3D printed swelling-driven shape-morphing pH-responsive hydrogel gripper.

Stimuli-responsive soft robots have provided new directions for obtaining advanced biomedical healthcare systems, such as targeted drug delivery capsules, less-invasive biopsy tools, and untethered microsurgical robots. We designed, 3D printed, and tested diverse time-dependent shape changeable 3D pH-responsive soft grippers consisting of N-isopropylacrylamide (NIPAM) and N-isopropylacrylamide-co-acrylic acid (NIPAM-AAc) bilayer. We found that the swelling/deswelling-driven actuation of the pH-responsive NIPAM/NIPAM-AAc gripper is primarily affected by the volume percent (% v/v) of the acrylic acid (AAc) and intensity of UV light. We expect that this study can be applied to untethered pH-responsive soft grippers as smart drug delivery capsules or biopsy tools in biomedical healthcare systems.

Highly Efficient Nitrogen-Fixing Microbial Hydrogel Device for Sustainable Solar Hydrogen Production.

Conversion of sunlight and organic carbon substrates to sustainable energy sources through microbial metabolism has great potential for the renewable energy industry. Despite recent progress in microbial photosynthesis, the development of microbial platforms that warrant efficient and scalable fuel production remains in its infancy. Efficient transfer and retrieval of gaseous reactants and products to and from microbes are particular hurdles. Here, inspired by water lily leaves floating on water, a microbial device designed to operate at the air-water interface and facilitate concomitant supply of gaseous reactants, smooth capture of gaseous products, and efficient sunlight delivery is presented. The floatable device carrying Rhodopseudomonas parapalustris, of which nitrogen fixation activity is first determined through this study, exhibits a hydrogen production rate of 104 mmol h-1  m-2 , which is 53 times higher than that of a conventional device placed at a depth of 2 cm in the medium. Furthermore, a scaled-up device with an area of 144 cm2 generates hydrogen at a high rate of 1.52 L h-1  m-2 . Efficient nitrogen fixation and hydrogen generation, low fabrication cost, and mechanical durability corroborate the potential of the floatable microbial device toward practical and sustainable solar energy conversion.

HPr prevents FruR-mediated facilitation of RNA polymerase binding to the fru promoter in Vibrio cholerae.

Phosphorylation state-dependent interactions of the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS) components with transcription factors play a key role in carbon catabolite repression (CCR) by glucose in bacteria. Glucose inhibits the PTS-dependent transport of fructose and is preferred over fructose in Vibrio cholerae, but the mechanism is unknown. We have recently shown that, contrary to Escherichia coli, the fructose-dependent transcriptional regulator FruR acts as an activator of the fru operon in V. cholerae and binding of the FruR-fructose 1-phosphate (F1P) complex to an operator facilitates RNA polymerase (RNAP) binding to the fru promoter. Here we show that, in the presence of glucose, dephosphorylated HPr, a general PTS component, binds to FruR. Whereas HPr does not affect DNA-binding affinity of FruR, regardless of the presence of F1P, it prevents the FruR-F1P complex from facilitating the binding of RNAP to the fru promoter. Structural and biochemical analyses of the FruR-HPr complex identify key residues responsible for the V. cholerae-specific FruR-HPr interaction not observed in E. coli. Finally, we reveal how the dephosphorylated HPr interacts with FruR in V. cholerae, whereas the phosphorylated HPr binds to CcpA, which is a global regulator of CCR in Bacillus subtilis and shows structural similarity to FruR.

Four-Dimensional Printing of Stimuli-Responsive Hydrogel-Based Soft Robots.

The present protocol describes the creation of four-dimensional (4D), time-dependent, shape-changeable, stimuli-responsive soft robots using a three-dimensional (3D) bio-printing method. Recently, 4D printing techniques have been extensively proposed as innovative new methods for developing shape-transformable soft robots. In particular, 4D time-dependent shape transformation is an essential factor in soft robotics because it allows effective functions to occur at the right time and place when triggered by external cues, such as heat, pH, and light. In line with this perspective, stimuli-responsive materials, including hydrogels, polymers, and hybrids, can be printed to realize smart shape-transformable soft robotic systems. The current protocol can be used to fabricate thermally responsive soft grippers composed of N-isopropylacrylamide (NIPAM)-based hydrogels, with overall sizes ranging from millimeters to centimeters in length. It is expected that this study will provide new directions for realizing intelligent soft robotic systems for various applications in smart manipulators (e.g., grippers, actuators, and pick-and-place machines), healthcare systems (e.g., drug capsules, biopsy tools, and microsurgeries), and electronics (e.g., wearable sensors and fluidics).

