Self-powered soft robot in the Mariana Trench.

The deep sea remains the largest unknown territory on Earth because it is so difficult to explore1-4. Owing to the extremely high pressure in the deep sea, rigid vessels5-7 and pressure-compensation systems8-10 are typically required to protect mechatronic systems. However, deep-sea creatures that lack bulky or heavy pressure-tolerant systems can thrive at extreme depths11-17. Here, inspired by the structure of a deep-sea snailfish15, we develop an untethered soft robot for deep-sea exploration, with onboard power, control and actuation protected from pressure by integrating electronics in a silicone matrix. This self-powered robot eliminates the requirement for any rigid vessel. To reduce shear stress at the interfaces between electronic components, we decentralize the electronics by increasing the distance between components or separating them from the printed circuit board. Careful design of the dielectric elastomer material used for the robot's flapping fins allowed the robot to be actuated successfully in a field test in the Mariana Trench down to a depth of 10,900 metres and to swim freely in the South China Sea at a depth of 3,224 metres. We validate the pressure resilience of the electronic components and soft actuators through systematic experiments and theoretical analyses. Our work highlights the potential of designing soft, lightweight devices for use in extreme conditions.

Rubber-glass nanocomposites fabricated using mixed emulsions.

Many composites consist of matrices of elastomers and nanoparticles of stiff materials. Such composites often have superior properties and are widely used. Embedding elastomers with nanoparticles commonly necessitates intense shear, using machines like extruders and roll millers, which cut polymer chains and degrade properties. Here, we prepare a rubber-glass nanocomposite by using two aqueous emulsions. Each emulsion is separately prepared with a single species of polymer chains. Each polymer chain is copolymerized with a small amount of silane coupling agent. Upon mixing the two emulsions, as water evaporates, the glassy particles retain the shape, and the rubbery particles change shape to form a continuous matrix. Subsequently, the silane coupling agent condensates, which cross-links the rubbery chains and interlinks the rubbery chains to the glassy particles. The cross-links and interlinks stabilize the nanostructure and lead to superior properties. The nanocomposite simultaneously achieves high modulus (~30 MPa), high toughness (~100 kJ m-2), and high fatigue threshold (~1,000 J m-2). The method of mixed emulsion is environmentally friendly and compatible with various open-air manufacturing processes, such as coat, cast, spray, print, and brush. Additionally, the silane coupling agent can interlink the nanocomposite to other materials. The method of mixed emulsion can be used to fabricate objects of complex shapes, fine features, and prescribed spatial variations of compositions.

Confining Nano-ZrO2 in Nanodomains Leads to Electroactive Artificial Muscle with Large Deformation.

Dielectric elastomers generate muscle-like electroactive actuation, which is applicable in soft machines, medical devices, etc. However, the actuation strain and energy density of most dielectric elastomers, in the absence of prestretch, have long been limited to ∼20% and ∼10 kJ m-3, respectively. Here, we report a dielectric elastomer with ZrO2 nanoparticles confined in nanodomains, which achieves an actuation strain >100% and an energy density of ∼150 kJ m-3 without prestretch. We decorate the surface of each nanoparticle with a layer of a diblock oligomer, poly(acrylic acid-b-styrene). The surface-decorated nanoparticles coassemble with a triblock copolymer elastomer, poly(styrene-b-(2-ethylhexyl acrylate)-b-styrene) during cosolvent casting. Consequently, the nanoparticles are confined in the polystyrene nanodomains, which results in a dielectric elastomer nanocomposite with a low modulus, high breakdown strength, and intense strain-hardening behavior. During the actuation, the nanocomposite avoids the snap-through instability that most elastomers would suffer and achieves a superior actuation performance.

Metal-Chelatable Porphyrinic Frameworks for Single-Cell Multiplexing with Mass Cytometry.

Single-cell multiplexing is key to exploration of the heterogeneous cell populations in biological systems. Although the state-of-the-art mass cytometry (CyTOF) possesses high resolution and multiple dimensions, the lack of suitable marker materials prohibits fully exploiting the available CyTOF detection channels. Here we report a new design strategy for CyTOF markers using functionalized mesoporous porphyrinic frameworks (MPFs) as scaffolds for chelating metals that have been unachievable by conventional approaches. We developed surface modification for stably dispersing the MPF nanoparticles (<40 nm) during the metalation and antibody conjugation processes. Our markers exhibit higher sensitivity and comparable specificity compared with a polymer-based commercial benchmark. Compatibility with commercial markers during co-staining was also confirmed. Furthermore, our markers show promising performance for immunophenotyping and potential implementation in CyTOF systems.

