Magnetic wire active microrheology of human respiratory mucus

TL;DR

This study uses magnetic wire microrheology to measure the viscoelastic properties of human respiratory mucus, revealing its complex relaxation behavior and inhomogeneities that influence mucus flow and clearance in the lungs.

Contribution

It introduces magnetic wire microrheology as a novel method to characterize the viscoelastic properties of human mucus at microscale.

Findings

Mucus exhibits a wide distribution of relaxation times from 1 to several hundred seconds.

Elastic modulus of mucus is approximately 2.5 Pa, and static viscosity is around 100 Pa·s.

Mucus shows secondary inhomogeneities related to mucin network relaxation times.

Abstract

Mucus is a viscoelastic gel secreted by the pulmonary epithelium in the tracheobronchial region of the lungs. The coordinated beating of cilia moves mucus upwards towards pharynx, removing inhaled pathogens and particles from the airways. The efficacy of this clearance mechanism depends primarily on the rheological properties of mucus. Here we use magnetic wire based microrheology to study the viscoelastic properties of human mucus collected from human bronchus tubes. The response of wires between 5 and 80 microns in length to a rotating magnetic field is monitored by optical time-lapse microscopy and analyzed using constitutive equations of rheology, including those of Maxwell and Kelvin-Voigt. The static shear viscosity and elastic modulus can be inferred from low frequency (from 0.003 to 30 rad s-1) measurements, leading to the evaluation of the mucin network relaxation time. This relaxation time is found to be widely distributed, from one to several hundred seconds. Mucus is identified as a viscoelastic liquid with an elastic modulus of 2.5 +/- 0.5 Pa and a static viscosity of 100 +/- 40 Pa s. Our work shows that beyond the established spatial variations in rheological properties due to microcavities, mucus exhibits secondary inhomogeneities associated with the relaxation time of the mucin network that may be important for its flow properties.