Flow Visualization for Multiple Fibers in Converging Flow: Exploring the Mechanical Manufacturing of Hydrogels

Abstract

This study presents a visualization of multiple long, flexible fibers interacting in confined flows through two experimental devices. In the first device, a range of initial fiber configurations and fiber--fiber interactions are observed and categorized. Also, the formation of (open) knots in both individual fibers and multiple fibers is imaged. The likelihood of interactions is shown to increase with increasing number of fibers, increased complexity of initial fiber configuration, increasing extensional rate, and decreasing effective stiffness.

The second experimental design incorporates the multiple processing and imaging steps required to conduct this visualization study onto a single lab-on-a-chip device by the integration of three steps previously performed separately: fabrication, `washing,' and imaging. The automated `washing,' or the exchange of the solution suspending the fiber, is a novel contribution that increases the efficiency of `washing' fibers, a step that needs to be proven possible for the scalable production of this material for potential commercial applications. Additionally, washing on chips limits the interaction of fibers before visualization, and allows for some control of the initial configuration and timing of fibers in the system. Since this device allows also for in situ fabrication with control over fiber properties (such as length, diameter, and Young's modulus) separately in two parallel fabrication channels, this device can be used as a test bed for future studies on the impact of various parameters on fiber--fiber interaction.

The design process to achieve these results is presented in detail. The design criteria and constraints are defined, several ideas are evaluated, iterations on the device's design are included along with calculations that guided the design, and comments on design revisions for future studies are made.