Experimental diffusion coefficients for three lots of five insulin drug products. 2D DOSY-NMR (solid circles) and DLS (open circles) results are plotted with the calculated diffusion coefficients of insulin (pdb 3aiy) monomer (1.61 × 10−6 cm2/s), dimer (1.22 × 10−6 cm2/s), and hexamer (0.87 × 10−6 cm2/s) shown as black, red, and blue dashed lines, respectively