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Autonomous robots are comprised of actuation, energy, sensory, and control systems built from materials and structures that are not necessarily designed and integrated for multifunctionality. Yet, humans and other animals that robots strive to emulate contain highly sophisticated and interconnected systems at the cellular, tissue, and organ levels, which allow multiple functions to be performed simultaneously. Here, we examine how nature builds to establish a new paradigm for autonomous robots with Embodied Energy. Currently, most untethered robots use batteries to store energy and power their operation. To extend their operating time, additional battery blocks must be added in tandem with supporting structures, increasing their weight and reducing their efficiency. Recent advancements in energy storage techniques enable chemical or electrical energy sources to be embodied directly within the materials and mechanical systems used to create robots. This perspective highlights emerging examples of Embodied Energy, focusing on the design and fabrication of enduring autonomous robots.

Whereas vision dominates sensing in robots, animals with limited vision deftly navigate their environment using other forms of perception, such as touch. Efforts have been made to apply artificial skins with tactile sensing to robots for similarly sophisticated mobile and manipulative skills. The ability to functionally mimic the afferent sensory neural network, required for distributed sensing and communication networks throughout the body, is still missing. This limitation is partially due to the lack of cointegration of the mechanosensors in the body of the robot. Here, lacings of stretchable optical fibers distributed throughout 3D-printed elastomer frameworks created a cointegrated body, sensing, and communication network. This soft, functional structure could localize deformation with submillimeter positional accuracy (error of 0.71 millimeter) and sub-Newton force resolution (~0.3 newton).

Microarchitectured materials achieve superior mechanical properties through geometry rather than composition. Although ultralightweight microarchitectured materials can have high stiffness and strength, application to durable devices will require sufficient service life under cyclic loading. Naturally occurring materials provide useful models for high-performance materials. Here, we show that in cancellous bone, a naturally occurring lightweight microarchitectured material, resistance to fatigue failure is sensitive to a microarchitectural trait that has negligible effects on stiffness and strength—the proportion of material oriented transverse to applied loads. Using models generated with additive manufacturing, we show that small increases in the thickness of elements oriented transverse to loading can increase fatigue life by 10 to 100 times, far exceeding what is expected from the associated change in density. Transversely oriented struts enhance resistance to fatigue by acting as sacrificial elements. We show that this mechanism is also present in synthetic microlattice structures, where fatigue life can be altered by 5 to 9 times with only negligible changes in density and stiffness. The effects of microstructure on fatigue life in cancellous bone and lattice structures are described empirically by normalizing stress in traditional stress vs. life (S-N) curves by √ψ, where ψ is the proportion of material oriented transverse to load. The mechanical performance of cancellous bone and microarchitectured materials is enhanced by aligning structural elements with expected loading; our findings demonstrate that this strategy comes at the cost of reduced fatigue life, with consequences to the use of microarchitectured materials in durable devices and to human health in the context of osteoporosis.

The force, speed, dexterity, and compact size required of prosthetic hands present extreme design challenges for engineers. Current prosthetics rely on high-quality motors to achieve adequate precision, force, and speed in a small enough form factor with the trade-off of high cost. We present a simple, compact, and cost-effective continuously variable transmission produced via projection stereolithography. Our transmission, which we call an elastomeric passive transmission (EPT), is a polyurethane composite cylinder that autonomously adjusts its radius based on the tension in a wire spooled around it. We integrated six of these EPTs into a three-dimensionally printed soft prosthetic hand with six active degrees of freedom. Our EPTs provided the prosthetic hand with about three times increase in grip force without compromising flexion speed. This increased performance leads to finger closing speeds of ~0.5 seconds (average radial velocity, ~180 degrees second−1) and maximum fingertip forces of ~32 newtons per finger.

