Gastric mucus and mucuslike hydrogels: Thin film lubricating properties at soft interfaces

Abstract

Mucus is a viscous slime that plays a vital role in protecting and lubricating biological tissues, in particular, soft epithelium interfaces such as in the stomach, intestines, and esophagus. Previous attempts to generate mucus models that mimick or simulate its characteristics have been predominantly focused on the rheological properties. This study investigates both rheological and tribological shear properties of thin films of gastric mucus from a porcine source and its mimics at compliant soft interfaces. The lubricating efficacy of biological mucus and its mimics was observed to be superior at hydrophilic tribological interfaces compared to hydrophobic ones. Facile spreading of all mucus samples at hydrophilic steel-polydimethylsiloxane (PDMS) interfaces allowed for the retainment of the lubricating films over a wide range of speed, slide/roll ratio, and external load. In contrast, poor wetting at hydrophobic PDMS-PDMS interfaces led to depletion of the mucus samples from the interface with increasing speed. Among the different mucus models investigated in this study, fluid mixtures of commercially available porcine gastric mucin (PGM) and polyacrylic acid (PAA) displayed the most persistent lubricating effects under various tribological experimental conditions. A mixture of PGM and PAA holds a high potential as mucus mimic, not only for its rheological similarity, but also for its excellent lubricity in soft compliant and hydrophilic contacts.

Macro- and Microrheological Properties of Mucus Surrogates in Comparison to Native Intestinal and Pulmonary Mucus

“…43 When combined with porcine mucins, it was shown to manifest lubricating effects on PDMS interfaces. 44 For both surrogates, a concentration of 0.9% PAA was adequate to render gel-like properties with G′/G″ in the same range as those of native mucus. This further confirms that the mucus surrogate developed by Boegh et al matches the bulk rheological behavior of native mucus.…”

“…PAA is a versatile polymer widely used in pharmaceutical applications and is also well known for its mucoadhesive properties . When combined with porcine mucins, it was shown to manifest lubricating effects on PDMS interfaces . For both surrogates, a concentration of 0.9% PAA was adequate to render gel-like properties with G ′/ G ″ in the same range as those of native mucus.…”

Emulsion Microgel Particles as High-Performance Bio-Lubricants

“…Biolubricants are in great demand to reduce friction between soft biological contacting surfaces, such as the eyes, the oral cavity, the gastrointestinal tract, and joints, to prevent discomfort and wear of epithelial tissues and cartilage. − The use of submicron to micron sized particles (e.g., microgels) as biolubricant additives has recently been a focal point in biomaterial science research due to their ability to reduce friction and wear in the boundary regime of sliding contact in biological areas, such as tongue-oral palate contacts, cartilage, or eye blinking. ,,, At low sliding speeds and contact pressures, these particles are able to enter the gap and reduce direct contact between the biological surfaces by acting as “true surface separators” by virtue of their rheological properties . The extent to which the friction reduces can be controlled by the particle properties, such as their size, volume fraction, surface roughness, and mechanical response …”

Development and validation of a porcine artificial colonic mucus model reflecting the properties of native colonic mucus in pigs

“…However, commercially available mucins have compromised amounts of glycans due to the purification process they undergo (Marczynski et al, 2021). The loss of functional groups results in limited gelling ability of the commercially available mucins (Marczynski et al, 2021), something extensively described in the literature (Kocevar-Nared, Kristl, and Smid-Korbar, 1997;Huck et al, 2019;Røn et al, 2017) and which can explain the liquid character of our samples. PAA is known to be a highly efficient thickener that cross-links heavily upon dispersion in water.…”