Fibrous Composites With Anisotropic Distribution of Mechanical Properties After Layer-by-Layer Deposition of Aligned Electrospun Fibers

Nanofibers and composite nanofibers have been used as mechanical reinforcement in a bulk matrix, but there is little research done on bulk nanocomposites made out of nanofibers. In the current study, in situ grown composite fibers of poly(DL-lactide) (PDLLA) and hydroxyapatite (HA) were obtained with uniaxial distribution, which were deposited by layer-by-layer with different interlayer angles, and hot-pressed into fibrous composites with anisotropic distribution of mechanical properties. Composite fibrous mats with the HA loading of 25.2 +/- 2.1% and orientation degree of 75.4 +/- 3.6% were obtained. Orthogonal experiments design was employed to qualitatively analyze effects of the hot-pressing parameters on the mechanical properties. The holding temperature, pressure, and duration were optimized as 60 degrees C, 2 MPa, and 10 min, respectively, to maintain the fibrous structure, strengthen the interfiber bondings, and eliminate the dimensional shrinkage of the hot-pressed fibrous composites. The ultimate tensile strength along the axial direction was 36.2 +/- 2.2 MPa, which was significantly higher than that along the transverse direction. Furthermore, the aligned composite fibers were deposited by layer-by-layer with different interlayer angles, and the quantitative equations of the ultimate tensile strength along the axial and transverse directions were drafted as a function of the interlayer deposition angles. The results of cell culture indicated that the presence of HA nanoparticles in the fibrous composites improved the hydrophilicity and provided favorable conditions for cell proliferation and osteogenic differentiation. It is suggested that hot-pressed fibrous composites with anisotropic distribution of mechanical properties be potential as bone substitutes and repairing devices.