Improvement of catalytic efficiency of immobilized enzymes via materials engineering was demonstrated through the preparation of bioactive nanofibers. Bioactive polystyrene (PS) nanofibers with a typical diameter of 120 nm were prepared and examined for catalytic efficiency for biotransformations. The nanofibers were produced by electrospinning functionalized PS, followed by the chemical attachment of a model enzyme, alpha-chymotrypsin. The observed enzyme loading as determined by active site titration was up to 1.4% (wt/wt), corresponding to over 27.4% monolayer coverage of the external surface of nanofibers. The apparent hydrolytic activity of the nanofibrous enzyme in aqueous solutions was over 65% of that of the native enzyme, indicating a high catalytic efficiency as compared to other forms of immobilized enzymes. Furthermore, nanofibrous alpha-chymotrypsin exhibited a much-improved nonaqueous activity that was over 3 orders of magnitude higher than that of its native counterpart suspended in organic solvents including hexane and isooctane. It appeared that the covalent binding also improved the enzyme's stability against structural denaturation, such that the half-life of the nanofibrous enzyme in methanol was 18-fold longer than that of the native enzyme.

A novel method for the electrospinning of multiple polymer jets into nanofibres is presented. In this work, 20 wt% nylon 6 solution was electrified and pushed by air pressure through the walls of a porous polyethylene tube. Multiple jets formed on the porous surface and electrospun into nanoscale fibres. The length weighted fibre diameters have a similar mean diameter to those from a single jet but broader in distribution. The mass production rate from the porous tube is 250 times greater than from a typical single jet.

No abstract

Electrospinning of polymer nanofibers often begins with a single, straight, elongating, and electrified fluid jet that emanates from a droplet tip when the electric field at the surface is high enough. After some distance an electrically driven bending instability of the elongating jet occurs. For a polymer solution suitable for electrospinning, capillary instability does not cause the jet to become a spray of droplets. Under some conditions, a sequence of secondary jet branches emanates from the primary jet. This paper describes an experiment in which many closely spaced branches along the jet were observed during the electrospinning of a polycaprolactone solution. A theoretical description of the branching phenomenon is proposed.

Electrospun nanofibers are made when electrostatic forces overcome the surface tension of a polymer solution, causing an electrically charged jet to be ejected; as the jet travels through the air, the solvent evaporates, leaving behind an electrically charged fiber, which can be collected in the form of a nonwoven sheet. A superabsorbent was added to a polymer solution containing an elastomer (concentrations ϭ 0 -85%). The mixture was electrospun, producing nanofibers in which the superabsorbent particles were held in place with nanoscale elastic fibers. The nanofibers were tested for absorbency in water and synthetic urine. Fluid absorption by the nanofibers led to the formation of structured hydrogels. Increases in the weight gain from water absorption ranged from 400 to 5000%. The linear dimensions of samples cut from the nonwoven sheet were measured; wetting the superabsorbent increased the thickness dimension of the sheet dramatically and produced a smaller change in the plane of the sheet. The rate of water absorption was calculated; the samples containing 0 -70% superabsorbent reached essentially their maximum absorbency within 5 s. The excellent strength and elasticity of the wet samples make these structured hydrogels ideal for many uses, including wound care, drug delivery, and sanitary goods.