Supramolecular Soft Biomaterials for Biomedical Applications - In-Situ Gelling Polymers: For Biomedical Applications - page 111

Fig. 4 Preparation route of biodegradable CD-based supramolecular hydrogels. Reproduced
from Ref. [ 37 ]
interaction of these host-guest molecules. The swelling ratio of the gel was then
investigated and it was shown that the swelling ratios of hydrogels increases with
the increasing content of modified gelatin, due to the hydrophilic nature of gela-
tin. Connected pores were observed in the hydrogel, which could be used for cell
adhesion and growth which are important in tissue engineering.
2.4 Metal-Ligand Complexation
The incorporation of metal ions within supramolecular gels can enhance the prop-
erties of the polymeric hydrogels and increase their utility. Metal complexes can
be used as organogelators to develop hydro- and/or organogels by virtue of their
rich optical, electronic, redox, or magnetic properties which increases the stabil-
ity of metal complexes in common organic solvents, and also imparts new physi-
cal and chemical properties to the resulted supramolecular gels. Metal ligand
ions incorporated in polymeric hydrogels can lead to the formation of ordered
2D and 3D structures with increased complexity and functions, which can serve
many functions such as the separation of heavy metal ions or creating new nano-
structures. Another added advantage of this approach is that they provide self-
assembled superstructures with specific physiochemical properties of metal ions.
In recent work, Zhang et al. incorporated a ruthenium-(II)tris(bipyridine), which
is a metal complex in a hydrogelator [ 38 ]. The hydrogelator demonstrates self-
assembly in water and is able to form nanofibers at low concentrations hydrogels
over a range of pH. The optical images together with the emission spectrum of
the hydrogel in water at pH 7 show the fluorescent ability of the hydrogel upon
excitation (Fig. 5 ). It was discovered that lower pH values decrease the solubility
of the complex and hence favours formation of the hydrogel. The hydrogel turns