Activity Microscopy: Measuring single filament mechanical properties for biological network characterization

Both within and outside of the cell, molecular scaffolds perform vital roles in structural organization and the determination of mechanical properties. Inside the cell, the cytoskeleton is responsible for organelle organization, cell division, and active transport. Outside the cell, collagen fibrils in the extracellular matrix (ECM) provide rigidity to connective tissue. Micron scale mechanical properties of the ECM are vital for cell differentiation and motility, and local rearrangements of the ECM by forces applied via embedded cells. While macroscopic mechanical properties can be studied with rheology, studying properties on the single fibril level requires new tools. Activity microscopy, an optical-tweezer-based technique developed by our group allows one to visualize the locations, thickness, and fluctuations of individual fibrils as well as their connectivity within the network. To demonstrate the utility of activity microscopy, we measured the Young's modulus of individual collagen fibrils. Understanding of single fibril mechanical properties and connectivity will allow for the design of engineered networks with desired qualities. Activity microscopy is also well suited for studying stress distribution within networks critical for mechanotransduction and cell motility.