PROBING MECHANICAL-PROPERTIES OF LIVING CELLS BY MAGNETOPNEUMOGRAPHY

Magnetopneumography (MPG) has been used to study long-term particle cl earance from human lungs as well as cellular motility of pulmonary mac rophages (PMs).((1,2)) This study describes an extension of the method enabling the measurement of mechanical properties of PM cells in vivo . Ferromagnetic microparticles are inhaled and then retained in the al veolar region of the lungs, where they are phagocytized within hours b y PMs. The magnetic particles can be rotated in weak magnetic fields, and the response to this twisting shear (force) is detected as a macro scopic magnetic field producing a measure of cytoskeletal mechanics, C ytoplasmic viscosity is very high compared with that of water and is s trongly non-Newtonian. Under rotational stresses from 0.4 to 6.4 Pa, i t acts like a pseudoplastic fluid showing a characteristic shear rate dependence, The viscosity as well as the stiffness of the cytoskeleton increases with increasing shear stress as seems typical for living ti ssue and evidence for an intact cytoskeletal matrix. The particle reco il as measured by the amount of recoverable strain following a short t wisting force describes a cytoplasmic elasticity that depends on both level and duration of stress, These investigations on the mechanical p roperties of living human cells are promising and should lead to bette r understanding of cellular dysfunction in disease as well as pathways for drug administration.