Electrospun thermo-responsive nanofibers of poly(hydroxyethylacrylate-co-coumaryl acrylate-co-ethylmethacrylate)

Abstract

Abstract Thermo-responsive nanofibers were prepared by electrospinning poly(hydroxylethylacrylate-co-coumaryl acrylate-co-ethylmethacrylate) (P(HEA–CA–EMA)) dissolved in methanol. P(HEA–CA–EMA)s were prepared by free radical reaction using the reaction mixture of which HEA/CA/EMA molar ratio was 98:0:2, 96:2:2, 95:2.5:2.5, 94:3:3, and 92:4:4. P(HEA–CA–EMA) solutions (30% (w/v), in HEPES buffer (30 mM, pH 7.4)) became gel after they were subjected to UV irradiation (254 nm, 6 W) for 20 h. P(HEA–CA–EMA) exhibited lower critical solution temperature (LCST) behavior in aqueous solution and the LCST decreased from about 40 °C to below 20 °C, when the content of hydrophobic monomers (CA and EMA) increased from 0.7% to 5.5%. By an electrospinning process, P(HEA–CA–EMA) solutions in methanol were micronized into beads when the copolymer concentration was relatively low (e.g., 30%), and they were spun into nanofibers when the concentration was 60–80%. The nanofibers were subjected to UV irradiation to cross-link the constituent copolymer chains. The release of CF (a hydrophilic dye) from UV-treated P(HEA–CA–EMA) nanofibers was suppressed below LCST and promoted above LCST. As long as the temperature of release medium was higher than LCST, the release degree at a given temperature was higher when the nanofiber was composed of a copolymer exhibiting lower LCST. As LCST decreases, the dehydration degree and the hydrophobicity of the copolymers at a given temperature will increase thus the thermodynamic activity of the hydrophilic dye in the nanofiber will also increase, giving a rise to a higher release degree.