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September 24-26, 2007, Turin, Ital

Controlled Release of Drugs FromHydrogel Based Matrices Systems: Experiments and Modeling

Hydrogels are materials largely used in the formulation of pharmaceuticals since, in principle, they could produce a release system of zero-order kinetics, which is of great therapeutic interest. In this paper, a model was proposed for the description of the main transport phenomena involved in the drug release process from hydrogel matrices (water diffusion, polymer swelling, drug diffusion and polymer dissolution); the model predictions are successfully compared with a large set of experimental data, obtained working with matrices systems based on HPMC (Hydroxy Propyl Methyl Cellulose). The proposed model was found able to reproduce main features of the observed phenomena, it can thus be adopted for prediction of the performances of drug release systems from hydrogel matrices

Scanning Nanocalorimetry at High Cooling Rate of Isotactic Polypropylene

A wide set of cooling scans and subsequent melting behavior of isotactic polypropylene (i-PP) were investigated using differential scanning calorimetry and nanocalorimetry at very high cooling rate. The latter technique offers, indeed, the distinctive possibility to perform heat capacity measurements at rates of more than 1000 K/s, both in cooling and in heating, to characterize the crystallization. When the i-PP sample was solidified with cooling rate larger than 160 K/s, a novel enthalpic process was observed that was related to the mesomorphic phase formation. Furthermore, at cooling rates higher than 1000 K/s, the i-PP sample did not crystallize neither in the α nor in the mesomorphic form. The subsequent heating scan starting from −15 °C showed an exothermic event, between 0 and 30 °C, ascribed to the mesophase cold crystallization

Ejection force of tubular injection moldings. Part II : a prediction model

The integrated knowledge of the injection molding process and the material changes induced by processing is essential to guarantee the quality of technical parts. In the case of parts with deep cavities, quite often the ejection phase of the molding cycle is critical. Thus, in the mold design stage, the aspects associated with the ejection system will require special consideration. In particular, the prediction of the ejection force will contribute to optimizing the mold design and to guarantee the integrity of the moldings. In this work, a simulation algorithm based on a thermomechanical model is described and their predictions are compared with experimental data obtained from a fully-instrumented mold (pressure, temperature, and force). Three common thermoplastics polymers were used for the tubular moldings: a semicrystalline polypropylene and two amorphous thermoplastics: polystyrene and polycarbonate. The thermomechanical model is based on the assumption of the polymer behavior changing from purely viscous to purely elastic below a transition point. This point corresponds to solidification determined by temperature in the case of amorphous materials and by critical crystallinity for semicrystalline polymers. The model results for the ejection force closely agree with the experimental data for the three materials used

Analysis and modeling of swelling and erosion behavior for pure HPMC tablet

This work is focused on the transport phenomena which take place during immersion in water of pure hydroxypropylmethylcellulose tablets. The water uptake, the swelling and the erosion during immersion were investigated in drug-free systems, as a preliminary task before to undertake the study of drug-loaded ones. The tablets, obtained by powder compression, were confined between glass slabs to allow water uptake only by lateral surface and then immersed in distilled water at 37 °C, with simultaneous video-recording. By image analysis the normalized light intensity profiles were obtained and taken as a measure of the water mass fraction. The time evolutions of the total tablet mass, of the water mass and of the erosion radius were measured, too. Thus a novel method to measure polymer and water masses during hydration was pointed out. Then, a model consisting in the transient mass balance, accounting for water diffusion, diffusivity change due to hydration, swelling and erosion, was found able to reproduce all experimental data. Even if the model was already used in literature, the novelty of our approach is to compare model predictions with a complete set of experimental data, confirming that the main phenomena were correctly identified and described

Swelling of cellulose derivative (HPMC) matrix systems for drug delivery

The water swellable hydrogels are commonly used in the production of solid pharmaceutical dosage systems for oral administration (matrices). Their use allows to obtain the controlled drug release. The key role is played by the transport phenomena which take place: water up-take, gel swelling and erosion, increase in diffusivity due to hydration. Thus, knowledge of these phenomena is fundamental in designing and realizing the pharmaceutical systems. In this work, tablets made of pure hydrogel, HydroxyPropyl-MethylCellulose (HPMC), were produced and immersed in a thermostatic bath filled with stirred distilled water (37 °C). The water up-take was allowed only by radial direction (from the lateral surface) by confining the tablet between two glass slides. Two distinct methods, an optical technique already described in a previous work, and a gravimetric procedure described here, were applied to measure the water concentration profiles along the radial direction in the tablets. The data obtained were used both to clarify the nature of the transport phenomena involved, and to perform a better tuning of a mathematical model previously proposed. doi:10.1016/j.carbpol.2009.05.00

Investigation of Pluronic (c) F127-Water Solutions Phase Transitions by DSC and Dielectric Spectroscopy

The water solutions of the block copolymers PEOn-PPOm-PEOn, known as pluronics, show a complex thermal behavior, since they are liquid at low temperature (5C), and they can give soft gel when heated at body temperature (37C). These properties are of great interest in biomedical applications. To properly design these applications, a prerequisite is the knowledge of the thermodynamics—how much—and of the kinetics—how fast—with which these transformations take place. In this work, solutions of F127 (the copolymer for which n ¼ 100 and m ¼ 65) were studied by varying the concentration and the temperature and analyzing their behavior when heated under several heating rates. The studies were performed by differential scanning calorimetry (DCS) and dielectric spectroscopy. The investigations carried out under equilibrium conditions allowed us to determine the thermodynamics of the phase transitions, whereas the investigations carried out under varying conditions allowed us to quantify the kinetics of the phase transitions. Empirical models were also proposed to describe both the thermodynamics and the kinetics observed