H.P. de Oliveira

Physical chemistry behavior of enteric polymer in drug release systems.

We report an analysis based on the electrical impedance (EI) spectrum of the samples of enteric random copolymer poly-methacrylic acid-co-methyl methacrylate as a function of pH of media. Important aspects of the charge transport and conformational processes in enteric polymer can be identified by mapping the complex impedance as a function of the frequency, which allows that some parallelism between titration and EI measurements can be obtained. However, the latter technique reveals details of this complex equilibrium that not appear using common titration methods. The relaxation frequency observed in the impedance spectrum act as a probe for the detection of phase transitions and conformational changes of the polymeric chains, once the distribution of size of particles can be related with this parameter. The progressive introduction of the alkali and the variation of pH between 4 and 10 are associated with a three steps process, related to the equilibrium shift from a precipitated solid or suspension, to a colloidal-like dispersion and to a complete solubilization of the copolymer. All those experimental features were reflected simultaneously as a turning point in plots of impedance, relaxation frequency and visible absorption with alkali addition giving a better and detailed insight to these processes.

Physico-chemical analysis of metronidazole encapsulation processes in Eudragit copolymers and their blending with amphiphilic block copolymers

A physico-chemical analysis of metronidazole-Eudragit copolymers L100 and RLPO (a cationic polymeric matrix with an electrophilic character) was carried out in order to explore the drug-polymer interaction and its possible effects on the encapsulation and release profiles. An oil-in-oil encapsulation procedure was designed to obtain more intimate drug-matrix mixtures and to obtain a better insight into the details of the interaction. The encapsulation efficiency obtained in these cases was high (in the range of 85-95%), but the release rates were quite rapid. Solubility and interaction between metronidazole and copolymers are discussed in detail with a view to explaining the results. Amphiphilic block copolymers of poly(ethylene)-b-(polyethylene oxide) (20, 50 and 80% PEO) were tested as a matrix for metronidazole release in order to improve drug profiles. The performance of RLPO as the matrix for drug release was improved by blending it with amphiphilic block copolymer poly(ethylene)-b-(polyethylene oxide) (20% PEO). The release mechanism of metronidazole is governed mainly by the swelling of RLPO, yielding a better fit with the second-order Schott equation.

Electrochemical Synthesis and Characterization of Multi-walled Carbon Nanotubes/Polypyrrole and Polypyrrole Hollow Nanotubes

We report the electrochemical synthesis and characterization of hybrid structures composed by hollow nanotubes of polypyrrole and core-shell composites of multi-walled carbon nanotubes (MWCNTs) coated by polypyrrole (PPy). The synthesis of these systems is critically dependent on relative concentration of carbon nanotubes (introduced as a template for polymerization) and affects the level of conductivity of media, the diameter and relative roughness of synthesized nanotubes. The competition induced by polymerization on the surface of different templates (aggregates of methyl orange and MWCNT) allows that smooth structures can be obtained, minimizing the synthesis of granules of polypyrrole, in a process that affects the morphology, thermal and electrical properties of synthesized materials. As a result, the impedance of mixed composite is lower than the other obtained for each system (MWCNT and hollow nanotubes of PPy), in an indication that synergistic interaction is favored during the synthesis.We report the electrochemical synthesis and characterization of hybrid structures composed by hollow nanotubes of polypyrrole and core-shell composites of multi-walled carbon nanotubes (MWCNTs) coated by polypyrrole (PPy). The synthesis of these systems is critically dependent on relative concentration of carbon nanotubes (introduced as a template for polymerization) and affects the level of conductivity of media, the diameter and relative roughness of synthesized nanotubes. The competition induced by polymerization on the surface of different templates (aggregates of methyl orange and MWCNT) allows that smooth structures can be obtained, minimizing the synthesis of granules of polypyrrole, in a process that affects the morphology, thermal and electrical properties of synthesized materials. As a result, the impedance of mixed composite is lower than the other obtained for each system (MWCNT and hollow nanotubes of PPy), in an indication that synergistic interaction is favored during the synthesis.

Composites of Enteric Polymer/Magnetite: Preparation and Application in Release Processes

The controlled release of drugs represents an interesting procedure applied in the minimization of side effects and in the therapeutic action of pharmacological molecules. With the aim of measuring the kinetics of release of aspirin dispersed in composite of an enteric polymer (Eudragit L-100) in the presence/absence of magnetic particles, we have considered the measurement of fluorescence as a convenient tool. The results indicate that rate of release and amount of dispersed drug in solution varies directly with the concentration of magnetite in the composite, as a consequence of strong interaction between components of microparticles.

Impedance spectroscopy investigation of the water-in-oil microemulsions formation.

In this work it was investigated the microemulsion formation using impedance spectroscopy analysis. The results indicated that the microemulsion formation is clearly observed on the impedance complex plane. The phase transition related with microemulsion formation is characterized by a time relaxation distribution. In the condition of the microemulsion formation, the impedance spectra are characterized by a single relaxation time.

Characterization and Electrical Response to Humidity of Sintered Polymeric Electrospun Fibers of Vanadium Oxide-(\({\hbox{TiO}}_{{2}} /{\hbox{WO}}_{{3}} \))

Metal oxide composites have attracted much consideration due to their promising applications in humidity sensors in response to the physical and chemical property modifications of the resulting materials. This work focused on the preparation, microstructural characterization and analysis of humidity-dependent electrical properties of undoped and vanadium oxide (V2O5)-doped titanium oxide/tungsten oxide (TiO2/WO3) sintered ceramic films obtained by electrospinning. The electrical properties were investigated by impedance spectroscopy (400 Hz–40 MHz) as a function of relative humidity (RH). The results revealed a typical transition in the transport mechanisms controlled by the appropriated doping level of V2O5, which introduces important advantages to RH detection due to the atomic substitution of titanium by vanadium atoms in highly doped structures. These aspects are directly related to the microstructure modification and structure fabrication procedure.