(Invited) TheSimultaneous 3D Printing of White and Transparent Gels for Medical Models
Authors: Yamazaki Yuta , Saito Azusa , Yamazaki Masahiro , Watanabe Yosuke , Shiblee MD Nahin Islam , Khosla Ajit , Ogawa Jun , Kawakami Masaru , Nango Jun , Furukawa Hidemitsu 
Published: December 2020

Polymer gels containing a large amount of water have biocompatibility and appropriate softness close to living biological tissue. For this reason, many studies focus on how to use the polymer gels in medical field. The generally organ model is made of a silicone resin and is transparent and hard. Therefore, excellent in confirming the position of blood vessels and the like. But it is not suitable for practice or simulation using medical device. So, we aim to develop the gel organ model that overcomes these problems.
We developed the desktop type 3D gel printer “RepRap SWIM-ER” which enables three-dimensional(3D) free printing of gels. RepRap SWIM-ER can move a light source at 405nm and form gels in the desired shape by localized photopolymerization. This gel printer irradiates a gel solution layer by layer with UV light. In the conventional printing process of RepRap SWIMER, it was difficult to change the photo polymerization reaction locally because constant speed, scan time and so on. There was also problem that it could use only one gel solution because it was bathtub type 3D gel printer.
Here, we developed new printing process of RepRap SWIMER that can change the transparency and mechanical properties of printed gels locally by changing the printing parameters such as the scan times of UV light. It can control gel turbidity which was previously only printed in a single color. This method can print two types of gel (transparent and white) only using RepRap SWIM-ER. By changing the printing conditions with RepRap SWIM-ER, a transparent gel with length and breadth of 20 mm, thickness of 2 mm and a white gel lattice can be printed at about 10 minutes. The transmittances of printed transparent gels and white gels were measured by a spectrophotometer to examine the color change (Figure 1). It can be seen from Fig.1, The white turbidity of the gel changes when the printing conditions are changed. This result showed that the appearance of color varied depending on the concentration of the hydrophobic initiator TPO used in the gel solution.
At the prototype, we tried to print using kidney data. From previous research, we have known that the gel prepared by soaking in pure water swells 1.5 to 2.0 times. In consideration of this result, when printing kidney data using RepRap SWIM-ER, it was printed at 70% of the size of the data, the color was entirely white. After swelling, this model became to be about the same size as the actual data. The kidney 70% data can be printed at 2h30min. We can create new gel organ models by using RepRap SWIM-ER and the above gel printing method. Gel organ models makes it possible to use medical devices and makes the touch feeling more realistic. For example, soft-transparent gel (organ model) and hard-white gel (blood vessel, tumor) can make the model with high precision and complexity. In addition, this technology can let the production spend lower cost and less time.

Figure 1