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In most macroscale robotic systems, propulsion and controls are enabled through a physical tether or complex onboard electronics and batteries. A tether simplifies the design process but limits the range of motion of the robot, while onboard controls and power supplies are heavy and complicate the design process. Here, we present a simple design principle for an untethered, soft swimming robot with preprogrammed, directional propulsion without a battery or onboard electronics. Locomotion is achieved by using actuators that harness the large displacements of bistable elements triggered by surrounding temperature changes. Powered by shape memory polymer (SMP) muscles, the bistable elements in turn actuate the robot’s fins. Our robots are fabricated using a commercially available 3D printer in a single print. As a proof of concept, we show the ability to program a vessel, which can autonomously deliver a cargo and navigate back to the deployment point.

Polydimethylsiloxane (PDMS)—the simplest and most common silicone compound—exemplifies the central characteristics of its class and has attracted tremendous research attention. The development of PDMS‐based materials is a vivid reflection of the modern industry. In recent years, PDMS has stood out as the material of choice for various emerging technologies. The rapid improvement in bulk modification strategies and multifunctional surfaces has enabled a whole new generation of PDMS‐based materials and devices, facilitating, and even transforming enormous applications, including flexible electronics, superwetting surfaces, soft actuators, wearable and implantable sensors, biomedicals, and autonomous robotics. This paper reviews the latest advances in the field of PDMS‐based functional materials, with a focus on the added functionality and their use as programmable materials for smart devices. Recent breakthroughs regarding instant crosslinking and additive manufacturing are featured, and exciting opportunities for future research are highlighted. This review provides a quick entrance to this rapidly evolving field and will help guide the rational design of next‐generation soft materials and devices. Polydimethylsiloxane (PDMS), transforms from the central component in children's toy—silly putty, to the material of choice for many emerging technologies such as flexible electronics, soft actuators, and more, thanks to the advancement in composite science, multifunctional surfaces, and additive manufacturing. This article reviews latest progress in PDMS‐based elastomers and the integrated functionalities, highlighting the opportunities as well as challenges.

For soft robotics and programmable metamaterials, novel approaches are required enabling the design of highly integrated thermoresponsive actuating systems. In the concept presented here, the necessary functional component was obtained by polymer syntheses. First, poly(1,10-decylene adipate) diol (PDA) with a number average molecular weight Mn of 3290 g·mol−1 was synthesized from 1,10-decanediol and adipic acid. Afterward, the PDA was brought to reaction with 4,4′-diphenylmethane diisocyanate and 1,4-butanediol. The resulting polyester urethane (PEU) was processed to the filament, and samples were additively manufactured by fused-filament fabrication. After thermomechanical treatment, the PEU reliably actuated under stress-free conditions by expanding on cooling and shrinking on heating with a maximum thermoreversible strain of 16.1%. Actuation stabilized at 12.2%, as verified in a measurement comprising 100 heating-cooling cycles. By adding an actuator element to a gripper system, a hen’s egg could be picked up, safely transported and deposited. Finally, one actuator element each was built into two types of unit cells for programmable materials, thus enabling the design of temperature-dependent behavior. The approaches are expected to open up new opportunities, e.g., in the fields of soft robotics and shape morphing.