Oxygen sensitive polymeric nanocapsules for optical dissolved oxygen sensors.

Immobilization of the oxygen-sensitive probes (OSPs) in the host matrix greatly impacts the performance and long-term usage of the optical dissolved oxygen (DO) sensors. In this work, fluorescent dyes, as the OSPs, were encapsulated with a crosslinked fluorinated polymer shell by interfacial confined reversible addition fragmentation chain transfer miniemulsion polymerization to fabricate oxygen sensitive polymeric nanocapsules (NCs). The location of fluorescent dyes and the fluorescent properties of the NCs were fully characterized by fourier transform infrared spectrometer, x-ray photoelectron spectrometer and fluorescent spectrum. Dye-encapsulated capacity can be precisely tuned from 0 to 1.3 wt% without self-quenching of the fluorescent dye. The crosslinked fluorinated polymer shell is not only extremely high gas permeability, but also prevents the fluorescent dyes from leakage in aqueous as well as in various organic solvents, such as ethanol, acetone and tetrahydrofuran (THF). An optical DO sensor based on the oxygen sensitive NCs was fabricated, showing high sensitivity, short response time, full reversibility, and long-term operational stability of online monitoring DO. The sensitivity of the optical DO sensor is 7.02 (the ratio of the response value in fully deoxygenated and saturated oxygenated water) in the range 0.96-14.16 mg l-1 and the response time is about 14.3 s. The sensor's work curve was fit well using the modified Stern-Volmer equation by two-site model, and its response values are hardly affected by pH ranging from 2 to 12 and keep constant during continuous measurement for 3 months. It is believed that the oxygen sensitive polymeric NCs-based optical DO sensor could be particularly useful in long-term online DO monitoring in both aqueous and organic solvent systems.

Core-shell nano-latex blending method to prepare multi-shape memory polymers.

Multi-shape memory polymers were prepared by blending a series of styrene (St)-block-(styrene-random-meth acrylate (MA))-block-styrene triblock copolymer nano-latexes. These latexes synthesized using a reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization method have a core-shell structure. The cores are formed by the middle poly(St-random-MA) blocks. They act as transition phases with variable transition temperatures via adjusting the St/MA ratio. When the latexes are blended with an identical PSt shell but different poly(St-random-MA) cores, the shells play a role in preventing the aggregation of these poly(St-random-MA) cores forming a crosslinked network after hot-press treatment. Therefore a polymer with well-distributed multiple nanophases is achieved, which shows a quadruple-shape memory behavior. Furthermore, the shape memory and recovery performance at a certain temperature can be improved on purpose by increasing the mass ratio of the corresponding transition phases, which can be realized via simply varying the blending ratio of different latexes. An optimized multi-shape memory polymer with the shape memory and recovery ratio higher than 80% at all the transition temperatures is achieved.

Thermoplastic Dielectric Elastomer of Triblock Copolymer with High Electromechanical Performance.

Dielectric elastomer (DE) actuators have been shown to have promising applications as soft electromechanical transducers in many emerging technologies. The DE actuators, which are capable of large actuation strain over a wide range of excitation frequencies, are highly desirable. Here, the first single-component DE of a triblock copolymer with attractive electromechanical performance is reported. Symmetric poly(styrene-b-butyl acrylate-b-styrene) (SBAS) is designed and synthesized. The SBAS actuator exhibits about 100% static actuation area strain and excellent dynamic performance, as evidenced by a wide half bandwidth of 300 Hz and a very high specific power of 1.2 W g-1 within the excitation frequency range of 300-800 Hz.

Multi-shape memory polymers achieved by the spatio-assembly of 3D printable thermoplastic building blocks.

Multi-shape memory polymers were prepared by the macroscale spatio-assembly of building blocks in this work. The building blocks were methyl acrylate-co-styrene (MA-co-St) copolymers, which have the St-block-(St-random-MA)-block-St tri-block chain sequence. This design ensures that their transition temperatures can be adjusted over a wide range by varying the composition of the middle block. The two St blocks at the chain ends can generate a crosslink network in the final device to achieve strong bonding force between building blocks and the shape memory capacity. Due to their thermoplastic properties, 3D printing was employed for the spatio-assembly to build devices. This method is capable of introducing many transition phases into one device and preparing complicated shapes via 3D printing. The device can perform a complex action via a series of shape changes. Besides, this method can avoid the difficult programing of a series of temporary shapes. The control of intermediate temporary shapes was realized via programing the shapes and locations of building blocks in the final device.

