Photografting, a new form of three-dimensional printing that uses lasers to precisely attach molecules at specific places in a material, could soon make it possible to grow biological tissue or to create microsensors. Many ways exist to create 3-D objects on the micrometer scale. But tuning chemical properties of materials at micrometer precision is extremely complicated. The new method was devised by two Vienna University of Technology teams led by professors Jürgen Stampfl and Robert Liska, both of whom have received considerable attention for previous work with 3-D printers. (See: Two-Photon Lithography Prints in Fine Detail) They built upon this work to develop the 3-D photografting technique. 3-D pattern, produced by photografting (180 µm wide). Fluorescent molecules are attached to the hydrogel, resulting in a microscopic 3-D pattern. (Images: TU Vienna) “Putting together a material from tiny building blocks with different chemical properties would be extremely complicated,” said Aleksandr Ovsianikov. “That is why we start from a three-dimensional scaffold and then attach the desired molecules at exactly the right positions.” The researchers introduced specially selected molecules into the hydrogel meshwork and irradiated certain points with a laser beam. A photochemically labile bond is broken at the positions where the focused laser beam is most intense. This, in turn, creates highly reactive intermediates, which locally attach to the hydrogel very quickly. The researchers achieved a resolution of 4 µm; precision depends on the laser’s lens system, they said. A laser shines into the hydrogel (yellow), attaching molecules to it at specific points in space (green). “Much like an artist placing colors at certain points of the canvas, we can place molecules in the hydrogel — but in three dimensions and with high precision,” Ovsianikov said. The technology enables the growth of biological tissue. It uses the laser to attract cells to a specific area on the scaffold so they can grow out to create the required tissue. While only in its infancy, the technique could in the near future be used to grow larger tissues with specific inner structures, such as capillaries. 3-D printing and related technologies also hold promise for sensor technologies such as 3-D lab-on-a-chip devices, and for photovoltaics. For more information, visit: www.tuwien.ac.at