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

University Of California-San Diego, La Jolla CA

Investigators

Abstract

1055697 del Alama The 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.