Phosphated crosslinked pectin as a potential excipient for specific drug delivery: preparation and physicochemical characterization

Pectin was chemically modified with different amounts of trisodium trimetaphosphate (STMP) in aqueous solution (pH = 12), thereby giving a material with reduced water solubility. The physiochemical characterization of this new material was carried out through Fourier transform infrared and thermogravimetric analyses. Phosphated pectin (Pect‐STMP) together with prebiotic (oligosaccharide) were incorporated into an aqueous dispersion of polymethacrylate (Eudragit^® RS 30 D) in order to obtain free films using a casting process (50 °C) on a Teflon plate. The free films were evaluated using water vapour transmission, average swelling index in simulated gastric fluid (SGF) and simulated intestinal fluid, scanning electron microscopy and a diffusion study with theophylline in buffer solution with and without pectinolytic enzyme. The results suggest that the new material can be used in the coating process for oral solid‐reservoir systems, to prevent the premature release of drugs in SGF (pH = 1.2). Furthermore, the presence of both Pect‐STMP and oligosaccharide favours the specific degradation of the pellicle by the action of the enzymes produced by colonic microflora. The material obtained in this work has the potential to be applied in devices for drug delivery in the colon, making possible modified release of drugs. Nevertheless, subsequent colon‐specific experiments in vivo need to be carried out in order to confirm the possible application of this new material. Copyright © 2009 Society of Chemical Industry     

Surface morphology evaluation of polymer beads based on divinylbenzene by atomic force microscopy

Macroporous poly(styrene‐co‐divinylbenzene) and poly(divinylbenzene) beads were synthesized by modified suspension polymerization in the presence of different mixtures of toluene and heptane as porogen agent. Through atomic force microscopy, it was possible to identify the microspheres and the channels between them that constitute the bead pores. It was also possible to make a comparison with the results obtained by nitrogen desorption, a traditional technique used to determine the porosity of macroporous copolymers in the dry state. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 541–551, 2002; DOI 10.1002/app.10290     

Topology optimization of periodic microstructures with a penalization of highly localized buckling modes

The problem of determining highly localized buckling modes in perfectly periodic cellular microstructures of infinite extent is addressed. A double scale asymptotic technique is applied to the linearized stability problem for a periodic structure built from linearly elastic microstructures. The obtained stability condition for the microscale level is then used to establish a comparative analysis between different material distributions in the base cell subjected to the same strain field at the macroscale level. The idea is illustrated by some two‐dimensional finite element examples and used to design materials with optimal elastic properties that are less prone to localized instability in the form of local buckling modes at the scale of the microstructure. Copyright © 2002 John Wiley & Sons, Ltd.     

Performance of curaua fibers in pullout tests

Natural lignocellulosic fibers are successfully replacing synthetic fibers as the reinforcement phase of composite materials in many engineering applications, including automobile parts. In addition to well-known conventional lignocellulosic fibers, others with promising properties, like that obtained from the leaves of the curaua plant (Ananas erectifolius) found in the Amazon region of Brazil, are now being considered. The present work investigated microstructural aspects associated with the performance of curaua fibers in pullout tests carried out to characterize the fibers interfacial strength with a polyester matrix. The results have shown that the naturally bonded filaments that constitute a curaua fiber present interspatial voids between them. These voids play an important role in providing adherence of the fiber surface to a polyester matrix, resulting in an effective reinforcement for a curaua-strengthened composite.     

Collapse analysis of steel jacket structures for offshore oil exploitation

This work describes the formulation of finite-element based numerical methods for global nonlinear collapse analyses of three-dimensional steel framed structures. Particular emphasis is dedicated to the reassessment and determination of residual strength of steel jackets that support offshore oil exploitation platforms. Two main aspects are considered: (1) the formulation for a three-dimensional geometric and material nonlinear frame element, and (2) the implementation of specialized techniques for the solution of the nonlinear problem. The formulation of the element combines a co-rotational approach to represent geometric nonlinearities, providing an accurate treatment of finite rotations, with the plastic hinge approach to represent material nonlinearities. The stiffness reduction due to yielding is performed through a smooth degradation, following a parabolic function. Effects of strain hardening, geometric imperfections and residual stresses are modeled in an efficient manner. In order to determine the full nonlinear equilibrium path and allow the correct determination of the collapse load, the solution strategies consider specialized “continuation” techniques such as the Arc-Length and the Generalized Displacement Control methods. Case studies are presented in order to demonstrate the accuracy, efficiency, and suitability of the implemented methods and techniques.     

A study of the drainages of the pyrite mines of Aljustrel (Portugal)

Characterization of the pollution charge of drainages from pyrite mines of Aljustrel (Portugal) was made. Laboratory experiments were performed in order to recover copper by cementation and remove iron, zinc and acidity by neutralization with lime. It was found that the removal of the metal ions is completed when pH reaches a step at 5.0–5.5, whichever the ratio between Fe(II) and Fe(III).     

A novel EspA-associated surface organelle of enteropathogenic Escherichia coli involved in protein translocation into epithelial cells

Enteropathogenic Escherichia coli (EPEC), like many bacterial pathogens, employ a type III secretion system to deliver effector proteins across the bacterial cell. In EPEC, four proteins are known to be exported by a type III secretion system_EspA, EspB and EspD required for subversion of host cell signal transduction pathways and a translocated intimin receptor (Tir) protein (formerly Hp90) which is tyrosine-phosphorylated following transfer to the host cell to become a receptor for intimin-mediated intimate attachment and 'attaching and effacing' (A/E) lesion formation. The structural basis for protein translocation has yet to be fully elucidated for any type III secretion system. Here, we describe a novel EspA-containing filamentous organelle that is present on the bacterial surface during the early stage of A/E lesion formation, forms a physical bridge between the bacterium and the infected eukaryotic cell surface and is required for the translocation of EspB into infected epithelial cells.     

Generalized topology design of structures with a buckling load criterion

Material based models for topology optimization of linear elastic solids with a low volume constraint generate very slender structures composed mainly of bars and beam elements. For this type of structure the value of the buckling critical load becomes one of the most important design criteria and so its control is very important for meaningful practical designs. This paper tries to address this problem, presenting an approach to introduce the possibility of critical load control into the topology optimization model.Using the material based formulation for topology design of structures, the problem of optimal structural reinforcement for a critical load criterion is formulated. The stability problem is conveniently reduced to a linearized eigenvalue problem assuming only material effective properties and macroscopic instability modes. The respective optimality criteria are presented by introducing the Lagrangian associated with the optimization problem. Based on this Lagrangian a first-order method is used as a basis for the numerical update scheme. Two numerical examples to validate the developments are presented and analysed.     

The use of magnesium silicate (talc) in a potentiometric sensor for hydrogen ions

The construction and analytical evaluation of a pH sensor based in a matrix containing 20% of [(Mg₆Si₈O₂₀)](OH)₄, a magnesium silicate, talc and 30% graphite dispersed in an epoxy resin (50%) is described. The data obtained from various acid–base titrations were compared with those using a glass electrode in the same conditions. The proposed electrode presented a linear response in the 1–12 pH range with a slope of −39.9±0.3 mV/pH (at 25 °C) and ca. 15 s of response time. The lifetime of this electrode was higher than 8 months (ca. 1500 determinations) and it showed a good performance for pH determination and end-point indication in the potentiometric titrations of acids and bases.