Advances in Biodegradable Soft Robots.

Biodegradable soft robots have been proposed for a variety of intelligent applications in soft robotics, flexible electronics, and bionics. Biodegradability offers an extraordinary functional advantage to soft robots for operations accompanying smart shape transformation in response to external stimuli such as heat, pH, and light. This review primarily surveyed the current advanced scientific and engineering strategies for integrating biodegradable materials within stimuli-responsive soft robots. It also focused on the fabrication methodologies of multiscale biodegradable soft robots, and highlighted the role of biodegradable soft robots in enhancing the multifunctional properties of drug delivery capsules, biopsy tools, smart actuators, and sensors. Lastly, the current challenges and perspectives on the future development of intelligent soft robots for operation in real environments were discussed.

4D Multiscale Origami Soft Robots: A Review.

Time-dependent shape-transferable soft robots are important for various intelligent applications in flexible electronics and bionics. Four-dimensional (4D) shape changes can offer versatile functional advantages during operations to soft robots that respond to external environmental stimuli, including heat, pH, light, electric, or pneumatic triggers. This review investigates the current advances in multiscale soft robots that can display 4D shape transformations. This review first focuses on material selection to demonstrate 4D origami-driven shape transformations. Second, this review investigates versatile fabrication strategies to form the 4D mechanical structures of soft robots. Third, this review surveys the folding, rolling, bending, and wrinkling mechanisms of soft robots during operation. Fourth, this review highlights the diverse applications of 4D origami-driven soft robots in actuators, sensors, and bionics. Finally, perspectives on future directions and challenges in the development of intelligent soft robots in real operational environments are discussed.

Tailorable Electronic and Electric Properties of Graphene with Selective Decoration of Silver Nanoparticles by Laser-Assisted Photoreduction.

While graphene shows great potential for diverse device applications, to broaden the scope of graphene-based device applications further, it would be necessary to tune the electronic state of graphene and its resultant electrical properties properly. Surface decoration with metal nanoparticles is one of the efficient doping methods to control the properties of two-dimensional materials. Here, we report the p-type doping effects in single-layer graphene decorated with silver nanoparticles (AgNPs) that were formed area-selectively by the facile one-step photoreduction (PR) process based on focused-laser irradiation. During the PR process, AgNPs were reduced on graphene in AgNO3 solution by laser-driven photoexcitation followed by chemical reactions. Based on scanning electron microscopy analyses, the morphology characteristics of AgNPs were shown to be modulated by the laser dwell time and power controllably. Further, p-type doping effects were demonstrated using graphene-field-effect transistor structures whose graphene channels were selectively decorated with AgNPs by the PR process, as validated by the decrease in channel resistance and the shift of the Dirac point voltage. Moreover, the growth of AgNPs was observed to be more active on the graphene channel that was laser-annealed ahead of the PR process, leading to enhancing the efficiency of this approach for altering device characteristics.

Light responsive plasmonic silicone elastomer/hydrogel soft actuator.

Soft robots offer unique advantages in their ability to interact with fragile organisms. Light responsive soft actuators are promising for the development of the untethered soft robots. However, this requires a mechanism for converting the externally applied light into mechanical actuation. We designed, fabricated, and tested a light responsive soft actuator consist of silicone elastomer with plasmonic metal nanoparticle embedment and temperature sensitive hydrogel. We found that the selection of the carrier solvent for the metal nanoparticle embedment in silicone elastomer to be crucial. The fabricated soft actuator showed a relatively fast response time (< 5 min) under light illumination.

A mannose-sensing AraC-type transcriptional activator regulates cell-cell aggregation of Vibrio cholerae.

