Biology Reference
In-Depth Information
Other Types of Microbeads
There has been a recent explosion in the development and application of a wide variety of
microbead technologies. One leading company, Phosphorex, Inc. (Fall River, MA), offers
micro- and nanospheres with sizes ranging from 20 nm to 1,000 microns. The beads are
made from polystyrene, poly(methyl methacrylate), poly(acrylic acid), nylon, poly(lactic
acid), PLGA (poly(lactic-co-glycolic acid)), chitosan, and many other synthetic and natural
polymers. They can be modified through attachment of several biomolecules including lec-
tins and antibodies. These micro- and nanospheres have the additional property of being
able to sequester molecules into their aqueous interiors, making them suitable as drug
delivery vehicles. Membrane separations with modified micro- and nanospheres parallel
methods discussed above for affinity chromatography.
Other Methodologies
Two Phase Partitioning
This unusual methodology is based on membranes partitioning between two co-existing
but immiscible liquid phases. The phases are somewhat analogous to what is seen in some
household novelty items that are commonly found in department stores. One is a slowly
rocking device that generates what resembles highly colored ocean waves. The second
is the more popular 'lava lamp'
[44]
The 'lava lamp' is a recent addition to pop culture,
invented by Edward Craven-Walker (
Figure 12.13
) in 1963. The immiscible 'lava lamp' solu-
tions are often water/glycerol and wax/carbontetrachloride. A heat source in the form of an
incandescent light bulb decreases the wax phase density, causing it to rise. The lighter wax
then rises as a blob and slowly cools, sinking back to the bottom in a lava-like display. For
membrane separations, partitioning is between two high molecular weight immiscible
FIGURE 12.13
E. Craven-Walker (1918
e
2000).
