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How to Measure the Diffusivity of Alginate Beads

Calcium alginate is a gelatinous material that can be formed into beads. These beads can be used to enclose enzymes, form artificial seeds for plant tissue culture, as wound dressing, and they are edible. The diffusivity of a bead is the measure of how well molecules diffuse across the material. The diffusivity of calcium alginate beads can be measured using observable data and applying a specific formula. This formula shows that diffusivity increases as concentration of calcium alginate increases in the bead.

Things You'll Need

Ruler, caliper or other measuring device
Calcium alginate bead

Instructions

- 1
  Measure the radius of a bead. Write this down. For example, suppose you measure a bead and it turns out to be 0.21 centimeters in radius.
- 2
  Look up the binding density for the type of bead you are measuring. This can be found in a calculation of diffusivities chart you can find online. For example, for a bead composed of 2 percent calcium alginate has a binding density of 3.69.
- 3
  Substitute the values discovered in the previous steps into the equation below to calculate the diffusivity of the bead. The symbol Co stands for binding density and the symbol R stands for radius (in centimeters), and the symbol ̶0;R^2̶1; means the square of the radius.
  
  D = 32.88 * Co *(R^2/6)
- 4
  Calculate the equation after substitution. For example, for a 2 percent calcium alginate bead that is 2 centimeters in radius, the substituted equation looks like this:
  
  D = 32.88 * 3.69 * (0.21^2/6)
- 5
  Enter the values into a calculator. The result is the diffusivity of the bead. The result is shown below:
  
  D = 0.89 cm^2/s

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