## 4 Conclusions  
In this study, a movable separator was proposed to facilitate separation between materials and dispersion of powder in order to print multi-composite materials using UV-DLP-based photo-polymerization 3D printing. The proposed system has a simpler structure and smaller size compared to the previous systems used for printing multi-materials, making it easy to install on existing equipment. In addition, the production speed and printing precision are also improved. In other words, if the proposed method is used, it is possible to change materials quickly without alignment errors, so it is possible to implement various types of printing based on multi-composite materials; therefore, two types of composite materials were prepared by mixing a photochromic powder with two resins with different mechanical properties, which were classified into a single material structure, a half-and-half structure, and a laminar composite structure according to the printed form. As a result of the bending test and rebound test on the fabricated specimen, when two materials with different mechanical properties were printed with a laminar composite structure, the mechanical properties showed intermediate values between the two materials. In other words, when two materials with different mechanical properties were continuously cross-printed in the micro region with a thin layer thickness, the structure resembled a plate-reinforced composite structure, making it possible to fabricate structures with new properties from a macroscopic point of view. On the other hand, in the half-and-half structure, since the material was changed in the macro area, the mechanical properties of each material were maintained; therefore, the mechanical properties were different for each printing area. Using these properties, it was possible to fabricate anisotropic structures and soft grippers capable of selective deformation. In addition, since composite materials mixed with photochromic powder responding to UV light were used, the mechanical strengths of the structures could be visually confirmed. Through this, it was possible to fabricate 3D structures with various strengths and functionalities through selective printing of multi-composite materials based on the proposed movable separator. This method of multi-composite material 3D printing can be combined with the design for additive manufacturing (DFAM) approach to further maximize functionality and versatility.  
**Supplementary Materials:** The following are available online at [[https://www.mdpi.com/article/10.3390/app11188545/s1](https://www.mdpi.com/article/10.3390/app11188545/s1)]([https://www.mdpi.com/article/10.3390/app11188545/s1](https://www.mdpi.com/article/10.3390/app11188545/s1)), Figure S1: STL image for the 3-point bending test, Figure S2: STL image for the ball rebound test, Figure S3: STL image of the anisotropic structures, Figure S4: STL image of the soft gripper.  
**Author Contributions:** Conceptualization, M.-S.P.; methodology, S.-R.H.; investigation, S.-R.H. and M.-S.P.; writing--original draft preparation, S.-R.H. and M.-S.P.; writing--review and editing, M.-S.P.; supervision, M.-S.P.; project administration, M.-S.P.; funding acquisition, M.-S.P. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (MSIT) (no. NRF-2020R1A2C1102556).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.