Controlled Formation of Oil-Free Soft Biomaterials Using All-Aqueous Fluid Systems

In this dissertation, I developed microfabrication techniques to produce oil-free soft materials  using all-aqueous fluid systems, for biological and biomedical applications. To generate soft- materials in conventional platforms, typically, organic solvents are used, which are not compatible  with biological environments and thus require extensive washing steps to remove the toxic phase. I first demonstrated a technique to fabricate non-spherical hydrogels based on electrohydrodynamic atomization. In this study, I investigated the effect of experimental parameter changes on the morphology of the fabricated particles. Moreover, carboxylated magnetic beads were used to functionalize the particles while the particle shape is preserved. These particles can be used for magnetic separation schemes. I used breast cancer cells (BT-474) to examine the potential of these particles for cell encapsulation. Aqueous-two phase systems (ATPS) are used as an organic solvent free two-phase system to generate single, double, and triple emulsions. However, most ATPSs have very low interfacial tensions, so conventional microfluidic methods cannot fabricate ATPS emulsions with a reasonable throughput, and in most cases, an external component to perturb the flow is needed to induce droplet formation. In the second half of this dissertation, I have designed and fabricated lithography-based microfluidic devices in which micro-conduits are embedded coaxially inside  iv  the microchannel to isolate the disperse phases from the channel walls, thereby circumventing the surface wetting problems that prevent successful droplet formation. This method benefits from the flexibility of choosing the disperse and continuous phases independently and permits the switching of the phase order to facilitate the formation of aqueous emulsions, regardless of their physical properties such as hydrophobicity. The configuration of this microfluidics platform also enables the focusing of two or three concentric threads of ATPS without channel-wetting problems.