Biomedical subjects

Behrooz Nasseri

Publications and source records attributed to Behrooz Nasseri.

6 recordsLinked to original sources

PubMed2005

Effect of cholesterol and temperature on the elastic properties of niosomal membranes.

The mechanical characteristics of non-ionic bilayer membranes composed of sorbitan monostearate, cholesterol and poly-24-oxyethylene cholesteryl were studied by measuring the modulus of surface elasticity (mu), a measure of membrane strength, as a function of cholesterol content and temperature. The modulus of surface elasticity increased slowly with increasing cholesterol concentration, with a sharp increase around 40 mol% cholesterol (on average an increment of 0.43x10(6) Nm(-2) per molar percentage), and displayed a maximum of 6.5x10(6) Nm(-2) around 47.5 mol% cholesterol. Further cholesterol resulted in a decrease in mu. Generally the interaction of cholesterol with sorbitan monostearate should increase the rigidity of the membrane. However, the latter effect may be due to the formation of cholesterol clusters at high cholesterol content where excess amounts of cholesterol cannot interact with the sorbitan monostearate, and deposits on the bilayers compromising their uniformity, strength and permeability. This behavior was evident when measurements were carried out above and below 25 degrees C.

Cholesterol↗

PubMed2005

The relative flow of the walls of phospholipid tether bilayers.

Lipid nanotubes or "tethers" can be formed from liposomes or niosomes, pulled from the parent vesicles by micromanipulation. The tethers are cylindrical multibilayer tubes. Here, we describe the movement of these multilamellar walls, initiated by creating a surface tension gradient along the tether. The movement of lipid can give rise to a visible moving boundary. In the case of bilayer membranes, a tangential gradient in surface tension produces membrane bulk flow toward regions of higher surface tension. The flow of the bilayers comprising the tether nanotubes seems to be restricted to the inner bilayers, creating a velocity gradient in the bilayers. In this study, we discuss the implementation of tension-driven flows as a transport method in a tether-vesicle network. Interactions between fluid within the tether channels and the lipid layers are important, leading to anomalies in the transport of fluids and particles compared to bulk systems.

Cholesterol↗

PubMed2003

Microtubules formed by capillary extrusion and fusion of surfactant vesicles.

Polyhedral non-ionic surfactant vesicles formed from mixtures of polyoxyethylene-5-cetyl ether (C(16)EO(5)) or polyoxethylene-5-stearyl ether (C(18)EO(5)) with poly-24-oxyethylene cholesteryl ether (Solulan C24) and low amounts of cholesterol, when extruded from microcapillaries under pressure fuse to form multi-lamellar tubules up to about 80 microm in length. The diameter of the extruded tubules depends on the exit diameter of the capillaries used, in this paper generally around 1 microm. Under some circumstances, instead of linear tubules, the tubules form as concentric whorls which can be unraveled into their constituent tubules, indicating the strength of the systems. Vesicles can be formed within these tubular structures to act as a model for vesicular flow in elastic capillaries. Microparticles encapsulated with the primary polyhedral vesicles after extrusion are seen within the tubules, promising the possibility of a model for the study of microparticle flow within vessels. Preliminary studies on the use of the tubules as templates for polymerisation are also presented.

Microspheres↗

PubMed2003

A vesicular shuttle: transport of a vesicle within a flexible microtube.

Micromanipulation of the external bilayers of nonionic surfactant vesicles (niosomes) and liposomes allows the formation of tethers, which are fluid state lipid/surfactant lamellar nanotubes. The technique allows investigation of some of the factors affecting tether formation and vesicle-tether interactions. In this paper the movement of a vesicle along, or more precisely in, tethers derived from the vesicle, has been studied. When a vesicle is supported by bipolar tethers, stretching the tether on one side of the vesicle, initiates the movement of the vesicle in the opposite direction, at velocities ranging up to 2.5 microm s(-1) thus creating a 'vesicular shuttle'. Movement of the vesicle occurs inside the tether structures, a process akin to the movement of a sphere in a flexible tube with a diameter much less than that of the sphere. The factors involved in the movement of vesicles in the tethers include the radial stretching and subsequently contraction of the tethers and the minimisation of elastic energies stored in the tether membranes. Vesicle velocity is not constant: there is deceleration near the end of the trajectory. While the relevance to the design of novel delivery systems is as yet tenuous, the system allows vesicle-vesicle collisions to be observed when the vesicle is propelled towards a stationary vesicle, and directly observation of the flow properties of vesicles in flexible 'capillaries', a neglected topic.

Algorithms↗

PubMed2003

Some properties of extruded non-ionic surfactant micro-tubes.

Polyhedral non-ionic surfactant vesicles (niosomes) undergo complex shape transitions as a result of mechanical stress. When extruded under pressure from capillaries with exit diameters smaller than the diameter of the vesicles, a series of novel structures comprising mostly of tubules, vesicles inside tubules and concentric structures can be formed. The microtubules (up to 80 microm in length) form as a result of the pressure exerted on polyhedral niosomes, this leading to the fusion of many vesicles, the relative shear giving movement of the vesicles giving rise to the formation of three distinctive structures, namely tubules, vesicle within tubule and concentric ("whorl") morphologies. The entrapment efficiency of the tubules has been studied using a model solute 5(6)-carboxyfluorescein (CF), as has the effect of shear stress this and compaction pressure on the release of the entrapped solute. Deformation of the structures affects their ability to retain entrapped solute. Tubular structures heated above their transition temperatures reversibly transform into discrete vesicular structures.

Chemistry, Pharmaceutical↗

PubMedDate not supplied

Exploring soft matter: liposomal vesicles and their tethers.

The malleability of soft matter such as vesicular systems, allows their mechanical manipulation into various interesting structures. Their inherent elastic membrane properties can be utilized in fabricating micro-scaled transport machineries. In this paper, we have described several features of research carried out in our laboratory. This includes the self-healing ability of multilamellar liposome on removal of their inner core. The formation of tethers from their outer bilayers into complex networks has been demonstrated. Photo enhancement of images has revealed the apparent existence of narrow channels inside such tethers. The tethers channels were subsequently used as transport conduits to carry solid polystyrene microspheres as well as large liposomes larger than the tether diameter under controllable speeds of up to 2 microm s(- 1). The possibility of producing multi-compartment liposomal systems connected to each other directly by fusion or indirectly via tether networks has provided us with a system capable of transporting components from one vesicle entity to another.

Biological Transport↗