| Electrospun fibrous scaffolds possess an extremely high surface-to-volume ratio, tunable porosity, and malleability to conform over a wide variety of sizes and shapes, which have found wide applications in biomedical fields. Fibrous nanocomposites of hydroxyapatite (HA) and biodegradable polymers capable of compositionally and structurally emulating the basic building blocks of those naturally mineralized collagen nanofibers, would possess great potential for engineering functional native bone-like substitutes. The composite fibers were usually fabricated by blend electrospinning of HA and biodegradable polymers. However, the poor dispersion and easy agglomeration of the ceramic particles were indicated within the polymeric matrix, and the mechanical strength of fibrous composites could not be significantly improved. In current study electrospun nanofibers were surface modified with gelatin grafts to control the nucleation and growth of HA in simulated body fluid (SBF). The in vivo degradation and healing capabilities of bone defects were investigated after implantation of fibrous composites into animals. In addition, to mimic the gradient features of nature tissues and their interfaces, fibrous composites were constructed with gradient distribution of gelatin densities and HA contents. The cell growth and extracellular matrix secretion were also evaluated on the gradient fibrous mats.Fibrous composites of HA and poly(DL-lactide) (IGC) were obtained through in situ growth of HA on electrospun fibers grafted with gelatin as the induction sites. The presence and location of HA nanoparticles within electrospun fibers were supposed to affect the in vivo degradation behaviors and repairing process of load-bearing bone. About 90% of mass loss and 75% of molecular weight reduction were found after 16 wk implantation into animals, which were significantly higher than those after in vitro degradation in buffer solutions. Femoral defects were created for in vivo evaluation of bone repairing, indicating that the entire defect was filled with newly formed bone with compact bone structure along with the resorption of fibrous scaffolds after 16 wk implantation of IGC. X-ray analysis and SEM observation demonstrated successful bridging of the critical-sized defect on the sides both adjacent to and away from the femora. The in situ grown HA nanoparticles on the surface of electrospun fibers improved the biocompatibility with defect sites, promoted the bone formation within fibrous scaffolds and enhanced the bone remodeling. The promoted bone healing capability suggested that IGC should be a potential scaffold for the replacement and repair of bone defects.Utilizing a microinfusion pump, gradients of amino groups were generated on the fibrous surface by controlling the aminolysis time. Immobilization of gelatin was performed by glutaraldehyde coupling to form the gelatin gradients. The amino groups and geltin densities on the fibrous mats were quantitatively determined by ninhydrin and hydroproline analysis, respectively. By using fluorescein isothiocyanate (FITC) labeling, the gradient profiles were directly monitored by a fluorescence microscope. Then the fibrous mats were mineralization in SBF for 3 d, and the HA growth was controlled by different gelatin grafts. Fibrous mats with HA contentst from 2.5% to 27.5% were obtained, and the crystal size were regulated from 20.5 to 40.1 nm. MC3T3-E1 cells were cultured on the gelatin and HA gradient fibrous mats to test their cellular responses. The cell growth, differentiation and collagen secretion were dependent on the surface gelatin density, HA contents and crystal sizes. The HA contents affected the cellualr behaviors more significantly. The loading of plasmid DNA on gradient fibrous mats indicated a gradient transfection effeicciency. These results indicated the gradient distribution of gelatin densities and HA contents could be used to modify the biological response of MC3T3-E1 cells. |
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