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Automation in the food services industry is not as developed as in the automotive and electrical industries. This may be because (1) the tasks involve high-speed operations in unstructured environments and (2) the lack of effective robotic end-effectors. In this letter, we focus on the automation of dishwashing operations and propose a robotic hand capable of withdrawing and grasping a dish plate from a pile, even when there is water or oil left on the plate in a post-meal scenario. The robotic hand consists of withdrawing and grasping mechanisms. Each mechanism is actuated by two bellows actuators. Soft pads with special groove patterns were fabricated and used to provide sufficient friction when they come into contact with the plate. A theoretical analysis of the withdrawing and grasping operations was performed, and an analytical model of the bellows actuator was established by considering both the pressure thrust force and the elastic force. Bellows actuators were designed based on the analysis and fabricated using both 3D printing and casting methods. Characterization of bellows actuator was performed to validate the analytical model, and agreement was found on the thrust force, but discrepancy occurred in the elastic force due to the complex structure and deformation mode of bellows. Finally, handling experiments on different plates were conducted and results demonstrated that the proposed robotic hand can successfully withdraw and grasp a plate from a pile.

Dynamic X-ray elastography using propagating shear waves is a novel technique to visualize the spatial distribution of elasticity in soft materials. We demonstrate that it can be applied to a gel sample with a fine structure. We prepared a viscoelastic gel sample with a two-dimensional lattice structure filled with ZrO2 particles, and applied the technique to map storage and loss moduli. The obtained storage modulus map successfully distinguished the harder lattice structure from the soft gel matrix with a spatial resolution much higher than those of other conventional elastography techniques using magnetic resonance and ultrasound.

Functional and intelligent soft materials are useful for controlled release of medicines and other molecules. Poly(N-isopropylacrylamide) (PNIPAm) gels are well known as thermo-responsive gels with large discontinuous volume change which is commonly called as the volume phase transition. PNIPAm gels are expected to be applied to controlled-releasable material for drug delivery systems. Furthermore, we can fabricate arbitrary shapes made of gels freely by using 3D hydrogel printing techniques. Here we report that the effect of capsule shapes on behaviors of the PNIPAm objects under water flow with Reynolds number 102. In addition, we compared the behaviors of 3D-printed PNIPAm gel objects with 3D-printed polylactic acid (PLA) objects. The velocity at the first period of 2 or 3 s from the beginning of movement is slower than that of second period in the case of PNIPAm objects with ellipsoidal and bullet shapes. In other words, the capsules are accelerated after the period of 2 or 3 s. For the bullet shape objects, the velocity of the PNIPAm gel is approximately three times faster than that of PLA. It is considered that the cause of the difference between the velocities of PLA and PNIPAm gel is the difference of their frictions. The hydrogels possess commonly low friction properties. Finally, it is demonstrated that the 3D-printed PNIPAm capsules can release the solution inside the capsules by shrinking the PNIPAm gels, caused by volume phase transition.

In microfabricated MEMS actuator, sensor and biomedical devices, soft polymeric materials like PDMS are widely used for lightweight, low cost, high corrosion resistance, high flexibility and high dimensional stability. Along with their numerous beneficial functions these materials have some shortcomings during real application for their hydrophobic high frictional surface and stiction. In this work we have developed a facile way of hydrogel coating on PDMS substrate by highly hydrophilic hydrogels N,N, dimethylacrylamide as a monomer. This gel is highly hydrophilic in nature having biocompatibility and shows very low friction coefficient value in wet condition. Frictional property, wettability and the surface morphology were studied and comparison between coated and uncoated surface has been made to understand the coating phenomenon clearly.