In addition to catalyzing coupled transport and phosphorylation of carbohydrates, the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) regulates various physiological processes in most bacteria. Therefore, the transcription of genes encoding the PTS is precisely regulated by transcriptional regulators depending on substrate availability. As the distribution of the mannose-specific PTS (PTSMan) is limited to animal-associated bacteria, it has been suggested to play an important role in host-bacteria interactions. In Vibrio cholerae, mannose is known to inhibit biofilm formation. During host infection, the transcription level of the V. cholerae gene encoding the putative PTSMan (hereafter referred to as manP) significantly increases, and mutations in this gene increase host survival rate. Herein, we show that an AraC-type transcriptional regulator (hereafter referred to as ManR) acts as a transcriptional activator of the mannose operon and is responsible for V. cholerae growth and biofilm inhibition on a mannose or fructose-supplemented medium. ManR activates mannose operon transcription by facilitating RNA polymerase binding to the promoter in response to mannose 6-phosphate and, to a lesser extent, to fructose 1-phosphate. When manP or manR is impaired, the mannose-induced inhibition of biofilm formation was reversed and intestinal colonization was significantly reduced in a Drosophila melanogaster infection model. Our results show that ManR recognizes mannose and fructose in the environment and facilitates V. cholerae survival in the host.

Functional dissection of the phosphotransferase system provides insight into the prevalence of Faecalibacterium prausnitzii in the host intestinal environment.

Faecalibacterium prausnitzii is a dominant member of healthy human colon microbiota, regarded as a beneficial gut bacterium due to its ability to produce anti-inflammatory substances. However, little is known about how F. prausnitzii utilizes the nutrients present in the human gut, influencing its prevalence in the host intestinal environment. The phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS) is a widely distributed and highly efficient carbohydrate transport system found in most bacterial species that catalyses the simultaneous phosphorylation and import of cognate carbohydrates; its components play physiological roles through interaction with other regulatory proteins. Here, we performed a systematic analysis of the 16 genes encoding putative PTS components (2 enzyme I, 2 HPr, and 12 enzyme II components) in F. prausnitzii A2-165. We identified the general PTS components responsible for the PEP-dependent phosphotransfer reaction and the sugar-specific PTS components involved in the transport of two carbohydrates, N-acetylglucosamine and fructose, among five enzyme II complexes. We suggest that the dissection of the functional PTS in F. prausnitzii may help to understand how this species outcompetes other bacterial species in the human intestine.

Vibrio cholerae FruR facilitates binding of RNA polymerase to the fru promoter in the presence of fructose 1-phosphate.

In most bacteria, efficient use of carbohydrates is primarily mediated by the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS), which concomitantly phosphorylates the substrates during import. Therefore, transcription of the PTS-encoding genes is precisely regulated by transcriptional regulators, depending on the availability of the substrate. Fructose is transported mainly through the fructose-specific PTS (PTSFru) and simultaneously converted into fructose 1-phosphate (F1P). In Gammaproteobacteria such as Escherichia coli and Pseudomonas putida, transcription of the fru operon encoding two PTSFru components, FruA and FruB, and the 1-phosphofructokinase FruK is repressed by FruR in the absence of the inducer F1P. Here, we show that, contrary to the case in other Gammaproteobacteria, FruR acts as a transcriptional activator of the fru operon and is indispensable for the growth of Vibrio cholerae on fructose. Several lines of evidence suggest that binding of the FruR-F1P complex to an operator which is located between the -35 and -10 promoter elements changes the DNA structure to facilitate RNA polymerase binding to the promoter. We discuss the mechanism by which the highly conserved FruR regulates the expression of its target operon encoding the highly conserved PTSFru and FruK in a completely opposite direction among closely related families of bacteria.

Untethered Single Cell Grippers for Active Biopsy.

Single cell manipulation is important in biosensing, biorobotics, and quantitative cell analysis. Although microbeads, droplets, and microrobots have been developed previously, it is still challenging to simultaneously excise, capture, and manipulate single cells in a biocompatible manner. Here, we describe untethered single cell grippers, that can be remotely guided and actuated on-demand to actively capture or excise individual or few cells. We describe a novel molding method to micropattern a thermally responsive wax layer for biocompatible motion actuation. The multifingered grippers derive their energy from the triggered release of residual differential stress in bilayer hinges composed of silicon oxides. A magnetic layer enables remote guidance through narrow conduits and fixed tissue sections ex vivo. Our results provide an important advance in high-throughput single cell scale biopsy tools important to lab-on-a-chip devices, microrobotics, and minimally invasive surgery.

Untethered Actuation of Hybrid Hydrogel Gripper via Ultrasound.

