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"DeLaune, Valerie"
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Mechanical stresses govern myoblast fusion and myotube growth
Myoblast fusion into myotubes is critical for muscle formation, growth and repair. While the cellular and molecular mechanisms regulating myoblast fusion are increasingly understood, the role of biomechanics in this process remains largely unexplored. Here, we reveal that a dynamic feedback loop between evolving cell mechanics and cell-generated stresses shape the fusion of primary myoblasts in vitro. Applying principles from active nematics, we show that myoblast and myotube patterning follows physical rules similar to liquid crystal organization. Remarkably, fusion predominantly occurs at comet-shaped topological defects in cellular alignment, which we identified as regions of high compressive stress. We further find that this stress-driven organization depends on extracellular matrix (ECM) deposition, which mirrors the nematic order of the cell population. Our integrated data, supported by active nematics-based mathematical modeling, accurately predict self-organization patterns and mechanical stresses that regulate myoblast fusion. By revealing the essential role of biomechanics and ECM interplay in myogenesis, this work establishes a foundational framework for understanding biomechanical principles in morphogenesis.Competing Interest StatementThe authors have declared no competing interest.
Paper
Motivations and Preliminary Design for Mid-Air Deployment of a Science Rotorcraft on Mars
Mid-Air Deployment (MAD) of a rotorcraft during Entry, Descent and Landing (EDL) on Mars eliminates the need to carry a propulsion or airbag landing system. This reduces the total mass inside the aeroshell by more than 100 kg and simplifies the aeroshell architecture. MAD's lighter and simpler design is likely to bring the risk and cost associated with the mission down. Moreover, the lighter entry mass enables landing in the Martian highlands, at elevations inaccessible to current EDL technologies. This paper proposes a novel MAD concept for a Mars helicopter. We suggest a minimum science payload package to perform relevant science in the highlands. A variant of the Ingenuity helicopter is proposed to provide increased deceleration during MAD, and enough lift to fly the science payload in the highlands. We show in simulation that the lighter aeroshell results in a lower terminal velocity (30 m/s) at the end of the parachute phase of the EDL, and at higher altitudes than other approaches. After discussing the aerodynamics, controls, guidance, and mechanical challenges associated with deploying at such speed, we propose a backshell architecture that addresses them to release the helicopter in the safest conditions. Finally, we implemented the helicopter model and aerodynamic descent perturbations in the JPL Dynamics and Real-Time Simulation (DARTS)framework. Preliminary performance evaluation indicates landing and helicopter operation scan be achieved up to 5 km MOLA (Mars Orbiter Laser Altimeter reference).
Paper