Programmable Morphing Hydrogels for Soft Actuators and Robots: From Structure Designs to Active Functions.

Nature provides abundant inspiration and elegant paradigms for the development of smart materials that can actuate, morph, and move on demand. One remarkable capacity of living organisms is to adapt their shapes or positions in response to stimuli. Programmed deformations or movements in plant organs are mainly driven by water absorption/dehydration of cells, while versatile motions of mollusks are based on contraction/extension of muscles. Understanding the general principles of these morphing and motion behaviors can give rise to disruptive technologies for soft robotics, flexible electronics, biomedical devices, etc. As one kind of intelligent material, hydrogels with high similarity to soft biotissues and diverse responses to external stimuli are an ideal candidate to construct soft actuators and robots.The objective of this Account is to give an overview of the fundamental principles for controllable deformations and motions of hydrogels, with a focus on the structure designs and responsive functions of the corresponding soft actuators and robots. This field has been rapidly developed in recent years with a growing understanding of working principles in natural organisms and a substantial revolution of manufacturing technologies to devise bioinspired hydrogel systems with desired structures. Diverse morphing hydrogels and soft actuators/robots have been developed on the basis of several pioneering works, ranging from bending and folding deformations of bilayer hydrogels to self-shaping of non-Euclidean hydrogel surfaces, and from thermoactuated bilayer gel "hands" to electrodriven polyelectrolyte gel "worms". These morphing hydrogels have demonstrated active functions and versatile applications in biomedical and engineering fields.In this Account, we discuss recent progress in morphing hydrogels and highlight the design principles and relevant applications. First, we introduce the fundamentals of basic deformation modes, together with generic structure features, actuation strategies, and morphing mechanisms. The advantages of in-plane gradient structures are highlighted for programmable deformations by harnessing the out-of-plane buckling with bistability nature to obtain sophisticated three-dimensional configurations. Next, we give an overview of soft actuators and robots based on morphing hydrogels and focus on the working principles of the active systems with different structure designs. We discuss the advancements of hydrogel-based soft robots capable of swift locomotion with different gaits and emphasize the significances of structure control and dynamic actuation. Then we summarize versatile applications of hydrogel-based actuators and robots in biomedicines, cargo delivery, soft electronics, information encryption, and so forth. Some hydrogel robots with a built-in feedback loop and self-sensing system exhibit collaborative functions and advanced intelligence that are informative for the design of next-generation hydrogel machines. Finally, concluding remarks are given to discuss future opportunities and remaining challenges in this field. For example, miniature hydrogel-based actuators/robots with therapeutic or diagnostic functions are highly desired for biomedical applications. The morphing mechanisms summarized in this Account should be applicable to other responsive materials. We hope that this Account will inspire more scientists to be involved in this emerging area and make contributions to reveal novel working principles, design multifunctional soft machines, and explore applications in diverse fields.

Healable, Recyclable, and Multifunctional Soft Electronics Based on Biopolymer Hydrogel and Patterned Liquid Metal.

Recent years have witnessed the rapid development of sustainable materials. Along this line, developing biodegradable or recyclable soft electronics is challenging yet important due to their versatile applications in biomedical devices, soft robots, and wearables. Although some degradable bulk hydrogels are directly used as the soft electronics, the sensing performances are usually limited due to the absence of distributed conducting circuits. Here, sustainable hydrogel-based soft electronics (HSE) are reported that integrate sensing elements and patterned liquid metal (LM) in the gelatin-alginate hybrid hydrogel. The biopolymer hydrogel is transparent, robust, resilient, and recyclable. The HSE is multifunctional; it can sense strain, temperature, heart rate (electrocardiogram), and pH. The strain sensing is sufficiently sensitive to detect a human pulse. In addition, the device serves as a model system for iontophoretic drug delivery by using patterned LM as the soft conductor and electrode. Noncontact detection of nearby objects is also achieved based on electrostatic-field-induced voltage. The LM and biopolymer hydrogel are healable, recyclable, and degradable, favoring sustainable applications and reconstruction of the device with new functions. Such HSE with multiple functions and favorable attributes should open opportunities in next-generation electronic skins and hydrogel machines.

Population-specific age estimation in Black Americans and Chinese people based on pulp chamber volume of first molars from cone beam computed tomography.

