Effect of pH on the rheological response of reconstituted gastric mucin

Abstract

The rheological response of reconstituted gastric mucin was studied by time dependent rheological experiments as function of pH. Mucin concentrations of 5 % and 10 % were prepared in buffer dispersions at pH of 1.15, 2.00, 2.55, 4.00 and 7.67. The isoelectric point was identified by z-potential between pH 2.00 to 2.55. Dynamic light scattering showed that as pH reduced, a second population of larger mucin aggregates was formed indicating the presence of new structures. Steady shear rheological measurements reflected the pseudoplastic behavior of mucin dispersions and the effect of concentration on viscosity. Creep-recovery measurements were performed on the regenerated mucus at different levels of pH. By creep, it was possible to determine the values of zero-shear-viscosity of mucin suspensions, with higher precision and in a lower experimental time than steady shear measurements. Additionally, it was found that at pH ∼1.15, the viscosity of the mucus increased to high values, which is an indicative of a gel-like structure. By recovery experiments, it was possible to find that even the very low viscosities the mucin suspensions at pH ∼1.15 possessed a defined elastic character. By the use of a four-element mechanistic viscoelastic model, it was concluded that this elasticity underwent retardation due to the combined effect of viscous and elastic responses.Keywords: Mucin, rheology, z-potential, creep, elasticity. RESUMENSe estudió la respuesta reológica de mucina gástrica reconstituida como función del pH mediante experimentos reológicos dependientes del tiempo. Se usaron concentraciones de mucina del 5 % y 10 % en soluciones buffer a valores de pH de 1.15, 2.00, 2.55, 4.00 y 7.67. Mediante potencial zeta se identifico que el punto isoeléctrico se ubicaba entre pH de 2.00 a 2.55. Los estudios de dispersión de luz dinámica mostraron que a mediada que el pH se reduce, una segunda población de agregados de mucina se forma, indicando el estructuramiento dentro del fluido. Las mediciones reológicas en estado estable, mostraron el comportamiento seudoplástico y el efecto de la concentración en las soluciones de mucina. Se llevaron a cabo determinaciones de fluencia lenta-recuperación sobre las suspensiones de mucina a diferentes valores de pH. Mediante fluencia lenta, se determinaron los valores de viscosidad a cero corte con mayor precisión y menor tiempo experimental que las mediciones de estado estable. Adicionalmente, se encontró que para pH ∼1.15 la viscosidad del mucus incrementó a valores altos, lo cual es una característica de las estructuras tipo gel. Los experimentos de recuperación mostraron que aun a bajas viscosidades las suspensiones de mucina a pH ∼1.15 poseían un carácter elástico definido. Mediante el uso de un modelo viscoelástico de cuatro elementos, se concluyó que esta elasticidad presentaba respuesta retardada debido al efecto combinado de los efectos viscoso y elástico.

Mucins and Their Role in Shaping the Functions of Mucus Barriers

“…The response of native mucus [including porcine gastric, intestinal, duodenal, and colonic mucus (Nordgård & Draget 2015;Philippe et al 2017;Sellers et al 1983Sellers et al , 1988Taylor et al 2003); equine respiratory mucus (Gross et al 2017); human saliva (Stokes & Davies 2007; cervical mucus (Critchfield et al 2013); and cervicovaginal mucus (Wang et al 2013)] under SAOS is predominantly solid like [storage or elastic modulus (G ) > loss or viscous modulus (G )], with slowly varying dependencies of both G and G on the oscillation frequency. Similar broad-spectrum responses were also observed during creep compliance measurements performed on Sigma-Aldrich mucin gels (Caicedo & Perilla 2015) and during stress relaxation experiments in native porcine gastric mucus (Philippe et al 2017).…”

Squaraine dyes as fluorescent turn-on sensors for the detection of porcine gastric mucin: A spectroscopic and kinetic study

“…To test if the dye-protein interaction is somehow dependent by the hydrophobic domains of mucin we recorded the emission of squaraines in presence of PGM at pH 2. It is known that at acidic pH, the hydrophobic domains of mucin are involved in non-covalent crosslinks via hydrophobic associations [3,40]. As can be seen in Figure 5, at acidic pH the emission intensity of the squaraines in presence of mucin is reduced.…”

Evaluation of the mucoadhesive properties of chitosan nanoparticles prepared using different chitosan to tripolyphosphate (CS:TPP) ratios

“…These formulations resulted in positively charged chitosan nanoparticles, which should facilitate electrostatic interactions with the negatively charged carboxylic acid groups of the mucin. Studies on native pig gastric mucin have previously shown an isoelectric point at ∼pH 2-2.5[39] and sialic acid has a pKa of 2.6[40]. Therefore, there is potential to interact with the positive charged amino groups of chitosan nanoparticles[41] when both sialic acid and chitosan are oppositely charged at therefore ~ pH 4.5 -5.…”