As polymer networks infiltrated with water, hydrogels constitute the major components of the human body; and hydrogels have been widely used in applications that closely interact with biological organisms, such as tissue engineering, drug delivery, and biological research. More recently, owing to their superior softness, wetness, responsiveness, biocompatibility, and bioactivity, hydrogels are being intensively investigated for versatile functions in devices and machines including sensors, actuators, coatings, optics, electronics, and water harvesters. A nascent field named hydrogel machines rapidly evolves, exploiting hydrogels as key components for devices and machines. While there are reviews on individual categories of hydrogel machines in literature, a comprehensive discussion on various categories of hydrogel machines that systematically correlate hydrogels’ properties and machines’ functions is still missing in the field. This review is aimed to provide such a panoramic overview. We first classify various hydrogel machines into a number of categories according to their applications. For each category, we discuss (i) the working principles of the hydrogel machines, (ii) the specific properties of hydrogels that enable the key functions of the machines, and (iii) challenges faced by hydrogel machines and recent developments to address them. The field of hydrogel machines will not only translate fundamental understanding of hydrogels into new applications, but also shift the paradigm in machine design by integrating hydrogels that can potentially minimize physical and physiological mismatches with biological organisms.

中文翻译：

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水凝胶机

作为渗入水的聚合物网络，水凝胶构成了人体的主要成分；和水凝胶已广泛应用于与生物有机体密切相互作用的应用，如组织工程、药物输送和生物研究。最近，由于其优异的柔软性、湿润性、响应性、生物相容性和生物活性，水凝胶在设备和机器中的多功能功能得到了深入研究，包括传感器、执行器、涂层、光学、电子和集水器。一个名为水凝胶机器的新兴领域迅速发展，利用水凝胶作为设备和机器的关键组件。虽然文献中有关于个别类别的水凝胶机器的评论，该领域仍然缺乏对系统地关联水凝胶特性和机器功能的各种类型水凝胶机器的全面讨论。这篇评论旨在提供这样一个全景概览。我们首先根据其应用将各种水凝胶机器分为多个类别。对于每个类别，我们讨论 (i) 水凝胶机器的工作原理，(ii) 实现机器关键功能的水凝胶的特定特性，以及 (iii) 水凝胶机器面临的挑战以及解决这些问题的最新进展。水凝胶机器领域不仅会将水凝胶的基本理解转化为新的应用，