Like an artist meticulously placing colors on a canvas, lasers could someday precisely place molecules in a meshwork to grow organs. Although there are many ways to create 3-D objects on the micron scale, tuning the chemical properties of a material at that level of precision has been difficult to achieve. A new technique, called 3-D photografting, developed by teams of materials scientists and chemists at Vienna University of Technology, ensures that the molecules attach at exactly the right place by precisely positioning chemical signals that tell the living cells where to adhere and grow. A complex 3-D pattern uses a photografting technique developed at TU Vienna. The method, which attaches fluorescent molecules to a hydrogel meshwork, could one day be used to grow biological tissues. Images courtesy of TU Vienna. “Conventional 3-D printing works by stacking up layer by layer, with the goal to build 3-D parts,” professor Jürgen Stampfl, leader of the materials science team, told BioPhotonics. “In our case, we don’t rely on layered manufacturing,” but, instead, on building 3-D parts within a liquid resin, or hydrogel, made of macromolecules. The researchers introduced specially selected molecules into the hydrogel meshwork and irradiated certain points with 100-fs pulses using an 800-nm infrared laser. A photochemically labile bond is broken at the positions where the focused laser beam is most intense, creating highly reactive intermediates that locally attach to the hydrogel very quickly. The researchers achieved a resolution of 4 µm; precision depends on the laser’s lens system, they say. “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,” team member Aleksandr Ovsianikov said in a university press release. The technology can be applied to growing biological tissue, the researchers say. A laser is used to attract cells at a specific area on the scaffold so that they can grow out to create the required tissue. “By guiding the laser beam according to the CAD [computer-aided design] file, 3-D parts are built within a liquid resin,” Stampfl said. “In the case of two-photon grafting, the chemical modification takes place in 3-D within a given bulk material.” Although only in its infancy, the technique could one day be used to grow larger tissues with specific inner structures, such as capillaries. A laser shines into the hydrogel (yellow), attaching molecules to it at specific points in space (green). “At the moment, our longest structures are around 25 mm,” Stampfl said. “For growing organs, we propose a different approach: Using 3-D grafting, we want to modify a soft hydrogel material. Specific growth factors will be grafted into the hydrogel, with the goal to direct specific cells to regions where they are supposed to grow.” Next, the team hopes to further develop its biocompatible photopolymers, “which have no negative physiological side effects, but which are still reactive toward photopolymerization,” Stampfl said. The scientists developed water-based polymers and water-soluble photoinitiators for this purpose. The report was published online in Advanced Functional Materials (doi: 10.1002/adfm.201290098).