Table 2.

Characterization of nanoparticle PEG surface coverage and nanoparticle diffusivity in human CF sputum (D_eff) compared to in water (D_w)

Formulation	Hydrodynamic Diameter a (nm)	PEG Surface Density b (molecules/100 nm2)	[Γ/SA] c	PEG Regime d	Dw/Deffe
CK30PEG10k	60	4.5 ± 0.4 – 9.0 ± 0.8	2.1 ± 0.2* – 4.1 ± 0.3*	Brush	6,000
CK30PEG5k	56	4.3 ± 0.2 – 8.6 ± 0.4	0.98 ± 0.05* – 2.0 ± 0.1*	Brush	5,000
CK30PEG2k	81	5.0 ± 0.1 – 10 ± 0.2	0.45 ± 0.01 – 0.9 ± 0.02	Mushroom	6,000
PS-PEG2k	210	120 ± 4**	11 ± 1**	Dense Brush	30

^aHydrodynamic diameter measured by dynamic light scattering.

^bFor DNA nanoparticles, PEG surface density calculated assuming stoichiometric ratios of poly-L-lysine ε-amines to DNA phosphate groups (N:P) in the range from 1 to 2. For PS-PEG_2k, PEG surface coverage reported previously [19]. ** denotes statistical significance (P < 0.01) as compared to all other groups.

^cRatio of total unconstrained PEG surface area coverage [Γ] to total particle surface area [SA]. For DNA nanoparticles, [Γ/SA] calculated assuming N:P ratios in the range from 1 to 2. * denotes statistical significance (P < 0.05) as compared to CK₃₀PEG_2k at the same N:P ratio. ** denotes statistical significance (P < 0.01) as compared to all other groups.

^dPEG regime defined as being mushroom coverage for [Γ/SA] < 1 and brush coverage for [Γ/SA] > 1, as illustrated in Figure 6.

^eD_w is the theoretical diffusivity of particles in water calculated from the Stokes-Einstein equation and the hydrodynamic diameter measured by dynamic light scattering. D_eff is the effective diffusivity in CF sputum measured at a time scale of 1 s. The D_w/D_eff ratio indicates by what multiple the average particle movement rate in fresh CF sputum is slower than in pure water.