3D printable inter cross-linking network (ICN) gels for reversible transparency control with water content

Yosuke Watanabe,Masasu Kawakawami,Azusa Saito,Shota Inoue,Hidemitsu Furukawa

doi:10.1007/s00542-019-04550-9

Abstract

A patient-specific phantoms, which are equivalent to human tissues, is needed in the experimental dosimetric verification before radiotherapy treatments. Most of the shape of gel phantoms have been structurally limited because of the fabrication method using mold technique. The present study focuses on direct freeform fabrication of gel phantom with the customized optical 3D gel printing system. Life-sized gel phantoms were replicated using conventional mold techniques, the 3D printer with two-step sequential free-radical polymerization process and inter cross-linking network gels as 3D printing materials. The gel phantoms are ultraviolet light-sensitive instead of radiation. The ultraviolet sensitivity of the gel phantoms (using mold techniques) with different molar ratios were experimentally evaluated with transmittance measurements, and were theoretically estimated by curve fitting to the observed data. This measurement gave us the insight that more vinyl monomers in the gel phantoms caused rapid polymerization and visibly opaque as well as conventional gel dosimeters. We confirmed that inter cross-linking network gel was 3D printable with the customized 3D printer, with resolution of fabrication 500 μm, as pre-finger-shaped phantom. The cross section of 3D printed gel phantom showed the distribution of opacity, that is, the distribution of UV irradiation. We expect that the 3D printer specialized gel materials and ICN gels are feasible for practical fabrication method of 3D gel phantom.

Highlights

Radiotherapy is one of standard treatments for cancer with fewer treatment-related side effects than chemotherapy and surgery (Etsuo 2017)
We expect that the 3D printer specialized gel materials and inter crosslinking network (ICN) gels are feasible for practical fabrication method of 3D gel phantom
The aim of this study is to develop the patient-specific phantoms that are equivalent to human tissues containing a lot of water, accidentally we found that ICN gels have a phase transition due to changing water content

Summary

Introduction

Radiotherapy is one of standard treatments for cancer with fewer treatment-related side effects than chemotherapy and surgery (Etsuo 2017). Suitable radiation should be delivered to the target volume as much as possible while less radiation should be directed at the normal cells that are nearby. The techniques, such as intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) (Etsuo 2017; Wagter 2004; Yuichiro 2004; Yuichiro et al 2002), for delivering radiation have recently been developed and the ultimate concentration of radiation have been achieved with them. As reported earlier (Hidemitsu et al 2013; Go et al 2012), high ductility of ICN gels with high water content was derived from a rare type of network which has crosslinking structure only between the different types of polymer, pDMAAm and HPC. The initiator of 2nd gel solution create the free radicals, which induce the polymerization led to opacity in the ICN gel phantom, instead of the free radicals resulting from water radiolysis

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