EXAMINATION OF DIVERSE 3-D MICROENVIRONMENTS USING ATOMIC FORCE MICROSCOPY
Nicole Carvajal1, Andrew Doyle2, Kenneth Yamada2, Raimon Sunyer3, Albert Jin1.
1National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD, 2National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, 3Institute for Bioengineering of Catalonia, Barcelona, Catalonia, ES.
The physical parameters of the microenvironment, such as extracellular matrix (ECM) rigidity and ligand density, can govern cell migratory responses on simple 2-dimensional (2D) substrates. However, little is known about how a complex 3-dimensional (3D) ECM can impact cell migration. Atomic force microscopy (AFM) can image, with nanoscale resolution, both the topological and mechanical properties of biological samples in a fluid environment. Here, we measure the local physical attributes of 3D collagen gels to further our understanding of how the ECM can alter the mechanisms of cell migration. Through AFM, we explore the topological and mechanical properties of collagen with different architectures. Various gels were created by polymerizing collagen solutions (3 mg/mL) at different temperatures (37 °C, 21 °C, 16 °C, and 4 °C). This generated ECMs with different architectures. We used the AFM force-volume feature to capture force-displacement curves in 32 µm2 areas for each gel. We obtained height maps showing local topographical features of the different ECM architectures together with mechanical properties derived from the full force-displacement curves. Analysis of the measurements showed an overall similar average elasticity for all the collagen gels at the macro/cellular scale. However, at the micron/cell protrusion level, while gels with homogeneous architectures (37 °C) showed relatively small changes in local stiffness or topography, heterogeneous gels (16 °C and 4 °C) demonstrated more than 10-fold local variability. These results show that the presence of stiff, parallel-bundled fibers can impact the properties of a 3D ECM. These differences within a 3D microenvironment have direct effects on cell adhesion and migration.