Well-Defined High Molecular Weight Polystyrene with High Rates and High Livingness Synthesized via Two-Stage RAFT Emulsion Polymerization.

A highly living polymer with over 100 kg mol(-1) molecular weight is very difficult to achieve by controlled radical polymerization since the unavoidable side reactions of irreversible radical termination and radical chain transfer to monomer reaction become significant. It is reported that over 500 kg mol(-1) polystyrene with high livingness and low dispersity could be synthesized by a facile two-stage reversible addition-fragmentation transfer emulsion polymerization. The monomer conversion reaches 90% within 10 h. High livingness of the product is ascribed to the extremely low initiator concentration and the chain transfer constant for monomer unexpectedly much lower than the well-accepted values in the conventional radical polymerization. The two-stage monomer feeding policy much decreases the dispersity of the product.

Composite elastomers with on-demand convertible phase separations achieve large and healable electro-actuation.

Phase separation has been widely exploited for fabricating structured functional materials. Generally, after being fabricated, the phase structure in a hybrid material system has been set at a specific length scale and remains unchanged during the lifespan of the material. Herein, we report a strategy to construct on-demand and reversible phase switches among homogenous, nano- and macro-phase separation states in a composite elastomer during its lifespan. We trigger the nanophase separation by super-saturating an elastomer matrix with a carefully selected small-molecule organic compound (SMOC). The nanoparticles of SMOC that precipitate out upon quenching will stretch the elastomer network, yet remain stably arrested in the elastomer matrix at low temperatures for a long time. However, at elevated temperatures, the nano-phase separation will transform into the macro-one. The elastic recovery will drive the SMOC onto the elastomer surface. The phase-separated structures can be reconfigured through the homogeneous solution state at a further elevated temperature. Taking advantage of the reversible phase switches leads to a novel strategy for designing high-performance dielectric elastomers. The in situ formed nanoparticles can boost the electro-actuation performance by eliminating electro-mechanical instability and lead to a very large actuation strain (∼146%). Once the actuator broke down, SMOC could on-demand be driven to the breakdown holes and heal the actuator.

Machine Learning-Assisted Identification of Copolymer Microstructures Based on Microscopic Images.

The microstructure of polymer materials is an important bridge between their molecular structure and macroproperties, which is of great significance to be effectively identified. With the increasing refinement of polymer material design, the microstructure of different polymer materials gradually converges, which is difficult to distinguish. In this study, the machine learning method is applied to recognize the microstructure. A highly accurate and interpretable model based on small experimental data sets has been completed by the methods of transfer learning and feature visualization, making the result of the model that can be explained from the perspective of physical chemistry. This work provides an idea for identifying microstructure and will help further promote intelligent polymer research and development.

Dielectric Polymer with Designable Large Motion under Low Electric Field.

Dielectric elastomers (DEs) can demonstrate fast and large in-plane expansion/contraction due to electric field (e-field)-induced Maxwell stress. For robotic applications, it is often necessary that the in-plane actuation is converted into out-of-plane motions with mechanical frames. Despite their performance appeal, their high driving e-field (20-100 V µm-1 ) demands bulky power accessories and severely compromises their durability. Here, a dielectric polymer that can be programmed into diverse motions actuated under a low e-field (2-10 V µm-1 ) is reported. The material is a crystalline dynamic covalent network that can be reconfigured into arbitrary 3D geometries. This gives rise to a geometric effect that markedly amplifies the actuation, leading to designable large motions when the dielectric polymer is heated above its melting temperature to become a DE. Additionally, the crystallization transition enables dynamic multimodal motions and active deployability. These attributes result in unique design versatility for soft robots.

pH Responsivity and micelle formation of gradient copolymers of methacrylic acid and methyl methacrylate in aqueous solution.

A series of gradient copolymers of methacrylic acid (MAA)/methyl methacrylate (MMA) with four end-to-end composition profiles (uniform, linear gradient, triblock with linear gradient midblock, and diblock) but all having an average chain composition of ̅F(MMA) ≈ 0.5 and an average chain length of 200 were synthesized via model-based, computer-programmed, semibatch atom-transfer radical copolymerization (ATRcoP). These samples allowed us to investigate systematically the effects of the gradient composition profile on the pH responsivity and micelle formation of the copolymers in an aqueous solution. Measurements included light transmittance, TEM, AFM, DLS, (1)H NMR, and pH titration. It was found that linear gradient, triblock, and diblock copolymers formed spherical micelles at high pH. The micelles of the linear gradient copolymer contained MMA units in their hydrophilic shells, and those of the triblock and diblock copolymers had all of their MMA units residing in their cores. The composition profile showed a strong effect on the degree of acid dissociation at a given pH. The conformational transition of the copolymer chains was determined by both the pH value and composition profile. Copolymers having sharper gradients required a lower pH to trigger the conformational transition and a narrower pH range to complete the transition.