Although several force application concepts are known that can be used to deform shape memory polymers (SMPs) within the scope of programming, controlled deformation is challenging in the case of samples with a cylinder-like shape, which need to be homogeneously compressed starting from the lateral surface. To solve this problem, this contribution follows a material approach that takes advantage of four-dimensional (4D) printing. Fused filament fabrication (FFF) was used as an additive manufacturing (AM) technique to produce a thermoresponsive tool in a cylindrical shape from a polyether urethane (PEU) having a glass transition temperature (Tg) close to 55 °C, as determined by differential scanning calorimetry (DSC). Once it was 4D-printed, a sample of laser cut polyester urethane urea (PEUU) foam with a cylindrical wall was placed inside of it. Subsequent heating to 75 °C and keeping that temperature constant for 15 min resulted in the compression of the foam, because the internal stresses of the PEU were transferred to the PEUU, whose soft segments were completely molten at 65 °C as verified by DSC. Upon cooling to −15 °C and thus below the offset temperature of the soft segment crystallization transition of the PEUU, the foam was fixed in its new shape. After 900 days of storage at temperatures close to 23 °C, the foam recovered its original shape upon reheating to 75 °C. In another experiment, a 4D-printed cylinder was put into hibernation for 900 days before its thermoresponsiveness was investigated. In the future, 4D-printed tools may be produced in many geometries, which fit well to the shapes of the SMPs to be programmed. Beyond programming SMP foams, transferring the forces released by 4D-printed tools to other programmable materials can further expand technical possibilities.

Life‐like materials that can dynamically morph their shape/texture, inspired by living organisms such as cephalopods are sought after for soft robotics and camouflage applications. Achieving such functions demands multimaterials with spatially programmed responses, yet their creation remains challenging. The existing approaches have been limited by the specific in situ polymerization conditions, fluidity of the synthetic components, and the complex, multi‐step processing requirements. Here, we propose a universal strategy that enables programming of material response within pre‐synthesized, ready‐to‐use, clickable microgels with different response behaviors. These microgels can be deposited within desired regions of the material structure via direct ink writing to enable pre‐programmed, localized responses to external stimuli. Spontaneous interparticle stabilization of the deposited microgels via a click reaction (Diels‐Alder bonding) yields shape‐stable, free‐form granular hydrogel multimaterials with reversible, repeatable, and spatially selective responses to stimuli (e.g., pH and temperature). The strategy establishes a 4D‐printing‐compatible, scalable modular platform for facile fabrication of soft materials with programmable shape adaptivity.

Analytical, numerical, and experimental methods are used to investigate the utility of metamaterials in controlling harmonic waves based on both their amplitude and frequency. By programming the metamaterials to support bi‐stable configurations (i.e., two stable phases), the required conditions are elucidated for a transition wave (i.e., a topological soliton) to nucleate due to harmonic excitation, causing a phase change within our metamaterial. As each of these phases has its own unique transmission frequency range, such phase change is harnessed to control harmonic waves based on both their amplitude and frequency. As a demonstration of principle, a low/high‐pass filter is shown by tuning the same metamaterial to change phase; from transmission to attenuation and vice versa. In addition, phase transitions taking place while preserving the metamaterial's state of attenuation or transmission are shown. Such materials can continue their functionality (i.e., either attenuation or transmission of waves) while keeping a record of extreme events that can cause their transition (i.e., have memory). These metamaterials can be useful in the next generations of advanced and functional acoustic devices. By inducing phase changes in metamaterials using topological solitons, the authors show effective control of harmonic waves based on frequency, amplitude, and specific combinations of both. In addition, the metamaterial retains a record (i.e., have memory) of extreme events without changing its main functionality of either blocking or transmitting waves. The proposed platform can be utilized in the next generation of advanced acoustic devices.

Battery thermal management systems (BTMSs) ensure that lithium-ion batteries (LIBs) in electric vehicles (EVs) are operated in an optimal temperature range to achieve high performance and reduce risks. A conventional BTMS operates either as an active system that uses forced air, water or immersion cooling, or as a complete passive system without any temperature control. Passive systems function without any active energy supply and are therefore economically and environmentally advantageous. However, today’s passive BTMSs have limited cooling performance, which additionally cannot be controlled. To overcome this issue, an innovative BTMS approach based on heat pipes with an integrated thermal switch, developed by the Fraunhofer Cluster of Excellence Programmable Materials (CPM), is presented in this paper. The suggested BTMS consists of switchable heat pipes which couple a passive fin-based cold plate with the battery cells. In cold state, the battery is insulated. If the switching temperature is reached, the heat pipes start working and conduct the battery heat to the cold plate where it is dissipated. The environmental benefits of this novel BTMS approach were then analysed with a Life Cycle Assessment (LCA). Here, a comparison is made between the suggested passive and an active BTMS. For the passive system, significantly lower environmental impacts were observed in nearly all impact categories assessed. It was identified as a technically promising and environmentally friendly approach for battery cooling in EVs of the compact class. Furthermore, the results show that passive BTMS in general are superior from an environmental point of view, due their energy self-sufficient nature.

