Nov_Dec_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 2 0 8 0 3D PRINTSHOP 3D-printed objects made (from left) with blue, green, and red light. Courtesy of Lynn Stevens. PHOTORESIST ENABLES SMALL, POROUS 3D-PRINTED STRUCTURES Researchers at Karlsruhe Institute of Technology (KIT) and Heidelberg Uni- versity have developed a photoresist for two-photonmicroprinting. Photoresists are printing inks used to print the small- est microstructures in three dimensions by so-called two-photon lithography. During printing, a laser beam is moved in all spatial directions through the initially liquid photoresist. The photo- resist hardens in the focal point of the laser beam only. In a second step, a sol- vent is used to remove those areas that were not exposed to radiation. Com- plex polymer architectures in themicro- meter and nanometer ranges remain. Two-photon polymerization—or two- photon microprinting based on this process—has been studied extensive- ly for some years now, specifically re- garding the production of microoptics, so-called metamaterials, and micro- scaffolds for experiments with single biological cells. “With the help of con- ventional photoresists, it was possible to print transparent, glassy polymers only,” says Frederik Mayer, physicist of KIT and main author of the study pub- lished in Advanced Materials. “Our new photoresist for the first time enables printing of 3D micro- structures from porous nanofoam. This polymer foam has cavities of 30 to 100 nm in size, which are filled with air.” “There has never been a photoresist for 3D laser microprinting, with which ‘white’ material can be printed,” Mayer points out. Mixing white particles into a conven- tional photoresist would not have this effect, be- cause the photoresist must be trans- parent for the (red) laser beam during printing. “Our photoresist,” Mayer says, “is transparent prior to printing, but the printed objects are white and have a high reflectivity.” The researchers from Karlsruhe and Heidelberg demonstrat- ed this by printing an Ulbricht sphere (an optical component) as fine as a hair. Another factor that opens up new applications is the extremely large in- ternal surface area of the porous ma- terial. It might be useful for filtration processes in small spaces, highly wa- ter-repellent coatings, or the cultivation of biological cells. kit.edu . ADDITIVE MANUFACTURING OF MULTI-FUNCTIONAL PARTS A team from the Fraunhofer In- stitute for Ceramic Technologies and Systems IKTS has developed a system that enables additive manufacturing of multi-material parts based on thermo- plastic binder systems. Known as multi material jetting, or MMJ, this process combines different materials and their various different properties into a sin- gle product. “Right now, we can process up to four different materials at a time,” says Uwe Scheithauer, a researcher at Fraunhofer IKTS. This opens the door to a diverse range of applications, allowing companies to produce highly integrated multi-functional components with indi- vidually defined properties. fraunhofer. de/EN. RAPID 3D PRINTING WITH VISIBLE LIGHT High-energy ultraviolet (UV) light is often used to cure liquid resins into solid objects. Visible-light curing, which would be more appropriate for some uses, such as tissue engineering and soft robotics, is slow. As reported in ACS Central Science, researchers from the University of Texas at Austin have devel- oped photopolymer resins that boost the speed of visible-light curing. The researchers developed violet-, blue-, green-, and red-colored resins that contained a monomer, a photore- dox catalyst (PRC), two co-initiators, and an opaquing agent. When the PRC absorbed visible light from LEDs, it cat- alyzed the transfer of electrons between the co-initiators, which generated radi- cals that caused themonomer topolym- erize. The opaquing agent helped con- fine curing to the areas struck by light, which improved spatial resolution. The optimized mix of components allowed the researchers to print stiff and soft objects with small features (less than 100 μm), mechanical uniformity, and build speeds up to 1.8 inches per hour. Although the best build speed is still less than half that of the fastest rate obtained using UV light, it could be fur- ther improved by increasing the light in- tensity or adding other components to the resin, the researchers say. research. utexas.edu . Color change: The right microcylinder printed with the novel photoresist appears white, because light is scattered in its sponge-like structure, whereas the cylinder printed with conventional photoresist appears transparent. Courtesy of 3DMM2O.