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.

A gel forming method with sections with different elastic modulus is developed. Gels with hardness distribution are formed from one base gel material by adjusting the crosslinking density of the polymer network using a 3D gel printer. It is confirmed that hardness is arranged as designed by using mixing rules of composite materials. Furthermore, as a prototype of a practical gel application, a gel finger model having a soft‐fleshy part and a hard‐bony part is printed. 3D printing of an organ model that reproduces a realistic feel that takes not only the shape of the organ but also the distribution of hardness into consideration may become possible.

Recently our group developed 3D gel printer named "SWIM-ER" (soft and wet industrial material -easy realizer). Here we aim to improve the gel materials used for SWIM-ER system about the problems around free-shaping, transparency, and mechanical strength. To overcome these problems, we tried to use UV absorbers, AS150 (Nippon Kayaku Co.,Ltd.) and KEMISORB11S (CHEMIPRO KASEI Co.,Ltd.) and found the latter absorber kept transparency well. We improved the maximum tensile stress about 2 times and the maximum tensile strain about 4 times by changing the kind of cross-linker from methylene bis-acrylamide (MBAA) type to diethylene glycol dimethacrylate (DEGDMA) type. We also found that the maximum tensile stress was improved about 1.3 times by changing the blend ratio of 1st gel powder and 2nd gel solution in the preparation of particle-double network gels (P-DN gel). Based on these two improvements, we 3D-printed the transparent and hollow structure of the high strength gels with the maximum tensile stress of 0.5 MPa, which will be comparable to the maximum tensile stress of living organs like the stomach and small intestine in our body.

In this work, we present a comparison of the mechanical properties of 3D printed structures with respect to the printing 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. Also, the fracture surface of the 3D model of the ABS resin has broken along the stacked line other than 0 degrees, and the maximum stress at that time is the peel strength. The yield point can be observed at the 0 degree specimen, the maximum stress at that time is tensile strength. Moreover, while comparing both materials, we observed that the dependency in the stacking direction is weak in the 3D model of the gel, strong in the 3D modeled material of the ABS resin, and the dependence on the stacking direction is strongly influenced by the way of bonding the materials in stacking.

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