Study On Mechanism And Application Of Electrospun Nano-/micro Fibers With Controlled Patterns Or Secondary Structures

It is critical in the application of tissue engineering (TE) and drug delivery system (DDS) that the materials possess satisfactory biocompatibility, porosity, surface area to volume ration (or to mass ratio), mechanical properties and degradation rate. In addition, the interface structures and properties of substrate (scaffold or drug-loading materials) can greatly influence cell proliferation, interaction effect between cell and scaffold, drug loading and release behavior. The upgrade of electrospinning can fabricate nanofibers from a rich variety of functional materials, and the resultant electrospun nanofibers not only offers several advantages, including high surface area to volume ration (or to mass ratio),formation of interconnected porous networks and small diameter, but also spatial orientation and special secondary structures. These characteristics can provide more diversiform interfacial function and micro-level structures, which make investigation of electrospun fibrous materials has become more and more important in the areas such as membrane science, sensor, TE, and DDS. So obtaining the nano-/micro electrospun fibers with controlled pattern or secondary structures via electrospinning, this would have important value of academic study and potential application in tissue engineering and drug delivery system.Based on the interdisciplinary knowledge of mechanics, electricity, mathematics, biomedical engineering and pharmacy, we investigated and simulated the mechanism of pattern fabrication in the electrospinning, and based on this mechanism, we have experimentally demonstrated that various collectors could be to fabricate nanofibers with desired patterns and ordered architectures. Secondly, the effects of the electrospun nanofibers with special spatial pattern and porous secondary structures on interfacial properties, mechanical properties, cell proliferation, cellular organization and drug-loading and release were studied for potential application in TE and DDS.The major contents and results of the research are as follows:①Based on Poisson Equation of electrostatic field issue, the mapping between collector's structures with 3D electrostatic field in space was simulated and discovered by used FEM. Through constructing a FE 3D computational model of the electrostatic force applied on charged electrospun fibers, effects of electrostatic field's distribution on mechanical behavior of charged fibers when it get close to a collector that usually has a certain distance from the spinneret in the process of electrospinning was analyzed, which discovers the mechanism of the electrostatic field on the orientation and alignment of nanofibers. In summary, the electrical field distribution in electrospinning process can be simulated using FEM, and electrostatic force acting on depositing fibers can be analyzed. When the fibers get close to a collector, the component forces (Fa, Fz and Fn) acting on the depositing fibers can be relatively analyzed based on simulation results of the electrical field distribution on a collector. The component forces of electrostatic force in different direction make the movement of fibers bending, whipping and stretch during electrospinning. When the charged fibers can be arrived a special position (e.g. Position CD, Figure 2.9), the fiber would be oriented and then come into being special topological structures. As a result, the movement of a depositing fiber can be predicted via analysis of electrical forces applied on the fiber, which provides a better fundamental understanding as to different pattern and architecture created using different type of collectors.②Based on above-mentioned results, it is also anticipated that electrospun nanofibers could be fabricated with predestined patterns and architectures by controlling the direction of electrostatic forces acting on the depositing fibers via controlled the structures of collectors. We have experimentally demonstrated that electrospun nanofibers with various desired patters and ordered architectures were prepared predesigned collectors: uniaxially aligned arrays (Figure.3.6), radicalized aligned arrays (Figure.3.7, Figure.3.8D and E), aligned fibrous arrays and patterned with hierarchical architectures (Figure.3.8C) and complex topological structures (Figure.3.8A, Figure.5.3). The effects of topological structures on properties of electrospun fibers film were studied by analysis of morphology, surface properties and mechanical properties. The result showed that PCL NF Mesh had improved the tensile strength with Young's modulus of 6.27±0.53 MPa, which is >40% higher than the modulus of 4.4±0.57 MPa as measured with the corresponding randomly oriented PCL nanofiber mats (RNF mat). On the other hand, the ultimate strain (87.30%) of this PCL NF mesh was distinctly lower than that of the PCL RNF mat (146.46%).③When cultured with a mouse osteoblastic cell line (MC3T3-E1), the electrospun PCL NF meshes gave a much higher proliferation rate as compared with the randomly oriented PCL RNF mats. More importantly, it was found that the cells grew and elongated along the fiber orientation directions, and the resulted cellular organization and distribution mimicked the topological structures of the PCL NF meshes. These results indicated that the electrospun nanofiber scaffolds with tailored architectures and patterns hold potential for engineering functional tissues or organs, where an ordered cellular organization is essential.④Electrospun fibers with nano-/micro-scale porous structures were successfully fabricated from polymer solutions that contained suspended micro-/nano-size salt particles, which were subsequently removed through a leaching process after electrospinning. It was found that the size and dispersion of the salt particles had significant effects on the pore size and pore distribution in the resulting electrospun fibers. Using sodium chloride salt particles in the electrospinning process should not induce any residual toxicity in the resulting porous fibers. Therefore, this approach provides a very simple and versatile method in the fabrication of electrospun fibers that have secondary nano-/micro-scale porous structures, and more diversiform choice for materials. The result shows that the porous structures of electrospun fibers can not only affect its morphology and surface properties, but also the physical absorption and release properties of model drug AAP, which demonstrated that drug-loading volume of the electrospun nanofibers with porous structures (EPF) was 1.6 times as long as those fibers with smooth surface (ESF). By contrast, the EPF can make more completely (the cumulative release is 0.98) and rapidly AAP release from AAP-PCL electrospun fibers than ESF (the cumulative release is 0.67).