Utilization of soft material like hydrogels for task-specific applications such as in soft robotics requires freedom in the manufacturing process and designability. Here, we have developed highly robust thermoresponsive poly(dimethyl acrylamide-co-stearyl acrylate and/or lauryl acrylate) (PDMAAm-co-SA and/or LA)-based shape memory gels (SMGs) using a customized optical 3D gel printer. This process enabled rapid and moldless fabrication of SMGs with a variety of shapes and sizes. By varying the compositions of the constituent monomers, a wide variety of SMGs with tunable mechanical, thermal, optical and swelling properties have been obtained. Printed SMGs with excellent fixity and recovery ratios have exhibited a wide range of values of Young's modulus (0.04-17.35 MPa) and strain (612-2363%) at room temperature when the acrylate co-monomer (SA and LA) content was varied and the value of strain has been found to be enhanced at elevated temperatures. Thermogravimetric analysis (TGA) of the SMGs shows one step peak degradation (407-417 °C) regardless of composition after an initial mass loss due to water evaporation. Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) revealed variable transition temperatures (29-49.5 °C) depending on the SA and LA content. SMGs with all of the composition ratios possess high transparency with variable swelling degrees in water and different organic solvents and exhibit refractive index values in the range of intraocular lenses, making them suitable for applications in the optical field. These unique properties of 3D printed SMGs with free formability and tunable properties are expected to generate rapid demand in a variety of sectors in biomedicine, robotics and sensing applications.

In this paper, we present the relationship between printing parameters of a 3D gel printer "Soft and Wet Intelligent Matter-Easy Realizer (SWIM-ER)" and mechanical properties of the fabricated gel objects by SWIM-ER. The printer is able to fabricate hydrogel objects by scanning of ultra-violet (UV) light irradiation (photopolymerization). Various hydrogels objects were printed with different scanning velocity of UV light. We measured the water content and mesh sizes of gel objects utilizing Scanning Microscopic Light Scattering (SMILS). Furthermore, we also printed the gel objects with multiple scan rates with constant UV light irradiation energy, and measured sizes of gel objects, and performed the compression test. It was observed that the physical properties of printed hydrogel objects are strongly related with 3D printing parameters (scan velocity and number of scans-scan rate) due to difference in crosslinking density of polymer network.

Development of conductive nanocomposites is critical to realize flexible electronics on diverse substrates. Tuning the electrical and mechanical characteristics of these nanocomposites can enable a spectrum of applications. Herein, we demonstrate a robust microfabrication protocol to implement electrically conductive polymer by doping polydimethylsiloxane (PDMS) with silver fibers, with potential applications in wearable devices, MEMS, and microfluidics. The conductive polymer was made by mixing silver fibers into uncured PDMS matrix. The prepared mixture was micromolded by three dimension (3D) printed master using soft lithography technique. Serpentine and spiral like microstructures were embedded on the nonconductive layer of PDMS. The SEM images show uniform dispersion of silver fibers in the composites. The percolation threshold for the prepared composite was found to be 25 wt%. Resistivity of the conductive elastomeric composite at 25 wt% was 0.013 Ω cm.

Recently high-strength and high-functional gels have been developed and are expected to be used in industrial and the medical fields. However, the research of gel application has not made much progress from the reason why an environmental range to use being small and properties of matter evaluation are not performed enough. To control the surface friction of gel mechanical materials by the electric field, here we study the effect of the applied voltage on the frictional properties of double-network gel (DN gel) with high strength. We found that impressed voltage on the gel has an ability to control the frictional force of the hydrogel. The results of the tensile and compression tests showed that the behavior of the DN gel was similar to a rubber, and effective data as mechanical materials were obtained. The results of friction measurement using reciprocating friction tester showed that the coefficients of friction depend on the sliding velocities. In the case of the cathode measurement ball, the coefficients of friction decreased with increase in voltage in the range of 0.0–3.0 V and increased with increase in the applied voltage in the range of 3.0–5.0 V. In the case of the anode measurement ball, the coefficient of friction increased with increase in the voltage. The current value measurement was performed in a measurement ball and a stainless-steel plate, and the electric current flowed at approximately 2.5 V and above. It is considered that the applied voltage controls the thickness of water lubricant layer and change the coefficient of friction of the gel. These findings provide a new insight into our understandings of application of the high-performance gels device as well as the development of high-performance gel materials.

