In vitro and vivo studies and observation of patients’ tissues have linked the occurrence of respiratory cancer to human exposure to asbestos fibers. While substantial evidences identified the ultra-fine fibers with diameter < 0.25 μm posing the highest carcinogenicity, the details of such correlation is still not fully understood. Particles in the submicron range are known to exhibit random Brownian motion and the intensity are well correlated to inversely to the particle dimension. The process of fiber Brownian motion and the extent that it affects the fiber transport and deposition in human tracheobronchial airways is very important but largely unknown. In this study, the motions of ultra-thin fibers were analyzed by solving the system of coupled equations for translational and rotation motion of fibers under the action of hydrodynamic drag and torque, shear induced lift, gravitational sedimentation, turbulence dispersion and Brownian diffusion in a human airway bifurcation model. Based on the performed simulations, the relationship of fibers’ hydrodynamic characteristics and Brownian dynamics on the fibers’ transport behavior were quantitatively explored. The carcinogenicity if fibers in the light of new findings was discussed.

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