Vapor-Phase Molecular Doping in Covalent Organosiloxane Network Thin Films Via a Lewis Acid-Base Interaction for Enhanced Mechanical Properties.

Incorporating inorganic components in organosiloxane polymer thin films for enhanced mechanical properties could enable better durability and longevity of functional coatings for a multitude of applications. However, molecularly dispersing the inorganic dopants while preserving the cyclosiloxane rings represents a challenge for cross-linked organosiloxane networks. Here, we report a molecular doping strategy using vapor-phase infiltration. On the basis of the proper Lewis acid-base interaction between diethyl zinc (DEZ) and cyclotrisiloxane rings, we achieved a complete infiltration of the organometallic precursors and well-distributed Zn-OH terminal groups formed in the initiated chemical vapor deposited poly(1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane) (PV3D3) films. X-ray photoelectron spectroscopy and nanoscale infrared spectroscopy together with density functional theory simulation reveal that the formation of a Lewis acid-base adduct rather than a ring-opening process is possibly involved in anchoring DEZ in the cross-linked network of PV3D3. Because of the incorporation of Zn-OH components, the organic-inorganic hybrid films obtained via our vapor-phase molecular doping exhibit a 10.2% larger elastic modulus and 67.0% higher hardness than the pristine PV3D3. Unveiling the reaction mechanisms between organometallic precursors and cross-linked organic networks provides new insights for expanding the vapor-phase processing strategies for engineering hybrid materials at the nanoscale.

Adaptively reconstructing network of soft elastomers to increase strand rigidity: towards free-standing electro-actuation strain over 100.

Soft biological tissues and muscles composed of semiflexible networks exhibit rapid strain-hardening behaviors to protect them from accidental rupture. In contrast, synthetic soft elastomers, usually featuring flexible networks, lack such behaviors, leading to a notorious issue when applying them to a promising artificial muscle technology (dielectric elastomer, DE), that is electromechanical instability (EMI) induced premature breakdown. We report that a facile thermomechanical training method can adaptively reconstruct the network of a soft triblock copolymer elastomer to transform its flexible network strands into semiflexible ones without extra chemical modifications and additives so that the electro-actuation performance is significantly enhanced by avoiding EMI. The free-standing actuators of trained elastomers exhibit a large stable electro-actuation strain and a high theoretical energy density (133%, 307 kJ m-3 at 158.1 V µm-1), and the capacity of actuating at low-temperature environments (-15 °C).

Bioinspired Multifunctional Cellular Plastics with a Negative Poisson's Ratio for High Energy Dissipation.

Cellular plastics have been widely used in transportation, aerospace, and personal safety applications owing to their excellent mechanical, thermal, and acoustic properties. It is highly desirable to impart them with a complex porous structure and composition distribution to obtain specific functionality for various engineering applications, which is challenging with conventional foaming technologies. Herein, it is demonstrated that this can be achieved through the controlled freezing process of a monomer/water emulsion, followed by cryopolymerization and room temperature thawing. As ice is used as a template, this method is environmentally friendly and capable of producing cellular plastics with various microstructures by harnessing the numerous morphologies of ice crystals. In particular, a cellular plastic with a radially aligned structure shows a negative Poisson's ratio under compression. The rigid plastic shows a much higher energy dissipation capability compared to other materials with similar negative Poisson's ratios. Additionally, the simplicity and scalability of this approach provides new possibilities for fabricating high-performance cellular plastics with well-defined porous structures and composition distributions.

Light-triggered topological programmability in a dynamic covalent polymer network.

