Polymeric Supramolecular Hydrogels as Materials for Medicine - In-Situ Gelling Polymers: For Biomedical Applications - page 167

Fig. 14 Linear dependence of the storage ( G ′) and loss ( G ″) shear moduli of low molecular-
weight chitosan hydrogels as a function of strain ( (filled circles G ′, empty circles G' ″; triangles
data calculated by the Kronig-Kramers equation). a Coacervate; b hydrogel prepared with-
out coacervation; c hydrogel after 24 h of coacervation. Reprinted from Dumitriu et al. [ 141 ].
Copyright 2004 Elsevier
Dumitriu and coworkers finished their study with a structural analysis of the
hydrogels by preparing hydrogel beads that were investigated by SEM. The beads
exhibit fibrillar porous structures with pore sizes of 100-250 nm and fiber diam-
eters of 1-10 µm. In previous publications, Dumitriu and Chornet observed the
diffusion of immobilized enzymes out of similar chitosan-xanthan hydrogel beads
[ 138 ]. This observation can be explained by the porous external and internal struc-
ture of the beads, as illustrated in Fig. 15 a, b.
With this latter work, Dumitriu and coworkers investigated the formation, the
physical-chemical properties, and the structural characteristics of chitosan-xan-
than based polyelectrolyte hydrogels. They could show the dependence of the
mechanical and swelling characteristics of the gels on to the length of the precur-
sor polymer chains and the pH value during gel probing. Microstructural investi-
gation of gel beads revealed a porous fibrillar structure, which makes this system
interesting for biomedical applications such as those in drug delivery.
Implants based on hydrogels might someday replace the need for invasive
surgery. A delicate example of invasive surgery is the epineural suture of nerves
after traumatic lesions. The outcome of these surgeries are disillusioning: often,
little or no functional recovery of the nerves can be obtained. In the worst case,
transplanted nerve tissue that is needed to close gaps between the nerve stumps
is rejected by the body and forms neuroma at the donor site [ 148 ]. To solve this