Techniques for Measurement of the Diffusion Coefficient

The protein diffusion coefficient in hydrophilic polymers can be measured by a variety of experimental techniques. Since the type of diffusion coefficient measured by each technique can be different, the method of choice will depend on the desired information and variable. A summary of the advantages and disadvantages of techniques available for diffusivity measurements is presented in Table I. 

Diffusion describes the random motion that transports matter from one part of a system at high concentration to another at low concentration. Mathematically, this process relates the mass-transfer rate of a substance through unit area to the concentration gradient normal to the section by a proportionality constant, D (cmVsec), also referred to as the diffusion coefficient (Crank, 1975). Factors that affect protein diffusion in polymers include properties that alter polymer chain segmental mobility (degree of crystallinity, chain stiffness, degree of cross-linking), deformations that alter the free volume, and factors that can immobilize or denature the protein (Rabek,1980). 

Techniques for Measuring the Diffusion Coefficient of Proteins in Hydrogels 

Membrane permeation Easy to use Pol5Tner in hydrogel state UV detection possible Long times required to reach steady state Potential to mpture membrane 

Absorption/desorption (dissolution) Easy method Options for data analysis UV-detectable groups are abundant in proteins Protein adsorption onto hydrogel is possible Pol5Tner swelling complicates diffusion process 

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