One of the major limitations to advancing the development of soft robots is the absence of lightweight, effective soft actuators. While synthetic systems, such as pneumatics and shape memory alloys, have created important breakthroughs in soft actuation, they typically rely on large external power sources and some rigid components. Muscles provide an ideal actuator for soft constructs, as they are lightweight, deformable, biodegradable, silent, and powered by energy-dense hydrocarbons such as glucose. Vertebrate cell lines and embryonic cultures have allowed critical foundational work to this end, but progress there is limited by the difficulty of identifying individual pathways in embryonic development, and the divergence of immortal cell lines from these normal developmental programs. An alternative to culturing muscles from embryonic cells is to exploit the advantages of species with metamorphic stages. In these animals, muscles develop from a predefined pool of myoblasts with well-characterized contacts to other tissues. In addition, the endocrine triggers for development into adult muscles are often known and tractable for experimental manipulation. This is particularly true for metamorphic muscle development in holometabolous insects, which provide exciting new avenues for tissue engineering. Using insect tissues for actuator development confers additional benefits; insect muscles are more robust to varying pH, temperature, and oxygenation than are vertebrate cells. Given that biohybrid robots are likely to be used in ambient conditions and changing environments, this sort of hardiness is likely to be required for practical use. In this study, we summarize key processes and signals in metamorphic muscle development, drawing attention to those pathways that offer entry points for manipulation. By focusing on lessons learned from in vivo insect development, we propose that future culture designs will be able to use more systematic, hypothesis-driven approaches to optimizing engineered muscle.

中文翻译：

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昆虫肌肉的变形：基于工程肌肉的执行器的见解

推进软机器人发展的主要限制之一是缺乏轻便、有效的软执行器。虽然气动和形状记忆合金等合成系统在软驱动方面取得了重要突破，但它们通常依赖于大型外部电源和一些刚性组件。肌肉为软结构提供了理想的执行器，因为它们重量轻、可变形、可生物降解、静音，并由高能量的碳氢化合物（如葡萄糖）提供动力。脊椎动物细胞系和胚胎培养物为此提供了重要的基础工作，但由于难以识别胚胎发育中的单个途径以及永生细胞系与这些正常发育程序的分歧，进展受到限制。从胚胎细胞培养肌肉的另一种方法是利用具有变质阶段的物种的优势。在这些动物中，肌肉是从预定义的成肌细胞池发育而来的，它们与其他组织有明确的接触。此外，发育成成人肌肉的内分泌触发因素通常是已知的，并且易于进行实验操作。对于全代谢昆虫的变质肌肉发育尤其如此，这为组织工程提供了令人兴奋的新途径。使用昆虫组织进行致动器开发具有额外的好处；昆虫肌肉比脊椎动物细胞更能适应不同的 pH、温度和氧合。鉴于生物混合机器人可能会在环境条件和不断变化的环境中使用，实际使用可能需要这种耐用性。在这项研究中，我们总结了变形肌肉发育的关键过程和信号，提请注意那些提供操作切入点的途径。通过专注于从中吸取的教训体内昆虫发育，我们建议未来的培养设计将能够使用更系统的、假设驱动的方法来优化工程肌肉。