Multi-material 3D printing has attracted much attention due to its ability to produce functional 3D structures. We have developed several types of multi-material micro stereolithography systems including multi-tank type and single cylinder type. Recently, a multi-material micro stereolithography system based on single-photon polymerization using multiple droplets was also developed. In the multi-material micro stereolithography system, several types of photocurable resins are stored on a palette that is moved by a translation stage. Heterogeneous 3D microstructures are formed by accumulating each layer while exchanging the resins. In this system, two cleaning tanks are installed to prevent contamination of resin. Additionally, to prevent inclusion of air bubbles into the 3D-printed parts, the platform supporting the 3D-printed part was moved in horizontal plane. As a result, air bubbles were successfully pushed out of the fabrication area. Using several types of photocurable resins with different colors, multicolor 3D microstructures such as cubes and lattices were fabricated. By adjusting the number of accumulated layers, the color of the 3D-printed structure can be controlled. These multi-material micro stereolithography systems will be useful for producing functional microdevices including microfluidic elements, micromachines and scaffolds.
Multi-material micro stereolithography systems based on single-photon and two-photon polymerization using multiple droplets have been developed. In the single-photon process, several types of photocurable resins are stored on a palette that is moved by a translation stage. Multi-material 3D microstructures are formed by accumulating each layer in z direction while exchanging the resins. Using this system, multicolor 3D microstructures were created with multicolor photocurable resins. In addition, a multi-material two-photon lithography system was also developed. Metamaterials and micro optical elements were fabricated using multiple photocurable resins. These multi-material micro stereolithography systems are useful to create functional microdevices.
A three-dimensional (3-D) molding process using a master polymer mold produced by microstereolithography has been developed for the production of piezoelectric ceramic elements. In this method, ceramic slurry is injected into a 3-D polymer mold via a centrifugal casting process. The polymer master mold is thermally decomposed so that complex 3-D piezoelectric ceramic elements can be produced. As an example of 3-D piezoelectric ceramic elements, we produced a spiral piezoelectric element that can convert multidirectional loads into a voltage. It was confirmed that a prototype of the spiral piezoelectric element could generate a voltage by applying a load in both parallel and lateral directions in relation to the helical axis. The power output of 123 pW was obtained by applying the maximum load of 2.8N at 2 Hz along the helical axis. In addition, to improve the performance of power generation, we utilized a two-step sintering process to obtain dense piezoelectric elements. As a result, we obtained a sintering body with relative density of 92.8%. Piezoelectric constant d31 of the sintered body attained to -40.0 pC/N. Furthermore we analyzed the open-circuit voltage of the spiral piezoelectric element using COMSOL multiphysics. As a result, it was found that use of patterned electrodes according to the surface potential distribution of the spiral piezoelectric element had a potential to provide high output voltage that was 20 times larger than that of uniform electrodes.
New concept of micro/nano tools working in water solutuon has been proposed by the author. A real three dimensional micro fabrication process using photo curable polymer named "micro/nano stereolithography" has been also developed by the author's group. The latest version of this process achieved 100 nm in 3D resolution and freely movable micro/nano mechanism are easily fabricated within 20 min. Nano tweezers and nano needle with two degrees of freedom were successfully fabricated without any assembly process. Cell and delicate biological materials can be remotely handled with neither any micro actuators nor lead wire. It was verified that this light-driven micro tool has precise force control with 10 FtN. These light-driven micro tools contribute to cellular biology as well as medical tools.
The second application of microstereolithography is the biochemical IC chips for both micro chemical analysis and synthesis. Unlike conventional "lab. on a chip" and "micro total analysis system" (micro-TAS), our biochemical IC has micro pumps and active valves in one chip. Users can construct their own micro chemical device by themselves. The advanced biochemical IC chip-set for "on chip cell-free protein synthesis" has been prototyped and verified experimentally. A luminous enzyme of fire fly so called "Luciferase" and useful bio-marker protein "GFP" were synthesized successfully. According to above results, the biomchemical IC chips will be useful to "Order-made medicine" in near future.
Optically driven nanomanipulators with two degrees-of-freedom have been developed by using two-photon microstereolithography. The nanomanipulators are worked by maneuvering their movable component with a focused laser beam. To control the movement just by a single laser beam, the nanomanipulators is attached to a column-like structure named "Optical trapping point." Since the driving performance of the nanomanipulators depends on the shape and size of the optical trapping point, we have optimized the column-like optical trapping point. By the optimization of the optical trap point, the driving frequencies of translational motion and rotational motion were attained to 12 Hz and 120 rpm, respectively. The nanomanipulators also offers the torque on the order of fN to pN. Such optically driven nanomanipulation tools will be widely applied to micro/nano biotechnology and micro total analysis systems (μ-TAS).
The world's first micro stereo lithography, named IH process, was proposed and developed by the speaker in 1992. By now, several types of micro stereo lithography systems have been developed. Three-dimensional resolution of solidification has reached to 0.2 micron at present. These 3D micro fabrication processes using UV curable polymer gave a big impact on not only MEMS but also optics. The latest version of IH process enables us to make a movable micro mechanism without assemble process or sacrificial layer technique often used in silicon process. It is well known that the IH process is the mother of two-photon micro stereo lithography and its applications. Recently new micro chemical device named Biochemical IC Chip was proposed and developed by the speaker. This chip is based on the module IC chip-set like today's TTL family. IH process enable to make the biochemical IC including real three-dimensional micro fluid channels. Various kinds of Biochemical IC chips such as micro pump, switching valve, reactor, concentrator and detector have already been fabricated successfully. Basic performance of micro chemical devices constructed by the biochemical IC chips were demonstrated. The biochemical IC chips will open new bioscience and medicine based on innovative technology.
We report the latest 3D fabrication system based on two- photon-initiated polymerization. In two-photon 3D microfabrication, 3D microstructures can be made by scanning an ultrashort-pulsed near-IR laser beam inside liquid photopolymer without layer-by-layer process. Our current system has achieved lateral and depth resolutions of 0.2 micrometers and 0.28 micrometers , respectively. Movable micromechanisms, i.e., microgears, can be also fabricated without any use of supporting parts. For instance, a microgear with an attached shaft was successfully fabricated. Rotation of a microgear was verified during washing out unsolidified photopolymer.
Fabrication technology for three-dimensional microstructures with submicrometer accuracy has been needed in the fields of modern optics, such as micro mechanical system driven with photon pressure[1, 2] and laser-trapping near-filed optical microscopy[3]. However, the present accuracy with stereolithography[4] is not yet satisfactory to this purpose. Moreover, it is not so flexible to make a three- dimensional structure with the present technique. In this paper, we propose a new microfabrication method in which a point in three-dimensional volume of UV photopolymerizing resin is photopolymerized through two-photon absorption process. The microfabrication with two-photon absorption drastically improves the depth resolution due to a nonlinearlity between the power of the irradiation and that of the absorption[5].
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