Cell migration is a fundamental biological process, which plays a pivotal role in wound healing, tissue morphogenesis and especially in diseased conditions like tumor metastasis. Previous studies have revealed how biophysical cues from the extracellular matrix (ECM) can modulate the nature of cell migration. Cells utilize a wide range of shapes (1, 2, and 3D) as they squeeze, push or tug, while navigating through a myriad of ECM architectures in a process commonly referred to as plasticity. While studies done on 2D flat continuous surfaces and 3D hydrogels have elucidated the role of material stiffness in influencing cell migration, they are unable to capture the role of fiber curvature, network architecture and density in a repeatable and controlled manner. Thus, here, using the non-electrospinning STEP (Spinneret Tunable Engineered Parameters) fiber manufacturing technique, we generate crosshatch fiber networks of controlled inter-fiber spacing (3, 6, 18, 36 and 54 µm) and investigate the role of fiber network density in influencing the plasticity of cell migration. For this study we primarily used metastatic thyroid cancer (Hras1) cells. Using 3 distinct levels of crosshatch inter-fiber spacing: Dense (3 µm, 6 µm), Intermediate (18 µm, 36 µm) and Wide (54 µm), we capture essential characteristics of 1, 2 and 3D migration. Unexpectedly, we observed that cells on dense inter-fiber spacing possessed elongated cell (aspect ratio \~5.5) and nuclear shapes with shorter focal adhesion clusters (FAC) and absence of well-developed actin stress fibers, features typical to cells moving in 3D gels. Additionally, confocal microscopy revealed significantly thicker nuclei in these cells. Quantitative video microscopy revealed that cells in these elongated 3D shapes migrated the fastest (46.2±2.5 µm/h on dense networks as compared to 25.3±1.5 µm/h on wide spacing networks) with high persistence (\~0.7). At intermediate spacing networks, cells demonstrated traditional 2D shapes featuring a broad leading edge and a narrow trailing edge, with their migration best described by the classical diffusive random walk model. At wide spacing, cells attain stable non-migratory kite shapes. In general, with increasing inter-fiber spacings, the FAC length increased, along with a concomitant emergence of well-defined actin stress fibers, thereby causing a reduction in the migration rate. Interestingly, migration on intermediate and wide crosshatch networks usually involved a distinctive recoil (detachment) of the trailing edge, which caused the nucleus to undergo significant deformation (\~35%) followed by gradual relaxation, while smoother movement of the trailing edge synchronously with the leading edge in dense networks resulted in significantly smaller nuclear deformations (\~5%). Thus, not surprisingly, faster relaxation times of the nucleus are recorded in cells migrating on very dense networks, thereby indicating potentially softer cell bodies, which is generally considered as a biomarker for enhanced metastatic potential. Taken altogether, our results using crosshatch networks of tunable inter-fiber spacing allows for studying *plasticity* in cell migration and, for the first time demonstrate that dense crosshatch networks are fertile environments for achieving persistent cell migration in 3D shapes.


Extracellular Matrix Fiber Density Regulates Plasticity in Cell Migration

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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