Doxorubicin-loaded microgels composed of cinnamic acid–gelatin conjugate and cinnamic acid–Pluronic F127 conjugate

Microgels were prepared by cinnamic acid–gelatin (type B) conjugate (CA-GelB) and cinnamic acid–Pluronic F127 conjugate (CA-Plur). 1H NMR confirmed that CA was conjugated to gelatin and the gelatin to CA residue molar ratio was estimated to be 1:4.7 by a colorimetric method. CA-Plur of which the CA residue to Plur molar ratio was 1.2:1 was used as a thermo-sensitive polymer. The CA residues of CA-Plur/CA-GelB mixture were readily photo-dimerized to form microgels by UV irradiation. The isoelectric point of the microgel was found to be pH 5.8 and the hydrodynamic diameter decreased when the suspension temperature increased. The microgel could hardly retard the release of doxorubicin (DOX) at pH 3.0 and pH 5.0, but it could suppress and control the release at pH 7.4 possibly due to electrostatic attraction. Meanwhile, the release of DOX at pH 7.4 was less suppressed when the medium temperature was higher, possibly because of thermal thinning of Pluronic chain layer.