Biomedical Engineering Reference
In-Depth Information
extensions beyond 60 hours. These sulfonated hydrogels have been
evaluatedforstemcelldelivery,scaffoldsforscaffoldfortissueengi-
neeringofcartilageandtherapeuticapplications.HyalformandPre-
velle have low stiffness (G'), which is a measurement of gel harness
or a measurement of resistance to deformation. These hydrogels
have been employed as dermal fillers.
9.4.1.4
In situ
HA hydrogels
•
Photo-cross-linkingmethods
47
,
48
The previous session indicated that a wide variety of HA hydrogels
can be synthesized by various cross-linking methods, but most of
theseprefabricatedhydrogelfabricationtechniqueshavesometimes
di
culties to be applied under physiological conditions. To con-
trol gel formation conditions and take advantages of cell or bioac-
tive moleculeencapsulation, the
in situ
photocross-linking method
has been developed, a method that reacts only on exposure to
the appropriate wavelength of light sources.
49
Since
in situ
hydro-
gels has been developed by using PEO flanked with oligo(hydroxy
acids) and (metha)acrylates (Fig. 9.16),
26
HA hydrogel was devel-
oped by Schmidt
et al
.
47
,
50
−
53
The functional groups for pho-
topolymerization come from the acrylated groups of HA, inducing
rapid polymerization on irradiation with visible light in the pres-
ence of a suitable photoinitiator, for example, 2-hydroxy-1-[4-(2-
hydroxyethoxy)phenyl]-2-methyl-1-propanone.
16
Furthermore, photo polymerization demonstrated normally
capabilityofthehydrogelproceedingunderphysiologicalconditions
without detrimental side effects to bioactive molecules or encap-
sulated cells in the gel. To this end, HA has been further modi-
fied with diverse photo-cross-linkable groups, including cinnamoyl,
Figure 9.16.
HA hydrogel by photopolymerization.
16
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