Biomedical Engineering Reference
In-Depth Information
To comply with these requirements, the authors prepared different blends and
investigated them in vitro with a view to their gelation mechanisms, degradation
profiles, and cell adhesion characteristics. In addition to these in vitro studies, the
authors also investigated the injectability, biocompatibility, and therapeutic effi-
cacy of these gels in vivo. The blends used were composed of 2 % hyaluronan
and 7 % methylcellulose, whereby one of these polymers was modified with ace-
tic hydrazide to investigate the effect of free carboxyl groups in the formation of
the HAMC hydrogel. This composition of HAMC was found to gel rapidly and
was therefore used for all further experiments. The two blends were compared to
hydrogels composed of 7 and 9 % MC only.
The first experiments comprised gelation studies and characterization of the
hydrogels by rheology. As a simple test, inverted-tube experiments were used to
determine the gelation time. HAMC took 2 min to gel in this assessment, whereas
the 9 % MC hydrogel took 10 min. The modified HAMC needed 20 min for gela-
tion, such as the hydrogel with 7 % MC. As this type of gelation is affected by tem-
perature, solutions of MC, HAMC, and modified HAMC were also investigated by
rheology with a constant frequency at increasing temperature, showing that HAMC
does gel at 18 °C, whereas the other samples gel between 27 and 32 °C, as shown
in Fig.
2
a. In addition to these gelation studies, the authors probed the result-
ing hydrogels in view of their thioxotropic response. This was done because the
HAMC hydrogel should later be applied to the host via syringe; thus, the viscosity
was measured as a function of increasing and decreasing shear stress, producing
a thioxotropic loop of the materials. Whereas the viscosities of the MC hydrogels
Fig. 2
Mechanical characterization of hydrogels based on hyaluonic acid and methyl cellu-
lose. To investigate the mechanical characteristics of these hydrogels as a function of increas-
ing temperature from room temperature to body temperature (37 °C), Shoichet and coworkers
probed the gels using a rheometer with a cone-plate geometry at 1 Hz. The degradation of the
gels was investigated in artificial cerebral spine fluid (
aCSF
) medium at 37 °C by the weight
loss.
a
Temperature-dependence of the elastic (
G
′) and the viscous (
G
″) part of the complex shear
modulus of 7 % MC (
circles
), 9 % MC (
squares
), HAMC (
triangles
), and acet-HAMC (
dia-
monds
) (
(filled symbols
represent
G
′,
open symbols
represent
G
″).
b
In vitro degradation of 7 %
MC (
(filled circles
), 9 % MC (
(filled squares
), HAMC (
open triangles
), and acet-HAMC (
open
diamonds
) in aSCF medium determined by dry mass over time. Reprinted from Shoichet et al.
[
87
]. Copyright 2006 Elsevier
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