Date of Award
Doctor of Philosophy
Mechanical Engineer ing
This thesis presents a study of viscoelasticity characterization of hydrogels, using diffusing colloidal probe microscopy (DCPM) and microrheology, and fabrication of soft functional materials using additive manufacturing techniques. For fabrication of functional materials, we proposed diverse approaches. We first examined directed self-assembly of micro- and nanoparticles on a vibrating substrate as a viable pathway to large-scale assembly of composite materials. The second approach focused on engineering magnetically sensitive structures or soft ferrofluid actuator, using 3D printing of ABS scaffolds. We also presented a method based on fused deposition modeling of ABS scaffolds for fabricating millimeter scale self-propelled floaters that move under their own power in random trajectories. In viscoelasticity characterization study, the viscoelasticity and internal mechanics of cell-culture grade gelatin hydrogel samples with concentrations ranging between 0.3 wt% and 0.6 wt%, are examined. We apply a combination of passive microrheology and diffusing colloidal probe microscopy to assess viscoelasticity and monitor the diffusion of particles throughout the hydrogel with optical video fluorescence microscopy and particle tracking algorithms. A force balance describing the interaction between the colloidal probes and the hydrogel as a spring-damper system lead to a simple model for mean square displacement. We also account for sources of static and dynamic errors to compare our results with conventional microrheology measurements. The results from our analysis shows a strong correlation between concentration increases and solidity of the hydrogel. Additionally, for the first time we successfully built and tested a low-cost portable microscope as an alternative to scientific grade microscope for observing particle diffusion in hydrogel mediums and complex fluids. We characterized the viscoelasticity of PVP hydrogel using the portable platform and validated the results by performing the same measurements on a scientific grade microscope. Overall, we demonstrate that the portable microscope viscometer is capable of many of the same measurements as the scientific grade microscopes, which has implications for a variety of portable image-based microscopy experiments such as flow cytometry, viscometry and forensic analysis. In vibration assembly study, we suspend glass bead microparticles and iron oxide nanoparticles in polyethylene glycol diacrylate hydrogel over an area of 3000 mm2 and then subject the hydrogel with suspended micro- and nanoparticles to vibration. After the particles form structure, we expose the hydrogel to UV light to cure the structure and fabricate functional particle-polymer composite. The competition between acoustic radiation force and vibration-generated fluid flow in a viscous medium above a vibrating plate determines the particle transport characteristics. The composites produced by this technique are robust and can be held by hand for application to tunable material properties for applications to bioelectronics and soft robotics. In actuator study, we introduce the 3D printing of scaffolds as a new mode of soft ferrofluid actuator fabrication. We use fused deposition modeling to create scaffolds that form fluid channels in polydimethysiloxane (PDMS) after removal. The open channels are then filled with a ferrofluid to render the structure sensitive to magnetic fields, thereby creating a soft functional actuator. A three-point flexural test shows that introducing a channel in this way does not significantly reduce the flexural modulus of the PDMS. We perform magnetic deflection experiments on samples with three different channel diameters. Our results show a linear dependence between applied magnetic field strength and deflection. In self-propelled floaters study, we demonstrate fabrication of self-propelled composite floaters, using 3D printing technique. Different shapes of floaters are fabricated using scaffolds encased in PDMS that are then evacuated and filled with ethanol-infused PEGDA hydrogel that serves as the fuel to drive propulsion in a fluid. The release of ethanol from the hydrogel leads to a self-propelled motion in complex trajectories. Videos of the floaters moving in water are captured and analyzed to extract the trajectory. The mean square displacement (MSD) was constructed from these trajectories to measure the effective diffusion coefficient and average velocity. We design a floating spinner to demonstrate one potential application of these floaters for mixing dye and water. Ultimately, the design process illustrated here may find use in variety of platforms that require sample mixing, cargo transport and sensing.
Shabaniverki, Soheila, "Directed Assembly and Mechanics of Functional Polymer Composites" (2021). Graduate Theses and Dissertations. 18609.
Available for download on Tuesday, December 07, 2021