Engineering Multiscale Fiber Structures Through Controlled Solvent Interactions

Abstract

Fibrous structures are among nature's most ancient and ubiquitous design motifs, recurring across length scales from nanometer-level protein filaments to centimeter-scale tendons and engineered textiles. In engineering these structures, the manufacturing process itself is not merely an intermediate step but an active determinant of molecular orientation, phase separation, and geometric form, factors that collectively govern the mechanical and functional performance of the resulting material. Across nearly all fiber fabrication platforms, solvents serve as a central yet often underexamined mediator linking molecular interactions to macroscopic structure. This thesis places solvent control at the forefront of fiber manufacturing and investigates how solvent-mediated processes can be exploited as active design parameters across three progressively larger length scales. At the molecular scale, the role of inorganic ions in restructuring the water network is harnessed to achieve sustainable protein denaturation and regeneration. At the single-fiber scale, a fiber spinning platform harnessing solvent-induced precipitation is designed to fabricate hierarchically aligned hydrogel microfibers with robust mechanical performance. At the scaffold scale, solvent-mediated spinning and removal of sacrificial fibers facilitates cell infiltration for thicker, more contractile cardiac ventricle models with programmable architecture. Together, these studies demonstrate that treating solvents as deliberate control variables, rather than passive carriers, provides a unifying framework for rational fiber manufacturing from the control of molecular conformation to organ-level function. Chapter 1 begins by reviewing common fiber fabrication platforms, their mechanisms, and structural design strategies, with an emphasis on how solvents influence fiber properties across scales. Building on this framework, Chapter 2 initiates this multiscale study at the molecular level, combining experimental, computational, and theoretical approaches to reveal that concentrated lithium bromide denatures proteins through an entropy-driven disruption of the surrounding water network rather than direct binding. Guided by this indirect mechanism, a closed-loop regeneration process is designed that yields a keratin gel capable of rapid solidification upon immersion in water, enabling sustainable protein manufacturing. Chapter 3 then moves to the single-fiber scale, introducing the wet rotary jet spinning (WRJS) system in which solvent-induced precipitation and a salting-out process produce hierarchically aligned hydrogel microfibers with flaw insensitivity, fracture resistance, and high mechanical strength. Extending to the macroscopic scaffold scale, Chapter 4 develops focused rotary jet co-spinning (FRJcS), a strategy that incorporates sacrificial fibers to increase scaffold porosity and promote cell infiltration in tissue-engineered cardiac ventricle models, and unveils that the heart's contra-rotating helical fiber architecture plays a critical functional role for pumping efficiency. Finally, Chapter 5 summarizes the findings, discusses limitations in cross-scale modeling and platform-specific transferability, and outlines future directions toward generalizable frameworks for solvent-guided fiber manufacturing.