The non-isothermal kinetics of the decomposition processes was analyzed using two different integral methods. The analysis included the calculation of the activation energy of the correspondent reactions.

A tractable approach to the firm location decision problem

Abstract: The conditional logit model based on random utility maximization has provided an adequate framework to model firm location decisions. However, in practice, the implementation of this methodology presents problems when one has to handle complex choice scenarios with a large number of spatial alternatives. We posit the Poisson regression as a tractable solution to these problems. We demonstrate that by taking advantage of an equivalence relation between the likelihood function of the conditional logit and the Poisson regression we can, under certain circumstances, easily estimate a conditional logit model regardless of the number of choices. This insight should be particularly useful for studies of economic location.

Neighborhood topologies in fully-informed and best-of-neighborhood particle swarms

Abstract: We vary the way an individual in the particle swarm interacts with its neighbors. Performance depends on population topology as well as algorithm version.

Fiber Optic Sensors for Bridge Monitoring

Abstract: Advances in the production of optical fibers made possible the recent development of innovative sensing systems for the health monitoring of civil structures. The main reasons for this development are the reduced weight and dimensions of fiber optic sensors, the strong immunity to electromagnetic interference, the improved environmental resistance and the scale flexibility for small-gauge and long-gauge measurements. These systems can provide high-resolution and measurement capabilities that are not feasible with conventional technologies. In addition, they can be manufactured at a low cost and they offer a number of key advantages, including the ability to multiplex an appreciable number of sensors along a single fiber and interrogate such systems over large distances. For these reasons, it is evident that fiber optic sensors will change the instrumentation industry in the same way fiber optics has revolutionized communications. This paper provides an overview of the intensity modulated and spectrometric fiber optic sensors and techniques to assess the condition of existing structures in order to enhance the durability of the new bridges, increasing lifetime and reliability and decreasing maintenance activities. Application of these sensors to monitoring strain, temperature, inclination, acceleration, load measurements, ice detection, vehicles speeds and weights, and corrosion and cracking of reinforced and prestressed concrete structures will be described.

Osteogenic Induction of Human Bone Marrow-Derived Mesenchymal Progenitor Cells in Novel Synthetic Polymer–Hydrogel Matrices

Abstract: The aim of this project was to investigate the in vitro osteogenic potential of human mesenchymal progenitor cells in novel matrix architectures built by means of a three-dimensional bioresorbable synthetic framework in combination with a hydrogel. Human mesenchymal progenitor cells (hMPCs) were isolated from a human bone marrow aspirate by gradient centrifugation. Before in vitro engineering of scaffold-hMPC constructs, the adipogenic and osteogenic differentiation potential was demonstrated by staining of neutral lipids and induction of bone-specific proteins, respectively. After expansion in monolayer cultures, the cells were enzymatically detached and then seeded in combination with a hydrogel into polycaprolactone (PCL) and polycaprolactone-hydroxyapatite (PCL-HA) frameworks. This scaffold design concept is characterized by novel matrix architecture, good mechanical properties, and slow degradation kinetics of the framework and a biomimetic milieu for cell delivery and proliferation. To induce osteogenic differentiation, the specimens were cultured in an osteogenic cell culture medium and were maintained in vitro for 6 weeks. Cellular distribution and viability within three-dimensional hMPC bone grafts were documented by scanning electron microscopy, cell metabolism assays, and confocal laser microscopy. Secretion of the osteogenic marker molecules type I procollagen and osteocalcin was analyzed by semiquantitative immunocytochemistry assays. Alkaline phosphatase activity was visualized by p-nitrophenyl phosphate substrate reaction. During osteogenic stimulation, hMPCs proliferated toward and onto the PCL and PCL-HA scaffold surfaces and metabolic activity increased, reaching a plateau by day 15. The temporal pattern of bone-related marker molecules produced by in vitro tissue-engineered scaffold-cell constructs revealed that hMPCs differentiated better within the biomimetic matrix architecture along the osteogenic lineage.

Immobilized laccase for decolourization of reactive black 5 dyeing effluent

Abstract: Reactive Black 5 industrial dyeing effluent was decolourized by free and immobilized laccase. The stability of the enzyme (194 h free and 79 h immobilized) depended on the dyeing liquor composition and the chemical structure of the dye. In the decolourization experiments with immobilized laccase, two phenomenons were observed – decolourization due to adsorption on the support (79%) and dye degradation due to the enzyme action (4%). Dyeing in the enzymatically recycled effluent provided consistency of the colour with both bright and dark dyes.

Watch thy neighbor or how the swarm can learn from its environment

Abstract: Particle swarm optimization is a novel algorithm where a population of candidate problem solution vectors evolves "social" norms by being influenced by their topological neighbors. Until now, an individual was influenced by its best performance acquired in the past and the best experience observed in its neighborhood. In this paper, we introduce new ways an individual can be influenced by its neighbors.

