Fluorescence imaging is an indispensable tool in biology, with applications ranging from single‐cell to whole‐animal studies and with live mapping of neuronal activity currently receiving particular attention. To enable fluorescence imaging at cellular scale in freely moving animals, miniaturized microscopes and lensless imagers are developed that can be implanted in a minimally invasive fashion; but the rigidity, size, and potential toxicity of the involved light sources remain a challenge. Here, narrowband organic light‐emitting diodes (OLEDs) are developed and used for fluorescence imaging of live cells and for mapping of neuronal activity in Drosophila melanogaster via genetically encoded Ca2+ indicators. In order to avoid spectral overlap with fluorescence from the sample, distributed Bragg reflectors are integrated onto the OLEDs to block their long‐wavelength emission tail, which enables an image contrast comparable to conventional, much bulkier mercury light sources. As OLEDs can be fabricated on mechanically flexible substrates and structured into arrays of cell‐sized pixels, this work opens a new pathway for the development of implantable light sources that enable functional imaging and sensing in freely moving animals.

Important dynamic processes in mechanobiology remain elusive due to a lack of tools to image the small cellular forces at play with sufficient speed and throughput. Here, we introduce a fast, interference-based force imaging method that uses the illumination of an elastic deformable microcavity with two rapidly alternating wavelengths to map forces. We show real-time acquisition and processing of data, obtain images of mechanical activity while scanning across a cell culture, and investigate sub-second fluctuations of the piconewton forces exerted by macrophage podosomes. We also demonstrate force imaging of beating neonatal cardiomyocytes at 100 fps which reveals mechanical aspects of spontaneous oscillatory contraction waves in between the main contraction cycles. These examples illustrate the wider potential of our technique for monitoring cellular forces with high throughput and excellent temporal resolution.

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SummaryDuring locomotion, soft-bodied terrestrial animals solve complex control problems at the substrate interface without needing rigid components, a capability that promises to inspire improved soft-robot design. However, the understanding of how these animals move remains fragmented, in part due to an inability to measure the involved ground reaction forces (GRFs). Here, we perform all-optical mapping and quantification of GRFs occurring during locomotion ofDrosophilalarvae with micrometre and nanonewton precision. We combine this with detailed kinematic analyses of substrate interfacing features to gain insight into the biomechanical control of larval locomotion. Crawling involves an intricate pattern of cuticle sequestration and planting, producing GRFs of 1-7μN.Drosophilalocomotion obeys Newton’s 3rdlaw of motion, with denticulated cuticle forming dynamically anchored proleg-like structures to compensate counteracting forces. Our work sheds light onto the mechanics underlying substrate interactions and provides a framework for future biomechanics research in a genetically tractable soft-bodied model organism.