Diffusion of macromolecules in a polymer hydrogel: from microscopic to macroscopic scales

Abstract

To gain insight into the fundamental processes determining the motion of macromolecules in polymeric matrices, the dynamical hindrance of polymeric dextran molecules diffusing as probe through a polyacrylamide hydrogel is systematically explored. Three complementary experimental methods combined with Brownian dynamics simulations are used to study a broad range of dextran molecular weights and salt concentrations. While multi-parameter fluorescence image spectroscopy (MFIS) is applied to investigate the local diffusion of single molecules on a microscopic length scale inside the hydrogel, a macroscopic transmission imaging (MTI) fluorescence technique and nuclear magnetic resonance (NMR) are used to study the collective motion of dextrans on the macroscopic scale. These fundamentally different experimental methods, probing different length scales of the system, yield long-time diffusion coefficients for the dextran molecules which agree quantitatively. The measured diffusion coefficients decay markedly with increasing molecular weight of the dextran and fall onto a master curve. The observed trends of the hindrance factors are consistent with Brownian dynamics simulations. The simulations also allow us to estimate the mean pore size for the herein investigated experimental conditions. In addition to the diffusing molecules, MFIS detects temporarily trapped molecules inside the matrix with diffusion times above 10 ms, which is also confirmed by anisotropy analysis. The fraction of bound molecules depends on the ionic strength of the solution and the charge of the dye. Using fluorescence intensity analysis, also MTI confirms the observation of the interaction of dextrans with the hydrogel. Moreover, pixelwise analysis permits to show significant heterogeneity of the gel on the microscopic scale.

Determining the scaling of gel mesh size with changing crosslinker concentration using dynamic swelling, rheometry, and PGSE NMR spectroscopy

“…For each hydrogel, the diffusion quotient () was fitted to eq. varying the dextran size, which yields one value of the mesh size for each crosslinker concentration (see Supporting Information Figure S8) . For the two lowest DAT concentration measured, values of were similar for all of the dextran probes used.…”

Quantitative assessment of passive electrical properties of the cardiac T-tubular system by FRAP microscopy

“…Control cardiomyocytes (n = 21 cells from N = 5 rats) show R c = 12.9 ± 0.4 μm and τ = 4.9 ± 0.3 s; thus, we calculate an apparent diffusion coefficient D′ = 6.5 ± 0.6 μm 2 ·s −1 . This is significantly smaller than the free diffusion coefficient D = 145 ± 3 μm 2 ·s −1 (22), underlining the impact of the TATS in slowing down the diffusion of the dextran in murine ventricular cardiomyocytes. Furthermore, simplifying the TATS geometry as an assembly of straight capillaries, and using published data regarding TATS morphology [σ ≈ 3·10 7 cm −2 (23) and r TT ≈ 100 nm (4)] we calculate an apparent diffusion D ′ Calc ≈ 1.4 μm 2 ·s −1 , which is of the same order of magnitude as the experimentally observed value.…”

Photofunctionalizable Hydrogel for Fabricating Volume Optical Diffractive Sensors

“…To be able to exploit this benefit of improved measurement sensitivity and LOD for analytes such as proteins, it is essential that the hydrogel is porous to macromolecules. This work demonstrated the incorporation of NVOC‐EA‐DMEMA in 5% w:v polyacrylamide hydrogels, which are reported to have pores with size in the range of 2 to 15 nm based on swelling, diffusion, and dynamic light scattering studies . Future work will investigate the effect of the incorporation of NVOC‐EA‐DMEMA in polyacrylamide hydrogels on their porosity to macromolecules.…”