Nanofiber scaffolds with gradations in mineral content for mimicking the tendon-to-bone insertion site

Abstract

We have demonstrated a simple and versatile method for generating a continuously graded, bonelike calcium phosphate coating on a nonwoven mat of electrospun nanofibers. A linear gradient in calcium phosphate content could be achieved across the surface of the nanofiber mat. The gradient had functional consequences with regard to stiffness and biological activity. Specifically, the gradient in mineral content resulted in a gradient in the stiffness of the scaffold and further influenced the activity of mouse preosteoblast MC3T3 cells. This new class of nanofiber-based scaffolds can potentially be employed for repairing the tendon-to-bone insertion site via a tissue engineering approach.

Figure 1

A schematic of the procedure for generating a graded coating of calcium phosphate on a nonwoven mat of electrospun nanofibers. Ten times concentrated simulated body fluid was added at a constant rate to linearly reduce the deposition time from the bottom to the top end of the substrate. The parameter d refers to the distance from the bottom edge of the substrate.

Figure 2

SEM images of calcium phosphate coatings on a plasma-treated nonwoven mat of PLGA nanofibers. The images were taken from different regions, with d corresponding to: (a) 0, (b) 6, (c) 9, and (d) 11 mm. The scale bars in the insets are 2 μm.

Figure 3

Characterization of the mineral content. The plots show average calcium content as a function of d along the direction of gradient for (a) plasma-treated PLGA scaffolds and (b) gelatin-coated PCL respectively.

Figure 4

Mechanical testing of the graded scaffolds. There was a gradation in mechanical properties along the length of the scaffolds (a representative PLGA scaffold is shown). (a) The strains in the x₁ direction for three values of stress are shown. Localized strains are shown on the left and average strains are shown on the right. Strain increased with increasing stress and was highest on the unmineralized side of the scaffold. (b) There was a linear decrease in calcium phosphate along the length of the scaffold. (c) Young's modulus decreased with decreasing calcium phosphate content.

Figure 5

Cell culture data for the graded scaffolds. Fluorescence micrographs of MC3T3-E1 cells cultured on a graded scaffold made of gelatin-coated PCL nanofibers for 3 days and the average cell density as a function of d along the gradient. The images were taken from different regions (as indicated by d) along the gradient of calcium phosphate.