Rapid transport of large polymeric nanoparticles in fresh undiluted human mucus

Abstract

Nanoparticles larger than the reported mesh-pore size range (10-200 nm) in mucus have been thought to be much too large to undergo rapid diffusional transport through mucus barriers. However, large nanoparticles are preferred for higher drug encapsulation efficiency and the ability to provide sustained delivery of a wider array of drugs. We used high-speed multiple-particle tracking to quantify transport rates of individual polymeric particles of various sizes and surface chemistries in samples of fresh human cervicovaginal mucus. Both the mucin concentration and viscoelastic properties of these cervicovaginal samples are similar to those in many other human mucus secretions. Unexpectedly, we found that large nanoparticles, 500 and 200 nm in diameter, if coated with polyethylene glycol, diffused through mucus with an effective diffusion coefficient (D(eff)) only 4- and 6-fold lower than that for the same particles in water (at time scale tau = 1 s). In contrast, for smaller but otherwise identical 100-nm coated particles, D(eff) was 200-fold lower in mucus than in water. For uncoated particles 100-500 nm in diameter, D(eff) was 2,400- to 40,000-fold lower in mucus than in water. Much larger fractions of the 100-nm particles were immobilized or otherwise hindered by mucus than the large 200- to 500-nm particles. Thus, in contrast to the prevailing belief, these results demonstrate that large nanoparticles, if properly coated, can rapidly penetrate physiological human mucus, and they offer the prospect that large nanoparticles can be used for mucosal drug delivery.

Fig. 1.

Transport rates of COOH-modified polystyrene particles in CV mucus. (A) Ensemble-averaged geometric mean square displacements (<MSD>) as a function of time scale. (B) Effective diffusivities (<D_eff>) as a function of time scale. (C) Comparison of average D_eff at a time scale of 1 s in water (W) vs. CV mucus of subfractions of particles, from fastest to slowest. Theoretical D_eff for same sized particles in water is shown as W. The dashed black line at <D_eff> = 1 × 10⁻⁴ signifies the microscope's resolution. Data represent ensemble average of three experiments, with n ≥ 120 particles for each experiment.

Fig. 2.

Transport rates of PEG-modified polystyrene particles in CV mucus. (A) Ensemble-averaged geometric mean square displacements (<MSD>) as a function of time scale. (B) Effective diffusivities (<D_eff>) as a function of time scale. (C) Comparison of average D_eff at a time scale of 1 s in water (W) vs. CV mucus of subfractions of particles, from fastest to slowest. Theoretical D_eff for same sized particles in water is shown as W. The dashed black line at <D_eff> = 1 × 10⁻⁴ signifies the microscope's resolution. Data represent ensemble average of three experiments, with n ≥ 120 particles for each experiment.

Fig. 3.

Transport mode distributions of COOH- and PEG-modified particles in CV mucus: immobile particles (A), immobile and hindered particles (B), and diffusive particles (C). Data represent mean ± SD of three experiments, with n ≥ 120 nanoparticles for each experiment. Immobile particles have an MSD below the microscope detection limit (10 nm) for entire length of video.

Fig. 4.

Viscosity of fresh human CV mucus samples measured as a function of shear rate. Thin black lines represent n = 13 CV mucus samples. Thick line represents the average. The estimated range of a variety of other human mucus samples, including lung, gastric, small intestine, sputum, and colon mucus is plotted (dashed lines) based on ref. .