Bioengineering (BIOE)

Ph.D. Dissertation Defense

"From experiments to models: Understanding the Mechanisms of Surface-Assisted Giant Vesicle Assembly"

Vaishnavi Girish

Bioengineering

University of California, Merced

ABSTRACT:

Giant Unilamellar Vesicles (GUVs) are simplified analogues of cell membranes that can be assembled in vitro from amphiphilic lipid molecules in aqueous environments. GUVs are of interest in therapeutics and synthetic biology due to their dimensional similarity with cells. However, the scale-up of GUV assembly techniques for these uses has been hampered by a lack of understanding of the mechanism of GUV assembly. Here, I report the quantitative impact of surface concentration, lipid headgroup charge, and salt in the hydration solutions on the yields and size distributions of GUVs. I expand on the budding and merging model previously proposed in the Subramaniam lab to explain the quantitative results. I simulate the distribution of zwitterionic lipid bilayers across sites on a substrate using a Poisson distribution, and I show that using the rules of the model, we can generate GUV yields and sizes that mimic the trends seen in experimental data. I also show that charged lipids at high surface concentrations deviate from the model. Instead, they form GUVs via an alternate bulk pathway which was named shear-induced fragmentation (SIF). This ability to model and predict the impact of important experimental parameters opens up avenues to large scale production, where the yields can be optimized depending on the required composition of lipids, hydration solutions, and substrates.

BIOGRAPHY:

Vaishnavi Girish received her B.S. and M.S. in Chemical Engineering at the University of Cambridge in the U.K. She worked in industry at Procter and Gamble, Singapore for 6 years as a process development engineer for colloidal systems in cosmetics. She started her Ph.D. at UC Merced in 2018 with the Subramaniam Lab. The focus of her research has been on understanding the mechanism underpinning the surface-assisted assembly of giant unilamellar vesicles in vitro. She received the graduate student opportunity program award for the year 2020 – 2021.