Biomedical Engineering Reference
In-Depth Information
surface” available for modifications and this may be the cause for the low degree of
(meth)acryloyl substitution usually found on the final macromers.
The amount of UV polymerizable unsaturated groups introduced onto the polysaccharide
would definitively affect the physical properties of the final hydrogels because it determines
the number of “junction-zones” that crosslink the linear polymer chains. Both the
substitution of the polar hydroxyl groups with the hydrophobic (meth)acryloyl moieties and
the increase of the number of crosslinks inside the hydrogel structures would determine a
minor absorption of water molecules with a consequent improvement in the mechanical
properties of the hydrogels (Anseth et al., 1996). To this view the mean number of
crosslinkable groups present in every repeating unit of Ulvan - expressed as substitution
degree (SD) - represents a key parameter to be evaluated.
The calculation of the substitution degree (SD) of the macromers obtained by the different
chemical routes reported in Figure 5, has been performed by
1
HNMR analyses (Figure. 6).
Fig. 6.
1
HNMR spectra in D
2
O of : a) Ulvan, b) Ulvan-methacrylate (UMA), c) Ulvan-acrylate
(UA). d) Ulvan-glycidyl methacrylate (UGMA). Chemical structures of the main
disaccharide repeating units of the polysaccharides are reported together with the relative
peak assignment as highlighted in the small boxes.
The SD has been calculated by comparing the peak areas relative to the vinyl protons of the
introduced (meth)acryloyl groups (Fig. 6b-d) with the peak area relative to the methyl group
of the rhamnose present in the native Ulvan (Fig. 6a). The SD values reported in Figure 5
represent only a rough estimation of the actual values because the chemical structure of the