OBJECTIVES: To validate the fitness of the age estimation model in Black Americans, which was previously and solely established for the Chinese population based on pulp chamber volume of the first molars from cone beam computed tomography (CBCT), and to establish a new age estimation model for Black Americans. MATERIALS AND METHODS: A total of 203 subjects with CBCT scans, including 119 Chinese and 84 Black Americans, were retrospectively identified. The age range of subjects was between 11 and 87 years. For both populations, automated 3D pulp chamber segmentation of the first molars was performed by deep learning, followed by volume calculation and age estimation by a logarithmic regression model, which was established in a prior study solely on Chinese population. Additionally, a separate logarithmic regression analysis was carried out on Black Americans. The performance of age estimation was assessed by the mean absolute error (MAE), root mean square error (RMSE), Wilcoxon signed rank test, and coefficient of determination (R2) between the actual and estimated human ages. RESULTS: When applying the age estimation model established in the prior study, MAE = 7.994 years and RMSE = 10.065 years were observed in the Chinese population, while MAE = 14.049 years and RMSE = 17.866 years were observed in Black Americans. The new age estimation model established for Black Americans was AGE = 89.752 - 21.176 × lnV (V = pulp chamber volume), with MAE = 7.930 years, RMSE = 10.664 years, and coefficient of determination (R2) = 0.600. CONCLUSIONS: Population-specific age estimation is needed when applied in Black Americans and Chinese people based on pulp chamber volume of the first molars from CBCT.

Age estimation based on 3D pulp chamber segmentation of first molars from cone-beam-computed tomography by integrated deep learning and level set.

OBJECTIVES: To develop an automatic segmentation method to segment the pulp chamber of first molars from 3D cone-beam-computed tomography (CBCT) images, and to estimate ages by calculated pulp volumes. MATERIALS AND METHODS: Patients with CBCT scans were retrospectively identified. The age estimation was formulated as CBCT image segmentation using a coarse-to-fine strategy by integrated deep learning (DL) and level set (LS), followed by establishing a linear regression model. On the training data, DL model was trained for coarse segmentation. The validation set was to determine the optimal DL model, and a LS method established on it was to refine the coarse segmentation. On the testing data, the integrated DL and LS method was applied for pulp chamber segmentation, followed by volume calculation and age estimation. Statistical analysis was performed by Wilcoxon rank sum test to demonstrate gender difference in pulp chamber volume, and volume difference between maxillary and mandibular molars. Wilcoxon signed-rank test was adopted to compare true and estimated ages. RESULTS: A total of 180 CBCT studies were randomly divided into 37/10/133 patients for training, validation, and testing data, respectively. In the training and validation sets, the results showed high spatial overlaps between manual and automatic segmentation (dice = 87.8%). For the testing set, the estimated human ages were not significantly different with true human age (p = 0.57), with a correlation coefficient r = 0.74. CONCLUSIONS: An integrated DL and LS method was able to segment pulp chamber of first molars from 3D CBCT images, and the derived pulp chamber volumes could effectively estimate the human ages.

Sequentially Controlled Deformations of Patterned Hydrogels into 3D Configurations with Multilevel Structures.

Sequential deformations of patterned hydrogels into 3D configurations with multilevel structures are reported, which are realized for the first time in self-shaping materials. The periodically patterned single-layer hydrogels with different polymers are fabricated by multi-step photolithography. After swelling in water, the expansion of compartmentalized high-swelling gels is constrained by the dispersed non-swelling gels, resulting in out-of-plane buckling with high cooperativity and thus forming alternating concave-convex configuration. When the dispersed non-swelling gels are partly replaced by thermoresponsive ones, the preformed overall flat, yet locally undulant, hydrogel deforms further into dome-, saddle-, or sandglass-like configurations at elevated temperature. As such, multilevel 3D structures can be achieved via prebuilt mechanical/geometric cues in a sequentially controlled manner. This conceptual design and sequential deformation of patterned hydrogels to form 3D configurations with multilevel structures should enrich the deformation/functioning modes of morphing materials and broaden their applications in diverse areas.

An NIR-Guided Aggregative and Self-Immolative Nanosystem for Efficient Cancer Targeting and Combination Anticancer Therapy.

