Operable under ambient light and providing chemical selectivity, stimulated Raman scattering (SRS) microscopy opens a new window for imaging molecular events on a human subject, such as filtration of topical drugs through the skin. A typical approach for volumetric SRS imaging is through piezo scanning of an objective lens, which often disturbs the sample and offers a low axial scan rate. To address these challenges, we have developed a deformable mirror-based remote-focusing SRS microscope, which not only enables high-quality volumetric chemical imaging without mechanical scanning of the objective but also corrects the system aberrations simultaneously. Using the remote-focusing SRS microscope, we performed volumetric chemical imaging of living cells and captured in real time the dynamic diffusion of topical chemicals into human sweat pores.

Three-dimensional engineered heart tissues (EHTs) derived from human induced pluripotent stem cells (iPSCs) have become an important resource for both drug toxicity screening and research on heart disease. A key metric of EHT phenotype is the contractile (twitch) force with which the tissue spontaneously beats. It is well-known that cardiac muscle contractility -its ability to do mechanical work -depends on tissue prestrain (preload) and external resistance (afterload). Objectives: Here, we demonstrate a technique to control afterload while monitoring contractile force exerted by EHTs. Methods: We developed an apparatus that can regulate EHT boundary conditions using real-time feedback control. The system is comprised of a pair of piezoelectric actuators that can strain the scaffold and a microscope that can measure EHT force and length. Closed loop control allows dynamic regulation of effective EHT boundary stiffness. Results: When controlled to switch instantaneously from auxotonic to isometric boundary conditions, EHT twitch force immediately doubled. Changes in EHT twitch force as a function of effective boundary stiffness were characterized and compared to twitch force in auxotonic conditions. Conclusion: EHT contractility can be regulated dynamically through feedback control of effective boundary stiffness. Significance: The capacity to alter the mechanical boundary conditions of an engineered tissue dynamically offers a new way to probe tissue mechanics. This could be used to mimic afterload changes that occur naturally in disease, or to improve mechanical techniques for EHT maturation.

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<p>Three-dimensional engineered heart tissues (EHTs) derived from human induced pluripotent stem cells (iPSCs) have become an important resource for both drug toxicity screening and research on heart disease. A key metric of EHT phenotype is the contractile force with which the tissue spontaneously beats. It is well-known that cardiac muscle contractility – its ability to do mechanical work – depends on tissue prestrain (preload) and external resistance (afterload). Objectives: Here, we demonstrate a technique to control both preload and afterload dynamically while monitoring contractile force exerted by EHTs. Methods: We developed an apparatus that uses real-time feedback control to monitor and regulate EHT forces. The system is comprised of a pair of high-speed piezoelectric actuators that can strain the EHT scaffold and a fast optical measurement tool to provide EHT contractile force feedback while monitoring tissue strain. Results: The system was used to regulate the effective stiffness of the scaffold. When controlled to have effectively isometric boundary conditions, EHTs exerted a contractile force that was almost twice as large as that observed under auxotonic conditions. Conclusion: These experimental results demonstrate that EHT contractility can be increased through feedback control to regulate boundary stiffness. Significance: The work advances our understanding of the role that mechanical environment plays in EHT contractility. This could be used to help study or alter EHT phenotype and potentially EHT maturation through controlled mechanical conditioning.</p>

<p>Three-dimensional engineered heart tissues (EHTs) derived from human induced pluripotent stem cells (iPSCs) have become an important resource for both drug toxicity screening and research on heart disease. A key metric of EHT phenotype is the contractile force with which the tissue spontaneously beats. It is well-known that cardiac muscle contractility – its ability to do mechanical work – depends on tissue prestrain (preload) and external resistance (afterload). Objectives: Here, we demonstrate a technique to control both preload and afterload dynamically while monitoring contractile force exerted by EHTs. Methods: We developed an apparatus that uses real-time feedback control to monitor and regulate EHT forces. The system is comprised of a pair of high-speed piezoelectric actuators that can strain the EHT scaffold and a fast optical measurement tool to provide EHT contractile force feedback while monitoring tissue strain. Results: The system was used to regulate the effective stiffness of the scaffold. When controlled to have effectively isometric boundary conditions, EHTs exerted a contractile force that was almost twice as large as that observed under auxotonic conditions. Conclusion: These experimental results demonstrate that EHT contractility can be increased through feedback control to regulate boundary stiffness. Significance: The work advances our understanding of the role that mechanical environment plays in EHT contractility. This could be used to help study or alter EHT phenotype and potentially EHT maturation through controlled mechanical conditioning.</p>

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