Development of a cross-linking agent and a system to improve the shape accuracy in 3D printing of the vascular structure

For accurate fabrication of a vascular structure by 3D gel printing, it is necessary to increase in the solidification rate of gel so that the gel can maintain its shape as it is printed. In this study, we developed a novel 3D gel printing system with a new cross-linking agent which enables solidification of alginic acid-based sol immediately after its mounting onto a targeted point. We proposed a new CaCl2-based cross-linking agent by mixing with agar which has high coagulation. Also, we installed two syringes filled with the cross-linking agent as they sandwich a syringe filled with alginic acid-based sol. Both the cross-linking agent and alginic acid-based sol are quantitatively discharged from the top of the device, enabling to add the cross-linking agent to both sides of the object at the same time. After the molding experiments of 200 layers and 300 layers of the vascular structures with changing concentration of agar in the cross-linking agent, the shape accuracy was evaluated from the following viewpoints; (i) inner radius, (ii) outer radius, (iii) thickness, (iv) aspect ratio. By cross-linking the inner and outer walls at the same time, gradual expansion of wall thickness from upper to lower layers was prevented. Because of shrinkage in the circumference direction caused by the cross-linking reaction, the outer wall contracted to the ideal shape, but the inner wall was narrowed to less than half of the ideal shape. Among 0, 2.0, 3.0 mg/mL concentration, the more agar was added into the cross-linking agent, the narrowing of the inner wall tended to be prevented, and the wall thickness did not become excessive. The accuracy of the shape in the case of 3.0 mg/mL agar concentration was the best, while that in the case of 4.0 mg/mL was worse in terms of inner radius, aspect ratio and wall thickness. This can be explained that increase in the viscosity of the cross-linking agent by increase in agar concentration induces large frictional resistance with the wall surface, and flow of the cross-linking agent dragged the gel to the center of the vascular structure. In summary, the effectiveness of addition of agar to a cross-linking agent was demonstrated by the fact of the achievement of high shape accuracy of a vascular structure, but excessive increase in the viscosity of the cross-linking agent due to high concentration of agar needs to be suppressed. © 2021 Japan Society for Precision Engineering. All rights reserved.