Central and peripheral corneal thickness measurement with Orbscan II and topographical ultrasound pachymetry

Abstract: Purpose To compare thickness measurements of the central 60 mm of the cornea obtained with the Orbscan® II topography system and topographical ultrasound pachymetry Setting School of Optometry, University of Santiago de Compostela, Galicia, Spain Methods In 24 right eyes, pachymetric measurements were taken at the center and 12 mm and 30 mm on the superior and inferior hemimeridians A 1-sample t test was applied to assess the significance of the relationship between Orbscan II and ultrasound methods The relationship between the 2 was assessed by analyzing regression and plotting the differences against the mean corneal thickness Orbscan II data were analyzed in 3 ways: (1) without the application of an acoustic equivalent correction factor; (2) with a correction factor of 092, as recommended by the manufacturer; (3) with correction using the equations derived in this study The data were systematically compared with those of ultrasound pachymetry Results Before the correction factor was applied, the Orbscan II overestimated the corneal thickness at all locations, with the mean difference (4815 μm ± 3374 [SD]) significantly different from zero (P 05) Conclusions The acoustic equivalent correction factor proposed by the manufacturer to obtain corneal thickness measurements with the Orbscan II compared to those from ultrasound pachymetry was not valid for all corneal topography positions Orbscan II measurements agreed better with those of ultrasound pachymetry when equations for the central and each peripheral location across the topography were applied

Assessing structural and functional ecosystem condition using leaf breakdown: studies on a polluted river

Abstract: Summary 1. Leaf breakdown rates of Alnus glutinosa were determined and the structure of decomposer assemblages associated with leaves were analysed to assess the effect of pollution on the ecological condition of the Ave River (North-west Portugal). 2. Increase in organic and inorganic nutrients was associated with an increase in density and a decrease in richness of macroinvertebrates, a dramatic decline in the conidial production of aquatic hyphomycetes, but no major change in the richness of aquatic hyphomycetes. 3. Downstream nutrient enrichment was correlated with accelerated leaf breakdown rates. 4. The degree of functional impairment assessed by the ratio of leaf breakdown rates in coarse-mesh and fine-mesh bags was in accordance with the gradient of pollution defined by two biotic indices. 5. This study supports the contention that leaf breakdown experiments are a valuable tool to assess the effect of pollution on the ecological condition of rivers.

Development and properties of polycaprolactone/hydroxyapatite composite biomaterials.

Abstract: Polycaprolactone/hydroxyapatite (PCL/HA) composites were prepared by two different procedures. The first one consists of a conventional blending of the polymer and the reinforcement material in an extruder. The second method consists of grafting of PCL on the surface of HA particles. This was achieved by a ring opening polymerization of caprolactone in the presence of HA, where its OH groups act as initiators. By this method, it was possible to obtain, in one step, a composite of PCL and surface modified HA. In both methods different percentages of filler were used to obtain several composites. These composites were characterized with respect to their mechanical properties, in the dry and wet state, by means of tensile tests on compression molded samples. The polymer/filler interface was analyzed by scanning electron microscopy. Water uptake and weight loss degradation experiments were also performed. An increase in the modulus for higher amounts of filler was, as expected, observed in the composites obtained by both processes. Furthermore, the mechanical properties of the materials in the wet state are considerably lower than those in the dry state. However, this difference is more significant for the composites obtained by conventional blending than for composites obtained by the grafting procedure, indicating that the later procedure can be an adequate route to reduce water susceptibility of PCL/HA composites.

A Role Based Model for the Normative Specification of Organized Collective Agency and Agents Interaction

Abstract: In this article we propose a role based model for the specification of organized collective agency, based on the legal concept of artificial person and on the normative perspective of organizational systems. We focus on the analysis of groups of agents (humans or not) that want to act collectively in a (more or less) permanent basis, and in a stable and organized way, as it is the typical case of organizations. We argue that in those cases such groups of agents should give rise to a new agent, that we call of institutionalized agent, with its own identity, whose structure is essentially defined through the characterization of a set of roles and whose behavior is determined by the acts of the agents that play such roles. We also present a deontic and action modal logic that captures the concept of acting in a role and relates it with the deontic notions of obligation, permission and prohibition. This logic is used in the formal specification of institutionalized agents and of societies of agents and in the rigorous analysis of them. We pay particular attention to the interaction between agents through contracts or other normative relations. A high level specification language is also suggested.

National versus International Mergers in Unionised Oligopoly

Abstract: We analyse how the presence of trade unions affects the pattern of mergers in an international oligopoly and the welfare implications thereof. We find that an international merger results in lower wages for all firms. A national merger results in higher wages, highest for the non-merging firms. Using a model of endogenous merger formation, we find that the equilibrium market structure, if it exists, always implies one or more international mergers. Unless products are close substitutes there are more mergers than socially preferred.