Gels, soft and wet materials, have unique properties such as biocompatibility, low friction, and material permeability which are hardly found in hard and dry materials. In recent years, gels are expected to industrial applications, because the various high-strength gels, functional gels, and 3D gel printer that enabled free form fabrication of gels have been developed. Our research group succeeded in developing transparent gels with shape memory properties (T-SMG). In this study, we aimed at free form fabrication of T-SMG with to apply T-SMG’s new medical materials, optical devices, and robot joints and so on. We also examined the internal network structure of T-SMG, since it is very important to know the internal network structure of the gels in order to improve the gels. We study the internal network structure of T-SMG through the dynamic light scattering, uniaxial tensile test, and swelling test. As a result, we found that T-SMG is a unique material that changes the internal structure considerably depending on the presence or absence of crystal components. The state of chemical components changes physical properties such as mechanical properties and swelling behavior, without changing the synthesis ratio. In addition, even though the crystals were melted, it showed a higher Young ‘s modulus than the amorphous gels, it was suggested that the crystal components contributes to the Young’ s modulus even though it melted. We tried free form fabrication of T-SMG using 3D printing system. As T-SMG become cloudy at the time of printing, the modeling accuracy become worse. However, by mixing UV absorbers, it was possible to improve the accuracy and suppression of clouding of gels. We successfully made the fine and complicated shaping of T-SMG which was difficult in the past processes. Based on this technology, we hope that T-SMG will be applied in various fields.

Hierarchical structures, also known as fractal structures, exhibit advantageous material properties, such as water- and oil-repellency as well as other useful optical characteristics, owing to its self-similarity. Various methods have been developed for producing hierarchical geometrical structures. Recently, fractal structures have been manufactured using a 3D printing technique that involves computer-aided design data. In this study, we confirmed the accuracy of geometrical structures when Koch curve-like fractal structures with zero to three generations were printed using a 3D printer. The fractal dimension was analyzed using a box-counting method. This analysis indicated that the fractal dimension of the third generation hierarchical structure was approximately the same as that of the ideal Koch curve. These findings demonstrate that the design and production of fractal structures can be controlled using a 3D printer. Although the interior angle deviated from the ideal value, the side length could be precisely controlled.

We have developed conductive microstructures using micropatternable and conductive hybrid nanocomposite polymer. In this method carbon fibers (CFs) were blended into polydimethylsiloxane (PDMS). Electrical conductivities of different compositions were investigated with various fiber lengths (50–250 μm), and weight percentages (wt%) (10–60 wt%). Sample composites of 2 cm × 1 cm × 500 μm were fabricated for 4-point probe conductivity measurements. The measured percolation thresholds varied with length of the fibers: 50 wt% (307.7 S/m) for 50 µm, 40 wt% (851.1 S/m) for 150 µm, and 30 wt% (769.23 S/m) for 250 μm fibers. The conductive composites showed higher elastic modulus when compared to that of PDMS.

Yamagata University established the Soft-Matter Robotics Consortium (SOFUMO) to study the extreme parts of robots and to construct epoch-making soft robots using such extreme parts. As a part of such effort, we study a gel piezoelectric sensor and construct a jellyfish-like robot using gel materials such as ion gel, composed of polymer network and ionic liquid, and shape memory gel. We revealed that the ion gel is more appropriate for pressure sensor that particle-doublenetwork hydrogel since impedance of ion gel is changed by application of load weights. In addition, the jellyfish-like robot was constructed using hydrogel and shrinkable wire using electric power. These techniques are expected to be applied to epoch-making soft-matter robots.

Gels have superior features such as high water content, permeability, extremely low friction, and biocompatibility, which are not found in the normal solids materials, because these features are due to their soft and wet properties. Now artificial gels approach the natural gels of the human body in property. In this study the frictional behavior of shape memory gel (SMG) was investigated. In addition to its shape-memory characteristic, SMG has low friction characteristics and better wear resistance than conventional gels. Its shape-memory characteristic is related to temperature. SMG is expected to be of practical use in medical and mechanical materials. This is because the SMG does not need chemical fixation, healing, placed around on object, and cools to conform to and grip the object, can expand it. This allows a decrease in solvent use and thus a decrease of patient burden in medical care, easier machine assembling and the design of machines with reduced part numbers, and the miniaturization of machines. In this study, implication water rate of SMGs of different composition is measured, and power by changing implication water rate reports the characteristic, and we performed the friction behavior of SMG for the purpose of the use to the underwater apparatus.

