Enhanced Viscoelasticity of Human Cystic Fibrotic Sputum Correlates with Increasing Microheterogeneity in Particle Transport

Abstract

Current biochemical characterizations of cystic fibrosis (CF) sputum do not address the high degree of microheterogeneity in the rheological properties of the mucosal matrix and only provide bulk-average particle diffusion coefficients. The viscoelasticity of CF sputum greatly reduces the diffusion rates of colloidal particles, limiting the effectiveness of gene delivery to underlying lung cells. We determine diffusion coefficients of hundreds of individual amine-modified and carboxylated polystyrene particles (diameter 100 -500 nm) embedded in human CF sputum with 5 nm and 33 ms of spatiotemporal resolution. High resolution multiple particle tracking is used to calculate the effective viscoelastic properties of CF sputum at the micron scale, which we relate to its macroscopic viscoelasticity. CF sputum microviscosity, as probed by 100-and 200-nm particles, is an order of magnitude lower than its macroviscosity, suggesting that nanoparticles dispersed in CF sputum are transported primarily through lower viscosity pores within a highly elastic matrix. Multiple particle tracking provides a non-destructive, highly sensitive method to quantify the high heterogeneity of the mucus pore network. The mean diffusion coefficient becomes dominated by relatively few but fast-moving particles as particle size is reduced from 500 to 100 nm. Neutrally charged particles with a diameter <200 nm undergo more rapid transport in CF sputum than charged particles. Treatment with recombinant human DNase (Pulmozyme®) reduces macroviscoelastic properties of CF sputum by up to 50% and dramatically narrows the distribution of individual particle diffusion rates but surprisingly does not significantly alter the ensemble-average particle diffusion rate.

An exploration of the microrheological environment around the distal ileal villi and proximal colonic mucosa of the possum ( Trichosurus vulpecula )

“…Similarly, it may allow membrane vesicles exocytosed from the enterocyte brush border to bypass the mucin layer and enter the lumen [52]. The heterogeneous microrheological structure also has important consequences for the process of mixing within the intervillous space and our understanding of the transit and absorption of nanoparticles containing therapeutic substances that might adhere to viscoelastic regions [20,28,53]. While previous reports have indicated that mucins can accumulate in the intervillous space [18], the current work is the first to report the heterogeneous microrheology therein, its similarity to that around the villous tips suggesting that there is ongoing admixture and transit of these elements between the lumen and the intervillous spaces during longitudinal [54] and circular [55] contractile activity.…”

Rheology of Gastric Mucin Exhibits a pH-Dependent Sol−Gel Transition

“…In addition, recent studies have examined the microrheology [17][18][19]25 of mucins and mucus. Microrheology studies are particularly relevant to the transport of drugs and infectious agents such as bacteria and viruses across the mucus barrier.…”

Methods to determine the interactions of micro- and nanoparticles with mucus

“…NPs through the sputum of cystic fibrosis patients and relating the respected transport to the micro-viscosity and macro-viscosity characteristics of the sputum [44]. The group has also used MPT to quantify, for example, the intracellular transport of non-viral polyethyleneimine/DNA nano-sized polyplexes [45].…”