Effects of Concentration, Cross-Linking, and Compression on Macromolecular Partitioning in Biological Hydrogels.

Transport of macromolecules in biological hydrogels is important for understanding delivery, distribution, and movement of growth factors, cytokines, and peptide- or protein-based drugs within and between biological tissues. This is primarily mediated by basement membranes and extracellular matrixes that separate tissue compartments and structurally support the extracellular microenvironment. Changes in the extracellular matrix (ECM) architecture alter molecular transport and have implications for delivery of biologically active agents in both normal and pathological settings. Matrix density and cross-linking are altered in cancer, fibrotic diseases, and diabetes. Under physiological conditions, ECMs may be compressed to varying degrees under normal or pathological stresses. Here we used multiple biological hydrogels including agarose, collagen I, and Matrigel to understand the relative effects of concentration, cross-linking, and compression on nanoscale molecular transport. We hypothesized that increasing concentration, enzymatic cross-linking, and imparting gel compression would all result in reduced molecular partitioning into hydrogels due to reductions in gel porosity. We found that concentration and compression had significant impacts on molecular partitioning into hydrogels. Cross-linking with multiple enzymatic and chemical cross-linkers increased gel stiffness but had minimal impact on diffusion-based molecular transport. These results indicate that changes in matrix architecture due to increased concentration or reductions in porosity induced by mechanical compression, but not cross-linking, significantly alter macromolecular transport in biological hydrogels.