Soft matter encapsulates a large array of materials ranging from electronics, plastics, and cosmetics to the biofluids making up all organisms. One of the most important properties of these materials that dictate their functionality is their rheology, which is the flow and deformation behavior in response to stress. The focus of this dissertation is on two vastly different types of materials: first is the bacterial biofilm and second is the metal paste. Biofilms function as a protective macro-environment for the bacteria within it, whereas the metal paste functions as the conductive wiring for stretchable electronics. Both of these materials experience similar transformations from low viscosity fluid comparable to water, to developing complex structure with gel-like properties and yield stress over some processing or incubation time.
Rheological techniques can characterize the strength and behavior of clinically relevant biological fluids such as mucus, plasma, and bacterial biofilm. More importantly, we can also use rheological measurements to drive the treatment of the biofluids toward a positive clinical outcome. In a similar manner, rheological characterization is not only an essential method of determining the printability of additive manufacturing materials such as metals and elastomers, it can guide the modification of existing unsuitable materials to construct new materials optimized for 3D printing.
This dissertation presents three manuscripts. The first manuscript describes the development of a non-destructive method of measuring the rheology of Pseudomonas aeruginosa biofilm. The second manuscript further develops this technique to measure the impact of substrate modification on the strength of the biofilm and the ferning geometries that form as a result. Finally, the third manuscript develops an original metal paste material, demonstrating how its rheological modification optimizes the 3D printability of the material.