Rada Pjanović

The influence of membrane composition on the release of polyphenols from liposomes

Polyphenols are compound which are widely studied because of their antioxidative and potential therapeutic properties. Systems for the controlled release of drugs offer a number of benefits comparing with traditional forms of medicines and because of that these systems are widely researched. The objective of this paper is to investigate the possibility of using liposomes as carriers of polyphenols and influence the membrane composition on the release rate of encapsulated polyphenols. Experiments show how the membrane modification affects the mass transfer comparing to a conventional liposomes. Liposomes were modified with surfactants Tween 20 and Tween 60, and thyme tea extract was used as a source of polyphenols. The diffusion of polyphenols from thyme extract, dispersion of conventional liposomes and liposomes modified with Tween 20 and Tween 60 was studied using Franz diffusion cell. From the experimental data diffusion coefficients were determined for each of the systems, as well as the corresponding diffusion resistances. From the obtained results it can be concluded that the encapsulation of polyphenols in liposomes significantly slows diffusion, and with membrane modification can be achieved further slowing. The diffusion resistance of the liposome membrane modified with Tween 20 and Tween 60 is about 5 times higher compared to the diffusion of unencapsulated polyphenols from the thyme extract.

Mass transfer and fluid flow visualization in packed and fluidized beds by the adsorption method

Mass transfer coefficient (jD) between fluid and column wall in liquid packed and fluidized beds of spherical inert particle has been studied experimentally using adsorption method. Experiments were conducted in column 40 mm in diameter for packed and fluidized beds. In all runs mass transfer rates were determined in presence of spherical glass particles 2.06 mm in diameter. This paper introduced adsorption method as very suitable method for studies of mass transfer and for fluid flow visualization. The adsorption method is based on the dynamic adsorption of an organic dye onto a surface covered with a thin layer of a porous adsorbent. Local and average mass transfer coefficients were determinated from the surface color intensity of the foils of silica gel. Correlation jD = f(Re) was derived using mass transfer coefficients data.

Hydrodynamics and Mass Transfer in Heterogeneous Systems

Research of transport phenomena in liquid – particles systems, in past years, had a more theoretical then practical importance (Coudrec, 1985; Lee et al., 1997; Schmidt et al., 1999). For industrial use, especially with fast development of bio and water cleaning processes, better knowing of these systems become more important. An industrial application of these systems requires determination of transfer characteristics, especially mass transfer. Frequently mass transfer is the rate determining step in the whole process. However, in the real systems, it is not always easy to differentiate the limitation due to the mass transfers from that due to the hydrodynamic. Mass transfer in liquid-solid packed and fluidized beds has been widely investigated in terms of particle–fluid mass transfer by dissolution, by electrochemical and by ion-exchange methods (Damronglerd et al. 1975; Koloini et al. 1976; Dwivedi & Upadhyay, 1977; Chun & Couderc, 1980; Kumar & Upadhyay, 1981; Rahman & Streat, 1981; Yutani et al. 1987). Some of the results of mass transfer in packed and fluidized beds have been obtained as the transfer between an immersed surface and the liquid (Riba et al. 1979; Boskovic et al. 1994; Boskovic-Vragolovic, et al., 1996&2005). Liquid fluidization of particulate solids has a history which predates the now more commonly applied gas fluidization. The broad range of operations to which liquid fluidization has found applications are: classification of particles by size and density, a special case being sink-and-float separation by density; backwashing of granular filters and washing of soils; crystal growth; leaching and washing; adsorption and ion exchange; electrolysis with both inert and electrically conducting fluidized particles; liquid-fluidized bed heat exchangers and thermal energy storage; and bioreactors. Fluidized-bed bioreactors, which have received much attention during the past thirty years, are usually characterized by the catalytic use of enzymes or microbial cells that are immobilized by attachment, entrapment, encapsulation or self-aggregation. The most common application of such bioreactors is probably in wastewater treatment and, as in the case of the other operations mentioned above, liquid fluidization must in each case be weighed against competing schemes for achieving the same objective before it is adopted commercially (Epstein, 2003). In contrast to fluidized beds data, there are no published data on mass transfer in vertical and horizontal hydrotransport of particles.

Comparative Effects of Span 20 and Span 40 on Liposomes Release Properties

Abstract Liposomes are known as convenient carriers for a broad range of actives. The release rate of actives can be adjusted/controlled by the addition of different surfactants. The aim of this study was to compare the effects of two surfactants, Span 20 and Span 40, on liposomes release properties. In particular, the study shows how the membrane modification affects the mass transfer resistances and liposome size compared with the common liposomes. The aqueous extract of thyme was used as a model substance. It is a valuable source of natural antioxidants – polyphenols. The diffusion of polyphenols from native thyme extract (un-encapsulated) and from different types of liposomes was conducted using Franz diffusion cell. The results were approximated with Fick’s second law and they implied that liposomes modified with Span 20 provided the slowest release of polyphenolic compounds due to the highest value of mass transfer resistance (2.523 × 106 s/m).