Solute transport in cyclically deformed porous tissue scaffolds with controlled pore cross-sectional geometries

Abstract

The objective of this study was to investigate the influence of pore geometry on the transport rate and depth after repetitive mechanical deformation of porous scaffolds for tissue engineering applications. Flexible cubic imaging phantoms with pores in the shape of a circular cylinder, elliptic cylinder, and spheroid were fabricated from a biodegradable polymer blend using a combined 3D printing and injection molding technique. The specimens were immersed in fluid and loaded with a solution of a radiopaque solute. The solute distribution was quantified by recording 20 microm pixel-resolution images in an X-ray microimaging scanner at selected time points after intervals of dynamic straining with a mean strain of 8.6+/-1.6% at 1.0 Hz. The results show that application of cyclic strain significantly increases the rate and depth of solute transport, as compared to diffusive transport alone, for all pore shapes. In addition, pore shape, pore size, and the orientation of the pore cross-sectional asymmetry with respect to the direction of strain greatly influence solute transport. Thus, pore geometry can be tailored to increase transport rates and depths in cyclically deformed scaffolds, which is of utmost importance when thick, metabolically functional tissues are to be engineered.

FIG. 1.

Schematic diagram (left) and photograph (right) of the experimental setup. The specimen is placed inside a fluid reservoir underneath a compression device. A molybdenum X-ray source is used to generate projection images of the specimen pore injected with X-ray contrast agent.

FIG. 2.

Representative micro-CT images (20 μm voxel size) of the specimens with pores in the form of a circular cylinder (1.5 mm), spheroid, and elliptic cylinder. White is scaffold material; black is air.

FIG. 3.

Projection X-ray images of the uncompressed specimen and the specimen at maximal level of compression. Side views are shown for the 1.5-mm-diameter circular cylinder (top left) and spheroid channel (bottom left). The elliptical channel is shown from the front with the compression perpendicular to (top right) and in parallel with (bottom right) the major axis of the elliptical cross section.

FIG. 4.

Consecutive projection X-ray images taken during compression-induced and passive removal of NaI from the specimen channels. Compression was performed at 1.0 Hz, such that 300 s correspond to 300 compressions. (A) Circular pore (1.5 mm diameter). (B) Spheroid pore. (C) Elliptic pore.

FIG. 5.

Relative iodine concentration in the specimen channel upon deformation-induced removal for the spheroid channel, 1.50 mm circular cylindrical channel, and elliptical channel. Data represent means ± SD for n = 5.

FIG. 6.

(A) Fraction of remaining iodine concentration after 300 s of passive transport (white bars) or deformation-induced transport (black bars). Data represent means ± SD for n = 5. *Significantly different compared to passive removal (p < 0.05). ^#Significantly different compared to 0.5-mm-diameter channel (p < 0.05). (B) Correlation between channel compression and remaining fraction of iodine after 300 s of compressions for the different channel shapes. Linear regression yielded a significant relationship (y = − 0.0131x +0.9735, R² = 0.9803). Note that the 2.0 mm circular channel was excluded from the regression.

FIG. 7.

Grayscale images of the measured intensities right after injection, subtracted from the measured intensity after 300 compression cycles. White pixels mean that contrast agent was completely removed at this position. Difference images are shown for the 1.5 mm circular cylinder pore (top left), the spheroid (top right), and the elliptic pore in both directions (bottom).

FIG. 8.

(A) Projection X-ray images of an imaging phantom with simple 2D pore network in the uncompressed state and at maximal level of compression (16.6% of the original height). (B) Consecutive projection X-ray images taken during compression-induced and passive removal of NaI from the phantom channels.