Nanosized drug delivery systems based on polymeric structures have been proven to be promising approaches for cancer treatments. However, few have been effective at selectively targeting cancer cells and releasing drug at desired tumor sites. Here, we report a "smart" polymeric nanoplatform, which could actively accumulate at tumor sites and dissociate to release encapsulated cargos upon the irradiation of a near-infrared (NIR) laser. This nanoplatform composed of a novel amphiphilic block copolymer poly(propylene sulfide)-poly( N-isopropylacrylamide- co- N, N-dimethylacrylamide) (PPS-P(NIPAM- co-DMAA)) formed spherical structures in aqueous solution and responded to both oxidants and elevated temperature. Upon laser irradiation at 808 nm, the NIR light was efficiently converted to local heat by the doxorubicin (DOX) and indocyanine green (ICG) co-loaded micelles for enhanced cell uptake and therapeutic efficacy. It showed that the micelles effectively accumulated at the tumor sites guided by the application of an NIR laser in in vivo studies, exhibiting a 6-time greater and much faster targeting effect compared to the nonirradiation group. The effective tumor growth inhibition by the drug-loaded micelles upon laser irradiation demonstrated significant tumor inhibition without regrowth in 16 days. This micellar nanoplatform for precise NIR-guided cancer targeting and combination therapy provides a novel and robust strategy for cancer therapy.

On the inherent properties of Soluplus and its application in ibuprofen solid dispersions generated by microwave-quench cooling technology.

Polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer, or Soluplus®, is a relatively new copolymer and a promising carrier of amorphous solid dispersions. Knowledge on the inherent properties of Soluplus® (e.g. cloud points, critical micelle concentrations, and viscosity) in different conditions is relatively inadequate, and the application characteristics of Soluplus®-based solid dispersions made by microwave methods still need to be clarified. In the present investigation, the inherent properties of a Soluplus® carrier, including cloud points, critical micelle concentrations, and viscosity, were explored in different media and in altered conditions. Ibuprofen, a BCS class II non-steroidal anti-inflammatory drug, was selected to develop Soluplus®-based amorphous solid dispersions using the microwave-quench cooling (MQC) method. Scanning electronic microscopy (SEM), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), Raman spectroscopy (RS), and Fourier transform infrared spectroscopy (FT-IR) were adopted to analyze amorphous properties and molecular interactions in ibuprofen/Soluplus® amorphous solid dispersions generated by MQC. Dissolution, dissolution extension, phase solubility, equilibrium solubility, and supersaturated crystallization inhibiting experiments were performed to elucidate the effects of Soluplus® on ibuprofen in solid dispersions. This research provides valuable information on the inherent properties of Soluplus® and presents a basic understanding of Soluplus® as a carrier of amorphous solid dispersions.

The Influence of Cellulosic Polymer's Variables on Dissolution/Solubility of Amorphous Felodipine and Crystallization Inhibition from a Supersaturated State.

The collective impact of cellulosic polymers on the dissolution, solubility, and crystallization inhibition of amorphous active pharmaceutical ingredients (APIs) is still far from being adequately understood. The goal of this research was to explore the influence of cellulosic polymers and incubation conditions on enhancement of solubility and dissolution of amorphous felodipine, while inhibiting crystallization of the drug from a supersaturated state. Variables, including cellulosic polymer type, amount, ionic strength, and viscosity, were evaluated for effects on API dissolution/solubility and crystallization processes. Water-soluble cellulosic polymers, including HPMC E15, HPMC E5, HPMC K100-LV, L-HPC, and MC, were studied. All cellulosic polymers could extend API dissolution and solubility to various extents by delaying crystallization and prolonging supersaturation duration, with their effectiveness ranked from greatest to least as HPMC E15 > HPMC E5 > HPMC K100-LV > L-HPC > MC. Decreased polymer amount, lower ionic strength, or higher polymer viscosity tended to decrease dissolution/solubility and promote crystal growth to accelerate crystallization. HPMC E15 achieved greatest extended API dissolution and maintenance of supersaturation from a supersaturated state; this polymer thus had the greatest potential for maintaining sustainable API absorption within biologically relevant time frames.

Polymeric micelles with dual thermal and reactive oxygen species (ROS)-responsiveness for inflammatory cancer cell delivery.

