Nutrient transport properties of tissue engineering membranes and scaffolds

There has been an increasing interest in the concept of growing artificial tissues in bioreactors which use numerous membranes and scaffolds to support the cellular processes such as cell growth and nutrient uptake. While these approaches are promising and may be considered to be successful in some circumstances, there is a general lack of quantitative information on the glucose (nutrient) diffusivity of these materials. In addressing this issue we have carried out a series of well-defined laboratory experiments to measure the glucose diffusion coefficient across a number of tissue engineering membranes and scaffolds saturated with water and cell culture medium (CCM). For this purpose, a diffusion cell was constructed and five different membranes and scaffolds with varying pore size and shapes were employed, which include cellulose nitrate membrane, polyvinylidene fluoride membrane, poly(L-lactide) scaffold, poly(caprolactone) scaffold and collagen scaffold. Pore size distribution, porosity and tortuosity of these materials were then determined and correlated to the glucose diffusivity values. As expected, we found that the diffusion coefficient increases with increasing pore size of the materials. These relationships are non-linear and may be non-monotonic in nature as they depend on a number of factors such as the basic building blocks of the materials which are non-periodic and heterogeneous in nature and vary within the same material, or from one material to another. We observed that glucose diffusivities in the materials saturated with CCM are not significantly different at a given temperature. Therefore, a conclusion can be drawn that despite the presence of extra components and difference in fluid properties of CCM compared to water the glucose diffusion coefficient in the tissue engineering membranes and scaffolds are not affected significantly due to the small molecular size of glucose.