Gels are an important class of soft and wet materials having superior properties with diverse applications in tissue engineering, bio-medical engineering, and electrochemistry. In order to accelerate the development of gels, it is required to synthesize multi-functional gels of high mechanical strength, ultra low surface friction and suitable elastic modulus with a variety of methods and new materials and investigate their internal structure to ensure the best implementation to any suitable fields. Among many types of gels, ionic gels made from ionic liquids (ILs) will be possibly used for diverse applications in electrochemical devices as sensors, actuators, batteries and in the field of tribology. ILs are characterized by many unique physico-chemical properties which make them a potential candidate for gel materials. In the present work a novel approach for preparing Ionic double-network gels (iDN gels) using IL have been synthesized utilizing photo-polymerization process. A hydrophobic monomer methyl methacrylate has been used as a first network and a hydrophobic IL monomer, N,N-diethyl-N-(2-mthacryloylethyl)-N-methylammonium bistrifluoromethylsulfonyl)imide has been used as a second network. The resulting iDN gels show transparency, flexibility and good mechanical toughness. An attempt to determine the mesh size of the iDN gels has been made for the first time to understand the internal structure of the ionic liquid based gels by scanning microscopic, light scattering. Three types of crosslinking densities of the iDN gels were experimentally determined from the size of internal structure, solvent content and Young's modulus. By comparing the three mesh densities, the relation between the network structure and mechanical properties of the gels is discussed. We compared the crosslinking densities of the iDN gels and conventional hydrogels to understand the network structure of the iDN gels and discussed its difference of structural behavior from that of hydrogels.

In this study, we evaluated the mechanical properties of printed structures with respect to the printing orientation for "SWIM-ER". The fracture surface of the 3D modeled object of the gel does not break along the stacked line, and the maximum stress at that time is the breaking strength. Moreover, the dependency in the stacking direction is weak in the 3D model of the gel. The gel printed at high speed scan showed lower elastic modulus and higher moisture content than gel printed at low speed scan. We discussed about crosslinking density calculated based on the compressive elastic modulus and moisture content, respectively. It was found that gels having different crosslinking density can be formed by the scanning speed of UV laser. In addition, we made a prototype of a gel finger model with different mechanical properties within the model.

Conducting polymer composites become increasingly significant for variety of applications in electrical and mechanical devices. Poly (ionic liquid)s (PILs) achieved remarkable interest in this field for the unique properties and added advantages in mechanical stability, improved processability, durability, and spatial controllability. Carbon nanotube (CNT) as filler material to the matrix of PIL can achieve the desired composite material with improved electrical and mechanical properties. In this work, we developed PIL-CNT nanocomposites by using quaternary ammonium type IL monomer and multiwall CNT. Their mechanical, thermal and thermomechanical properties have been studied and future possibilities of employing in electromechanical devices have been explored.

Gels are soft and wet materials having low friction, good biocompatibility, and material permeability. It is expected that gel materials will be used as new kinds of industrial materials in the engineering and medical applications. But it cannot build a complicated shape. Soft & Wet Matter Engineering Laboratory developed a 3D gel Printer "SWIM-ER", has enabled modeling of complex shapes of the gel. However, this is expensive. Therefore not all of the gel researchers and the companies have such a device. To solve this problem, we manufacture a low-cost open-source 3D gel printer "RepRap SWIM-ER" from the RepRap. We made the components required to manufacture the “RepRap SWIM-ER” from the 3D printer and chose a light source. In addition, we produced the P-DN gel for RepRap SWIM-ER and conducted the molding test to confirm whether RepRap SWIM-ER can used it.

