Stiffness-tuned matrices for tumor cell studies

Abstract

The stiffness of a cell’s microenvironment influences its behavior. Testing the effect of stiffness, or elasticity, on tumor cell behavior requires a matrix that provides the integrin binding sites that are found in stroma. Collagen I is a major component of stroma and allows integrin binding, but when it is reconstituted after extraction and solubilization, it is difficult to work with and too soft to model tumor tissue. Although the stiffness of collagen I matrices can be adjusted by changing collagen concentration, doing so also affects the number of integrin binding sites available to cells, confounding experimental variables. The goal of this work was to tune collagen I matrices over a range of elasticities (1–6 kPa) relevant for modeling normal and tumorous breast tissue, without altering the density of cell-matrix ligands. This was accomplished by functionalizing collagen I with glycidyl methacrylate (GMA), and using lithium acylphosphinate (LAP) as a photoinitiator of GMA cross-linking. Cross-links were photoactivated by irradiating the GMA-functionalized collagen at 365 nm for 2 min or less (4.4 mW/cm2). Breast cancer cells (MDA-MB-231) survived and migrated on these matrices. Collagen I-GMA gels can be used to ascertain how varying extracellular matrix elasticity affects breast cancer cell behavior.