Synthesis of PEGylated chitosan
The synthesis of PEGylated chitosan (chitosan with grafted side
chains) was carried out as a two-step procedure involving the
synthesis of thiolated chitosan, followed by the conjugation of
polyethylene glycol di-acrylate (PEG-DA) to the thiolated
chitosan through the sulfide end group. This conjugation,
termed the Michael type addition reaction, occurs between
molecules carrying an electronegative vinyl end group such as
acrylate and electronegative neighboringgroups suchas sulfide.
The process of synthesizing thiolated chitosan was
adopted from Bernkop-Schnurch, Hornof, and Zoidl (2003).
In brief, 1 g of chitosan was dissolved in 1 l of 2% acetic–acid
aqueous solution. 0.4 g of 2-iminothiolane was added to the
solution while the pH was adjusted to 6.3. The reaction was
allowed to proceed for 24 h. The final product was dialyzed
using a cellulose tube having a 12–14 kDa molecular weight
cutoff against 5 mM HCl, two times against 5 mM HCl
containing 1% NaCl, once against 5 mM HCl, and finally, once
against 1 mM HCl. The final sample was lyophilized by drying
a frozen aqueous polymer solution at 30 8C and 0.01 mbar
and stored at 4 8C until further use.