Diffusion in biological gels

Table 3.2 Typical Effective Diffusivities of Solutes in Biological Gels in Aqueous Solution...

Example 6.11 Diffusion of solutes in biological gels A 0.02-m-long tube of a gel solution connects two chambers of agitated solutions of dextrose in water. The gel solution is 0.79 wt% agar in water and is at 278 K. The dextrose concentration in the first chamber is 0.4 g mol dextrose per liter solution and the other chamber concentration is 0.01 g mol dextrose per liter solution. Estimate the flow of dextrose in kg mol/s m2 at steady state. 

Diffusion coefficients for fluorescein, BSA, and human antibodies (IgG and IgM) in biological gels. Data from [5]. The diffusing probes were fluorescein, BSA, human IgG, and human IgM. The gels were formed from (a) collagen (l.Omg/mL), (b) freshly collected human cervical mucus, and (c) gelatin (lOOmg/mL). Lines indicate fits of data to Equation 4-27 with Tp equal to 500, 75, and 6nm. 

Hydrated bilayers containing one or more lipid components are commonly employed as models for biological membranes. These model systems exhibit a multiplicity of structural phases that are not observed in biological membranes. In the state that is analogous to fluid biological membranes, the liquid crystal or La bilayer phase present above the main bilayer phase transition temperature, Ta, the lipid hydrocarbon chains are conforma-tionally disordered and fluid ( melted ), and the lipids diffuse in the plane of the bilayer. At temperatures well below Ta, hydrated bilayers exist in the gel, or Lp, state in which the mostly all-trans chains are collectively tilted and pack in a regular two-dimensional... 

Brown, W Stilbs, P Lindstrom, T, Self-Diffusion of Small Molecules in Cellulose Gels using FT-Pulsed Field Gradient NMR, Journal of Applied Polymer Science 29, 823,1984. Brownstein, KR Tarr, CE, Importance of Classical Diffusion in NMR Studies of Water in Biological Cells, Physical Review A 19, 2446, 1979. 

Gel diffusion assays (biological target is mixed in soft agar and spread as a thin film the compound library is spread on the surface of the film after allowing for compound... 

In the 1970s, the fluid mosaic concept emerged as the most plausible model to account for the known structure and properties of biological membranes [41]. The fact that membranes exist as two-dimensional fluids (liquid disordered) rather than in a gel state (solid ordered) was clearly demonstrated by Frye and Ededin [42], who showed that the lipid and protein components of two separate membranes diffuse into each other when two different cells were fused. Since that time, numerous studies have measured the diffusion coefficient of lipids and proteins in membranes, and the diffusion rates were found to correspond to those expected of a fluid with the viscosity of olive oil rather than a gel phase resembling wax. 

Percolation is widely observed in chemical systems. It is a process that can describe how small, branched molecules react to form polymers, ultimately leading to an extensive network connected by chemical bonds. Other applications of percolation theory include conductivity, diffusivity, and the critical behavior of sols and gels. In biological systems, the role of the connectivity of different elements is of great importance. Examples include self-assembly of tobacco mosaic virus, actin filaments, and flagella, lymphocyte patch and cap formation, precipitation and agglutination phenomena, and immune system function. 

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