Patterning and 3D fabrication techniques have enabled the use of hydrogels for a number of applications including microfluidics, sensors, separations, and tissue engineering in which form fits function. Devices such as reconfigurable microvalves or implantable tissues have been created using lithography or casting techniques. Here, we present a novel open microfluidic patterning method that utilizes surface tension forces to pattern hydrogel layers on top of each other, producing 3D hydrogel structures. We use a patterning device to form a temporary open microfluidic channel on an existing gel layer, allowing the controlled flow of unpolymerized gel in regions defined by the device. Once the gel is polymerized, the patterning device can then be removed, and subsequent layers added to create a multi-layered 3D structure. The use of open-microfluidic and surface tension-based methods to define the shape of each layer enables patterning to be performed with a simple pipette, minimizing dead-volume and shear stress applied on the fluid. Our method is compatible with unmodified (native) biological hydrogels, or other non-biological materials with fluid properties compatible with capillary flow. With our open-microfluidic layer-by-layer fabrication method, we demonstrate the capability to build agarose and type I collagen structures featuring asymmetric designs, multiple components, overhanging features, and cell laden regions.
