Advances in soft robotics, materials science, and stretchable electronics have enabled rapid progress in soft grippers. Here, a critical overview of soft robotic grippers is presented, covering different material sets, physical principles, and device architectures. Soft gripping can be categorized into three technologies, enabling grasping by: a) actuation, b) controlled stiffness, and c) controlled adhesion. A comprehensive review of each type is presented. Compared to rigid grippers, end-effectors fabricated from flexible and soft components can often grasp or manipulate a larger variety of objects. Such grippers are an example of morphological computation, where control complexity is greatly reduced by material softness and mechanical compliance. Advanced materials and soft components, in particular silicone elastomers, shape memory materials, and active polymers and gels, are increasingly investigated for the design of lighter, simpler, and more universal grippers, using the inherent functionality of the materials. Embedding stretchable distributed sensors in or on soft grippers greatly enhances the ways in which the grippers interact with objects. Challenges for soft grippers include miniaturization, robustness, speed, integration of sensing, and control. Improved materials, processing methods, and sensing play an important role in future research.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201707035

Soft Robotic Grippers.

Among the several approaches for harnessing solar energy and converting it into electricity, dye-sensitized solar cells (DSSC) represent one of the most promising methods for future large-scale power production from renewable energy sources. In these cells, the sensitizer is one of the key components harvesting solar radiation and converting it into electric current. The electrochemical, photophysical, and ground and excited state properties of the sensitizer play an important role for charge transfer dynamics at the semiconductor interface. Moreover, for long-term stability and practical applications, electrolytes based on the iodine/triiodine couple also suffer from two other disadvantages: the corrosive effect toward the metal electrodes, and the partial absorption of the visible light by triiodine anions. These issues hence constitute one of the reasons that have encouraged the development of alternative iodine-free redox couples in liquid electrolytes for DSSCs.

Meso-Substituted Porphyrins for Dye-Sensitized Solar Cells

Electronic skin devices capable of monitoring physiological signals and displaying feedback information through closed-loop communication between the user and electronics are being considered for next-generation wearables and the 'Internet of Things'. Such devices need to be ultrathin to achieve seamless and conformal contact with the human body, to accommodate strains from repeated movement and to be comfortable to wear. Recently, self-healing chemistry has driven important advances in deformable and reconfigurable electronics, particularly with self-healable electrodes as the key enabler. Unlike polymer substrates with self-healable dynamic nature, the disrupted conducting network is unable to recover its stretchability after damage. Here, we report the observation of self-reconstruction of conducting nanostructures when in contact with a dynamically crosslinked polymer network. This, combined with the self-bonding property of self-healing polymer, allowed subsequent heterogeneous multi-component device integration of interconnects, sensors and light-emitting devices into a single multi-functional system. This first autonomous self-healable and stretchable multi-component electronic skin paves the way for future robust electronics.

/pdf/an-integrated-self-healable-electronic-skin-system-2189f4dkao.pdf

An integrated self-healable electronic skin system fabricated via dynamic reconstruction of a nanostructured conducting network.

Interest in new thermal diodes, regulators, and switches has been rapidly growing because these components have the potential for rich transport phenomena that cannot be achieved using traditional thermal resistors and capacitors. Each of these thermal components has a signature functionality: Thermal diodes can rectify heat currents, thermal regulators can maintain a desired temperature, and thermal switches can actively control the heat transfer. Here, we review the fundamental physical mechanisms of switchable and nonlinear heat transfer which have been harnessed to make thermal diodes, switches, and regulators. The review focuses on experimental demonstrations, mainly near room temperature, and spans the fields of heat conduction, convection, and radiation. We emphasize the changes in thermal properties across phase transitions and thermal switching using electric and magnetic fields. After surveying fundamental mechanisms, we present various nonlinear and active thermal circuits that are based on ana...

