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

囊泡是由脂质双层膜包围的小囊，包裹着细胞间和细胞内通讯、运输和其他生理功能所必需的生物分子。囊泡可以与细胞和其他囊泡融合，在广泛的医学治疗中递送指定的药物、基因治疗的DNA片段和神经递质。了解膜融合的机制对于解释自然现象以及设计和促进药物传递至关重要。这个由东北大学和哈佛大学合作的项目的总体目标是通过协调实验和理论建模来研究膜和脂质体融合的潜在生物力学和生物化学。具有脂质和伪脂质、微观结构和尺寸范围的囊泡将使用专门的微流体设备制造。在生理相关条件下，将使用原子力显微镜进行力学表征和融合的中间步骤。囊泡融合的机制模型，包括膜性质和表面间力，将发展揭示分子和膜的相互作用。这项研究的结果将导致对哺乳动物细胞中普遍存在的运输过程的新见解，以及制造用于药物输送的合成囊泡的指导方针。该项目将涉及所有学术水平的学生参与。研究成果将纳入两所大学的本科和研究生课程。将制作教育视频，为K-12学生和公众演示囊泡动力学。该奖项的目标是研究相似和不同脂质双分子层和囊泡融合的基本原理，并通过探索广泛的实验参数空间来开发通用的融合指数。广泛的已知脂质与药物传递相关，脂质来源于健康和患病细胞系，以及共阻断聚合物作为伪脂质将被研究。新的微流体装置将被设计和制造，以制造均匀的、非均匀的和多层的囊泡，具有广泛的直径范围。原子力显微镜将用于确定压缩模式下单个脂质体的膜性质，以及在生理相关条件下两个相似和不同的囊泡半融合和融合所涉及的能量屏障。半融合和融合将监测原位荧光显微镜，以及荧光共振能量转移技术。我们将检验内部和表面间力、囊泡大变形和相关应变能的力学以及表面域的统计力学在囊泡融合中起重要作用的假设。基于基本的工程原理，可熔性指数将作为脂质膜材料特性、囊泡几何形状、界面和表面化学以及生理环境的函数来推导。

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.