The ability to print 3D objects has allowed for manufacturing materials ranging from biomedical implants to flexible electronics. Unlike conventional 2D printing technology, which is used to print everything from paper-based books, newspapers, office documents, and money, 3D printing uses inks composed of self-supporting materials such as pastes, hydrogels, and foams.
In a recent communication in Advanced Materials, Massachusetts Institute of Technology (MIT) researchers Hyunwoo Yuk and Professor Xuanhe Zhao report a new strategy to overcome the limitations associated with direct ink writing, a common fabrication method used in 3D printing.
In conventional direct ink writing (DIW), the nozzle tip moves at a certain height (H) and speed (V) while depositing fibers of the viscoelastic ink. The moving speed of the nozzle tip is set to the speed at which the ink is extruded, causing the resolution of the printed fibers to be limited by the diameter of the nozzle.
The researchers have devised a setup in which six new modes of DIW 3D printing can be realized to generate complex patterns, including non-linear, continuous, and discontinuous patterns. A single nozzle can print various diameters much smaller than the diameter of the nozzle itself, significantly enhancing the resolution of the printed fibers. A quantitative phase diagram with non-dimensional nozzle speed (V*) and height (H*) could be constructed to illustrate the conditions for the different printing modes, and different values of the speed and height parameters were tested, which generated data in close agreement with the phase diagram.
Using the experimental data and silicone elastomer ink, different printing patterns and fiber diameters could be “programmed” by varying the nozzle speed and height. Continuously varying the speed of the nozzle from 0.3 to 2.5 and height from 5 to 2 allows for printing a single fiber with different printing modes and diameters without interruption.
3D solid pyramids with different resolutions and layer thicknesses can be printed in different modes using this approach, and other viscoelastic inks, such as a hydrogel ink, are also compatible with this new printing strategy with the appropriate printing parameters. A gradient can even be introduced over different layers of 3D mesh structures, where each layer has a different pattern and fiber diameter. A gradient 3D mesh actuator with two different diameters shows different swelling times when placed in tetrahydrofuran, demonstrating that structures can be printed to have different kinetic properties.
To find out more about this novel 3D printing strategy, please visit the Advanced Materials homepage.