A research team at Northwestern University developed a method that uses light to improve the speed and precision of 3D printing. The method features a light-activated robotic arm paired with a liquid photopolymer. The system ensures free motion — the ability to rotate or dilate each individual printed layer — in the 3D-printing process as the structure is being built. More conventional 3D-printing processes replicate a digital design model that is sliced or split into layers; each layer is printed and assembled in an upward-building pattern to build a complete structure. The ability to manipulate the original structure’s design layer-by-layer and pivot the printing direction without re-creating the model allowed the researchers to print more complicated structures, and with increased flexibility throughout the process. According to Cheng Sun, associate professor of mechanical engineering at Northwestern University’s McCormick School of Engineering and leader of the study describing the method, the team’s result moves the 3D-printing process beyond simply replicating the designed model. "Now we have a dynamic process that uses light to assemble all the layers but with a high degree of freedom to move each layer along the way,” Sun said. The dynamic 3D-printing method developed at Northwestern University uses light and a high-precision robot arm to print a variety of structures. A double helix is shown. Courtesy of Northwestern University. In the process, as demonstrated by the Northwestern team, the high-precision robot extracts sophisticated 3D structures from a bath of liquid resin. Compared to the traditional printing process, the researchers said, the robot features enhanced geometric complexity, efficiency, and quality. The robotic arm then changes the direction of the printing process, influencing the way in which the structure is completed. “We are using light to do the manufacturing,” Sun said. “Shining light on the liquid polymer causes it to crosslink, or polymerize, converting the liquid to a solid. This contributes to the speed and precision of our 3D-printing process — two major challenges that conventional 3D printing is facing.” The process is continuous, without interruptions occurring between layers as the system performs; the researchers showed the ability to print 4000 layers in approximately 2 min. Sun said that because the general printing method is compatible with a wide range of distinct materials, including multiple, different materials simultaneously, he is hopeful that the manufacturing industry will find benefit in the new approach. This tiny Eiffel Tower was produced using a new dynamic 3D-printing method that has the ability to change printing direction on the fly. The printing path is shown on the right. Courtesy of Northwestern University. The researchers 3D-printed a customized vascular stent; a soft pneumatic gripper made of two different materials, one hard and one soft; a double helix; and even a tiny Eiffel Tower. Sun said the process could additionally be applied to other additive as well as traditional subtractive manufacturing processes, establishing a hybrid 3D-printing method bridging the two processes. The research was supported by the National Institutes of Health and the National Science Foundation. The research was published in Advanced Materials (www.doi.org/10.1002/adma.202005672).