FIG. 1.

Capillary tube diffusion experimental set-up. (a) For microscope imaging, three capillary tubes filled with hydrogel and protein solution were affixed to a glass slide (approximately 0.5 mm apart) using Silly Putty™. (i) Bright field image of capillary tubes filled with 2% (w/v) collagen hydrogels. Fluorescence [green fluorescent protein (GFP) channel] images of free fluorescein dye, fluorescein-labeled bovine α-chymotrypsin, and fluorescein-labeled bovine serum albumin diffusing through collagen hydrogels at (ii) 0 h and (iii) 2 h. (b) Experimental profiles of fluorescence intensity signals obtained from images taken 4 and 60 min after the start of protein diffusion. Fluorescence intensity signals were normalized to the signal of the protein reservoir. Theoretical profiles of normalized fluorescence calculated using a one-dimensional model of diffusion [Eq. (1)] for diffusion through capillary tubes. Experimental and calculated profiles are comparable. (Chi-square tests, p = 0.95 at 4 min, p = 0.99 at 60 min.)