Electrospun nanoscale polymer fibers and their biomedical applications.

摘要

Electrospinning has been emerging as a novel nanofabrication technology to prepare continuous one-dimensional (1D) nanostructurc materials, which have found numerous applications in advanced nanocomposites and biomedical engineering.; In this dissertation, electrospun polystyrene (PS) nanocomposite fibers incorporated with nanofillers such as organoclay and carbon nanotubes (CNTs) have been successfully fabricated with controllable diameters from 50 nm to 5 mum. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to characterize the interior structure and the surface morphology of electrospun PS nanocomposite fibers. TEM micrographs demonstrated that the high shear force coupled with the rapid evaporation of the organic solvent during the electrospinning process results in the alignment of nanofillers parallel to the fiber axis direction. Shear Modulation Force Microscopy (SMFM) and an AFM based three-point bending measurement were utilized to investigate the glass transition temperature (Tg) and Young's modulus (E) of an individual electrospun fiber as a function of the fiber diameter and the nanofiller concentration. In the absence of nanofillers, no change in Tg was observed, even though a large increase of shear modulus below Tg was found, which is postulated to result from the molecular chain orientation during the electrospinning process. The incorporation of nanofillers in the fiber matrix significantly enhances the Tg of PS nanocomposite fibers, which can be attributed to the reduced mobility of molecular chains locally in contact with nanofillers. AFM three-point bending tests showed that the existence of nanofillers in the fiber matrix further increases the Young's modulus of the electrospun fibers especially when the fiber diameter is less than 250 nm.; To study the biomedical application of electrospun polymer nanofibers, a Hyaluronic acid (HA) derivative, 3,3-dithiobis(propanoic dihydrazide)-modified HA (HA-DTPH), was introduced to fabricate a three-dimensional (3D) nanofibrous scaffold. A homobifunctional cross-linker, Poly (ethylene glycol)-diacrylate (PEGDA), was selected to form cross-linked HA-DTPH nanofibers, which retained a fibrillar structure after hydration. The cross-linking reaction occurred simultaneously during the electrospinning process using a dual-syringe mixing technique. Poly(ethylene oxide) (PEO) was added into the spinning solution as a viscosity modifier to facilitate the fiber formation and was selectively removed with water after the electrospinning process. The nanofibrous structure of the electrospun HA scaffold was well preserved after hydration with an average fiber diameter of 110 nm. Cell morphology study on fibronectin (FN)-adsorbed HA nanofibrous scaffolds showed that the NIH 3T3 fibroblasts migrated into the scaffold via the nanofibrous network structure, demonstrating elaborate 3D dendritic morphologies within the scaffold, which reflect the dimensions of the electrospun HA nanofibers. These results suggest the application of electrospun HA nanofibrous scaffolds as a potential material for cell encapsulation and tissue regeneration.