Diffusion in hydrogels

Figures 6a,b. Effect of bioproduct diffusivity in hydrogel (D) and in adsorbent matrix (D ) on ligand consumption using immobilized adsorbent beads.

In summary, models with a variety of assumptions have been developed to explain diffusion in polymer gels. A recent review of the models for solute diffusion in hydrogels [85] compares data from the literature with a variety of models, including models that attempt to account for reduced diffusion by reduction in free volume (see, e.g., [86]), by the increase in hydrodynamic drag experienced by the solute and created by polymer chains (see, e.g.. Equation 4-32), and by the presence of physical obstructions to solute diffusion (see, e.g.. 

No. 22,21st Oct. 1996, p.7124-9 INVESTIGATION OF POLYMER DIFFUSION IN HYDROGEL LAMINATES USING NEAR-FIELD FTIR SPECTROSCOPY... 

Amsden, B., 1998b. Solute diffusion in hydrogels. Polym. Gels Networks, 6 13-43. 

Tabatabaei F, Lenz O, Holm C (2011) Simulational study of anomalous tracer diffusion in hydrogels. Colloid Polym Sci 289(5-6) 523-534... 

Marko JF and Siggia ED. (1995) Stretching DNA. Macromolecules, 28, pp. 8759-8770. Sivasubramanian A. (2003) Molecular Dynamics Simulations of Small Molecule Diffusion in Hydrogels. Philadelphia Drexel University. 

Amsden, B, An Obstruction-Scaling Model for Diffusion in Homogeneous Hydrogels, Macromolecules 32, 874, 1999. 

Diffusion in highly swollen matrices such as hydrogels involves a three-component system in which the polymer-solvent matrix constitutes a continuum through which the solute diffuses. The mode and rate of transport through the... 

Solute diffusion through hydrogels has been described in terms of two basic mechanisms, the partition and pore mechanisms. The partition mechanism... 

Figure 13 Theoretical predictions of Eq. (31) for diffusion in a hydrogel (jlVfMv -1.8 nnT3) for solutes of different hydrodynamic radii. (From Ref. 174.)... 

Bell CL, Peppas NA. Water, solute and protein diffusion in physiologically responsive hydrogels of poly(methacrylic acid-g-ethylene glycol). Biomaterials 1996, 17, 1203-1218. 

Escherichia coli cells (BL21) were entrapped in hydrogel micropatches. The cells were found to remain viable in the patches. Furthermore, diffusion of small molecules through the polymer (with 1-10 nm pores) to the cells allows cell reactions to be studied. For example, the fluorescent dye BCECF-AM diffused to the cells and the dye was converted to BCECF by intracellular enzymes present only in live cells [1053]. 

When a slab of the PE0/PU hydrogel 2.8mm thick was swollen to equilibrium in an aqueous solution of morphine hydrochloride at 37°C, briefly rinsed, then transferred to water at 37°C, the rate of release of morphine was, as predicted by theory, proportional to time t O and 50° 0f the morphine content was released in the first 45 minutes. The release/time plot is shown in Figure 1. Results from experiments like this one can be used to calculate diffusion coefficients (8) in fully swollen hydrogels and help interpret the complex mechanism of diffusion in swelling hydrogels. 

D is inversely related to the incidence of junction zones in hydrogels and directly related to the uniformity of the distribution of pores (Silberberg, 1989). Major difficulties in applying Eqs. (3.25)-(3.28) to polysaccharides arise from their polymolecularity and vex effects, because molecules of different sizes diffuse at different rates and interactions preclude the fundamental independent motion implicit in Fick s first law. 

Reactive or catalytic systems are based on pH-responsive hydrogels where the chosen reaction generates a pH shift, which in mm leads to a swelling change in the hydrogel. This response can either be used to increase the internal mesh size to increase solute diffusivity in the gel phase for a diffusive membrane [44] or alternatively the gel can be used as a mechanical valve within the pores of a microporous membrane such that a convective flux may be mmed on or off in response to analyte... 

The relative mobility of a drug diffusing in the swelling hydrogel is given by the swelling... 

Aoki, A. and Heller, A. (1993) Electron-diffusion coefficients in hydrogels formed of cross-linked redox polymers. Journal of Physical Chemistry, 97 (42), 11014-11019. 

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