Molecular Gels for Tissue Engineering - Soft Fibrillar Materials: Fabrication and Applications - page 138

Compared to peptide-based molecular gels, studies and applications of
saccharide-based molecular gels are still limited. Despite their potential as a
matrix for cell immobilization and encapsulation, saccharide-based gelators
usually have complex structures, which have limited their application for tissue
engineering [48].
Investigators' attention to saccharide-based gelators stemmed from the stud-
ies on organogels of aliphatic amide derivatives, a typical example of hydrogen
bond-based gelators. The analysis of the structures of aliphatic amide derivatives
organogels showed that these molecules themselves have complementary donors
and acceptors to form intermolecular hydrogen-bonding interactions [49-53]. This
observation directed investigators' attention to saccharides, because saccharides
can also form hydrogen bonding, and new saccharide-integrated gelators can be
readily designed by replacing the hydrogen-bond-forming segment of a parental
gelator with a saccharide. Taking a library screening strategy, the Shinkai group
examined saccharide-based aggregates by introducing a variety of hydrogen-bond-
forming segments into existing gelators by appropriate selection from a saccharide
library [49].
Some excellent low-molecular-weight hydrogelators which gelate at a concen-
tration of less than 0.1 wt% were identified from a saccharide library made by
solid-phase (glycol)lipid synthesis [54]. The structural studies on the gels de-
rived from one of the gelators showed how the hierarchal assembly of this
gelator is formed on top of the one-dimensional fiber structure [18]. On nano-
scale, the amphiphilic structure of this gelator leads to a bimolecular layer
that is maintained by both hydrophobic tails and hydrogen-bondings. The bi-
molecular layer further gives rise to thin fibers with a hydrophobic core and
an oriented saccharide interface. The thin fibers are entangled and give rise to
thick fibers which immobilize water molecules [18]. Thus a hydrogel is formed
as a result of self-assembly of a small-molecular-weight gelator and is further
applied to distinguish different phosphate derivatives [12]. The hydrogels de-
rived from other excellent saccharide-based hydrogelators have been applied for
trace insulin detection [55], or in cell culture for efficient encapsulation and dis-
tribution of live Jurkat cells under physiological conditions [56], as shown in
Figure 4.6.
Hydrogen bonding is not the only mechanism for saccharide-based gel forma-
tion. Saccharide-based glycolipids were reported to form gels in a self-assembly
manner when mixed with a 1 : 1 ratio of alcohol/water or acetone/water [57].
These glycolipids dissolved in boiling water, and fine fibers were generated
during the period that the solution was gradually cooled down to room tem-
perature. Nano-fiber association and network formation induce efficient gelation,
and the gels formed in alcohol/water or acetone/water are thermo-reversible
in nature. Interestingly, instead of hydrogen bonding, the driving force for

the gel interactions, because the

limited number of hydroxyl groups in the glycolipids made hydrogen bond-
ing unlikely to be a dominant force in directing the gel formation in one
dimension [57].

formation process is thought to be π - π