Stimuli-responsive hydrogels that exhibit reversible volume changes in response to stimulus cues such as heat, pH, and light have been utilized in soft robotics, microfluidics, electronics, and biomedical surgical tools. While the development of the soft robotics has widely expanded, most external triggering systems still have limited utilities due to the low selectivity. We present a hybrid gripper capable of undergoing preprogrammed shape transformation utilizing ultrasound energy on-off processes as the external triggering system, which can be utilized in invisible and nonselective environments. Furthermore, we describe the magnetic locomotion of the soft gripper enabled by the introduction of iron oxide (Fe2O3) ferrogel. By integrating these dual ultrasonic and magnetic control systems, we demonstrate the soft gripper could actively and safely perform pick-and-place tasks on a biological salmon roe in the aqueous maze environment. We expect that this study can provide the groundwork for the further important advances to the creation of ultrasound-responsive shape programmable and multifunctional smart soft robots.

Advances in biomimetic stimuli responsive soft grippers.

A variety of biomimetic stimuli-responsive soft grippers that can be utilized as intelligent actuators, sensors, or biomedical tools have been developed. This review covers stimuli-responsive materials, fabrication methods, and applications of soft grippers. This review specifically describes the current research progress in stimuli-responsive grippers composed of N-isopropylacrylamide hydrogel, thermal and light-responding liquid crystalline and/or pneumatic-driven shape-morphing elastomers. Furthermore, this article provides a brief overview of high-throughput assembly methods, such as photolithography and direct printing approaches, to create stimuli-responsive soft grippers. This review primarily focuses on stimuli-responsive soft gripping robots that can be utilized as tethered/untethered multiscale smart soft actuators, manipulators, or biomedical devices.

Biodegradable Thermomagnetically Responsive Soft Untethered Grippers.

Soft-robotic devices such as polymeric microgrippers offer the possibility for pick and place of fragile biological cargo in hard-to-reach conduits with potential applications in drug delivery, minimally invasive surgery, and biomedical engineering. Previously, millimeter-sized self-folding thermomagnetically responsive soft grippers have been designed, fabricated, and utilized for pick-and-place applications but there is a concern that such devices could get lost or left behind after their utilization in practical clinical applications in the human body. Consequently, strategies need to be developed to ensure that these soft-robotic devices are biodegradable so that they would disintegrate if left behind in the body. In this paper, we describe the photopatterning of bilayer gels composed of a thermally responsive high-swelling poly(oligoethylene glycol methyl ether methacrylate ( Mn = 500)-bis(2-methacryloyl)oxyethyl disulfide), P(OEGMA-DSDMA), and a low-swelling poly(acrylamide- N, N'-bis(acyloyl)cystamine) hydrogel, in the shape of untethered grippers. These grippers can change shape in response to thermal cues and open and close due to the temperature-induced swelling of the P(OEGMA-DSDMA) layer. We demonstrate that the grippers can be doped with magnetic nanoparticles so that they can be moved using magnetic fields or loaded with chemicals for potential applications as drug-eluting theragrippers. Importantly, they are also biodegradable at physiological body temperature (∼37 °C) on the basis of cleavage of disulfide bonds by reduction. This approach that combines thermoresponsive shape change, magnetic guidance, and biodegradability represents a significant advance to the safe implementation of untethered shape-changing biomedical devices and soft robots for medical and surgical applications.

Stimulation of Vibrio vulnificus Pyruvate Kinase in the Presence of Glucose to Cope With H2O2 Stress Generated by Its Competitors.

The bacterial phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS) regulates a variety of cellular processes in addition to catalyzing the coupled transport and phosphorylation of carbohydrates. We recently reported that, in the presence of glucose, HPr of the PTS is dephosphorylated and interacts with pyruvate kinase A (PykA) catalyzing the conversion of PEP to pyruvate in Vibrio vulnificus. Here, we show that this interaction enables V. vulnificus to survive H2O2 stress by increasing pyruvate production. A pykA deletion mutant was more susceptible to H2O2 stress than wild-type V. vulnificus without any decrease in the expression level of catalase, and this sensitivity was rescued by the addition of pyruvate. The H2O2 sensitivity difference between wild-type and pykA mutant strains becomes more apparent in the presence of glucose. Fungi isolated from the natural habitat of V. vulnificus retarded the growth of the pykA mutant more severely than the wild-type strain in the presence of glucose by glucose oxidase-dependent generation of H2O2. These data suggest that V. vulnificus has evolved to resist the killing action of its fungal competitors by increasing pyruvate production in the presence of glucose.

A GPU-Accelerated Model-Based Tracker for Untethered Submillimeter Grippers.

