title: The microstructure and bulk rheology of human cervicovaginal mucus are remarkably resistant to changes in pH.
abstract: The protective barrier, lubricant, and clearance functions of mucus are intimately coupled to its microstructure and bulk rheology. Mucus gels consist of a network of mucin biopolymers along with lipids, salts, and other proteins and exhibit similar biochemical and physical properties across diverse mucosal surfaces. Nevertheless, mucus is exposed to a broad range of pH values throughout the human body. Protein functions are typically sensitive to small changes in pH, and prior investigations using reconstituted, purified mucin gels suggested mucus undergoes a transition from a low-viscosity liquid at neutral pH to a highly viscoelastic solid at low pH. We sought to determine whether those observations hold for fresh, minimally perturbed human mucus ex vivo by using different-sized muco-inert nanoparticles to probe microstructure and cone-and-plate rheometry to measure bulk rheology. We demonstrate that both the microstructure and bulk rheology of fresh, undiluted, and minimally perturbed cervicovaginal mucus exhibit relatively minor changes from pH 1-2 to 8-9, in marked contrast with the pH sensitivity of purified mucin gels. Our work also suggests additional components in mucus secretions, typically eliminated during mucin purification and reconstitution, may play an important role in maintaining the protective properties of mucus.
authors.affiliation: Center for Nanomedicine, ‡Department of Biomedical Engineering, and §Department of Ophthalmology, Johns Hopkins University School of Medicine , Baltimore, Maryland 21231, United States.
authors.forename: Ying-Ying
authors.initials: YY
authors.lastname: Wang
authors.forename: Samuel K
authors.initials: SK
authors.lastname: Lai
authors.forename: Laura M
authors.initials: LM
authors.lastname: Ensign
authors.forename: Weixi
authors.initials: W
authors.lastname: Zhong
authors.forename: Richard
authors.initials: R
authors.lastname: Cone
authors.forename: Justin
authors.initials: J
authors.lastname: Hanes
mesh_terms: D002582:Cervix Mucus / Q000737:chemistry*; D002614:Chelating Agents / Q000737:chemistry; D004533:Egtazic Acid / Q000737:chemistry; D055119:Elastic Modulus; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017137:Nonoxynol / Q000737:chemistry; D010316:Particle Size; D010720:Phosphines / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D016062:Porosity; D019163:Reducing Agents / Q000737:chemistry; D012212:Rheology; D014783:Viscosity
chemical_list: D002614:Chelating Agents; D004533:Egtazic Acid; D017137:Nonoxynol; D010720:Phosphines; D011092:Polyethylene Glycols; D019163:Reducing Agents; C080938:tris(2-carboxyethyl)phosphine