Alexa Fluor 647 conjugated
OVA (Thermo
Fisher Scientific),
rhodamine conjugated Poly(I:C) (Invivogen), and
rhodamine conjugated HPMC–C
12 were used to visualize
the diffusion of the cargo and gel. Samples were photobleached with
a 50 μm diameter for the region of interest (ROI). Different
tests (
n = 5) were made for three different samples
from the same batch at different locations of the sample. A spot was
bleached with a pixel dwell time of 177.32 μs. A total of 500
postbleach frames were recorded at 1 frame/s to form the recovery
exponential curve. The diffusion coefficient was calculated as
70 (link) where the constant
γD = τ
1/2/
τD, with τ
1/2 being the half-time of the
recovery,
τD being the characteristic
diffusion time,
both yielded by the ZEN software, and ω being the radius of
the bleached ROI (25 μm).
The diffusivity of cargo in
PBS was calculated using the Stokes–Einstein law equation for
diffusion
71 where
kB is Boltzmann’s constant,
T is temperature
in Kelvin, η is solvent viscosity, and
R is
the solute hydrodynamic radius The diffusivity of cargo in a model covalent
PEG gel was calculated using the multiscale diffusion model (MSDM)
assuming 25 °C, a 5% volume fraction, and 35 nm mesh size.
72 (link) The calculated values are comparable to experiment
diffusivities of similar sized cargoes found in the literature.
73 (link)
Roth G.A., Gale E.C., Alcántara-Hernández M., Luo W., Axpe E., Verma R., Yin Q., Yu A.C., Lopez Hernandez H., Maikawa C.L., Smith A.A., Davis M.M., Pulendran B., Idoyaga J, & Appel E.A. (2020). Injectable Hydrogels for Sustained Codelivery of Subunit Vaccines Enhance Humoral Immunity. ACS Central Science, 6(10), 1800-1812.