why cryogels are becoming popular in several sectors of life science research and
development.
Use of chromatographic supports is frequent in many different subdisciplines of
the life sciences. One may then ask, why should cryogels be used? There are several
properties of these gels that make them well suited to meet some of the challenges
that bioseparation and other aspects of life science are facing.
Cryogels are supermacroporous materials with a network of interconnected
pores of diameters from a few micrometers up to 100 μm. This makes such
structures attractive when dealing with particulate-containing fluids such as crude
cell homogenates or even cell suspensions. Furthermore, it is possible to produce
cryogels without use of toxic chemicals, and the gels may be produced from
biocompatible polymers.
The high porosity may also be advantageous when cells are kept within such
gels, since it gives good mass transport of substrates to the cells and waste products
from the cells. This can apply to cell separation, cell adsorption, and even cell
immobilization. A special aspect of the latter is cell culture for use in tissue
engineering.
Cryogels may be produced as beads, but more frequently they are in the shape of
monoliths or sheets. The gel structure is normally elastic and spongy, which makes
it possible to use such monoliths in column operation without any leakage along the
column walls. A column is used with a slightly smaller inner diameter than the outer
diameter of the cryogel; the elasticity helps to tighten the column along the walls.
The elasticity makes it possible to use cryogels for protein separation by letting the
target protein bind to a cryogel in its “native” form, and then compressing the gel
before elution. This leads to elution in a smaller volume and, thus, to an increased
concentration of the recovered protein. A twofold increase in concentration has
been obtained [3].
The large pores of cryogels contribute to a relatively small inner surface of such
structures and, thus, a lower capacity than reported for conventional chromatographic materials.
It should be stressed that one can produce cryogels in many different shapes.
There are, however, some limitations with regard to size. Since the production is
based upon freezing and subsequent polymerization, it is problematic to generate
homogeneous cryogels if larger dimensions are used. Up to 20–25 mm thickness is
regarded as acceptable; above that, inhomogeneities will disturb the picture. If one
wants to use wide columns, then the cryogel is produced as sheets that are stacked
on top of each other. It has been demonstrated that scaling up from small column
chromatography to a large column composed of stacked sheets is easy and that the
performance is as predicted. Furthermore, no material is lost between the different
sheets.
Cryogels for Biotechnological Applications
247
development.
Use of chromatographic supports is frequent in many different subdisciplines of
the life sciences. One may then ask, why should cryogels be used? There are several
properties of these gels that make them well suited to meet some of the challenges
that bioseparation and other aspects of life science are facing.
Cryogels are supermacroporous materials with a network of interconnected
pores of diameters from a few micrometers up to 100 μm. This makes such
structures attractive when dealing with particulate-containing fluids such as crude
cell homogenates or even cell suspensions. Furthermore, it is possible to produce
cryogels without use of toxic chemicals, and the gels may be produced from
biocompatible polymers.
The high porosity may also be advantageous when cells are kept within such
gels, since it gives good mass transport of substrates to the cells and waste products
from the cells. This can apply to cell separation, cell adsorption, and even cell
immobilization. A special aspect of the latter is cell culture for use in tissue
engineering.
Cryogels may be produced as beads, but more frequently they are in the shape of
monoliths or sheets. The gel structure is normally elastic and spongy, which makes
it possible to use such monoliths in column operation without any leakage along the
column walls. A column is used with a slightly smaller inner diameter than the outer
diameter of the cryogel; the elasticity helps to tighten the column along the walls.
The elasticity makes it possible to use cryogels for protein separation by letting the
target protein bind to a cryogel in its “native” form, and then compressing the gel
before elution. This leads to elution in a smaller volume and, thus, to an increased
concentration of the recovered protein. A twofold increase in concentration has
been obtained [3].
The large pores of cryogels contribute to a relatively small inner surface of such
structures and, thus, a lower capacity than reported for conventional chromatographic materials.
It should be stressed that one can produce cryogels in many different shapes.
There are, however, some limitations with regard to size. Since the production is
based upon freezing and subsequent polymerization, it is problematic to generate
homogeneous cryogels if larger dimensions are used. Up to 20–25 mm thickness is
regarded as acceptable; above that, inhomogeneities will disturb the picture. If one
wants to use wide columns, then the cryogel is produced as sheets that are stacked
on top of each other. It has been demonstrated that scaling up from small column
chromatography to a large column composed of stacked sheets is easy and that the
performance is as predicted. Furthermore, no material is lost between the different
sheets.
Cryogels for Biotechnological Applications
247