Collaborative Research: Mechanics of fusion of dissimilar lipid bilayers and multi-lamellar vesicles

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Vesicles are small sacs surrounded by a lipid bilayer membrane and enclosing biomolecules essential for inter- and intra-cellular communication, transportation, and other physiological functions. Vesicles can fuse with cells and other vesicles to deliver designated drugs, segments of DNA for gene therapy, and neurotransmitters in a wide spectrum of medical treatments. Understanding the mechanism of membrane fusion is critical to interpret natural phenomena and to design and facilitate drug delivery. The overarching goal of this collaborative project between Northeastern University and Harvard University is to investigate the underlying biomechanics and biochemistry of membrane and liposome fusion by coordinated experiments and theoretical modeling. Vesicles with ranges of lipids and pseudo-lipids, microstructures, and size will be fabricated using specialized microfluidic devices. Mechanical characterization and intermediate steps of fusion under physiologically relevant conditions will be performed using atomic force microscopy. A mechanistic model of vesicle fusion, including membrane properties and inter-surface forces, will be developed to reveal molecular and membrane interactions. Outcomes of this study will lead to new insights into transport processes that are ubiquitous in mammalian cells, as well as guidelines to fabricate synthetic vesicles for drug delivery. The project will involve participation of students at all academic levels. Research outputs will be incorporated into undergraduate and graduate level courses at both universities. Educational videos will be developed to demonstrate vesicle dynamics for K-12 students and for the general public.The goal of this award is to investigate the underlying principles of fusion of similar and dissimilar lipid bilayers and vesicles and to develop a universal fusibility index by probing an extensive experimental parameter space. A wide range of known lipids relevant to drug delivery, lipids derived from healthy and diseased cell lines, and co-block polymer as pseudo lipids will be investigated. New microfluidics devices will be designed and built to manufacture homogeneous, heterogeneous, and multi-lamellar vesicles, with a wide range of diameters. Atomic force microscopy will be used to determine membrane properties of single liposomes in compression mode, as well as the energy barrier involved in hemifusion and fusion of two similar and dissimilar vesicles under physiologically relevant conditions. Hemifusion and fusion will be monitored in-situ by fluorescence microscopy, as well as a fluorescence resonance energy transfer technique. We will test the hypothesis that mechanics in terms of internal and intersurface forces, large deformation of the vesicles and associated strain energy, and statistical mechanics of surface domains plays a significant role in vesicle fusion. The fusibility index will be derived as a function of material properties of lipid membranes, vesicle geometry, interface and surface chemistry, and physiological environments, based on fundamental engineering principles.