Most current biochips rely on conventional lithography techniques to construct channels through which liquid can flow on a chip's surface. Although it's possible to position a few layers on top of one another to approximate three dimensions, this procedure is time-consuming because it requires a separate mask or stamp for each layer. Now Jennifer A. Lewis and her colleagues at the University of Illinois at Urbana-Champaign have demonstrated an easy and quick approach to manufacture true three-dimensional arrays of microchannels. The procedure, Lewis says, "opens up new avenues for device design that are currently inaccessible by conventional methods."
To make their 3-D network of cylindrical channels, the researchers employed a robotic apparatus that squeezed out trails of organic ink from a syringe, in much the same way as a cake decorator lays down tracks of icing. The platform was then rotated 90 degrees before each additional trail was applied, resulting in a scaffold made of 16 layers of ink. The team next applied a resin around the scaffold. Once it had hardened, the material was heated and the ink, which liquefied, was removed. Finally, the scientists applied a second resin that can be cured by ultraviolet (UV) light. By monitoring which sections of the network were exposed to UV light, they controlled which channels remained open and which were closed off. The researchers tested the channels' mixing efficiency by monitoring the progress of two different colored dye streams through the towers they had created. "Due to their complex architecture, these three-dimensional towers dramatically improve fluid mixing compared to simple one- and two-dimensional channels," study co-author Scott White comments. Indeed, these three-dimensional networks (see image, above) can accomplish the same amount of mixing as their two-dimensional counterparts in much less space. Notes Lewis, "Full-fledged 'factories-on-a-chip' for any of the long-term applications envisioned may require these more complex structures."