Existing tactile stimulation technologies powered by small actuators offer low-resolution stimuli compared to the enormous mechanoreceptor density of human skin. Arrays of soft pneumatic actuators initially show promise as small-resolution (1- to 3-mm diameter), highly conformable tactile display strategies yet ultimately fail because of their need for valves bulkier than the actuators themselves. In this paper, we demonstrate an array of individually addressable, soft fluidic actuators that operate without electromechanical valves. We achieve this by using microscale combustion and localized thermal flame quenching. Precisely, liquid metal electrodes produce sparks to ignite fuel lean methane–oxygen mixtures in a 5-mm diameter, 2-mm tall silicone cylinder. The exothermic reaction quickly pressurizes the cylinder, displacing a silicone membrane up to 6 mm in under 1 ms. This device has an estimated free-inflation instantaneous stroke power of 3 W. The maximum reported operational frequency of these cylinders is 1.2 kHz with average displacements of ∼100 µm. We demonstrate that, at these small scales, the wall-quenching flame behavior also allows operation of a 3 × 3 array of 3-mm diameter cylinders with 4-mm pitch. Though we primarily present our device as a tactile display technology, it is a platform microactuator technology with application beyond this one.

Advancements in 3D additive manufacturing have spurred the development of effective patient‐specific medical devices. Prior applications are limited to hard materials, however, with few implementations of soft devices that better match the properties of natural tissue. This paper introduces a rapid, low cost, and scalable process for fabricating soft, personalized medical implants via stereolithography of elastomeric polyurethane resin. The effectiveness of this approach is demonstrated by designing and manufacturing patient‐specific endocardial implants. These devices occlude the left atrial appendage, a complex structure within the heart prone to blood clot formation in patients with atrial fibrillation. Existing occluders permit residual blood flow and can damage neighboring tissues. Here, the robust mechanical properties of the hollow, printed geometries are characterized and stable device anchoring through in vitro benchtop testing is confirmed. The soft, patient‐specific devices outperform non‐patient‐specific devices in embolism and occlusion experiments, as well as in computational fluid dynamics simulations.

Text 2 Microarchitectured materials achieve superior mechanical properties through geometry 17 rather than composition 1-4 . Although lightweight, high-porosity microarchitectured materials can 18 have high stiffness and strength, stress concentrations within the microstructure can cause flaw 19 intolerance under cyclic loading 5,6 , limiting fatigue life. However, it is not known how 20 microarchitecture contributes to fatigue life. Naturally occurring materials can display 21 exceptional mechanical performance and are useful models for the design of microarchitectured 22 materials 7,8 . Cancellous bone is a naturally occurring microarchitectured material that often 23 survives decades of habitual cyclic loading without failure. Here we show that resistance to fatigue 24 failure in cancellous bone is sensitive to the proportion of material oriented transverse to applied 25 loads -a 30% increase in density caused by thickening transversely oriented struts increases 26 fatigue life by 10-100 times. This finding is surprising in that transversely oriented struts have 27 negligible effects on axial stiffness, strength and energy absorption. The effects of transversely 28 oriented material on fatigue life are also present in synthetic lattice microstructures. In both 29 cancellous bone and synthetic microarchitectures, the fatigue life can be predicted using the 30 applied cyclic stress after adjustment for apparent stiffness and the proportion of the 31 microstructure oriented transverse to applied loading. In the design of microarchitectured 32 materials, stiffness, strength and energy absorption is often enhanced by aligning the 33 microstructure in a preferred direction. Our findings show that introduction of such anisotropy, 34 by reducing the amount of material oriented transverse to loading, comes at the cost of reduced 35 fatigue life. Fatigue failure of durable devices and components generates substantial economic 36 costs associated with repair and replacement. As advancements in additive manufacturing expand 37 the use of microarchitectured materials to reusable devices including aerospace applications, it is 38 increasingly necessary to balance the need for fatigue life with those of strength and density. 39 Text 3Fatigue failure is caused by the accumulation of microscopic damage following repeated loading 40 and generates substantial economic costs associated with repair and replacement of durable devices. 41Microarchitectured materials are particularly susceptible to fatigue failure because the complex 42 geometry can result in local stresses an order of magnitude greater than stresses applied to the bulk 43 material 5,6,9 . The presence of large stress concentrations can promote damage initiation and 44 accumulation under cyclic loading and thereby reduce the fatigue life. Naturally occurring 45 microarchitectured materials also experience cyclic loading and provide a model for strategies to resist 46 fatigue failure. 47