Facile synthesis of calcium carbonate/polyacrylic acid hydrogels for pH-responsive delivery of cytarabine

Cytarabine (Cyt) encapsulated calcium carbonate (CaCO₃) nanospheres were facilely synthesized through a simple co-precipitation method, and the Cyt encapsulated CaCO₃ nanospheres (CaCO₃/Cyt) were modified by polyacrylic acid (PAA) hydrogels through in situ polymerization of acrylic acid (AA) monomer on the surface of the CaCO₃/Cyt. Successful preparation of the Cyt loaded CaCO₃/PAA hydrogels were confirmed by the characterization of SEM, TEM and FT-IR. Premature release of Cyt in acidic medium (pH = 1.2) could be effectively circumvented by the introduction of the PAA hydrogels. More importantly, pH-responsive delivery of Cyt from the as-prepared CaCO₃/PAA hydrogels could be achieved due to the pH-sensitivity of the PAA. Although the highest swelling ratio of PAA was obtained at pH 7.3 (27.7), the highest cumulative release of Cyt from the carrier was achieved at pH 5.3 (86.75%), which might be attributed to the high stability of CaCO₃ at pH 7.3. That is to say, the highest cumulative release of Cyt at pH 5.3 was a compromise by considering the relatively high swelling ratio of PAA and the relatively low stability of CaCO₃.