(255aj) 3 Use of Chaotic Flows for Microfabrication of Complex Tissue-like Structures and Bioinspired Catalytic Surfaces in Hydrogels

Chaotic flows have the ability to create complex but predictable, controlled, and modelable 2D and 3D structures. These structures can vary from quite simple to extremely complex arrangements, depending on the â??mixing recipeâ? and the time of mixing. In chaotic mixing, any flow filament grows exponentially over time, which makes this type of mixing a highly effective tool for quickly creating interfaces.

 In tissue engineering, the creation of complex tissue-like structures remains challenging. We are presently using simple chaotic flows to create, in a reproducible and predictable manner, complex microstructures that resemble biological tissue. To that end, a drop of particles (microbeads or cells) is injected into a cross-linkable viscous liquid and dispersed under the action of the chaotic flow. We are currently using gelatin methacryloyl (GelMA) as a model fluid and cell suspensions or fluorescent microparticles as â??ink.â? GelMA is a viscous fluid (as a pre-gel) that renders a hydrogel when crosslinked by exposure to UV light. This crosslinking therefore can preserve the high resolution microstructure originated by a chaotic flow. Chaotic printing can be applied to many relevant tissue engineering and organ-on-a-chip scenarios, ranging from the study of fundamental questions related to cellâ??cell interactions at material interfaces with different degrees of vicinity, to the development of vascularized functional tissues.

 We also demonstrate the use of chaotic flows in the fabrication of convoluted bio-catalytic surfaces bioinspired by the endoplasmic reticulum (ER). A system of two sequential reactions, glucose oxidation and hydrogen peroxide conversion, is taken as our model. We independently immobilized biotinylated horseradish peroxidase and glucose oxidase in nanoparticles functionalized with streptavidin. We imprinted these two types of nanoparticles in a GelMA construct to fabricate a convoluted multi-sheet structure where both enzymes are immobilized in close proximity. The addition of glucose to the construct triggers an oxidation reaction, mediated by the glucose oxidase, to produce hydrogen peroxide, which then serves as the substrate for the peroxidase. The reaction is visualized by the development of red fluorescence due to the oxidation of Amplex� red.

These two applications illustrate the potential of chaotic flow as a novel and powerful platform for the microfabrication of bioinspired systems.