O Direito de Arrependimento do consumidor nos contratos celebrados à distância: um estudo de Direito Comparado

Dissertação de mestrado em Direito dos Contratos e da Empresa

Extremely strong and tough hydrogels as prospective candidates for tissue repair – A review

Ideal candidates for the repair of robust biological tissues should exhibit diverse features such as biocompatibility, strength, toughness, self-healing ability and a well-defined structure. Among the available biomaterials, hydrogels, as highly hydrated 3D-crosslinked polymeric networks, are promising for Tissue Engineering purposes as result of their high resemblance with native extracellular matrix. However, these polymeric structures often exhibit a poor mechanical behavior, hampering their use in load-bearing applications. During the last years, several efforts have been made to create new strategies and concepts to fabricate strong and tough hydrogels. Although it is already possible to shape the mechanical properties of artificial hydrogels to mimic biotissues, critical issues regarding, for instance, their biocompatibility and hierarchical structure are often neglected. Therefore, this review covers the structural and mechanical characteristics of the developed methodologies to toughen hydrogels, highlighting some pioneering efforts employed to combine the aforementioned properties in natural-based hydrogels.

Characteristics and identification of sites of chagasic ventricular tachycardia by endocardial mapping

OBJECTIVE: To study electrophysiological characteristics that enable the identification and ablation of sites of chagasic tachycardia. METHODS: Thirty-one patients with chronic Chagas' heart disease and sustained ventricular tachycardia (SVT) underwent electrophysiological study to map and ablate that arrhythmia. Fifteen patients had hemodinamically stable SVT reproducible by programmed ventricular stimulation, 9 men and 6 women with ages ranging from 37 to 67 years and ejection fraction varying from 0.17 to 0.64. Endocardial mapping was performed during SVT in all patients. Radiofrequency (RF) current was applied to sites of presystolic activity of at least 30 ms. Entrainment was used to identify reentrant circuits. In both successful and unsuccessful sites of RF current application, electrogram and entrainment were analyzed. RESULTS: Entrainment was obtained during all mapped SVT. In 70.5% of the sites we observed concealed entrainment and ventricular tachycardia termination in the first 15 seconds of RF current application. In the unsuccessful sites, significantly earlier electrical activity was seen than in the successful ones. Concealed entrainment was significantly associated with ventricular tachycardia termination. Bystander areas were not observed. CONCLUSION: The reentrant mechanism was responsible for the genesis of all tachycardias. In 70.5% of the studied sites, the endocardial participation of the slow conducting zone of reentrant circuits was shown. Concealed entrainment was the main electrophysiological parameter associated with successful RF current application. There was no electrophysiological evidence of bystander regions in the mapped circuits of SVT.

Removal of ochratoxin A from contaminated white and red wines using oenological fining agents

Mycotoxins are toxic secondary metabolites produced by certain moulds, being ochratoxin A (OTA) one of the most relevant. Its chemical structure is a dihydro-isocoumarin connected at the 7-carboxy group to a molecule of L--phenylalanine via an amide bond. OTA contamination of wines might be a risk to consumer health, thus requiring treatments to achieve acceptable standards for human consumption [1]. According to the Regulation No. 1881/2006 of the European Commission, the maximum limit for OTA in wine is 2 µg/kg [2]. Therefore, the aim of this work was to know the effect of different fining agents on OTA removal, as well as their impact on white and red wine physicochemical characteristics. To evaluate their efficiency, 11 commercial fining agents (mineral, synthetic, animal and vegetable proteins) were used to get new approaches on OTA removal from white and red wines. Trials were performed in wines artificially supplemented (at a final concentration of 10 µg/L) with OTA. The most effective fining agent in removing OTA (80%) from white wine was a commercial formulation that contains gelatine, bentonite and activated carbon. Removals between 10-30% were obtained with potassium caseinate, yeast cell walls and pea protein. With bentonites, carboxymethylcellulose, polyvinylpolypyrrolidone and chitosan no considerable OTA removal was verified. In red wine, removals between 6-19% were obtained with egg albumin, yeast cell walls, pea protein, isinglass, gelatine, polyvinylpolypyrrolidone and chitosan. The most effective fining agents in removing OTA from red wine were an activated carbon (66%) followed again by the commercial formulation (55%), being activated carbon a well-known adsorbent of mycotoxins. These results may provide useful information for winemakers, namely for the selection of the most appropriate oenological product for OTA removal, reducing wine toxicity and simultaneously enhancing food safety and wine quality.