Shear and extensional rheological characterisation of mucin solutions

The objective of this work is to obtain a concise image of mucin's assembly, structure and mechanics in saliva imitating buffer, in comparison to low ionic strength solutions. The systems show shear and extensional thinning, coupled with very high Trouton ratios, that is an extensional viscosity dominated mucin flow. Low-shear oscillation shows weak gels forming at low ionic strengths, while viscous systems form at high ionic strength saliva imitating buffer. Nanoparticle tracking results suggest that ionic environment affects the self-assembly of mucin. Extensional elasticities are within the size order of the shear ones; while extensional elastic moduli are smaller to the shear ones. Relaxation times and surface tensions are concentration-dependent, suggesting the build-up of aggregated structures with the addition of new material. The above conclude to the existence of finely-tuned, weak structure-spanning mucin networks in saliva imitating buffer, reminiscent to the ones proposed for the bulk self-assembly of mucus.