Animate materials
Animate materials
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动画材质
DOI：
10.1557/s43577-021-00141-0
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发表时间：
2021
期刊：
影响因子：
5
通讯作者：
P. Ball
中科院分区：
文献类型：
--
作者：
P. Ball
553夫人公报•第46卷•2021年7月•mrs.org/bulletin介绍W的东西坏了，他们需要修理。我们可能会去拿胶水或修补裂缝。但当我们的骨头断裂时，它们会自我修复：新材料出现并密封骨折处。然而，骨头的作用远不止于此。它能感知并对压力做出反应，在压力大的地方变厚，在压力小的地方变薄。骨头在原位生长到需要的形状，然后一旦达到这个形状就停止生长。当然，骨骼是一种有生命的物质：是活跃的生物细胞生态系统中的一个组成部分。但这些自我修复、自我组装和调节以及对环境的响应性的特性并不局限于生物材料。它们也都是在无生命的合成材料中获得的。通常，这种设计的特性是有限的，难以精确控制，而且可能是短暂的；它们与骨头的功能不匹配。但它们表明，我们至少可以渴望制造出一些具有同样显著和有用特性的材料：我们可以称之为有活力的材料真正有生命的材料将改变整个工程概念，为社会带来巨大的潜在利益。今天，我们的工程结构和社会基础设施的维修成本是巨大的，包括在维修期间使系统（比如公路或铁路）停止服务的间接经济成本。无论是桥梁或隧道的倒塌，还是生物医学植入物的失效和腐蚀，忽视损害累积和结构失效的后果都可能是毁灭性的和致命的。制造新材料和新结构通常不仅是一个非常耗能的过程，而且还很浪费。制造一台台式电脑要消耗大约1.5吨的水和240公斤的化石燃料——如果这样的设备出了故障，更换它往往比修理它更便宜、更容易。具有“动画”特性的材料不仅会使制造和工程更便宜、更可持续，还会改变这些词的整个概念。一种能够适应环境形状和结构的材料，并不需要在一开始就针对特定的情况进行优化（如果条件发生变化，它可能会表现不佳）。而且，一种可以自行建造的材料在放置之前不需要费力地组装。未来的“智慧城市”可能不得不适应气候的重大变化：更高的温度、更多的湿度、更大的波动和极端天气。在太空探索中，一种自我修复的材料可能决定任务的成败，甚至可能决定生死。像这样的材料不需要失去它们的价值和被扔掉，尽管它们可能需要嵌入一个有效的“代谢生态系统”中，提供新鲜的原料和能量，使材料能够维持其功能。这篇文章是一个呼吁，致力于开发动画材料。这些材料不仅应被视为一种新型材料，而且应被视为重新思考从土木工程到生物医学等大部分应用科学目标的基础，这些目标是由面临严重经济、人口和环境挑战的社会的迫切需求所驱动的。动画材料的概念反映了一种日益增长的观点，即如果我们要在不久的将来迎接这些挑战，我们的制作理念需要改变。动画材料应该放在哪里？自从人类开始用材料建造人工制品——无论是石桥还是太空火箭——我们就把设计视为一个固定的目标，并选择了我们认为能尽可能完成任务的材料和结构。维护、修理和改造被认为是额外的任务——在大多数情况下是必要的，但是是事后制定的。通常，目标是使用抵抗变化的材料：不会破裂、腐蚀或变形。如果这些事情发生了，就需要一整套新的干预措施。但对于动画材料，对这些变化的反应从一开始就被预见和适应。实际上，它们甚至可以被视为机会：随着约束条件的改变，这些材料可能会交互地改进原始设计（参见图1）。真正有生命的材料——那些在自然界中发现的——已经做到了这一点（见图2）。木头、贝壳和皮肤也能自我修复并适应当时的环境。几十年来，人们一直对制造能够模仿自然界中发现的某些物质的材料产生浓厚的兴趣，从而获得它们的一些优越性能。例如，一些坚硬的陶瓷复合材料采用了取自贝壳微观结构的技巧，比如珍珠母，在这种结构中，坚硬的坚硬板由较软较弱的材料粘合在一起，这样撞击的能量就会被这些层的分层吸收，从而防止裂缝像穿过单片材料那样扩散。仿生材料工程这一领域已经产生了一些奇妙的成果，但它并没有真正抓住生物材料的真正非凡之处：它们的适应性以及自我组装和自我修复的能力。正是这样的能力将区分有生命的材料与智能和仿生材料，这是迄今为止主要开发的。与仿生学相关的是生物相容性和生物活性材料领域，材料新闻
553 MRS BULLETIN • VOLUME 46 • JULy 2021 • mrs.org/bulletin Introduction W things break, they need repairing. We might reach for the glue or patch over the crack. But when our bones break, they repair themselves: new material appears and seals the fracture. Bone does more than this, however. It senses and responds to stress, thickening where the stress is high and thinning where it is low. Bone grows to the required shape in situ, and then stops growing once it has done so. Bone is, of course, a living material: a component in an active ecosystem of biological cells. But these properties of self-healing, self-assembly and regulation, and responsiveness to the environment are not limited to biological materials. They have all been attained too in nonliving, synthetic materials. Typically, such designed properties have been limited, difficult to control precisely, and perhaps short-lived; they do not match the capabilities of bone. But they show that we can at least aspire to making materials with some of those same remarkable and useful characteristics: materials that we might designate as animate.1 Genuinely animate materials would transform the whole notion of engineering, with tremendous potential benefits for society. Today, the cost of repair in our engineering structures and societal infrastructure is huge—including the indirect economic costs of taking the system (a road or rail track, say) out of service while it is under repair. The consequences of neglecting the accumulation of damage and of structural failures can be devastating and fatal, whether that involves collapse of a bridge or a tunnel, or failure and corrosion of a biomedical implant. Making new materials and structures is typically not only a very energy-intensive process but also wasteful. Making a desktop computer consumes around 1.5 tonnes of water and 