Nature generates densely packed micro- and nano-structures that enable key functionalities in cells, tissues, and other materials. Current fabrication tech- niques are far less effective at creating microstructure, due to limitations in resolution and speed. Chaos is one of the many mechanisms that nature exploits to create complexity with simple “protocols.” For example, chaotic flows have the extraordinary capacity to create microstructure at an exponential rate. We are currently developing a set of microfabrication strategies that we term chaotic printing -- the use of chaotic flows for rapid generation of complex, high-resolution microstructures.
In our experiments, we use two classic mixing systems as models -- Journal Bearing (JB) flow and the Kenics mixer -- to demonstrate the usefulness of chaotic printing. In a miniaturized JB flow (miniJB), we induced deterministic chaotic flows in viscous liquids (i.e., methacryloyl-gelatin and poly-dimethylsiloxane), and deformed an “ink” (i.e., a drop of a miscible liquid, fluorescent beads, or cells) at an exponential rate to render a densely packed lamellar microstructure that is then preserved by curing or photocrosslinking. In a continuous version of chaotic printing, we created chaotic flows by co-extruding two streams of alginate (two inks) through a printing head that contains an on-line miniaturized Kenics mixer. The result was a continuous 3-D-printing of multi-material lamellar structures with different degrees of surface area and full spatial control of the internal microstructure. The combined outlet stream was then submerged in an aqueous calcium chloride solution to crosslink the emerging alginate fibers containing the microstructure.
The exponentially rapid creation of fine microstructure achievable through chaotic printing exceeds the limits of resolution and speed of the currently available 3-D printing techniques. Moreover, the architecture of the microstructure created with chaotic printing can be predicted using computational fluid dynamic (CFD) techniques. We envision diverse applications for this technology, including the development of densely packed catalytic surfaces and highly complex multi-lamellar and multi-component tissue-like structures for biomedical and electronics applications.