Miniaturized grippers that possess an untethered structure are suitable for a wide range of tasks, ranging from micromanipulation and microassembly to minimally invasive surgical interventions. In order to robustly perform such tasks, it is critical to properly estimate their overall configuration. Previous studies on tracking and control of miniaturized agents estimated mainly their 2D pixel position, mostly using cameras and optical images as a feedback modality. This paper presents a novel solution to the problem of estimating and tracking the 3D position, orientation and configuration of the tips of submillimeter grippers from marker-less visual observations. We consider this as an optimization problem, which is solved using a variant of the Particle Swarm Optimization algorithm. The proposed approach has been implemented in a Graphics Processing Unit (GPU) which allows a user to track the submillimeter agents online. The proposed approach has been evaluated on several image sequences obtained from a camera and on B-mode ultrasound images obtained from an ultrasound probe. The sequences show the grippers moving, rotating, opening/closing and grasping biological material. Qualitative results obtained using both hydrogel (soft) and metallic (hard) grippers with different shapes and sizes ranging from 750 microns to 4 mm (tip to tip), demonstrate the capability of the proposed method to track the agent in all the video sequences. Quantitative results obtained by processing synthetic data reveal a tracking position error of 25 ± 7 µm and orientation error of 1.7 ± 1.3 degrees. We believe that the proposed technique can be applied to different stimuli responsive miniaturized agents, allowing the user to estimate the full configuration of complex agents from visual marker-less observations.

Multitemperature Responsive Self-Folding Soft Biomimetic Structures.

Untethered, millimeter-scale, stimuli-responsive shape change structures are critical to the function of autonomous devices, smart materials, and soft robotics. Temperature in a range compatible with physiological or ambient environmental conditions is an excellent cue to trigger actuation of soft structures for practical biomimetic applications. Previously, a range of thermally responsive self-folding soft structures has been described and utilized in a variety of applications from tissue engineering to minimally invasive surgery. In order to extend these concepts to more complex devices, thermally responsive bilayer structures composed of poly[oligo (ethylene glycol) methyl ether methacrylate] (POEGMA) gels that swell at three different temperatures are described. The lower critical solution temperature and volume transition temperature of POEGMA are tuned by varying the side chain length and the extent of copolymerization. The swelling properties of the POEGMA gels are characterized and a multilayer photopatterning process is described that is used to create soft biomimetic structures that change shape in a sequential manner while displaying multistate behaviors.

Autonomous planning and control of soft untethered grippers in unstructured environments.

The use of small, maneuverable, untethered and reconfigurable robots could provide numerous advantages in various micromanipulation tasks. Examples include microassembly, pick-and-place of fragile micro-objects for lab-on-a-chip applications, assisted hatching for in-vitro fertilization and minimally invasive surgery. This study assesses the potential of soft untethered magnetic grippers as alternatives or complements to conventional tethered or rigid micromanipulators. We demonstrate closed-loop control of untethered grippers and automated pick-and-place of biological material on porcine tissue in an unstructured environment. We also demonstrate the ability of the soft grippers to recognize and sort non-biological micro-scale objects. The fully autonomous nature of the experiments is made possible by the integration of planning and decision-making algorithms, as well as by closed-loop temperature and electromagnetic motion control. The grippers are capable of completing pick-and-place tasks of biological material at an average velocity of 1.8 ±0.71 mm/s and a drop-off error of 0.62 ±0.22 mm. Color-sensitive sorting of three micro-scale objects is completed at a velocity of 1.21 ±0.68 mm/s and a drop-off error of 0.85 ±0.41 mm. Our findings suggest that improved autonomous untethered grippers could augment the capabilities of current soft-robotic instruments especially in advancedtasks involving manipulation.

DNA sequence-directed shape change of photopatterned hydrogels via high-degree swelling.

Shape-changing hydrogels that can bend, twist, or actuate in response to external stimuli are critical to soft robots, programmable matter, and smart medicine. Shape change in hydrogels has been induced by global cues, including temperature, light, or pH. Here we demonstrate that specific DNA molecules can induce 100-fold volumetric hydrogel expansion by successive extension of cross-links. We photopattern up to centimeter-sized gels containing multiple domains that undergo different shape changes in response to different DNA sequences. Experiments and simulations suggest a simple design rule for controlled shape change. Because DNA molecules can be coupled to molecular sensors, amplifiers, and logic circuits, this strategy introduces the possibility of building soft devices that respond to diverse biochemical inputs and autonomously implement chemical control programs.