Biomedical Engineering Reference
In-Depth Information
Photopolymerization has several advantages over conventional polymerization and
crosslinking techniques. These include spatial and temporal control over polymerization,
fast curing rates at room or physiological temperatures and minimal heat production
(Nguyen & West, 2002). Moreover photopolymerization does not require the use of many
reactive species, initiator and catalysts usually involved in the conventional chemical
crosslinking methods, thus representing a potentially safer technique.
The condition for UV photopolymerization is that polymeric materials need to be
conjugated with radically polymerizable groups. In this context, methacryloyl or acryloyl
groups, when grafted to the chain backbone via an oxygen or a nitrogen atom usually
represent a good candidates for this function, as they work as degradable crosslinks
sensitive to either hydrolysis (Benoit et al., 2006) or cell-mediated proteolysis (Mahoney &
Anseth, 2006).
The introduction of vinyl or vinylidenic polymerizable groups on Ulvan has been conducted
by using several different (meth)acryloyl precursors and conditions (Morelli & Chiellini,
2010) (Figure 5).
Fig. 5. Reaction of Ulvan with (Meth)acryloyl precursors and relative experimental
conditions. Next to every macromer preparation are reported the mean values of the yield
(%) of the final products and the degree of substitution (DS) expressed as the mean number
of (meth)acryloyl group present in every repeating unit.
The reaction of Ulvan with organic chemical precursors is not straightforward because
partially hampered by its insolubility in the common organic solvents. This compels its
modification under heterogeneous and not favourable conditions as the ones reported in
Figure 5. Also the aggregative behaviour of Ulvan in aqueous solutions limits its “reactive
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