Ionic gels (IGs) using ionic liquids (ILs) can propose diverse applications in the field of optics, sensors and separation have opened wide prospects in materials science. ILs have attracted remarkable interest for gel polymer electrolytes and batteries based on their useful properties such as non-volatility, non-flammability, a wide electrochemical window, high thermal stability and a high ionic conductivity. The formation of gel in IL media makes it possible to immobilize ILs within organic or inorganic matrices and to take advantage of their unique properties in the solid state, thus eliminating some shortcomings related to shaping and risk of leakage. In this work for the first time we used multifunctional thiol monomers having uniform structure and good compatibility with the IL of our interest. Therefore we focused on developing thiol monomer-based IGs using multifunctional thiol monomers and acrylate crosslinkers utilizing thiol-ene reaction between monomer and crosslinking molecules in an IL medium and characterize their physico-chemical properties like thermal, conductive, mechanical properties etc.. This work has been focused mainly to improve the mechanical strength of IGs and make prospects of IGs in tribology and lubricants.

Medical doctors use artificial blood vessels and organ models, which are usually made of plastic, to explain operations to students, or patients awaiting treatment. However, there are some problems such as the high cost of making the model and there is not a realistic feel because the model is hard. These problems can be solved using soft and wet material for instance gel. Gels are materials with unique properties such as transparency, biocompatibility, and low friction. In recent years, high strength gel has been developed and is expected to be applied in medical fields in the future. Artificial models of gel can be produced by 3D gel printers. Our group has been developing a 3D gel printer with 1mm precision in printing, but the shape, size and mechanical strength are not sufficient for medical models. In this study, we overcome these problems and make a gel model which is transparent, mechanically strong with a fine shape. The strength and molding accuracy is improved by changing and preparing the cross linker and ultraviolet absorber. We conducted mechanical and molding tests to confirm that the gel material properties improved.

In the last decade, several innovative polymer gel materials with enhanced mechanical proper ties have been invented by Japanese researches. In 2003, a most effective but simple way was proposed to synthesize double network gels, with compression fracture stress of about 30MPa, compared to several tens of kPa for common gels. In this study, we evaluate the wear of a double network gel, both with and without water lubrication. In the un-lubricated experiment, the gel surface is worn with a stainless steel ball. In the other experiment with water lubrication, the gel surface is worn by different counter surfaces because the stainless steel ball was too smooth to wear. It was found that frictional vibration of wear gel is transitioning to steady sliding in lubricated. As conventional reduction method of the friction by the contact between general solids, there are surface processing such as the texturing, attachment of lubrication materials. In the case of gel, the minute processing to the surface such as the texturing is difficult, because the gel is soft in comparison with the hard materials such as the metal. By proceeding with this study, the surface processing of low-frictional gels will be enabled.

In our group, highly transparent shape memory gels were successfully synthesized for the first time in the world. These gels have the high strength of 3MPs modulus even with the water content of 40wt% water and high transparency. We consider that these highly transparent and high strength gels can be applied to the optical devices such as intraocular-lenses and optical fibers. In previous research by our group, attempts were made to manufacture the gel intraocular-lenses using highly transparent shape memory gels. However, it was too difficult to print the intraocular-lens finely enough. Here, we focus on a 3D printer, which can produce objects of irregular shape. 3D printers generally we fused deposition modeling (FDM), a stereo lithography apparatus (SLA) and selective laser sintering (SLS). Because highly transparent shape memory gels are gelled by light irradiation, we used 3D printer with stereo lithography apparatus (SLA). In this study, we found the refractive index of highly transparent shape memory gels depend on monomer concentration, and does not depend on the cross-linker or initiator concentration. Furthermore, the cross-linker and initiator concentration can change the gelation progression rate. As a result, we have developed highly transparent shape memory gels, which can have a range of refractive indexes, and we defined the optimal conditions that can be modeling in the 3D printer by changing the cross-linker and initiator concentration. With these discoveries we were able to produce a gel intraocular-lens replica.

Nano-structure of soft and wet materials are making important roles in radiation therapy, as a three-dimensional (3D) gel dosimeter. In the last decades, radiation therapy instruments have had a large progressive of the accuracy, therefore more precise measurements have became important. We study new materials and apparatus, which measure three dimensional absorbed dose distributions. New materials are double network (DN 2 ) gel and improved PAGAT (yDAGAT) gel, the former has several good points, high transparency, high water content, high mechanical strength, and toughness, the later has similar properties of PAGAT gel but will be more tractable. The new type of optical-CT machine is Scanning Microscopic Light Scattering System (SMILS). Usual optical-CT uses the opacity, which is measured by the intensity, however SMILS also uses dynamic light scattering (DLS) theory with original ensemble average method. By using the intensity and DLS information, more accurate information are expected. We have established one-dimensional measurement by SMILS using irradiated DN gel. Additionally, yDAGAT is successfully composed. In the future, we are planning to develop three-dimensional radiation measurement apparatus by 3D printable gel and 3D SMILS.