BACKGROUND: The object of this study was to develop a thermally and reactive oxygen species-responsive nanocarrier system for cancer therapy. RESULTS: PPS-PNIPAm block copolymer was designed and synthesised using a combination of living anionic ring-opening polymerization and atom transfer radical polymerization. The synthesized polymer formed micellar aggregates in water and demonstrated dual responsiveness towards temperature and oxidants. Using doxorubicin (DOX) as a model drug, encapsulation and in vitro release of the drug molecules in PPS-PNIPAm nanocarriers confirmed the responsive release properties of such system. Cell uptake of the DOX loaded micelles was investigated with human breast cancer cell line (MCF-7). The results showed Dox-loaded micelles were able to be taken by the cells and mainly reside in the cytoplasma. In the stimulated cells with an elevated level of ROS, more released DOX was observed around the nuclei. In the cytotoxicity experiments, the Dox-loaded micelles demonstrated comparable efficacy to free DOX at higher concentrations, especially on ROS stimulated cells. CONCLUSIONS: These results demonstrated that PPS-PNIPAm nanocarriers possess the capability to respond two typical stimuli in inflammatory cells: temperature and oxidants and can be used in anticancer drug delivery.

Light Responsive Microstructured Surfaces of Liquid Crystalline Network with Shape Memory and Tunable Wetting Behaviors.

Using adaptive soft materials to fabricate microstructured surfaces renders them with tunable topographic feature and thus controllable physical properties. Here, light responsive microstructured surfaces are reported with shape memory and tunable wetting behaviors; the surfaces are covered with micropillar arrays and constructed by lightly crosslinked azo-containing liquid crystalline network (LCN). UV light irradiation induces 25% contraction in length of the micropillars along their long axes and, as a consequence, the variations of topographic feature and wetting behavior of the surfaces. In addition, the LCNs exhibit shape memory properties, which can freeze the temporary topographic feature of microstructured surfaces (formed under UV irradiation and relatively high temperature) and enable application of their functionalities at mild conditions. This light responsiveness makes it feasible to remotely and precisely tune the local regions of microstructured surfaces, which should broaden the applications of adaptive surfaces in regulating the wetting, optical, and adhesion properties in selected regions.

[Rules and characteristics of crystallization inhibition of cellulose polymers against drugs in supersaturated states].

This study aims to explore the characteristics of crystallization inhibition by cellulose polymers at the supersaturated states of drugs. The study was performed by simulating supersaturated process and preparing supersaturated drug solid, and was carried out by measuring the content of drugs at different time points using dissolution apparatus. The types, amounts, ionic intensity and viscosity of cellulose polymers were examined to assess the crystallization inhibition effect on BCS II class drug indomethacin. HPMC E15 exhibited the strongest crystallization inhibition effect. The more added, more obvious crystallization suppression was observed against indomethacin. The decrease in viscosity and increase in ionic intensity led to an enhanced inhibition. The research provides a scientific guide for the crystallization inhibition of supersaturated drug by cellulose polymers.

Three-dimensional poly-(ε-caprolactone) nanofibrous scaffolds directly promote the cardiomyocyte differentiation of murine-induced pluripotent stem cells through Wnt/ß-catenin signaling.