In this work, a novel type of polyester urethane urea (PEUU) foam is introduced. The foam was produced by reactive foaming using a mixture of poly(1,10–decamethylene adipate) diol and poly(1,4–butylene adipate) diol, 4,4′-diphenylmethane diisocyanate, 1,4–butanediol, diethanolamine and water as blowing agent. As determined by differential scanning calorimetry, the melting of the ester-based phases occurred at temperatures in between 25 °C and 61 °C, while the crystallization transition spread from 48 °C to 20 °C. The mechanical properties of the foam were simulated with the hyperplastic models Neo-Hookean and Ogden, whereby the latter showed a better agreement with the experimental data as evidenced by a Pearson correlation coefficient R² above 0.99. Once thermomechanically treated, the foam exhibited a maximum actuation of 13.7% in heating-cooling cycles under a constant external load. In turn, thermal cycling under load-free conditions resulted in an actuation of more than 10%. Good thermal insulation properties were demonstrated by thermal conductivities of 0.039 W·(m·K)−1 in the pristine state and 0.052 W·(m·K)−1 in a state after compression by 50%, respectively. Finally, three demonstrators were developed, which closed an aperture or opened it again simply by changing the temperature. The self-sufficient material behavior is particularly promising in the construction industry, where programmable air slots offer the prospect of a dynamic insulation system for an adaptive building envelope.

The material bone has attracted the attention of material scientists due to its fracture resistance and ability to self-repair. A mechanoregulated exchange of damaged bone using newly synthesized material avoids the accumulation of fatigue damage. This remodeling process is also the basis for structural adaptation to common loading conditions, thereby reducing the probability of material failure. In the case of fracture, an initial step of tissue formation is followed by a mechanobiological controlled restoration of the pre-fracture state. The present perspective focuses on these mechanobiological aspects of bone remodeling and healing. Specifically, the role of the control function is considered, which describes mechanoregulation as a link between mechanical stimulation and the local response of the material through changes in structure or material properties. Mechanical forces propagate over large distances leading to a complex non-local feedback between mechanical stimulation and material response. To better understand such phenomena, computer models are often employed. As expected from control theory, negative and positive feedback loops lead to entirely different time evolutions, corresponding to stable and unstable states of the material system. After some background information about bone remodeling and healing, we describe a few representative models, the corresponding control functions, and their consequences. The results are then discussed with respect to the potential design of synthetic materials with specific self-repair properties.

This work presents a topology optimization method for the design of programmable lattice materials whose struts can be activated/deactivated by some actuation mechanism. The proposed method simultaneously determines the spatial layout of struts in the unit cell, and two or more programs corresponding to the open/close states of the struts in order to attain desired effective properties. A high-level parametric description of the cylindrical struts in the unit cell is smoothly mapped onto a fixed mesh for analysis via the geometry projection method. Desired material symmetries are imposed by reflections with respect to the symmetry planes in the computation of the projected density. The open/close state of a strut is modeled by assigning a state variable per program to each strut, and a discreteness constraint in the optimization ensures these variables are zero or unity in the optimal design. To aid manufacturability, a no-cut constraint is imposed to preclude partial cuts of the struts by the symmetry planes or the unit cell boundaries and thus ensure that struts are whole in the optimal design. The effectiveness of the proposed method is demonstrated with examples of minimal volume design for two and three programs with target bulk moduli and for two programs with a bulk modulus target and a Poisson’s ratio target.