title: Decoupling directed and passive motion in dynamic systems: particle tracking microrheology of sputum.
abstract: Probing the physical properties of heterogeneous materials is essential to understand the structure, function and dynamics of complex fluids including cells, mucus, and polymer solutions. Particle tracking microrheology is a useful method to passively probe viscoelastic properties on micron length scales by tracking the thermal motion of beads embedded in the sample. However, errors associated with active motion have limited the implementation to dynamic systems. We present a simple method to decouple active and Brownian motion, enabling particle tracking to be applied to fluctuating heterogeneous systems. We use the movement perpendicular to the major axis of motion in time to calculate rheological properties. Through simulated data we demonstrate that this method removes directed motion and performs equally well when there is no directed motion, with an average percent error of <1%. We use this method to measure glycerol-water mixtures to show the capability to measure a range of materials. Finally, we use this technique to characterize the compliance of human sputum. We also investigate the effect of a liquefaction agent used to prepare sputum for diagnostic purposes. Our results suggest that the addition of high concentration sodium hydroxide increases sample heterogeneity by increasing the maximum observed creep compliance.
authors.affiliation: Department of Biomedical Engineering, Boston University, 36 Cummington St, Boston, MA 02215, USA.
authors.forename: Erika J
authors.initials: EJ
authors.lastname: Fong
authors.forename: Yasha
authors.initials: Y
authors.lastname: Sharma
authors.forename: Brian
authors.initials: B
authors.lastname: Fallica
authors.forename: Dylan B
authors.initials: DB
authors.lastname: Tierney
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Fortune
authors.forename: Muhammad H
authors.initials: MH
authors.lastname: Zaman
mesh_terms: D000465:Algorithms; D001698:Biomedical Engineering; D003187:Compliance / Q000502:physiology; D004548:Elasticity; D005990:Glycerol; D006801:Humans; D057446:Hydrodynamics; D009038:Motion; D012212:Rheology / Q000379:methods* / Q000706:statistics & numerical data; D012972:Sodium Hydroxide; D013183:Sputum / Q000502:physiology*; D014783:Viscosity; D014867:Water
chemical_list: D014867:Water; D012972:Sodium Hydroxide; D005990:Glycerol