Biomedical Engineering Reference
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Figure 9.21. Activation of carboxylic acid of DBC by employing DCC/NHS
andsynthesisofHA-DBCandreductionofitsdisulfidebondstoobtainHA-
BC-L-benzoyl-cysteine; DBC, tetra- butylammonium hydroxide (TBA-OH),
5,5- di -thio-bis(2-nitrobenzoicacid) (DTNB). 66
Oxidation-based in situ hydrogels
Another type of in situ HA hydrogel for tissue engineerings such as
regenerationofintervertebraldiskwasobtainedbyoxidation-based
auto-cross-linkingofHAbyusingsodiumperiodate. FabioSalvatore
Palumbo et al. synthesizedauto-cross-linkingHAhydrogelshavinga
fibril structure (Fig. 9.21). 66 The activation of the carboxylic groups
of N , N -dibenzoyl-L-cystine (DBC) was performed with the activa-
tors NHS and dicyclohexylcarbodimide. The solution of DBC-NHS
was reacted with HA-tetrabutyl ammonium (TBA) in the presence
of a catalyst (see Fig. 9.21). After reduction of the -S-S- bridges to
-SH groups with a reducing agent(DTT), HA-benzoylcysteine (HA-
BC)wasobtainedandsolutionsofHA-BCwereautomaticallyturned
into an HA gel viaoxidation mechanims. 66 , 67
Michael-type reaction method
Fabrication of in situ HA hydrogels via the Michael-type reaction
mechanism is well-known chemistry, 30 and it is carried out over
time by employing the end-group reaction between unstaurations
and thiol groups of HA (Fig. 9.22). 26 32 While the HA-NH 2 or HA-
acrylate has been obtained by using ADH by the cross-linking with
bis(sulfosuccinimidyl) suberate or methacrylated HA (HA-MA) or
acrylated HA, the HA with thiol groups (HA-SH) were synthesized
 
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