BACKGROUND: Environmental factors are important for stem cell lineage specification, and increasing evidence indicates that the nanoscale geometry/topography of the extracellular matrix (ECM) directs stem cell fate. Recently, many three-dimensional (3D) biomimetic nanofibrous scaffolds resembling many characteristics of the native ECM have been used in stem cell-based myocardial tissue engineering. However, the biophysical role and underlying mechanism of 3D nanofibrous scaffolds in cardiomyocyte differentiation of induced pluripotent stem cells (iPSCs) remain unclear. RESULTS: Here, we fabricated a 3D poly-(ε-caprolactone) (PCL) nanofibrous scaffold using the electrospinning method and verified its nanotopography and porous structure by scanning electron microscopy. We seeded murine iPSCs (miPSCs) directly on the 3D PCL nanofibrous scaffold and initiated non-directed, spontaneous differentiation using the monolayer method. After the 3D PCL nanofibrous scaffold was gelatin coated, it was suitable for monolayer miPSC cultivation and cardiomyocyte differentiation. At day 15 of differentiation, miPSCs differentiated into functional cardiomyocytes on the 3D PCL nanofibrous scaffold as evidenced by positive immunostaining of cardiac-specific proteins including cardiac troponin T (cTnT) and myosin light chain 2a (MLC2a). In addition, flow cytometric analysis of cTnT-positive cells and cardiac-specific gene and protein expression of cTnT and sarcomeric alpha actinin (α-actinin) demonstrated that the cardiomyocyte differentiation of miPSCs was more efficient on the 3D PCL nanofibrous scaffold than on normal tissue culture plates (TCPs). Furthermore, early inhibition of Wnt/ß-catenin signaling by the selective antagonist Dickkopf-1 significantly reduced the activity of Wnt/ß-catenin signaling and decreased the cardiomyocyte differentiation of miPSCs cultured on the 3D PCL nanofibrous scaffold, while the early activation of Wnt/ß-catenin signaling by CHIR99021 further increased the cardiomyocyte differentiation of miPSCs. CONCLUSION: These results indicated that the electrospun 3D PCL nanofibrous scaffolds directly promoted the cardiomyocyte differentiation of miPSCs, which was mediated by the activation of the Wnt/ß-catenin signaling during the early period of differentiation. These findings highlighted the biophysical role of 3D nanofibrous scaffolds during the cardiomyocyte differentiation of miPSCs and revealed its underlying mechanism involving Wnt/ß-catenin signaling, which will be helpful in guiding future stem cell- and scaffold-based myocardium bioengineering.

Enhanced mechanical and long-lasting antibacterial properties of starch/PBAT blown films via designing of reactive micro-crosslinked starch.

A functional starch (TPS-E) was designed and constructed by incorporating epoxy soybean oil (ESO) and an antibacterial agent polyhexamethylene guanidine hydrochloride (PHMG), then the film was prepared by reaction extrusion and blow molding using TPS-E and poly(butylene adipate-co-terephthalate) (PBAT). The micro-crosslinking structure, forming through ring-opening reaction between the epoxy active site of TPS-E and the end group of PBAT, improved the compatibility of starch/PBAT blend and reduce the dispersed starch phase size, leading to significantly increase the tensile strength. Compared to starch/PBAT films, the tensile strength of TPS-E/PBAT in the longitudinal direction increase by 112% with the same starch content of 30%. Furthermore, these TPS-E/PBAT films demonstrated long-lasting antibacterial performance with a 98% inhibition ratio even after 10 cycles, without any observed leaching of the antibacterial agent, highlighting the high coupling efficiency of PHMG. TPS-E with the degradable ESO also promotes the degradation of PBAT. Thus, an important method of synergistic improving the mechanical, degradable and antibacterial properties of blown films through the design of reactive micro-crosslinked starch structures was established.

The synthesis of multifunctional cellulose graft alternating copolymers of 3,4-dihydrocoumarin and epoxides in DBU/DMSO/CO2 solvent system.

Cellulose graft copolymers having well-defined structures could incorporate the characteristics of both the cellulose skeleton and side chains, providing a new method for the preparation functionalised cellulose derivatives. Herein, a series of multifunctional cellulose grafted, alternating 3,4-dihydrocoumarin (DHC) and epoxide (EPO) copolymers (cell-g-P(DHC-alt-EPO)) were prepared in a metal-free DBU/DMSO/CO2 solvent system without adding additional catalyst. Four examples of cell-g-P(DHC-alt-EPO) with tunable thermal and optical properties were synthesized by copolymerization of DHC with styrene oxide (SO), propylene oxide (PO), cyclohexene oxide (CHO) or furfuryl glycidyl ether (FGE) onto cellulose. The nonconjugated cell-g-P(DHC-alt-EPO) showed UV absorption properties with the maximum absorption peak at 282 nm and 295 nm and photoluminescence performance. A clustering-triggered emission mechanism was confirmed and consistent with DFT theoretical calculations. In DMSO solution, the copolymer (DHCSO5) with DP of 11.64 showed ACQ behaviour as the concentration increased. In addition, DHCSO5 had good antioxidant capacity with an instantaneous radical scavenging activity of 2,2-diphenyl-1-picrylhydrazine (DPPH) up to 65 % at a concentration of 40 mg/ ml and increased to 100 % after 30 min. Thus, the multifunctional cell-g-P(DHC-alt-EPO) materials had a variety of potential applications in the fields of fluorescent printing, bio-imaging, UV- shielding and antioxidants.

