Functionalization of Electrospun Poly(vinyl alcohol) (PVA) Nanofiber Membranes for Selective Chemical Capture

Electrospun poly­(vinyl alcohol) (PVA) nanofiber membranes were functionalized by incorporating either poly­(methyl vinyl ether-<i>alt</i>-maleic anhydride) (PMA) to create negative charges, or poly­(hexadimethrine bromide) (PB) and chitosan (CS) to create positive charges on the fiber surface. The functionalized PVA nanofiber membranes were heat-treated at elevated temperatures to impart cross-linking and improve the water-resistance. The optimum heat-treatment temperatures for both PVA/PMA and PVA/PB/CS systems were screened by Fourier transformed infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Formation of cross-linked structure and increased crystallinity were triggered by the heat-treatment. A cationic dye, methylene blue (MB), and an anionic dye, acid red 1 (AR1), were used to represent charged moieties in solution. The surface-charged PVA nanofiber membranes were able to selectively capture counter-charged dye molecules from aqueous solutions. The capture processes obey the pseudo-second-order kinetic model. The capture equilibrium can be well-described by the Langmuir model. Chemically cross-linked PVA/PMA nanofiber membranes exhibited higher strength in capturing counter-charged dyes than physically cross-linked PVA/PB/CS nanofiber membranes. Selective chemical capture studies indicated that, by tailoring the surface, functionalized PVA nanofiber membranes were able to selectively remove charged chemicals with potential applications for purifying mixed liquids and delivering a pure sample for detection in small-scale testing systems

Increasing Stability of Biotin Functionalized Electrospun Fibers for Biosensor Applications

This paper describes the effects of both solvent and copolymer block lengths on the stability of electrospun poly­(lactic acid)/​poly­(lactic acid)-<i>b</i>-poly­(ethylene glycol) (PLA/​PLA-<i>b</i>-PEG) and PLA/​PLA-<i>b</i>-PEG-Biotin fibers in water. By tailoring the block length of copolymers PLA-<i>b</i>-PEG, water stability of electrospun fibers is improved over fibers reported previously. The solvent used also influenced the stability and hydrophilicity of resulting fibers. Fibers formed using 1,1,1,3,3,3-hexa­fluoro-2-propanol (HFIP) have greater water stability, but less PEG at the surface of fibers than fibers spun from dimethyl­formamide (DMF). Attaching biotin to the end of PLA(3600)-<i>b</i>-PEG­(2000) and spinning from DMF resulted, initially, in 7.6% of the total biotin incorporated into the fiber, assuming every PEG terminal had one biotin attached (1.1 mg of biotin per gram of fiber) available at the fibers’ surface. In addition, PLA/​PLA­(3600)-<i>b</i>-PEG­(2000)-Biotin spun from DMF hindered biotin migration to the aqueous phase, leaving 2% of the incorporated biotin remaining at the surface of fibers after 7 days of water exposure. The water wicking ability of DMF spun fibers also increased significantly with the biotin attachment to the PEG terminal. While HFIP spun fibers lost little biotin from fibers, there was no detectable surface available biotin, indicating biotin was at the interior. With biotin and PEG at the interior of the fibers spun from HFIP, the water wicking remained the same for PLA/​PLA­(3600)-<i>b</i>-PEG­(2000) spun samples and decreased for PLA/​PLA­(5700)-<i>b</i>-PEG­(1000). The dissimilarities observed in water wicking for HFIP spun samples are primarily the result of differences in fiber morphology