Oluwaseun Daini

Topic

Microfluidic Droplet Interface Bilayers: A platform to study Fundamental Biophysics, Multi-Bilayer Engineering, and Disease Modelling

Department of Chemistry

Date & location

• Thursday, September 10, 2026
• 1:00 P.M.
• Elliott Building, Room 226

Examining Committee

Supervisory Committee

• Dr. Katherine Elvira, Department of Chemistry, University of Victoria (Supervisor)
• Dr. Dennis Hore, Department of Chemistry, UVic (Member)
• Dr. David Goodlett, Department of Biochemistry and Microbiology, UVic (Outside Member)

External Examiner

• Dr. Jose Moran-Mirabal, Department of Chemistry and Chemical Biology, McMaster University

Chair of Oral Examination

• Dr. Justin Albert, Department of Physics and Astronomy, UVic

Abstract

Drug discovery is a slow and expensive process, especially when dealing with the central nervous system (CNS), where the blood-brain barrier (BBB) prevents approximately 98% of small-molecule candidates from reaching their targets in pharmacologically relevant amounts. A central contributor to this attrition is the limited physiological fidelity of the in vitro models used to screen for membrane permeability: the parallel artificial membrane permeability assay (PAMPA) is high-throughput but relies on solvent-impregnated filter supports that bear little structural resemblance to a biological bilayer, whereas cell-based Transwell and organ-on-chip models capture cellular biology but bundle together the contributions of the tight junctions, the active transporters, and the lipid membrane, making any single component difficult to interrogate in isolation. Droplet interface bilayers (DIBs), formed when two lipidmonolayer-coated aqueous droplets are brought together in oil, occupy a distinct position between these approaches: they are solvent-free bilayers of defined lipid composition, assembled without cells at cellular length scales, and, when generated on a microfluidic device, are rapid, reproducible, and compositionally tunable. This thesis characterizes and extends microfluidic DIBs as quantitative tools for membrane permeability research, with application to the BBB and Alzheimer’s disease.

I first established the biophysical rules governing DIB permeability, showing that the apparent permeability (P_app) of sodium fluorescein depends on lipid concentration in a manner conditional on the lipid delivery method and the cholesterol content of the membrane; doubling the total lipid concentration from 2mM to 4mM increased P_app by 27–38% at medium and high cholesterol levels but produced no significant change in its absence, an effect I attribute to a solubility-driven enrichment of cholesterol in the assembled bilayer rather than to a change in the energetics of permeation. More generally, whenever a model bilayer is assembled from components that differ in oil solubility or interfacial affinity, the composition that assembles at the interface departs from the nominal mixing ratio dosed into the oil. I then applied DIBs to a disease question, forming bilayers from lipids extracted from isogenic human induced pluripotent stem cell-derived brain microvascular endothelial cells carrying a PSEN2 N141I familial Alzheimer’s disease mutation and from an isogenic healthy control; across two analytes of differing size and charge (sodium fluorescein and niacin) and parallel Transwell assays on the same cell lines, no significant difference in P_app was observed between the disease and control conditions, indicating that the lipidomic changes associated with this variant are insufficient to alter passive membrane permeability and supporting a protein-centric account of BBB dysfunction in Alzheimer’s disease. Finally, I developed bespoke three-row DIB networks in which a pH gradient of less than one unit drove a 16-fold selective accumulation of fluorescein into a high-pH compartment, and demonstrated that the position of this ionization sink within a sequential pathway, rather than the downstream pH, governs whether onward transport is sustained or reduced more than 30-fold, a property of the multi-barrier arrangement that no single-membrane measurement can reveal. Taken together, these results demonstrate the ability of microfluidic-based DIBs to function as a complementary tool to existing in vitro models rather than as a simple alternative. They allow us to isolate the contribution of the lipid membrane, in a way cell-based systems cannot, while being fast, scalable, and highly tunable.