Mucus viscoelastic properties

Thim L., Madsen F. and Poulsen S.S. (2002) Effect of trefoil factors on the viscoelastic properties of mucus gels. Eur J Clin Invest 32, 519-527 Tomasetto C., Masson R., Linares J.L., Wendling C., Levebvre O. and Chenard M.P. (2000) pS2/TFFl interacts directly with the VWFC cysteine-rich domains of mucins. Gastroenterology 118, 70-80... 

Mucus possesses both solid-like (elastic) and liquid-like (viscous) attributes simultaneously and is therefore termed a viscoelastic gel. The viscoelastic properties arise from the non-covalent interactions (entanglements) between the predominantly anionic mucin molecules, although weak hydrogen-bonding and ligand-like attractions between protein regions of adjacent molecules may also play a role. Gel properties are affected by ... 

Mucociliary clearance is an organized, complex process which is highly dependent upon the composition and depth of the epithelial lining fluid and the viscoelastic properties of the mucus. In many airways diseases there is hypersecretion of mucus. This may cause an overloading of the ciliary transport process, resulting in... 

The viscosity of mucus is affected by binding between calcium and the mucus, which probably arises from an ionic interaction with the sialic acid in the mucin. These variations are indicated by a change in the pH, viscoelastic properties, water, and protein content of cervical mucus. Calcium is needed to establish an intercellular contact and the assembly of tight junction in the cervical epithelium. Changes in extracellular calcium affect the permeability of tight junctions and play a role in regulating the production of cervical mucus.Prostaglandin concentrations... 

Microscopic examination of mounted mucosal sections slit lamp and pachymeter Relates spinability to viscoelastic property of the mucus... 

In asthmatic patients, the most common symptoms are dyspnea and bronchospasm than can usually be reversed with bronchodilatation therapy that probably has no effect on mucus clearance transport (20). Hypersecretion is usually present in the acute episodes of asthma and normally mucus transport is impaired due to reduction of ciliary activity (21). Mucus hypersecretion and changes in the rheological or surface properties of mucus may also cause reduction of ciliary activity (6). In these patients, mucus transport can be recovered or remain reduced, despite favorable changes in mucus viscoelasticity after an exacerbation. 

Chitosan is also mucoadhesive [29]. Mucus is a blend of molecules including salts, lysozyme, and mucins, which are highly hydrated glycoproteins primarily responsible for the viscoelastic properties of mucus. Sialic acid residues on mucin have a pKa of 2.6, making them negatively charged at physiological pH [29, 187]. The microspheres with a... 

Respiratory mucus is a complex mixture of glycoproteins, proteoglycans, lipids, and smaller quantities of other proteins (82). Glycoproteins appear to be the most important component conferring viscoelastic properties to the mucus (see also Chap. 13). 

Mucus behaves as a nonnewtonian fluid that is, the viseosity decreases with increased applied force. The measurement of mucus s viscosity and elasticity, therefore, depends on the given shear rate and stress. The viscoelastic properties of mucus in normal humans showed no great differences from those observed in normal dogs, but high variability within individuals (13). Yeates (14) measured... 

The effect of cellular debris, and other particulate matter, on the mechanical properties of mucus depends on the strength of the interaction. It has generally been assumed that cells act as a neutral filler, adding relatively little to the viscoelastic properties of mucus in comparison with other sources of variation in mucous gel viscoelasticity. 

Tracheal mucous samples obtained by scraping, for which the eellularity is high, show little variation in viscoelastic properties from samples obtained by more gentle approaches (7). In the referenced study, the cellular contents of the samples of mucus were not measured however, the fraction of cellular debris in the samples obtained by tracheal scraping was probably higher than in those obtained from the eytology brush. In nonpurulent sputum, the nondispersable dry... 

Puchelle E, Zahm JM, Duvivier C. Spinnability of bronchial mucus relationship with viscoelasticity and mucus transport properties. Biorheology 1993 20 239-249. 

Mucus serves as a lubricant and protective layer. Its most important property is its viscoelasticity, which enables it to act as a mechanical barrier, but also allows it to flow. The presence of a mucus layer has important implications for drag delivery. Mucus acts as a physical barrier through which drug molecules must diffuse, prior to reaching the absorbing surface. The rate of diffusion through the mucus will be dependent upon such factors as the thickness of the mucus layer, mucus viscosity and any interactions which may occur between the drag and mucus. 

In the respiratory tract, mucus is also involved in the process of mucociliary clearance, which contributes to the epithelial barrier properties by entrapping potentially hazardous substances, such as dust and microorganisms, within a viscoelastic mucus blanket. The mucus is then propelled by the claw-like tips of hair-like cilia towards the throat (movement occurs in a downwards direction from the nasal epithelium, or... 

Knowledge of the structure and behavior of mucus glycoproteins in solution is crucial for a proper understanding of their behavior in situ, where they often exist in a more concentrated form. It is these molecules which generally dictate the physical properties of mucus (namely, high viscosity, viscoelastic... 

Cationic polymers were probably superior mucoadhesives due to the ability to develop molecular attraction forces by electrostatic interactions with the negative charges of the mucus the polyca-tionic chitosan was investigated as an ophthalmic vehicle. The polymer is biodegradable, biocompatible, and non-toxic. It possesses antimicrobial and wound-healing properties. Moreover, chitosan exhibits a pseudoplastic and viscoelastic behavior. ... 

The relation between the viscosity and elasticity of the secretions is one of the determining factors in transport velocity. If the gel phase is in practice the only one really transported, the sol phase creates a low-resistance milieu where the cilia can beat, an environment that is essential for transport in the direction of the upper airways. One of the most important rheological properties of mucus is viscosity. Viscosity is resistance to flow and represents the capacity of a material to absorb energy while it moves. Elasticity is the capacity to store the energy used to move or deform material. The ratio between viscosity and elasticity appears to be an important determinant of the transport rate (6,10). Mucus transport by ciliary beating is influenced by the viscoelastic and surface properties of the mucus. Theoretical models suggest that a decrease in the ratio of viscosity to elasticity can result in an increase in mucociliary transport (13). 

This chapter will deal with how the mucus reacts to particles and particulate loads, thereby altering its rate of clearance. Particles can stimulate secretion and modulate ciliary function, either by mechanical factors or irritation, or by the ehemicals they contain or are capable of releasing. Particles have a direct effect on the physical properties of mucus, even when acting as a neutral filler, for whieh their contribution to viscoelasticity is a simple function of their volume fraction. Beyond this, particles may interact with the mucous gel network, and add multiple cross-link points. 

Water can bind to mucous glycoprotein (MGP) macromolecules and influence viscosity. Viscosity can be increased by dehydration of the mucus, as can adhesion of mucus-epithelium. In purulent sputum, the correlation between viscosity and dry weight of solids is poor and may explain why mucous glycoprotein content is a poor index of viscoelasticity in chronic bronchitis, bronchiectasis, and cystic fibrosis. Mucus s viscoelasticity increases with acidic pH (3), causing reduced mucociliary clearance. Its viscoelasticity is also dependent on the content of low molecular weight electrolytes. These properties reflect the polyelectrolyte nature of mucins (4-6). 

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