Ron Avrahami

Encapsulation of Bacterial Cells in Electrospun Microtubes

Encapsulation of whole microbial cells in microtubes for use in bioremediation of pollutants in water systems was the main focus of this investigation. Coelectrospinning of a core polymeric solution with bacterial cells and a shell polymer solution using a spinneret with two coaxial capillaries resulted in microtubes with porous walls. The ability of the microtubes structure to support cell attachment and maintain enzymatic activity and proliferation of the encapsulated microbial cells was examined. The results obtained show that the encapsulated cells maintain some of their phosphatase, β-galactosidase and denirification activity and are able to respond to conditions that induce these activities. This study demonstrates electrospun microtubes are a suitable platform for the immobilization of intact microbial cells.

Buckling behaviour of electrospun microtubes: a simple theoretical model and experimental observations

The final form of tubular nanofibres produced by the co-electrospinning of two solutions (core/shell) is largely determined by the kinetics governing the buckling phenomenon. The buckling mechanism involves the evaporation of the core solution through a solidified shell resulting in a pressure difference across the fibre shell. Buckling can take place when the pressure drop across the fibre shell exceeds a critical value. In this work the physical conditions leading to fibre buckling are analysed from a kinetic point of view. A time interval, Δt, during which buckling may occur, is introduced as a single criterion determining the buckling probability. Different core/shell systems were spun by varying the surface tension, viscosity, flow rate, electric field and the diffusion coefficient of the core solvent through the fibre shell. The imaged as-spun nanofibres were analysed statistically to determine the buckling probability, and the corresponding Δt values were calculated using the values of the spinning parameters. The obtained data were fitted with an exponential distribution function which afforded determination of the characteristic time to buckling, tb. The results provide a means of predicting the buckling of tubular nanofibres. In particular, one can conclude that the dominant parameter determining the final form of the as-spun tubular nanofibres is the diffusion coefficient of the core solvent through the fibre shell.

Fabrication of thermoset polymer nanofibers by co-electrospinning of uniform core-shell structures

Continuous nanofibers consisting of a thermosetic polymer are described. The fibers were obtained using a two-fluid coaxial electrospinning technique. The type of coaxial electrospinning developed in this research is unique, in that the core structure is fabricated from a 100% volume fraction oligomer liquid encapsulated within a polymer shell, instead of a polymer dissolved in organic/aqueous solvents, as is customarily used. The core mass is subsequently polymerized by UV radiation. Post-spinning dissolving of the polymer shell yields defect-free thermosetic polymer nanofibers that have uniform morphology and diameter (50–800 nm). These nanofibers exhibit superior mechanical properties in comparison to those observed in the material bulk form.