Thermo-soil weathering and life cycle assessment of carbon black, silica and cellulose nanocrystal filled rubber nanocomposites.

Carbon black (CB) and silica (Sil) as rubber reinforcement have raised environmental concerns for being high resources consumptive and less susceptible towards biodegradability. Cellulose nanocrystal (CNC) has demonstrated great potentials for use as biodegradable nanofillers in rubber nanocomposites while evaluation of its environmental impacts with optimal end-of-life (EOL) choices is not carried out. To simulate realistic EOL, thermo-oxidative aging and soil burial aging behaviors of rubber nanocomposites with 33.3% filler were performed. The environmental weathering performance modeled with the help of life cycle assessment (LCA) illustrates increased biodegradation susceptibility with partial replacement of CB or Sil with CNC in the nanocomposites, hence promoting the environmental solutions for waste minimalization by enhancing the biodegradability potentials. In terms of LCA, the CNC incorporation contributes more to the environmental impacts in manufacturing but greatly lowers the EOL choices, by reducing the global warming potential values.

A universal post-treatment strategy for biomimetic composite hydrogel with anisotropic topological structure and wide range of adjustable mechanical properties.

The development of biomimetic materials with anisotropic topological structure and wide range of adjustable mechanical properties is central to tissue engineering fields. In this work, on the basis of a stiff/stretchable dually crosslinked hydrogel, we paid more attention to the synergistic contribution of the confined drying and re-swelling (CDR) effect and Hofmeister effect to its micro structures, polymer aggregation states and mechanical strength. Specifically, by changing the pre-strains of the CDR procedure and the soaking time during the salting-out procedure, the arrangement structure orientation, chain-entanglement density, and supramolecular interaction strength within the polymer can be adjusted by changing the processing sequence of the two procedures, so that to obtain anisotropic biomimetic hydrogels with adjustable mechanical properties in a wide range. Thus, this engineered anisotropic polymer can mimic the natural tissues' mechanical properties in regeneration. Moreover and importantly, these anisotropic hydrogels exhibit prominent self-recovery properties. In summary, with the integration of molecular and structural engineering approaches, this study presents a universal strategy for developing anisotropic hydrogels, which could be widely used as biomimetic substitutes with anisotropic features in tissue regeneration.

3D printing of a tough double-network hydrogel and its use as a scaffold to construct a tissue-like hydrogel composite.

To mimic biological tissues with high toughness such as cartilage, it is highly desired to fabricate stable and tough hydrogels with intricate shapes to act as a structural support. Extrusion-based 3D printing is a promising method to fabricate 3D scaffolds with various architectures; however, printing tough hydrogel structures with high fidelity and resolution is still a challenge. In this work, we adopt the fast sol-to-gel transition of κ-carrageenan in the solution of acrylamide upon cooling to fix the printed scaffolds and polymerize the precursor solution to form the second network. The printed constructs of κ-carrageenan/polyacrylamide double-network gels are toughened by soaking in an aqueous solution of zirconyl chloride to form coordination complexes between the Zr4+ ions and sulfate groups of κ-carrageenan. The obtained hydrogels are stable in water and possess good mechanical properties, with a tensile breaking stress of 1-2 MPa, breaking strain of 100-150%, and Young's modulus of 4-10 MPa. The printed grid can hold 150 times its own weight. 3D printed constructs with a high aspect ratio and shape fidelity are obtained by optimizing the printing parameters. Furthermore, a biomimetic strategy is applied to construct a hydrogel composite by filling the printed tough hydrogel scaffold with a cell-laden fibrin hydrogel as the soft substance. Chondrocytes in the hydrogel composite maintain high viability after cyclic compression, demonstrating the load-bearing capacity of the tough scaffold and favorable microenvironment for cells provided by the embedded soft fibrin gel. We envision that this printing strategy for hydrogel constructs with high toughness and good stability, as well as the method to form tough-soft hydrogel composites, can be extended to other systems to develop structural elements and scaffolds towards applications in biomedical devices and tissue engineering.

Manta Ray Inspired Soft Robot Fish with Tough Hydrogels as Structural Elements.

