Uniaxial cell stretcher enables high resolution live cell imaging

Imaging adherent cells cultured on commercially available stretchable substrates presents challenges for high-magnification objectives. Namely, short working distances between the objective and focal plane, a moving focal plane due to Poisson's contraction with stretching, and issues of optical transparency or non-matching refractive indices. Beyond the advantages of visualizing biological structures in detail, we seek to implement specialized high-resolution fluorescence microscopy techniques such as Förster Resonance Energy Transfer (FRET) microscopy while stretching. Enabling FRET imaging of stretched cells provides a powerful tool for modern cell biology and mechanobiology [1]. FRET techniques require high magnification as well as a stable focal plane for imaging. Here, we address this requirement for stretchable substrates with a microfabricated cell strain device suitable for live cell imaging while allowing high-resolution FRET microscopy of cells. We adapt a uniaxial cell stretching concept previously demonstrated by Huh [2] for high magnification imaging by using thin bottom channels and membranes supported above an inverted oil immersion objective. This work presents a major advance for research in cell mechanobiology as it enables direct mechanical actuation combined with imaging of FRET probes engineered to report strained proteins in live cells.