Mechanical power limitations emerge from the physical trade-off between force and velocity. Many biological systems incorporate power-enhancing mechanisms enabling extraordinary accelerations at small sizes. We establish how power enhancement emerges through the dynamic coupling of motors, springs, and latches and reveal how each displays its own force-velocity behavior. We mathematically demonstrate a tunable performance space for spring-actuated movement that is applicable to biological and synthetic systems. Incorporating nonideal spring behavior and parameterizing latch dynamics allows the identification of critical transitions in mass and trade-offs in spring scaling, both of which offer explanations for long-observed scaling patterns in biological systems. This analysis defines the cascading challenges of power enhancement, explores their emergent effects in biological and engineered systems, and charts a pathway for higher-level analysis and synthesis of power-amplified systems.

Additive manufacturing processes enable fabrication of complex and functional three-dimensional (3D) objects ranging from engine parts to artificial organs. Photopolymerization, which is the most versatile technology enabling such processes through 3D printing, utilizes photoinitiators that break into radicals upon light absorption. We report on a new family of photoinitiators for 3D printing based on hybrid semiconductor-metal nanoparticles. Unlike conventional photoinitiators that are consumed upon irradiation, these particles form radicals through a photocatalytic process. Light absorption by the semiconductor nanorod is followed by charge separation and electron transfer to the metal tip, enabling redox reactions to form radicals in aerobic conditions. In particular, we demonstrate their use in 3D printing in water, where they simultaneously form hydroxyl radicals for the polymerization and consume dissolved oxygen that is a known inhibitor. We also demonstrate their potential for two-photon polymerization due to their giant two-photon absorption cross section.

functionality of LM composites relies on assembly and interactions between the matrix and filler. [11,23,24] To date, most of these LM composites have utilized silicone rubbers, where the functionality imparted by the matrix is limited to mechanical compliance and deformability, although a few meaningful exceptions exist (e.g., where the LM catalyzes/initiates poly mer ization). [19,21,25,26] Synthetic polymers can be designed with properties like stimuli responsivity, self-healing, processability, shape-morphing, and dynamic compliance and could be combined with LM to permit novel functionalities and processing capabilities. [27] The combination of finely tuned polymer synthesis with LM composite engineering will enable advanced applications like soft prosthetics, self-healing artificial skins, and 3D electronic materials. To achieve electrical conductivity, LM droplets within a composite must coalesce, for example, through an applied pressure (termed "mechanical sintering"). [28] Notably, the curing conditions and precursor composition dictate the network topology and resulting mechanical properties of the silicone matrix, which appear to influence whether an applied pressure forms percolation pathways for a LM composite. For example, LM composites using a commercially available silicone formulation (Sylgard 184, 10:1 weight ratio of Part A and Part B) can be electrically conductive after application of localized pressure [28] that coalesces LM droplets. However, permanent electrical conductivity has not been observed in LM composites that use a different commercially available silicone formulation (Ecoflex 00-30, 1:1 weight ratio of Part A and Part B), which is softer and more deformable than Sylgard 184. [8,20,29] This difference poses a limitation in generality of functionality for LM composites. Progress in LM composite engineering depends on a framework for materials synthesis that overcomes this limitation and enables integration of electrically conductive networks of LM in a wider range of media. Importantly, progress toward multifunctionality should include a focus on the properties of the matrix material. For LM composites, our group and others have demonstrated LM incorporation in functional matrix materials like hydrogels and shape-morphing polymers, but the predominate choice of matrix material has been silicone rubbers. [19,21,25,26] The development of an approach to achieve electrical conductivity by incorporating LM in functional polymer networks will facilitate Soft composites that use droplets of gallium-based liquid metal (LM) as the dispersion phase have the potential for transformative impact in multifunctional material engineering. However, it is unclear whether percolation pathways of LM can support high electrical conductivity in a wide range of matrix materials. This issue is addressed through an approach to LM composite synthesis that focuses on the interrelated effects of matrix curing/solidification and droplet formation. The combined influence of LM concentration, particle size, and ...

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A novel all-elastomer MEMS tactile sensor with high dynamic force range is presented in this work. Conductive elastomeric capacitors formed from electrodes of varying heights enable robust sensing in both shear and normal directions without the need for multi-layered assembly. Sensor geometry has been tailored to maximize shear force sensitivity using multiphysics finite element simulations. A simple molding microfabrication process is presented to rapidly create the sensing skins with electrode gaps of 20 μm and sensor spacing of 3 mm. Shear force resolution was found to be as small as 50 mN and tested up to a range of 2 N (dynamic range of : 40 1). Normal force resolution was found to be 190 mN with a tested range of 8 N (dynamic range of : 42 1). Single load and multiload tests were conducted and the sensor exhibited intended behavior with low deviations between trials. Spatial tests were conducted on a × 2 2 sensor array and a spatial resolution of 1.5 mm was found.

The inherent force–velocity trade-off of muscles and motors can be overcome by instead loading and releasing energy in springs to power extreme movements. A key component of this paradigm is the latch that mediates the release of spring energy to power the motion. Latches have traditionally been considered as switches; they maintain spring compression in one state and allow the spring to release energy without constraint in the other. Using a mathematical model of a simplified contact latch, we reproduce this instantaneous release behaviour and also demonstrate that changing latch parameters (latch release velocity and radius) can reduce and delay the energy released by the spring. We identify a critical threshold between instantaneous and delayed release that depends on the latch, spring, and mass of the system. Systems with stiff springs and small mass can attain a wide range of output performance, including instantaneous behaviour, by changing latch release velocity. We validate this model in both a physical experiment as well as with data from the Dracula ant, Mystrium camillae , and propose that latch release velocity can be used in both engineering and biological systems to control energy output.

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Elastomer-based electroadhesion can be an effective method to provide tunable adhesion between robots and grasped objects or surfaces. However, there has been little work to develop models of electroadhesion and characterization of adhesive performance relative to these models. In this paper, a basic friction model is proposed to describe the critical shear force for a single electrode electroadhesive fabricated from conductive PDMS encased in parylene. The use of parylene results in thin dielectrics that require only tens of Volts to achieve shear pressures greater than 100 kPa. The experimental results gathered by characterizing voltage, dielectric thickness, adhesive area, and adhesive thickness follow the trends predicted by theory with some important deviations that are studied using high speed video capture of the soft adhesive failure.