Fabrication Of Porous Polymer Ultrafine Fibers Through Electrospinning And Its Application

Electrospinning is a simple and versatile technique for generating ultrafine fibers with tens to hundreds of nanometers in diameter. In comparison with traditional non-porous fibers, the electrospun porous fibers have higher surface area and greater roughness, which assure its promising applications in various areas, such as tissue engineering scaffolds, catalyst carriers, high sensitivity biological sensors and filters. This thesis research work includes the following aspects:(1) Porous cellulose acetate (CA) ultrafine fibers with pores of 60-750 nm in diameter were prepared by electrospinning. The fiber morphology and pore structure were characterized by scanning electron microscopy. The specific surface areas were measured by the BET method. The effects of solvent types, solvent composition, CA concentration and environmental relative humidity on the pore structure of CA fibers were studied. It was found that the pore diameter and distribution could be regulated by adjusting the nature of the spinning solutions and electrospinning parameters. The pore structure of CA ultrafine fibers substantially increased the specific surface areas, as a result, the specific surface areas of porous CA fibers was 10 times more than that of pore free CA fibers.(2) Porous polycaprolactone (PCL) ultrafine fibers were prepared by electrospinning. The fiber morphology and pore structure were characterized by scanning electron microscopy and atomic force microscopy. Elliptical pores were generated on fiber surfaces with most pore size of a few hundred nanometers. The pore diameter was affected by solvent, temperature, relative humidity, and PCL concentration. Porous fibers were easily produced using chloroform (TCM) as the solvent, whereas non-porous fibers were obtained with acetone solvent though those two solvents have similar vapor pressure. The pore size of porous PCL fiber increased from 238×318 (width x length) nm to 1277×1325 nm with relative humidity increasing from 30% to 80%, while it increased from 120×293 nm to 1277×1325nm with temperature increasing from 15℃to 25℃. Porous structure increases fiber surface roughness and surface area. Thus such fibers favor cell adhesion, and can be used as a promising scaffold. Dental pulp stem cells (DPSCs) were cultured on scaffolds, in comparison with non-porous fiber scaffolds, the electrospun porous fiber scaffolds promoted the adhesion and proliferation of seed cells.(3) Cellulose acetate (CA) ultrafine fibers was spun and hydrolyzed into cellulose nanofibers (CNF), and phosphorylation cellulose fibers (PCNF) were prepared by phosphorylation reaction. According to the principle of biomimetic synthesis, hydroxyapatite (HAp)/CNF and HAp/PCNF composite materials were synthesized by soaking in simulated body fluid solution (SBF) for 7,14,21 and 28 days at 37℃. Composite materials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), field emission transmission electron microscopy (HRTEM), Fourier infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS). The XRD studies showed that the HAp was formed on the surface of the CNF and PCNF after 14 days in the SBF solution. The crystallite sizes of the HAp crystals were respective 20 nm, and 24 nm for thel4-HAp/CNF,14-HAp/PCNF samples. After soaking in 1.5 SBF for 14 days, SEM observations demonstrated that HAp crystals were uniformly formed on PCNF whereas little HAp was observed on individual CNF. The thickness of HAp crystal layer increased with the cultured time. XPS results showed that phosphate was grafted to CNF by phosphorylation process, and HAp was formed on the surface of PCNF after soaking in the SBF solution. FTIR results revealed that the crystals formed on the CNF and PCNF were calcium-deficient hydroxyapatite, PO4 sites of the HAp structure were partially substituted by CO32- and HPO42-.(4) Polyacrylonitrile fiber was spun and hydrolyzed with 1 mol/L NaOH/EtOH solution into carboxyl-containing PAN fiber (H-PANF). HAp/H-PANF composite materials with a 3-dimensional (3-D) network were synthesized by biomimetic method in SBF of soaking at 37℃. Composite materials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS). The XRD studies showed that the HAp was formed on the surface of H-PANF after 14 days in the SBF solution. The crystallite sizes of the HAp crystals were 16.4 nm for the 14-HAp/H-PANF samples. SEM observations demonstrated that HAp crystals were uniformly formed on H-PANF after soaking in 1.5 SBF. The thickness of HAp crystal layer increased with the cultured time. XPS results showed that PAN hydrolyzed product contains carboxylic and amide groups, and HAp were formed on the surface of H-PANF after soaking in the SBF solution. FTIR results revealed that PAN hydrolyzed product was multi-block copolymer composed by polyacrylonitrile, polyacrylamide and polyacrylic acid. The HAp/H-PANF composites are promising for applications in tissue engineering.