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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.

Hydrogels are three-dimensional polymeric networks capable of absorbing large amounts of water or biological fluids. Due to their high water content, porosity and low friction they closely simulate natural living tissue. The properties of a polymer gel depend on the chemical structures of the component molecule and can be controlled or tuned by external stimuli such as heat, optics, solvent, and pH. Shape-memory gels (SMGs) are unique materials that have the ability to return from a temporary deformed state to their permanent i.e. original shape induced by an external stimulus like temperature change. Poly(dimethyl acrylamide-co-stearyl acrylate) (DMMA-co-SA)-based SMGs show such behavior with high mechanical strength, transparency and moderate water content (≈30wt%). In this work, we applied stereolithography process to fabricate DMMA-co-SA SMGs and printed sample models like gel sheets and tubes. However, printing a transparent SMG was not an easy task due to several problems like sample turbidity, swelling during printing and shape deformation. We critically maintained these uses and compared the properties of 3D printed SMGs with that of conventionally synthesized SMGs. Finally, we analyzed the limitation and potential of 3D printing process and discussed a suitable approach for application of 3D printed SMGs as an actuator.

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.

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.

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, various high-strength gels having strength of several MPa have been developed one after another by devising the internal structure of the gel. They have attracted attention as a new material. High-strength double network gel (DN gel) is a gel consisting of a hard 1st network and a soft 2nd network and have excellent properties such as super low friction, flexibility and biocompatibility. Particle double network gel (P-DN gel) consisting of powdered 1st network and 2nd network is a high strength gel capable of 3D free form fabrication by using 3D gel printer. Utilizing these advantages, there are expectations for soft robot materials and mechanical materials. It is also important to grasp the number of deformation of the gel and how much fatigued it is when the gel material is industrially used. Specifically, by attaching a fatigue sensor to a soft robot, it is possible to predict the optimum time to replace the parts. When it is used for mechanical materials, we need to judge on the necessity of emergency treatment. It will be considered to lead to comfortable use of things. In this study, we aimed to develop a gel fatigue sensor with reference to the internal structure and destruction phenomenon of P-DN gel. P-DN gels of various compositions were prepared and mechanical tests and evaluation of internal structure by dynamic light scattering were carried out to investigate the physical properties of these gels. As a result, the P-DN gel using super absorbent polymer (SAP) as the 1st gel showed the most suitable physical properties for use as a fatigue sensor.