240 kg of fossil fuels—and if a device like this fails, it is often cheaper and easier to replace it than repair it. Materials with “animate” properties would not only make manufacturing and engineering cheaper and more sustainable, they would alter the whole notion of what these words mean. A material that adapts its shape and structure to the environment does not have to be optimized at the outset for a given situation (with the risk that it then performs poorly if the conditions change). And a material that builds itself does not have to be painstakingly assembled before being placed. “Smart cities” of the future are likely to have to adapt to significant changes in climate: higher temperatures, more humidity, greater fluctuations and extremes. In space exploration, a selfhealing material could make the difference between mission success and failure, and possibly between life and near-instant death. Materials like this need not lose their value and be thrown away, although they will probably need to be embedded in an efficient “metabolic ecosystem” that supplies fresh raw ingredients and energy to enable the materials to sustain their function. This article is a call for a dedicated effort to develop animate materials. These should be regarded not merely as a new class of material, but as a basis for rethinking the goals of a large segment of applied science, from civil engineering to biomedicine, driven by the urgent needs of a society facing grave economic, demographic, and environmental challenges. The concept of animate materials reflects a growing view that something needs to shift in our philosophy of making if we are to meet these challenges in the near future. Where do animate materials fit in? Ever since humans began constructing artifacts from materials—whether a stone bridge or a space rocket—we have regarded design as a fixed objective, and have selected materials and structures that we believe will do the job as well as possible. Maintenance, repair, and alteration have then been regarded as additional tasks—necessary in most cases, but enacted post hoc. Typically, the aim has been to use materials that resist change: that will not break or corrode or deform. If these things happen, a whole new train of interventions is required. But for animate materials, responses to such changes are foreseen and accommodated from the outset. Indeed, they can even be seen as opportunities: such materials might interactively improve the original design as the constraints change (see Figure 1). Genuinely animate materials—those found in nature—do this already (see Figure 2). Wood, shell, and skin are also able to self-heal and adapt to the prevailing conditions. There has been intense interest for many decades in making materials that can mimic some of those found in nature, thereby capturing some of their superior properties. For example, some tough ceramic composites use tricks taken from the microstructure of shells, such as mother-ofpearl, in which strong, hard plates are bonded together in stacks by softer, weaker material so that the energy of an impact is absorbed by the delamination of these layers, preventing a crack from spreading as it would through a monolithic material. This field of biomimetic materials engineering2 has produced some wonderful results, but it does not really capture what is truly remarkable about biomaterials: their adaptability and their capacity for self-assembly and self-repair. It is capabilities like those that will distinguish animate materials from the smart and biomimetic materials that have been mostly developed to date. Allied to biomimetics is the field of biocompatible and bioactive materials, MATERIALS NEWS