A handheld tissue force microscope - Cell and tissue mechanical properties play critical roles in physically shaping animals, organs, and tissues during development, growth, maintenance, regeneration, and disease. Early embryonic development and later growth utilize cell-generated physical forces to sculpt the body and organs. The micro-architecture and composition of these tissues is spatially, geometrically, and temporally complex. Adjacent tissues can differ widely in elastic modulus and can change greatly in a few hours as cells differentiate and gene expression changes. However, real-world knowledge of these properties is limited to a few model systems, where physical access and size of samples allow direct measurement. This gap is not due to lack of effort. Numerous technologies have been developed to sense these properties, but the applicability of these technologies has been limited by the need for samples with regular shape or with a quasi-planar geometry that is amenable to scanning with table-mounted mechanisms. To advance our understanding of embryonic development, there is a great unmet need for mechanical testing instrumentation that can handle more complex 3D geometry. We propose to address this problem by developing a handheld tissue force microscope. Our team has experience in atomic force microscopy and related techniques, and has developed an actuated handheld micromanipulator that enhances accuracy by performing active compensation of physiological hand tremor and that incorporates force sensing, highly accurate optical tracking of both the handle and the manipulated instrument tip, and camera-based visual tracking through the optical microscope. Based on our expertise in this area, we propose to develop a convenient and easy-to-use active handheld instrument that can perform dynamic mechanical analysis of embryos, organoids, and small tissue samples. Tremor compensation provided by the instrument will enable the user to precisely target desired locations for testing. Frequency sweeps will be performed automatically by the instrument. The sensing capabilities of the instrument will automatically ensure that the sinusoidal oscillation is applied perpendicularly to the local tissue surface. In data analysis, optical tracking of the instrument handle will allow the system to automatically correct for any residual motion disturbance that remains after active tremor compensation. Visual tracking will automatically register local point measurements to photographic images of the sample, enabling scans of any area of interest, up to and including the entire surface if desired. The specific aims are to develop a prototype capable of manipulating with accuracy of approximately 1 μm. (This will represent the “coarse” portion of a coarse-fine manipulation system); to develop a “fine” manipulator and sensing system for the tip of the instrument; and to integrate and evaluate the full prototype.
