Self-healing materials and multinozzle printheads with embedded microvascular networks

Microvascular networks are pervasive in biological systems, assisting in the repair of tissue damage, regulation of temperature, and efficient distribution of nutrients. Emulating these functional attributes in engineering contexts such as self-healing materials, microfluidic temperature regulation, and tissue engineering is gaining significant attention. Yet, the ability to design and replicate synthetic microvascular networks remains a challenge with limited progress to date. The objectives of this dissertation are to (1) create self-healing materials with interpenetrating microvascular networks via direct-write assembly of fugitive organic inks, (2) design systems with controlled thermal regulation and investigate their self-healing behavior, and (3) produce multinozzle printheads composed of biomimetic microvascular networks for high-throughput printing. Self-healing materials with embedded interpenetrating microvascular networks in an epoxy substrate/coating architecture are fabricated by direct-write assembly. Two key fabrication advancements were required: (1) dual ink printing to produce separate interpenetrating networks and (2) vertical ink printing to provide a healing agent transport pathway from the embedded network to the damage region. Each network is filled with one component of a two-part epoxy resin, which flow into the crack plane upon fracture and polymerize to restore mechanical strength. This microvascular platform enables the use of new liquid healing chemistries and repeated healing of at least 30 cycles of mechanical damage in the coating by independently supplying both healing agents to the damaged region(s). To overcome slow healing kinetics that require multiple days between damage events to recover mechanical performance under ambient conditions, their design is modified to include a third interpenetrating microvascular network within these epoxy coating/substrate architectures. Two of these networks contain epoxy resin and hardener healing agents, which remain sequestered until mechanical fracture of the coating triggers their release to the damaged region. The third interpenetrating network is used to circulate a temperature-controlled fluid that locally heats the damaged region. Temperature isotherms of 30, 50 and 70°C are achieved within minutes, yielding a sharp reduction in the healing time, from 48 to 4 hr, required for mechanical property restoration. Finally, multinozzle printheads for high throughput direct-write assembly are designed and implemented. These hierarchical microvascular networks, which are composed of 6 bifurcating generations, are fabricated by CNC-milling of an acrylic substrate to create 64 square nozzles (~200 x 200 μm2 with a center-to-center spacing of 400 μm) that are bonded by solvent welding to a solid acrylic substrate. Computational fluid modeling reveals that a uniform velocity profile within each generation of the bifurcating network is established independent of the specific ink rheology. Microvascular printheads demonstrate equal printing rates that produce filamentary features of uniform width and height. Multiple multinozzle networks are also coupled with prescribed offset distances to create multi-material printheads. Due to the highly parallel nature of the deposition, 3D structures are rapidly fabricated within minutes over large areas (~1 m^2)