Fabrication And Properties Evaluation Of Aligned Ultrafine Composite Fibers With Core-Shell Structure

Using electrospinning technique to fabricate scaffolds biologically mimicking the natural extracellular matrix (ECM), has become one of the most intensively researched topics in the field of tissue engineering for regenerative medicine. However, the fibers from traditional electrospinning are usually produced in a randomly oriented form, which fails to meet the requirement for engineering some structurally anisotropic tissues (e.g., tendon and ligament) requiring aligned fibers. Previously, some researchers used high speed rotating drum (or other devices) as the collector to obtain aligned polymer fibers. However, due to the intrinsic jet bending instability or whipping in electrospinning, thus achieved fibers are still of inadequacy for practical applications in terms of the degree of fiber alignment, productivity and performance. A very recent approach termed ’stable jet electrospinning (SJES)’, which in principle is free of the instable whipping motion of electrospinning jet, offers a facile route to fabricate well-aligned polymeric fibers with high mechanical properties. However, how to functionalize the aligned ultrafine fibers with appropriate bioactivity has yet to be explored. Based on the SJES and the principle of coaxial electrospinning, the goal of this thesis is to have some natural biopolymeric components directly coated onto the surface of the synthetic polymer poly(L-lactic acid)(PLLA) through SJES, from which functional composite fibers with core-shell structure, high mechanical properties, bioactivity, and good alignment can be achieved for engineering the tendon tissue in a biomimetic manner.In this study, using PLLA as the inner component and some representative natural polymers (e.g., gelatin, collagen, hyaluronic acid and chitosan) as the outer component, we explored the feasibility of fabricating a variety of aligned ultrafine composite fibers with core-shell structure via SJES, in which a coaxial spinneret was otherwise used. This was accordingly called as the stable jet coaxial electrospinning (SJCES). Based on SJCES technique, a variety of combinations of polymers including PLLA-gelatin, PLLA-collagen, PLLA-hyaluronic acid, and PLLA-chitosan were experimentally attempted to systematically investigate:(1) mechanism and process control of SJCES;(2) performance evaluation of thus prepared aligned composite fibers in core-sheath configuration; and (3) the relationship between the process-structure-performance of the core-shell structured composite fibers from SJCES.The results indicated that the solution properties for electrospinning (e.g., concentration and viscosity) and process parameters (e.g., applied voltage, collecting distance, feeding rate and rotational speed of collector) play important roles in forming a stable jet with core-shell structure. Among the different process variables, solution feeding rate and rotational speed of collector were identified as the dominant factors influencing the diameters and shell thickness of the composite fibers from SJCES. It was also found that the wettability of pure PLLA become hydrophilic when natural biopolymers are coated onto the surface of PLLA. When rotational speed of collector is the same for fiber collection, the degree of fibers orientation and mechanical strength prepared from SJCES were outstanding than traditional instable jet based coaxial electrospinning. Finally, in order to make thus prepared composite fiber applicable in tissue engineering, the composite fibers of PLLA-gelatin and PLLA-hyaluronic acid were crosslinked in the steam of glutaraldehyde for rendering the outer component of natural biopolymers water indissoluble.