A multi-material microstereolithography system in which multiple photocurable resins are stored on a single glass palette was developed to produce multicolor three-dimensional (3D) models. Multiple photocurable resins with different colors are replaced by moving a linear translational X-stage that supports the glass palette. A Z-stage moves radially to remove the air bubbles that adhere around the 3D model when replacing the resins. The uncurable resin was washed out by sequentially immersing the 3D structure in two tanks containing a cleaning solvent. This makes it possible to produce multicolor 3D models without contaminating the resins and air bubbles.
Stereolithography is the most precise three-dimensional (3D) printing technology and has been applied to various applications with various photocurable materials. However, most 3D-printed objects produced using conventional methods are made of uniform materials, limiting their functions. In this study, to produce heterogeneous 3D-printed objects, microphase-separated structures were controlled by the copolymerization of a photoinduced macro-reversible addition−fragmentation chain-transfer (macro-RAFT) agent and a monomer at different scanning speeds of an ultraviolet laser beam using a laboratory-constructed laserscanning micro-stereolithography system based on a bottom-up configuration in a fully open-to-air system. First, we demonstrated 3D printing using a RAFT agent by fabricating a pyramidal structure using a 375 nm laser. Copolymerization with styrene was performed to confirm that the synthesized poly(butyl acrylate) with dormant species at the end (DTC-PBA) formed block polymers upon photoirradiation. Nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) results indicated the formation of a block polymer. A homogeneous photocurable resin was prepared by mixing the synthesized DTC-PBA with multifunctional monomers, and 3D printing was performed using the prepared photocurable resin at different scanning speeds. As the scanning speed increased, the transparency of the 3D-printed model increased, whereas the mechanical strength decreased. It was suggested from scanning probe microscopy (SPM) observations that these differences were due to differences in the microphase-separation structure. As a result, it was demonstrated that heterogeneous 3D structures with sites have different mechanical and optical properties from those of a single material. Controlling the physical properties of 3D-printed parts by controlling the laser irradiation conditions is useful for functionalizing 3D-printed microdevices.
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