A 3D printer is a device which can directly produce objects whose shape is the same as the original 3D digital data. Hydrogels have unique properties such as high water content, low frictional properties, biocompatibility, material permeability and high transparency, which are rare in hard and dry materials. These superior characteristics of gels promise useful medical applications. We have been working on the development of a 3D gel printer, SWIM-ER (Soft and Wet Industrial – Easy Realizer), which can make models of organs and artificial blood vessels with gel material. However, 3D printing has a problem: the mechanical properties of the printed object vary depending on printing conditions, and this matter was investigated with SWIM-ER. In the past, we found that mechanical properties of 3D gel objects depend on the deposition orientation in SWIM-ER. In this study, gels were printed with different laser scanning speeds. The mechanical properties of these gels were investigated by compression tests, water content measurements and SMILS (Scanning Microscopic Light Scattering).

In recent years, the fabrication of patient organ replicas using 3D printers has been attracting a great deal of attention in medical fields. However, the cost of these organ replicas is very high as it is necessary to employ very expensive 3D printers and printing materials. Here we present a new gel organ replica, of human kidney, fabricated with a conventional molding technique, using a particle-double network hydrogel (P-DN gel). The replica is transparent and has the feel of a real kidney. It is expected that gel organ replicas produced this way will be a useful tool for the education of trainee surgeons and clinical ultrasonography technologists. In addition to developing a gel organ replica, the internal structure of the P-DN gel used is also discussed. Because the P-DN gel has a complex structure comprised of two different types of network, it has not been possible to investigate them internally in detail. Gels have an inhomogeneous network structure. If it is able to get a more uniform structure, it is considered that this would lead to higher strength in the gel. In the present study we investigate the structure of P-DN gel, using the gel organ replica. We investigated the internal structure of P-DN gel using Scanning Microscopic Light Scattering (SMILS), a non-contacting and non-destructive.

We measured the friction forces and calculated the friction coefficients of non-processed and laser-processed surfaces of a double network hydrogel (DN gel), which is one of the more famous high-strength gels. The results indicate that laser processing has the ability to reduce the friction coefficients of the gel surfaces. The observation of gel surfaces suggests that the cause of friction reduction is a change in the roughness of the gel surfaces due to laser processing. This finding is expected to lead us to further understanding of the physicochemical properties of hydrogels.

Single-molecule force spectroscopy using an atomic force microscope (AFM) can be used to measure the average unfolding force of proteins in a constant velocity experiment. In combination with Monte Carlo simulations and through the application of the Zhurkov-Bell model, information about the parameters describing the underlying unfolding energy landscape of the protein can be obtained. Using this approach, we have completed protein unfolding experiments on the polyprotein ${(I27)}_{5}$ over a range of pulling velocities. In agreement with previous work, we find that the observed number of protein unfolding events observed in each approach-retract cycle varies between one and five, due to the nature of the interactions between the polyprotein, the AFM tip, and the substrate, and there is an unequal unfolding probability distribution. We have developed a Monte Carlo simulation that incorporates the impact of this unequal unfolding probability distribution on the median unfolding force and the calculation of the protein unfolding energy landscape parameters. These results show that while there is a significant, unequal unfolding probability distribution, the unfolding energy landscape parameters obtained from use of the Zhurkov-Bell model are not greatly affected. This result is important because it demonstrates that the minimum acceptance criteria typically used in force extension experiments are justified and do not skew the calculation of the unfolding energy landscape parameters. We further validate this approach by determining the error in the energy landscape parameters for two extreme cases, and we provide suggestions for methods that can be employed to increase the level of accuracy in single-molecule experiments using polyproteins.