Three-dimensional (3-D) microvascular networks with pervasive, interconnected channels less than 300 pm in diameter may find widespread application in microfluidic devices, biotechnology, sensors, and autonomic healing materials. Although microchannel arrays are readily constructed in two-dimensions by photolithographic or soft lithographic techniques, their construction in three-dimensions remains a challenging problem. The development of a microfabrication method to build 3-D microvascular networks based on direct-write assembly is described is this thesis. The method is based on the robotic deposition of a fugitive organic ink to form a free-standing scaffold structure. Secondary infiltration of a structural resin followed by setting of the matrix and removal of the scaffold yields an embedded pervasive network of smooth cylindrical channels (~ 10-500 μm) with defined connectivity.

Rheological and other material properties studies of fugitive organic ink were performed in order to identify the critical characteristics required for successful deposition of 3-D scaffolds by direct-write assembly. Guided by the results of these studies, several new ink formulations were screened for improved deposition performance. The most successful of these inks (40wt% microcrystalline wax, 60wt% petroleum jelly) showed excellent deposition and had an equilibrium modulus at room temperature (G’_eq ~ 7.70 kPa @ 1 Hz) nearly two orders of magnitude higher than the original ink. The optimized ink was used to successfully build thick (i.e., ~ 100 layers) scaffold structures at room temperature with negligible time-dependent deformation post-deposition. Secondary infiltration of the resin was accomplished at room temperature while maintaining the scaffold architecture. The optimized ink was also successfully extruded through small micronozzles (1 μm).

The construction of 3-D microvascular networks enables microfluidic devices with unparallel geometric complexity. In one example, a 3-D microfluidic mixing device was demonstrated with square-spiral mixing towers isolated within the vascular network by a secondary photopatteming process. These vertical towers give rise to chaotic advection of the fluid streams and dramatic improvements in mixing relative to simple straight (1-D) and square-wave (2-D) channels while significantly reducing the device planar footprint.