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Microstructuration of nanofibrous membranes by electrospinning : application to tissue engineering

Abstract : The aim of this thesis was to develop new architectured nanofibrous biomaterials (2D or 3D) using the electrospinning method and to study the influence of these nanofibrous structures on bone cells behaviors. Electrospinning is a technique allowing the production of nanofibers by projecting, under the action of a strong electric field, a polymer solution on a collector. The nanofibers are generally randomly deposited and form mats or scaffolds. These scaffolds are interesting for tissue engineering applications because of their structure mimicking the extracellular matrix of living tissues. However, it has been shown that when the collector is microstructured, it is possible to control the organization of the fibers during their deposition through the local perturbation of the electric field at the vicinity of the surface of the collector. These micropatterned collectors act as "electrostatic templates". First, 2D honeycomb nanofibrous scaffolds were elaborated using micropatterned honeycomb collectors during the electrospinning process. These scaffolds were made either with poly(ε-caprolactone) (PCL) or poly(lactic acid) (PLA). We showed that the morphology of the PCL nanofibers (bimodal distribution of the fiber diameter) led to a scaffold with a strong relief. Despite, with PLA fibers which presented a monomodal distribution of the fiber diameter, the obtained scaffolds were much flatter. It was possible to control the spatial organization of bone-like cells MG-63 (osteoblasts), playing on the relief and the architecture of the scaffold. Subsequently, 3D materials were elaborated using micropatterned collectors in order to open new paths for the development of filling materials for bone regeneration. Microstructuration of PCL nanofibers (by the use of micropatterned honeycomb collector during the electrospinning process) coupled with the self-assembling properties of the PCL lead to the development of new 3D nanofibrous scaffolds, with controlled pore size and porosity gradient in the thickness of the scaffold. Afterwards, micropatterned composite 2D and 3D membranes were elaborated. By coupling the process of electrospinning with the process of electrospraying on micropatterned collector, we demonstrated that we can deposit the particles in a controlled way, especially on the walls of honeycomb patterns thanks to the presence of a thin fiber layer first deposited on the collector. This thin nanofiber layer plays the role of an "electrostatic template" for the particles deposition. Thereafter, this technique was applied to develop bilayers composite nanofibrous membranes containing PCL nanofibers and hydroxyapatite (HA) microparticles. These membranes consisted of 21 different microarchitectures (bars, blocks, hexagons, maze) were then incorporated into a small cell culture plate, thereby forming a new type of biochip for the screening of nanofibrous architectures. Indeed, these biochips allowed the screening of nanofibrous microarchitectures to identify the most relevant for bone regeneration. It turned out that the HA hexagonal structures (with an average diameter of 300 microns) and circular HA structures (with an average diameter of 150 microns) are the structures that enhance the most the mineralization process of bone cells. Finally, by combining simultaneously electrospinning nanofibers and electrospraying particles on micropatterned honeycomb collector, 3D composite scaffolds were elaborated. It was possible to control the size of cylindrical pores of these 3D composite from tens to hundreds of microns by changing the size of the honeycomb patterns of the collector.
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Salima Nedjari. Microstructuration of nanofibrous membranes by electrospinning : application to tissue engineering. Biomaterials. Université de Strasbourg, 2014. English. ⟨NNT : 2014STRAE027⟩. ⟨tel-01673838⟩

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