Thermal diodes, regulators, and switches: Physical mechanisms and potential applications

Thermoregulation has substantial implications for energy consumption and human comfort and health. However, cooling technology has remained largely unchanged for more than a century and still relies on cooling the entire space regardless of the number of occupants. Personalized thermoregulation by thermoelectric devices (TEDs) can markedly reduce the cooling volume and meet individual cooling needs but has yet to be realized because of the lack of flexible TEDs with sustainable high cooling performance. Here, we demonstrate a wearable TED that can deliver more than 10°C cooling effect with a high coefficient of performance (COP > 1.5). Our TED is the first to achieve long-term active cooling with high flexibility, due to a novel design of double elastomer layers and high-ZT rigid TE pillars. Thermoregulation based on these devices may enable a shift from centralized cooling toward personalized cooling with the benefits of substantially lower energy consumption and improved human comfort.

/pdf/wearable-thermoelectrics-for-personalized-thermoregulation-1nseszbdvz.pdf

Wearable thermoelectrics for personalized thermoregulation

Solid-state refrigeration offers potential advantages over traditional cooling systems, but few devices offer high specific cooling power with a high coefficient of performance (COP) and the ability to be applied directly to surfaces. We developed a cooling device with a high intrinsic thermodynamic efficiency using a flexible electrocaloric (EC) polymer film and an electrostatic actuation mechanism. Reversible electrostatic forces reduce parasitic power consumption and allow efficient heat transfer through good thermal contacts with the heat source or heat sink. The EC device produced a specific cooling power of 2.8 watts per gram and a COP of 13. The new cooling device is more efficient and compact than existing surface-conformable solid-state cooling technologies, opening a path to using the technology for a variety of practical applications.

http://science.sciencemag.org/content/sci/357/6356/1130.full.pdf

Highly efficient electrocaloric cooling with electrostatic actuation

Fiber-based sensors are desirable to provide an immersive experience for users in the human–computer interface. We report a hierarchically porous silver nanowire-bacterial cellulose fiber that can ...

Silver Nanowire-Bacterial Cellulose Composite Fiber-Based Sensor for Highly Sensitive Detection of Pressure and Proximity.

Electrocaloric (EC) cooling is an emerging technology that has broad potential to disrupt conventional air conditioning and refrigeration as well as electronics cooling applications. EC coolers can be highly efficient, solid state, and compact; have few moving parts; and contain no environmentally harmful or combustible refrigerants. We report a scalable, high-performance system architecture, demonstrated in a device that uses PbSc0.5Ta0.5O3 EC multilayer ceramic capacitors fabricated in a manufacturing-compatible process. We obtained a system temperature span of 5.2°C and a maximum heat flux of 135 milliwatts per square centimeter. This measured heat flux is more than four times higher than other EC cooling demonstrations, and the temperature lift is among the highest for EC systems that use ceramic multilayer capacitors.

https://science.sciencemag.org/content/sci/370/6512/129.full.pdf

A high-performance solid-state electrocaloric cooling system.

Cooling technology that is both compact and flexible is increasingly vital for the thermal management of wearable electronics and personal comfort. Electrocaloric (EC) cooling provides a potential solution, but the low adiabatic temperature change of EC materials has been the bottleneck in its progress. We demonstrate a cascade EC cooling device that increases the temperature change, with enhanced cooling power and cooling efficiency at the same time. The device integrates multiple units of EC polymer elements and an electrostatic actuation mechanism, all operating in synergy. Every two adjacent EC elements function in antiphase (in terms of both actuation and EC effect) to allow heat flow to be continuously relayed from the heat source to the heat sink. The antiphase operation also enables internal charge recycling, which enhances the energy efficiency. Operating at the EC electric field at which the adiabatic temperature change of the material is 3.0 K, a four-layer cascade device achieves a maximum temperature lift of 8.7 K under no-load conditions. The coefficient of performance is estimated to be 9.0 at the temperature lift of 2.7 K and 10.4 at zero temperature lift. Solid-state caloric cooling is a promising alternative to vapour-compression refrigeration yet practical devices are not sufficiently efficient for applications. Meng et al. combine cascade device design with charge recovery and improve the cooling efficiency and temperature lift of an electrocaloric device.

Ziyang Zhang

Papers

Highly efficient electrocaloric cooling with electrostatic actuation

Silver Nanowire-Bacterial Cellulose Composite Fiber-Based Sensor for Highly Sensitive Detection of Pressure and Proximity.

A high-performance solid-state electrocaloric cooling system.

A cascade electrocaloric cooling device for large temperature lift

Self-Actuating Electrocaloric Cooling Fibers