Fiber Matrix Descriptors from Permeability Data Without Requiring Membrane Thickness: Theory, Results, and Optimization

Objective: Permeability of basement membrane and all other barriers contains a term for membrane thickness (Δ x ). This naturally leads to development of methods for measuring Δ x that are imprecise, inaccurate, expensive, subject to preparation artifact, and inattentive to variability. Although height and shape of permeability ( P ) vs. probe radius (α) curves are sensitive to Δ x , ln( P ) or ln( P /free diffusivity or D o ) curves have shapes independent of Δ x. It should, thus, be possible using such characteristics to determine fiber radius ( r f ) and void volume ratio (ε) without Δ x. We developed such a method to derive membrane structure by the standard model of Ogston and present its experimental evaluation. Methods: Basement membranes were self‐assembled using 1: 1 Matrigel: 0.01 M Tris/150 mM NaCl/1.0 mM CaCl 2 buffer on 0.4‐μ polycarbonate supports with transport measured in diffusion chambers using FITC‐labeled hydroxyethyl starch probes from 25 to 102 Å in radius. Sampling was at 0.5 hr and then for each hour up to 5. Other membranes were measured 7 days after formation. Results: The best fit of the new technique occurred at 3 hr with R 2 = 0.949 ± 0.003 SEM, r f = 36.8 ± 2.4 Å, and ε = 0.87 ± 0.02. Membranes studied for 7 days showed more variability but essentially the same characteristics. Conclusions: Membrane thickness is not necessary to reduce permeability of basement membrane to structure, and optimum sampling time is 3 hr.