title: Microrheology of human lung epithelial cells measured by atomic force microscopy.
abstract: Lung epithelial cells are subjected to large cyclic forces from breathing. However, their response to dynamic stresses is poorly defined. We measured the complex shear modulus (G(*)(omega)) of human alveolar (A549) and bronchial (BEAS-2B) epithelial cells over three frequency decades (0.1-100 Hz) and at different loading forces (0.1-0.9 nN) with atomic force microscopy. G(*)(omega) was computed by correcting force-indentation oscillatory data for the tip-cell contact geometry and for the hydrodynamic viscous drag. Both cell types displayed similar viscoelastic properties. The storage modulus G'(omega) increased with frequency following a power law with exponent approximately 0.2. The loss modulus G"(omega) was approximately 2/3 lower and increased similarly to G'(omega) up to approximately 10 Hz, but exhibited a steeper rise at higher frequencies. The cells showed a weak force dependence of G'(omega) and G"(omega). G(*)(omega) conformed to the power-law model with a structural damping coefficient of approximately 0.3, indicating a coupling of elastic and dissipative processes within the cell. Power-law behavior implies a continuum distribution of stress relaxation time constants. This complex dynamics is consistent with the rheology of soft glassy materials close to a glass transition, thereby suggesting that structural disorder and metastability may be fundamental features of cell architecture.
authors.affiliation: Unitat de Biofísica i Bioenginyeria, Facultat de Medicina, Universitat de Barcelona-IDIBAPS, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Alcaraz
authors.forename: Lara
authors.initials: L
authors.lastname: Buscemi
authors.forename: Mireia
authors.initials: M
authors.lastname: Grabulosa
authors.forename: Xavier
authors.initials: X
authors.lastname: Trepat
authors.forename: Ben
authors.initials: B
authors.lastname: Fabry
authors.forename: Ramon
authors.initials: R
authors.lastname: Farré
authors.forename: Daniel
authors.initials: D
authors.lastname: Navajas
mesh_terms: D002460:Cell Line; D004548:Elasticity; D006801:Humans; D018625:Microscopy, Atomic Force / Q000379:methods*; D010812:Physical Stimulation / Q000379:methods; D011673:Pulsatile Flow; D020545:Respiratory Mucosa / Q000502:physiology* / Q000648:ultrastructure; D012212:Rheology / Q000379:methods*; D033081:Shear Strength; D013314:Stress, Mechanical; D014783:Viscosity; D016474:Weight-Bearing / Q000502:physiology