Dynamic covalent polymer networks exhibit unusual adaptability while maintaining the robustness of conventional covalent networks. Typically, their network topology is statistically nonchangeable, and their material properties are therefore nonprogrammable. By introducing topological heterogeneity, we demonstrate a concept of topology isomerizable network (TIN) that can be programmed into many topological states. Using a photo-latent catalyst that controls the isomerization reaction, spatiotemporal manipulation of the topology is realized. The overall result is that the network polymer can be programmed into numerous polymers with distinctive and spatially definable (thermo-) mechanical properties. Among many opportunities for practical applications, the unique attributes of TIN can be explored for use as shape-shifting structures, adaptive robotic arms, and fracture-resistant stretchable devices, showing a high degree of design versatility. The TIN concept enriches the design of polymers, with potential expansion into other materials with variations in dynamic covalent chemistries, isomerizable topologies, and programmable macroscopic properties.

Anisotropic electroactive elastomer for highly maneuverable soft robotics.

Dielectric elastomers (DEs) are promising electroactive artificial muscles for use in soft machines. However, achieving anisotropy and sub-kV actuation voltage remains a great challenge for DE actuators. Herein, we report a facile method to fabricate ultrathin anisotropic DE films of an amorphous triblock copolymer poly(styrene-b-butyl acrylate-b-styrene) (SBAS) for soft actuators. The modulus of anisotropic SBAS in one direction can be modulated from 0.3 MPa to 10.5 MPa, and the modulus in the orthogonal direction remains the same as that of the pristine film (0.3 MPa). The anisotropy endows soft DE actuators with the directional-preferred response to an applied electric field and programmable multiple actuation morphs. These anisotropic SBAS films allowed us to fabricate compact soft robotics with high maneuverability, including soft grippers for object manipulation and crawling robots with reversible moving ability under an actuation voltage around 800 V.

Tumor extravasation and infiltration as barriers of nanomedicine for high efficacy: The current status and transcytosis strategy.

Nanotechnology-based drug delivery platforms have been explored for cancer treatments and resulted in several nanomedicines in clinical uses and many in clinical trials. However, current nanomedicines have not met the expected clinical therapeutic efficacy. Thus, improving therapeutic efficacy is the foremost pressing task of nanomedicine research. An effective nanomedicine must overcome biological barriers to go through at least five steps to deliver an effective drug into the cytosol of all the cancer cells in a tumor. Of these barriers, nanomedicine extravasation into and infiltration throughout the tumor are the two main unsolved blockages. Up to now, almost all the nanomedicines are designed to rely on the high permeability of tumor blood vessels to extravasate into tumor interstitium, i.e., the enhanced permeability and retention (EPR) effect or so-called "passive tumor accumulation"; however, the EPR features are not so characteristic in human tumors as in the animal tumor models. Following extravasation, the large size nanomedicines are almost motionless in the densely packed tumor microenvironment, making them restricted in the periphery of tumor blood vessels rather than infiltrating in the tumors and thus inaccessible to the distal but highly malignant cells. Recently, we demonstrated using nanocarriers to induce transcytosis of endothelial and cancer cells to enable nanomedicines to actively extravasate into and infiltrate in solid tumors, which led to radically increased anticancer activity. In this perspective, we make a brief discussion about how active transcytosis can be employed to overcome the difficulties, as mentioned above, and solve the inherent extravasation and infiltration dilemmas of nanomedicines.

Development of a Highly Sensitive, Broad-Range Hierarchically Structured Reduced Graphene Oxide/PolyHIPE Foam for Pressure Sensing.

Highly sensitive pressure sensors are usually made from soft materials that allow large deformations to be obtained when very small pressures are applied. Unfortunately, this current paradigm limits the ability to create sensors capable of high sensitivities and broad dynamic ranges as these materials are prone to saturation responses when attempting to obtain measurements involving high pressures. In this paper, we detail a piezoresistive pressure sensor that is capable of high sensitivity over a pressure range spanning from 0.6 Pa (a mosquito touching a surface) to 200 kPa (an elephant standing on the surface). The sensor's ability to cover such a broad dynamic range is made possible by the fairly hard foam used in its construction as this material is capable of propagating strain in a highly effective manner due to its hierarchical porous structure. The material was fabricated by using high-internal-phase emulsion (HIPE) as a template to generate a highly porous material consisting of small pores packed between larger ones whose inner walls are lined with reduced graphene oxide. The developed foam exhibits very fast response times (less than 15.4 ms) and excellent cyclic stability (at least 10,000 cycles). Furthermore, it is capable of responding to the entire tactile pressure range, and it can be formatted as pixelated arrays, which makes it highly suitable for integration into wearable electronic devices. Such arrays were built and used to identify and render the shape of objects with different geometries, including a sphere, a triangle, a square, and two nearly identical rods differing only by 0.4 mm in diameter.