Marcos A. d'Ávila

Magnetic resonance imaging (MRI): a technique to study flow an microstructure of concentrated emulsions

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) have recently been recognized as important techniques for R&D of products and processes, as is attested by several successful applications in different areas of chemical engineering in recent years. In this article we present new experimental methods based on MRI to study flow and microstructure of concentrated emulsions. The objective is to present the unique features of this noninvasive technique to accurately measure different properties of flowing particulate opaque systems. Experimental results of velocity profiles, spatial distribution of droplet sizes and spatial homogeneity of an oil-in-water dispersion in a horizontal, concentric cylinder geometry using different pulse sequences are presented. The application of these techniques allowed probing important information on flow and microstructure of multiphase systems of interest in chemical engineering and food science.

Non-woven nanofiber chitosan/peo membranes obtained by electrospinning

The present work focused on the preparation and morphological characterization of chitosan-based nanofiber membranes, aiming at applications in medical and pharmacological areas. Membranes with nanofiber diameters ranging from 50 - 300 nm were prepared from polymer solutions through the electrospinning process. To stabilize the process, it was necessary to use poly(ethylene oxide) (PEO), which is a biocompatible synthetic polymer. Pure chitosan solutions, as well as chitosan and PEO solution blends, were characterized by their rheological behavior, conductivity, and surface tension measurements. The electrospun fiber thermal characteristics and crystalline structures were investigated through thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). Scanning electron microscopy images (SEM) were used for the morphological evaluations of the membranes. The addition of PEO to the chitosan solutions improved their electrical conductivity, surface tension and viscosity, greatly favoring the electrospinning process. Thus, membranes with 80% chitosan could be electrospun.

Electrospinning of Gelatin/Poly (Vinyl Pyrrolidone) Blends from Water/Acetic Acid Solutions

Electrospinning is a versatile and efficient technique for obtaining polymeric microfibers and nanofibers with great potential for applications in tissue engineering, biosensors, filtration, wound dressings, controlled drug release and enzyme immobilization. Electrospun fibers are obtained by applying an electric field in a polymer solution resulting in non-woven fibrous mats with high surface area relative to volume and high porosity. In this work, the electrospinning of gelatin/poly(vinyl pyrrolidone) (PVP) blends was investigated. The polymers were electrospun from solutions containing different concentrations of water and acetic acid. Solutions were characterized by measuring the pH, electrical conductivity, surface tension and viscosity. The influence of acetic acid concentration in solution properties and its influence in the spinnability were investigated. The resulting non-woven membranes were characterized by using scanning electron microscopy (SEM), thermogravimetric analysis (TG) and cytotoxicity.

In vitro and in vivo evaluation of electrospun membranes of poly (ε-caprolactone) and poly (rotaxane)

• PCL/PR electrospun membranes were not cytotoxic and can be used as a bioactive material.

Poly (L-Lactic Acid) and Hydroxyapatite Scaffold for Bone Regeneration: In Vivo Study

In bone tissue engineering, synthetic scaffolds are commonly used and this should present the following requirements; (i) recapitulate the native three-dimensional (3D) hierarchical fibrous structure, (ii) possess biomimetic surface properties and (iii) demonstrate mechanical integrity. However, some methods of producing scaffolds do not achieve these requirements. The present study aims the application of a composite of poly (L-lactic acid) (PLLA) and Hydroxyapatite (HA) produced by rotary jet spinning, which can be used to obtain scaffolds that meet the above requirements with affordable costs (regarding materials and production). The morphology and thermal properties of the scaffolds were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). For the in vivo tests, 20 Wistar rats, distributed into two groups, in which critical defects were performed in cranial calotte were used. Then scaffolds of PLLA/HA were implanted and compared with the control group that didn’t receive the implant. The results have shown that in the cases where only the defects in cranial caps were performed, bone healing did not occur. In cases where the scaffolds of PLLA/HA were used, rich neovascularization was noted, accompanied by foreign body type reaction and presence of reactive bone around the implants. The evaluation of PLLA/HA scaffolds used in the rat calvarial defect model, according to the criteria surveyed was favorable, showed the implants insurance and that they are suitable materials to be used as substitutes of calvarial bone tissue in these animals.