CAREER: Dynamics of anisotropic fluids: a frontier in intracellular microrheology

胞内结构域由嵌入在流体相中的半稀丝状网络组成。这种多相系统的流变特性在许多细胞功能中起决定性作用，从细胞迁移（参与癌症扩散、免疫反应等）到细胞将机械刺激转化为化学活性的能力（参与干细胞分化、内皮细胞对血流的反应等）。目前的实验方法是通过测量细胞内亚微米颗粒在细胞质中扩散时的布朗迁移率来估计细胞内的刚度和粘度。由于缺乏对颗粒在复杂的各向异性环境中所引起的流动的基本认识，限制了我们解释细胞内微流变学实验的能力，并阻碍了我们对调节细胞功能的机械过程的理解。该项目的目标是了解活动物细胞细胞质内亚微米大小颗粒的流体动力学。该项目将采用综合方法，包括：1)分析和计算研究，这将为一种新型定向微流变技术奠定基础，该技术能够测量各向异性半稀网络的粘弹性特性；2)该技术的实验实施，以量化活细胞的各向异性微流变特性；3)阐明这些性质与细胞骨架结构排列之间的关系。知识的优点。微流变粒子在现实细胞内环境中的流体力学提出了许多开放的流体力学问题。微流变学的首要问题是如何将探测粒子所经历的阻力与介质的潜在特性联系起来。这个问题的答案涉及到各向异性介质，其中应变和应力之间的关系随着施加应力/应变的方向而变化，并且定义这种变化的参数数量可能超过在实验中可观察到的独立量的数量。系统的多相特性使问题进一步复杂化，多相特性表现为网络的可压缩性以及网络与背景液体之间的相对运动。更广泛的影响。这项研究产生的新见解和实验工具将有利于社会，使人们能够更深入地了解和更早地诊断致命疾病。血管内皮细胞的微流变学特征将提高我们对动脉粥样硬化性血管疾病进展的认识，动脉粥样硬化性血管疾病是美国死亡的主要原因。细胞内微流变学对癌症的早期诊断也有直接的应用，因为转移癌细胞的细胞内粘度与非癌细胞的细胞内粘度有很大的不同。目前癌症的主要诊断标准是可疑组织的形态学改变，这只能在疾病的晚期发现，往往导致致命的结果。通过剥脱细胞学获得的单细胞样品的微流变学测量将允许筛选癌症固有的细胞内特性的变化。类似的筛选可用于检测与细胞内粘度变化相关的其他疾病。这个多学科项目将吸引来自流体力学中代表性不足的群体的学生，并为他们提供将定量研究应用于细胞生物学中高影响力问题的机会。这项研究的具体方面将适用于大学预科学生，并将以动手环节的形式进行，学生将在其中进行实验并玩诸如玉米淀粉或橡皮泥之类的物质，目的是使科学对他们更有吸引力和更容易接触。

1055697del AlamaThe intracellular domain consists of a semi-dilute filamentous network embedded in a fluid phase. The rheological properties of this multiphase system play a determinant role in many cellular functions, ranging from cell migration (involved in cancer spreading, immune response, etc.) to the ability of the cell to convert mechanical stimuli into chemical activity (involved in stem cell differentiation, endothelial response to flow, etc). Current experimental methods estimate intracellular stiffness and viscosity by measuring the Brownian mobility of intracellular submicron particles as they diffuse through the cytoplasm. The lack of fundamental knowledge about the flow elicited by the particles in such complex anisotropic environment constrains our ability to interpret intracellular microrheology experiments, and obstructs the advancement in our understanding of the mechanical processes regulating cell function. The goal of this project is to understand the hydrodynamics of submicron size particles inside the cytoplasm of live animal cells. The project will follow an integrated approach consisting of 1) analytical and computational studies that will set the foundations of a novel directional microrheology technique capable of measuring the viscoelastic properties of anisotropic semi-dilute networks, 2) the experimental implementation of this technique to quantify the anisotropic microrheological properties of live cells, and 3) the elucidation of the relation between these properties and the structural alignment of the cytoskeleton.Intellectual Merits. The hydrodynamics of microrheological particles in realistic intracellular environments presents many open fluid mechanics problems. The overarching question of interest to microrheology is how to connect the drag force experienced by the probing particle to the underlying properties of the medium. The answer to this question becomes involved in anisotropic media where the relation between strain and stress varies with the direction of the applied stress / strain, and the number of parameters defining this variation may exceed the number of independent quantities that are observable in an experiment. The problem is complicated further by the multiphase nature of the system, which manifests itself through the compressibility of the network and the relative motion between the network and the background liquid. Broader Impacts. The novel insight and experimental tools produced by this study will benefit society by enabling a deeper understanding and an earlier diagnosis of deadly diseases. The microrheological characterization of vascular endothelial cells will improve our knowledge about the progression of atherosclerotic vascular disease, which is the leading cause of death in the US. Intracellular microrheology also has immediate applications to the early diagnosis of cancer because the intracellular viscosity of metastatic cancer cells is dramatically different from that of non-cancerous cells. The current primary diagnostic criterion for cancer is morphological change in suspect tissue, which can only be detected in advanced stages of the disease that often lead to fatal outcomes. Microrheological measurements of samples of single cells obtained by exfoliative cytology would allow for screening for changes in intracellular properties that are inherent to cancer. Similar screenings could be applied to detect other diseases associated with changes in intracellular viscosity.This multidisciplinary project will engage students from underrepresented groups in fluid mechanics and give them the opportunity to apply quantitative research to high-impact problems in cell biology. Specific aspects from this research will be adapted for precollege students and will be delivered in the form of hands-on sessions in which students will perform experiments and play with substances such as corn starch or Silly Putty with the purpose of making science more appealing and accessible to them.