How could diffusion across a biological membrane differ from diffusion across dialysis tubing?

Diffusion difference: Diffusion (D) is the process of passive (without loss of energy) movement of any substance from higher concentration to the lower concentration of that substance. D depends on the membrane and varies from membrane to membrane. There is no diffusion across dialysis tubing. Dialyzer (D) membranes vary as well so they is no accurate way to correlate the rate of D from a biological membrane and D.