Jet stability in yield stress materials



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Supportive material-based printing is a soft-matter manufacturing approach that has successfully addressed challenges inherent to classic fused deposition modeling techniques by allowing 3-dimensional patterning of materials with low mechanical properties such as cell constructs, hydrogels or polymeric networks. It consists of a two-phase system where an ink is deposited inside a soft yield stress matrix that supports the structure and prevents it from collapsing during and after the printing process. The success of this new printing approach relies on understanding how the processing parameters such as the ink flow rate and nozzle velocity impacts the print fidelity. In this thesis we investigate the influence of those printing parameters but also the printing angle and outer matrix concentration in a system composed of a Newtonian fluid (silicone oil) extruded inside a Carbopol-based gel that exhibits yield stress properties. We demonstrate that the flow conditions and overall print fidelity are highly dependent on those parameters and accurate predictions of flow type and structure shape can be made using state diagrams of flow behavior based on flow rate and nozzle velocity. Lastly, alginic acid and agarose were blended with the Carbopol hydrogel to explore their crosslinking ability and solidify the outer matrix. Carbopol / Agarose blends demonstrated good gelation potential appropriately maintaining the aspect and geometry of the outer matrix and printed channels prior to gelation, allowing the fabrication of a simple hydrogel microfluidic device.



Three-dimensional (3-D) printing, Hydrogel, Yield stress fluid, Carbopol