THE INFLUENCE of FIELD STRENGTH, SUGAR and SOLID CONTENT ON ELECTRICAL CONDUCTIVITY of STRAWBERRY PRODUCTS

Abstract: The effects of field strength, soluble solids (from 14 to 59.5 °Brix) and particle size (using two size distributions) on electrical conductivity were investigated. Electrical conductivity increased with temperature for all the products and conditions tested following linear or quadratic relations. Electrical conductivity was found to vary greatly between strawberry-based products. an increase of electrical conductivity with field strength was obvious for fresh strawberries and strawberry jelly but not for strawberry pulp, probably due to the presence of texturizing agents. This parameter decreases with the increase of solids and sugar content. For some of the formulations tested (solid content over 20% w/w and over 40 °Brix) a different design of ohmic heater may be necessary because of the low values of electrical conductivity.

Electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ

Abstract: We study the electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ by means of density-functional band theory, Hubbard model calculations, and angle-resolved photoelectron spectroscopy (ARPES). The experimental spectra reveal significant quantitative and qualitative discrepancies to band theory. We demonstrate that the dispersive behavior as well as the temperature dependence of the spectra can be consistently explained by the finite-energy physics of the one-dimensional Hubbard model at metallic doping. The model description can even be made quantitative, if one accounts for an enhanced hopping integral at the surface, most likely caused by a relaxation of the topmost molecular layer. Within this interpretation the ARPES data provide spectroscopic evidence for the existence of spin-charge separation on an energy scale of the conduction bandwidth. The failure of the one-dimensional Hubbard model for the low-energy spectral behavior is attributed to interchain coupling and the additional effect of electron-phonon interaction.

Highly polymorphic microsatellite for identification of Candida albicans strains.

Abstract: The polymorphism of a new microsatellite locus (CAI) was investigated in a total of 114 Candida albicans strains, including 73 independent clinical isolates, multiple isolates from the same patient, isolates from several episodes of recurrent vulvovaginal infections, and two reference strains. PCR genotyping was performed automatically, using a fluorescence-labeled primer, and in the 73 independent isolates, 26 alleles and 44 different genotypes were identified, resulting in a discriminatory power of 0.97. CAI was revealed to be species specific and showed a low mutation rate, since no amplification product was obtained when testing other pathogenic Candida species and no genotype differences were observed when testing over 300 generations. When applying this microsatellite to the identification of strains isolated from recurrent vulvovaginal infections in eight patients, it was found that 13 out of 15 episodes were due to the same strain. When multiple isolates, obtained from the same patient and plated simultaneously, were typed for CAI, the same genotype was found in each case, confirming that the infecting population was clonal. Moreover, the same genotype appeared in isolates from the rectum and the vagina, revealing that the former could be a reservoir of potentially pathogenic strains. This new microsatellite proves to be a valuable tool to differentiate C. albicans strains. Furthermore, when compared to other molecular genotyping techniques, CAI proved to be very simple, highly efficient, and reproducible, being suitable for low-quantity and very-degraded samples and for application in large-scale epidemiological studies.

Nature-inspired calcium phosphate coatings : present status and novel advances in the science of mimicry

Abstract: There has been a growing awareness in materials science that the adaptation of nature biological processes can lead to significant progresses in the controlled fabrication of advanced materials for an all range of applications. To learn from, understand and apply these natural processes for producing calcium phosphate coatings that are biologically similar to bone apatite, mimicking its properties, has driven the attention of many researchers in recent years. This article reviews the most relevant advances in this emerging research field, pointing out several approaches being introduced and explored by distinct laboratories.

p-q Theory power components calculations

Abstract: The "generalized theory of the instantaneous reactive power in three-phase circuits", proposed by Akagi et al., and also known as the p-q theory, is an interesting tool to apply to the control of active power filters, or even to analyze three-phase power system in order to detect problems related to harmonics, reactive power and unbalance. In this paper it will be shown that in three phase electrical systems the instantaneous power waveform presents symmetries if 1/6, 1/3, 1/2 or 1 cycle of the power system fundamental frequency, depending on the system being balanced or not, and having or not even harmonics (interharmonics and subharmonics are not considered in this analysis). These symmetries can be exploited to accelerate the calculations for active filters controllers based on the p-q theory. In the case of the conventional reactive power or zero-sequence compensation, it is shown that the theoretical control system dynamic response delay is zero.

An improved method for high-quality RNA isolation from needles of adult maritime pine trees

Abstract: When conventional RNA isolation methods optimized for pine seedlings are applied to needles of adult pine trees, poor-quality RNA results. Here we describe a modified procedure to isolate high-quality RNA from needles of 30-year-old maritime pines, exhibiting high levels of phenolics, polysaccharides, and RNases. Major changes are the inclusion of proteinase K in the extraction medium followed by incubation at 42°C. Integrity and purity were evaluated by using denaturing gel electrophoresis and spectrophotometry (A260/A230 and A260/A280). The total RNA could be successfully used for poly(A)+-RNA isolation and cDNA library construction.

Laccases to Improve the Whiteness in a Conventional Bleaching of Cotton

Abstract: This study reports for the first time on the enhancement of the bleaching effect achieved on cotton using laccase enzyme. Laccases applied in short-time batchwise or pad-dry processes prior to conventional peroxide bleaching, improved the end fabric whiteness. The whiteness level reached in the combined enzymatic/peroxide process was comparable to the whiteness in two consecutive peroxide bleaches.