Biomedical Engineering Reference
In-Depth Information
repeating unit of Ulvan used for the calculations (Fig. 6a) can not be considered univocal
(Lahaye & Robic, 2007).
The most effective procedure for the preparation of macromers has been shown to utilize a
large excess of methacrylic anhydride in slightly basic conditions for 24 hours at 4°C (Fig. 5).
A fairly large amount of reactive is required because of the competitive hydrolysis that
spoils the methacryloyl precursor during the reaction. The formation of the methacryloyl
derivative of Ulvan was further confirmed by FT-IR analysis (Fig. 7).
Fig. 7. FT-IR spectra of Ulvan and Ulvan methacrylate (UMA) macromer with the structure
of the conjugated methacryloyl group and the relative absorption frequency reported in
small boxes.
The spectra of the native Ulvan and the Ulvan methacrylate derivative are completely
overlapping except for the peak at 1718 cm
-1
likely attributable to the presence of an α,β-
unsaturated carboxylic ester.
The preparation of hydrogels has been carried out by using a small amount of a
cytocompatible photoinitiator - IRGACURE
®
2959 - and exposing the polymeric solution to
UV light - 365 nm - at short irradiation times. The mechanism of the covalent crosslinking
between the polymeric chains involves the radical polymerization of the conjugated
(meth)acryloyl groups and the formation of degradable carboxylic ester based “junction-
zones” that act as crosslink moieties (Figure 8).
The crosslinking degree (CD) of Ulvan macromers have been evaluated by
1
HNMR analyses
of the solutions before and after definite times of irradiation by monitoring the peak areas
of the reacting unsaturated protons (
b
and
c
, Figure 9). This technique has been applied to
UMA because the preparation of this macromer proved to be the most effective in terms of
yield and SD.
