Dissertation Defense: Peiran Jin
Candidate Name: Peiran Jin
Advisor: Peter Olmsted, Ph.D.
Title: Modeling for structure change of reconstituted fibroin gels during deformation
Silk has been used in the textile industry for thousands of years. Silk from silk- worms (e.g., Bombyx mori) and orb-weaving spiders (e.g., Nephila clavipes) has been studied because of its impressive mechanical properties and its use in biomaterials. Instead of using silk from spiders or silkworms directly, people managed to reconstitute it to get silk-based biomaterials with enhanced properties. Recently, an "e-gel" was produced by first extracting fibroin from Bombyx mori silk and then applying a current through the fibroin solvent. Tabatabai et al. found that these e-gels exhibit distinctive strain hardening and are strain recoverable.
This dissertation aims to understand the structure change and mechanical properties of the gel during the deformation using modeling and simulation methods. We propose the first simulation model of the silk fibroin gel, which can also be generalized to other physical gels. First of all, we build a coarse-grained model of the silk fibroin based on its molecule structure and properties. We estimate the free energy of the crystallizable domains by fitting the theoretical calculation with the experimental results. Brownian Dynamics (BD) is used to simulate the dynamics of the domains and the Monte Carlo (MC) calculation is used to determine the unfolding and refolding of the crystallizable domains.
We then use our model to simulate the deformation and predict nonlinear behavior of the gel. Specifically, we repeatedly shear the gel with different shear rates, applied strains, and volume fractions of the gel. We reveal that new crosslinks forming during the shear steps is the main reason for the stiffening of the gel. More importantly, we show that local forces generated during the deformation is another reason for the increase of the modulus. Yet at the same time, these forces can also make the gel more brittle.
Thursday, May 30 at 12:30pm to 5:30pm
Regents Hall, 351
3700 O St. NW