chitosan base [385]. Wide-pore sponges of this material were also used as scaffolds
for the 3D culturing of animal cells [386].
Thus, there are wide opportunities for the creation of diverse polyelectrolytebased cryostructured gel-like matrices, whose properties and porous morphology
can be varied in desired directions by an appropriate choice of the polymeric
precursor and the respective counterions, their concentrations, by the freezing
conditions, and by the procedure for the removal of frozen solvent.
3 Concluding Remarks
Fundamental studies and applied research on cryotropic gelation and various
polymeric cryogels have been in progress for more than 40 years. As a result,
numerous interesting observations have been made, mechanisms of the processes
contributing to the formation of cryogels have been established, a series of cryogels
possessing remarkable properties have been developed, and diverse practical applications have been realized (see reviews [1, 18–29, 184, 232–265, 387–404]).
It is evident that this part of polymer science did not start from a “clean slate.”
First of all, there were different empiric observations on the freeze–thaw-caused
gelation in systems like the above mentioned kori-tofu case. Second, it is necessary
to emphasize the key role of the knowledge accumulated on the specific features of
various chemical reactions in non-deeply frozen multicomponent solutions. In this
respect, the pioneering studies that revealed the occurrence per se of such reactions
in the moderately frozen systems were of great significance (see, e.g., [405–408]).
These studies identified the existence of an unfrozen liquid microphase, and gave
quantitative descriptions of the kinetic peculiarities of the relevant cryochemical
reactions [2, 409–412]. Third, another important basis for the development of
research on cryotropic gel formation was information on routes for the preparation
of conventional covalent and noncovalent gels, their properties, and the factors that
influence them. Moreover, a series of studies on frozen polymer–solvent systems
should also be noted (e.g., [413–417]). The results of these studies allow a deeper
understanding of the important fact that, in moderately frozen macromolecular
solutions and even in frozen gels, the chain segments do not lose a certain degree
of mobility and, hence, interaction of such segments can cause further transformations within the system up to the formation of a spatial polymeric network.
Therefore, all the listed sources can be considered as the roots that supplied the
“tree of polymeric cryogels” with the necessary primary “nutrients” available at the
time when intense studies on cryotropic gel formation began. The subsequent
growth and branching of this tree produced fine fruits, these being both new
fundamental knowledge and the development of such wonderful gel materials as
polymeric cryogels with their multitudinous practical applications, which are
discussed in some of the subsequent chapters of this volume.
A Brief History of Polymeric Cryogels
37
for the 3D culturing of animal cells [386].
Thus, there are wide opportunities for the creation of diverse polyelectrolytebased cryostructured gel-like matrices, whose properties and porous morphology
can be varied in desired directions by an appropriate choice of the polymeric
precursor and the respective counterions, their concentrations, by the freezing
conditions, and by the procedure for the removal of frozen solvent.
3 Concluding Remarks
Fundamental studies and applied research on cryotropic gelation and various
polymeric cryogels have been in progress for more than 40 years. As a result,
numerous interesting observations have been made, mechanisms of the processes
contributing to the formation of cryogels have been established, a series of cryogels
possessing remarkable properties have been developed, and diverse practical applications have been realized (see reviews [1, 18–29, 184, 232–265, 387–404]).
It is evident that this part of polymer science did not start from a “clean slate.”
First of all, there were different empiric observations on the freeze–thaw-caused
gelation in systems like the above mentioned kori-tofu case. Second, it is necessary
to emphasize the key role of the knowledge accumulated on the specific features of
various chemical reactions in non-deeply frozen multicomponent solutions. In this
respect, the pioneering studies that revealed the occurrence per se of such reactions
in the moderately frozen systems were of great significance (see, e.g., [405–408]).
These studies identified the existence of an unfrozen liquid microphase, and gave
quantitative descriptions of the kinetic peculiarities of the relevant cryochemical
reactions [2, 409–412]. Third, another important basis for the development of
research on cryotropic gel formation was information on routes for the preparation
of conventional covalent and noncovalent gels, their properties, and the factors that
influence them. Moreover, a series of studies on frozen polymer–solvent systems
should also be noted (e.g., [413–417]). The results of these studies allow a deeper
understanding of the important fact that, in moderately frozen macromolecular
solutions and even in frozen gels, the chain segments do not lose a certain degree
of mobility and, hence, interaction of such segments can cause further transformations within the system up to the formation of a spatial polymeric network.
Therefore, all the listed sources can be considered as the roots that supplied the
“tree of polymeric cryogels” with the necessary primary “nutrients” available at the
time when intense studies on cryotropic gel formation began. The subsequent
growth and branching of this tree produced fine fruits, these being both new
fundamental knowledge and the development of such wonderful gel materials as
polymeric cryogels with their multitudinous practical applications, which are
discussed in some of the subsequent chapters of this volume.
A Brief History of Polymeric Cryogels
37