The design of soft robots capable of navigation underwater has received tremendous research interest due to the robots' versatile applications in marine explorations. Inspired by marine animals such as jellyfish, scientists have developed various soft robotic fishes by using elastomers as the major material. However, elastomers have a hydrophobic network without embedded water, which is different from the gel-state body of the prototypes and results in high contrast to the surrounding environment and thus poor acoustic stealth. Here, we demonstrate a manta ray-inspired soft robot fish with tailored swimming motions by using tough and stiff hydrogels as the structural elements, as well as a dielectric elastomer as the actuating unit. The switching between actuated and relaxed states of this unit under wired power leads to the flapping of the pectoral fins and swimming of the gel fish. This robot fish has good stability and swims with a fast speed (∼10 cm/s) in freshwater and seawater over a wide temperature range (4-50 °C). The high water content (i.e., ∼70 wt %) of the robot fish affords good optical and acoustic stealth properties under water. The excellent mechanical properties of the gels also enable easy integration of other functional units/systems with the robot fish. As proof-of-concept examples, a temperature sensing system and a soft gripper are assembled, allowing the robot fish to monitor the local temperature, raise warning signals by lighting, and grab and transport an object on demand. Such a robot fish should find applications in environmental detection and execution tasks under water. This work should also be informative for the design of other soft actuators and robots with tough hydrogels as the building blocks.

Paracoccus beibuensis sp. nov., isolated from the South China Sea.

A Gram-negative, non-motile, short rod-shaped or spherical bacterial strain that accumulates poly-ß-hydroxybutyrate (PHB) granules was isolated from the Beibu Gulf in the South China Sea. Cells have no polar or subpolar flagella, dividing by binary fission. Phylogenetic analyses based on 16S rRNA gene sequences showed that the strain formed a monophyletic branch at the periphery of the evolutionary radiation occupied by the genus Paracoccus, family Rhodobacteraceae, order Rhodobacterales, class Alphaproteobacteria. The closest neighbours were Paracoccus aestuarii strain B7(T) (97.2% similarity), Paracoccus zeaxanthinifaciens ATCC 21588(T) (97.1% similarity) and Paracoccus homiensis DD-R11(T) (96.8%). The predominant fatty acids were C(18:1) ω7c (82.1%), and significant amounts of C(18:0) (5.6%), C(10:0) 3-OH (2.3%) and C(16:0) (1.5%) were present. The predominant respiratory ubiquinone of strain JLT1284(T) was Q-10 and the DNA G+C content of strain JLT1284(T) was 67.0 mol%. The isolate was also distinguishable from members of the genus Paracoccus on the basis of phenotypic and biochemical characteristics. It is evident from the genotypic, chemotaxonomic and phenotypic data, therefore, that strain JLT1284(T) represents a novel species of the genus Paracoccus, for which the name Paracoccus beibuensis sp. nov. is proposed. The type strain is JLT1284(T)=LMG 24871(T)=CGMCC 1.7295(T)).

Synergic influences of network topologies and associative interactions on the microstructures and bulk performances of hydrogels.

Revealing the relationship between network topologies and mechanical properties of hydrogels is fundamental yet challenging in the design of tough soft materials. Here, we report a series of hydrogels using N-isopropyl acrylamide (NIPAm) and acrylic acid (AAc) as the basic units to form a single network of the copolymer, a semi-interpenetrated network of two homopolymers, and a grafted network with homopolymer chains anchored on another homopolymer network, to investigate the influence of network architectures on the mechanical properties and thermal responses of the gels. We found that the properties of the gels are also significantly influenced by the formation of hydrogen bonds between poly(N-isopropyl acrylamide) (PNIPAm) and poly(acrylic acid) (PAAc) segments. The gels with the single network of poly(NIPAm-co-AAc) are mechanically weak due to the low efficiency for forming robust hydrogen bonds, while micro-segregated domains are formed in the hydrogels with a semi-interpenetrated network structure due to the formation of inter-chain hydrogen bonds that favors energy dissipation and toughening of the gels. On the other hand, dense hydrogen bonds form between the grafted PNIPAm chains and the PAAc network, resulting in nano-segregated domains and excellent mechanical properties of the gels. The hydrogels with the grafted network structure exhibit a more repeatable response to temperature than those with the semi-interpenetrated network structure due to the relatively stable hydrogen-bond network. The comparison of the mechanical properties and thermal stability of the hydrogels with the same composition but different topological networks should be informative for engineering hydrogel properties or functions by tailoring the network structures.