Lipid membrane microrheology

ID: MPS/DMR/BMAT(7623) 1006171 PI: Parthasarathy， Raghuveer ORG: University of俄勒冈大学标题：脂质膜微流变学知识优势：脂质膜流动性尚未被很好地理解，膜粘度，描述流体反应的关键性质，仍然缺乏定量。本提案描述了一个协调的实验和理论程序，将阐明脂质双分子层粘度和粘弹性响应。在实验上，脂质膜将使用最近开发的两点微流变学方法进行探测，其中布朗示踪粒子轨迹之间的动态相关性提供了对复杂流体物理学的见解。这种方法以前从未应用于脂质膜。实验将使用高速视频显微镜观察与平面无支撑脂质双层相连的纳米颗粒，随后进行图像分析和颗粒跟踪。理论工作将分析扩展理想二维流体响应的最新模型，以涵盖弹性、粘弹性和张力——这些对膜有重要影响的关键物理性质。由此产生的理论框架将使实验观察到的示踪剂动力学和潜在的膜集体动力学之间的定量图成为可能。本研究针对三种重要的膜系统：(1)实验将研究均质脂双层膜的粘度与分子结构和温度的关系。结构研究将检验粘度对脂质酰基链长度的依赖性，这将揭示是疏水核心还是亲水头基主导了流体反应。更重要的是，这些数据和新的理论模型将量化脂质膜作为粘性流体和粘弹性流体的表现程度。(2)该项目还将研究相分离膜。细胞膜的组成不均匀，这一特征被认为有助于控制蛋白质©\蛋白质相互作用。异质性的机械后果仍然知之甚少。因此，实验将探测模型双层的粘度，在低于临界温度时，表现出胆固醇©\依赖的相分离为共存的流体相。(3)最后，PI将研究不对称膜。细胞膜的两个脂质小叶的组成不同。通过构建不对称的脂质双层膜，提出的研究将检查不对称的后果和存在的机械耦合在小叶。更广泛的影响：本项目将推进生物脂膜黏性和粘弹性流动的实验方法和理论。对膜蛋白的扩散和组装以及脂质结构域形成的机制有了更好的了解。PI已经开发并将继续提供一门通识教育课程“生命的物质”，为非科学成员探索生物物理学。通过阅读、讨论和动手练习，学生探索生物材料的物理特性以及这些特性对生物体的限制。本课程包括讨论物理学和生物学之间的相互作用，实验分析的新模式（例如，粒子跟踪）如何实现新发现，以及生物材料（例如膜）和非©\生物软物质（例如肥皂膜）之间的相似性。他将继续领导他的部门为经济状况不佳的高中生组织为期一周的物理日营。他的实验室将接待参加REU项目的本科生，该项目针对的是女性物理科学专业的学生，以及来自另一个项目的学生，该项目将社区大学生带到校园进行暑期研究体验。作为nsf赞助的GK-12项目的共同负责人，他指导了一项活动，该活动将俄勒冈大学的研究生与俄勒冈州偏远学区的学校合作，引入探究驱动的科学课程元素，包括参与学校保留的科学工具包。

ID: MPS/DMR/BMAT(7623) 1006171 PI: Parthasarathy, Raghuveer ORG: University of OregonTitle: Lipid Membrane MicrorheologyINTELLECTUAL MERIT: Lipid membrane fluidity is not well understood and membrane viscosity, the key property that describes fluid response, remains poorly quantified. This proposal describes a coordinated experimental and theoretical program that will illuminate lipid bilayer viscosity and viscoelastic response. Experimentally, lipid membranes will be probed using recently developed methods of two point microrheology, in which dynamic correlations between the trajectories of Brownian tracer particles provide insights into the physics of complex fluids. This approach has never before been applied to lipid membranes. The experiments will involve high-speed video microscopy of nanoparticles linked to planar, unsupported lipid bilayers, followed by image analysis and particle tracking. Theoretical work will analytically extend recent models of the response of ideal two-dimensional fluids to encompass elasticity, viscoelasticity, and tension ¨C key physical properties of consequence to membranes. The resulting theoretical framework will enable quantitative maps between experimentally observed tracer dynamics and the underlying collective dynamics of membranes. The studies target three important membrane systems: (1) Experiments will address homogenous lipid bilayer membranes to correlate viscosity with molecular structure and temperature. Structural studies will examine the dependence of viscosity on the lipids¡¯ acyl chain length, which will reveal whether the hydrophobic core or the hydrophilic headgroup dominates the fluid response. More fundamentally, the data together with new theoretical models will quantify the extent to which lipid membranes behave as viscous versus viscoelastic fluids. (2) The project will also study phase-separated membranes. Cellular membranes are not homogenous in composition, a feature that is believed to help govern protein©\protein interactions. The mechanical consequences of heterogeneity remain poorly understood. Experiments will therefore probe viscosity in model bilayers that, below a critical temperature, exhibit cholesterol©\dependent phase separation into coexisting fluid phases. (3) Finally, the PI will investigate asymmetric membranes. The two lipid leaflets of cellular membranes differ with respect to composition. By constructing asymmetric lipid bilayer membranes, the proposed studies will examine the consequences of asymmetry and the existence mechanical coupling across the leaflets.BROADER IMPACTS: This project will advance the experimental methodology and the theory of viscous and viscoelastic flow in biological lipid membranes. A better understanding of membrane protein diffusion and assembly and of the mechanism of lipid domain formation should emerge. The PI has developed and will continue to deliver a general education course, The Stuff of Life, that explores biophysics for non-science members. Through readings, discussions, and hands©\on exercises, students explore the physical properties of biological materials and the constraints these properties place on living organisms. The course includes discussions of the interplay between physics and biology, of how new modes of experimental analysis (e.g., particle tracking) enable new discoveries, and of the similarities between biomaterials (e.g. membranes) and non©\biological soft matter (e.g. soap films). He will continue to lead efforts in his Department to organize weeklong Physics Day Camps for low economic status high school students. His lab will host undergraduate students participating in an REU program targeting female physical sciences students and students from another program that brings community college students to the campus for a summer research experience. As co-PI on an NSF-sponsored GK-12 project, he directs an activity that partners University of Oregon graduate students with schools in remote Oregon school districts to introduce inquiry-driven science curriculum elements, including science kits that remain with the participating schools.