Dave Mangindaan

Modulation of biocompatibility on poly(vinylidene fluoride) and polysulfone by oxygen plasma treatment and dopamine coating

Poly(vinylidene fluoride) (PVDF) and polysulfone (PSf) are two polymers with excellent mechanical properties but insufficient biocompatibility mainly due to their surface hydrophobicity. This study has applied oxygen plasma treatments and dopamine coating on the two polymers and investigated the changes of the surface properties and interactions with mammalian cells. All modification steps were verified by means of Electron Spectroscopy for Chemical Analysis and contact angle measurements. Surface topology of materials and biomolecules was studied by atomic force measurements (AFM) and scanning electron microscopy (SEM). Protein adsorption was quantified by fluorescent imaging and Bradford method. The results showed that O(2) plasma altered the surface hydrophilicity effectively on PSf and more than two folds of oxidation were obtained, when compared with the pristine one. The change of surface wettability was less significant on the O(2) plasma treated PVDF due to less oxidation extent, which was identified by analyzing the chemical compositions. The provided functionalized PVDF and PSf surfaces were tested with bovine serum albumin and L-929 mouse fibroblasts to evaluate the effects of surface modifications on protein adsorption and cell attachments. The biocompatibility was effectively promoted to fourfold and twofold on the hydrophobic PVDF and PSf by applying O(2) plasma treatments within short treatment time. Moreover, the simple immobilization of polymers in dopamine solution resulted in hydrophilic surface coating with stability that caused threefold and twofold increases of biocompatibility on PVDF and PSf correspondingly.

Application of the reaction engineering approach (REA) for modeling of the convective drying of onion

ABSTRACT In this study, the drying of thin layers of the “Violet de Galmi” onion (a variety mainly grown in West Africa) is presented in this article, along with the reaction engineering approach (REA) modeling for a comprehensive understanding of the drying kinetics. The experiments were conducted on a lab-scale dryer to form thin layer of cylindrical onion slice. By performing this experiment, the standard activation energy is evaluated and modeled. The model is validated by simulating the drying rates under various drying conditions. The comparison of simulation and experimental data is found to be satisfactory. This approach allows the determination of the internal characteristics of the onion for the further studies such as design of solar dryer for onion.