549f Selective Control of Mucus Mesh Size and Nanorheology for Prevention of Infectious Diseases

Samuel K. Lai¹, Ying-Ying Wang², Kaoru Hida², Richard Cone³, Denis Wirtz⁴, and Justin Hanes¹. (1) Department of Chemical and Biomolecular Engineering, The Johns Hopkins University, 221 Maryland Hall, 3400 N. Charles Street, Baltimore, MD 21218, (2) Department of Biomedical Engineering, The Johns Hopkins University, 221 Maryland Hall, 3400 N. Charles Street, Baltimore, MD 21218, (3) Department of Biophysics, Johns Hopkins University, 221 Maryland Hall, 3400 N. Charles St, Baltimore, MD 21218, (4) Department of Chemical & Biomolecular Engineering, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218

Mucus covers the luminal surfaces of the respiratory, digestive, and reproductive tracts, as well as the surface of the eye and peritoneal surfaces of intra-abdominal organs. The ability of mucus to accomplish its critical functions as a lubricant and protective barrier against infection rests on its viscoelastic properties, which remain poorly understood at the length scales in which it functions as a selective barrier against pathogens and bacteria.

We engineered synthetic particles that readily penetrate human mucus, and used them as non-destructive nanoprobes to accurately measure the structural architecture of fresh undiluted human cervicovaginal mucus for the first time. We discovered that the average interfiber spacing of mucus is much larger than expected—large enough to allow nearly unhindered penetration of toxins and the largest viruses if they are not slowed by adhesive interactions. We then showed that mucus behaves as a viscoelastic solid barrier to objects 1 um and larger (phase angle ~12-30 degrees), but as a permissive viscoelastic liquid to objects with sizes ~500 nm and below (phase angle >60 degrees). At the 200 nm length scale, the local viscosity of human mucus is more than 3-orders of magnitude lower than its macro- (bulk) viscosity, highlighting the length scale-dependent barrier behavior of human mucus. Most viruses have evolved to possess sizes of ~100 nm or smaller and, therefore, are small enough to access the low-viscosity pathways in human mucus.

We have subsequently discovered that we can significantly tighten the mesh spacing of human mucus, and thereby vastly improve the barrier properties of mucus at smaller length scales, by application of a nonionic detergent, N9. Mucus treated with N9 behaves as a highly viscoelastic solid to 200 and 500 nm particles. This shift in nanoscale barrier behavior is caused by a partial dissociation of bundled mucin fibers, which shifts the viscoelastic solid-liquid transition of CVM to below 200 nm. In contrast to classical theories for crosslinked or entangled semiflexible polymer networks, N9 treatment did not alter the macroscopic viscous and elastic moduli of mucus, probably because N9 reduces adhesive (enthalpic) mucin interactions that counteract the increased entanglement (entropic) contributions to macro-rheology. This unexpected and highly evolved behavior of human mucus provides new clues for development of disruptive new technologies, from medical therapies to prevent infection to production of biomimetic materials with highly tunable behavior.