Temperature/pH Responsive Hydrogels Based on Poly(ethylene glycol) and Functionalized Poly(e-caprolactone) Block Copolymers for Controlled Delivery of Macromolecules.

Purpose: To assess the potential of triblock copolymers based on poly(ethylene glycol) (PEG) and functionalized poly(ε-caprolactone) as temperature/pH responsive gels for controlled delivery of macromolecules.

Methods: Poly(α-carboxylate-co-α-benzylcarboxylate-ε-caprolactone)-PEG-poly(α-carboxylate-co-α-benzylcarboxylate-ε-caprolactone) (PCBCL-PEG-PCBCL) was synthesized through ring opening polymerization of α-benzyl carboxylate-ε-caprolactone by PEG, followed by 30% debenzylation of the lateral blocks. The effect of Tris buffer and pH on the sol-gel transition temperature of PCBCL-PEG-PCBCL was assessed. The temperature/pH responsive release of tetramethylrhodamine-dextran (TMR-D) (10 and 40 kDa) from PCBCL-PEG-PCBCL was investigated.

Results: Replacement of water with Tris buffer reduced PCBCL-PEG-PCBCL sol-gel transition temperature. Thermo-reversible hydrogels were only formed at pHs ≥ 5.0, but PCBCL-PEG-PCBCL transition temperature was not affected by pH above pH 5.0. In contrast to Pluronic F127 that released 100% of TMR-D within 2 h, PCBCL-PEG-PCBCL hydrogel controlled TMR-D release efficiently at pH = 7.4 and 37°C (~27 and 11% TMRD 10 and 40 kDa release within 150 h, respectively). At 50°C or pH = 9.0, TMR-D release was increased slightly, while at room temperature or pH = 5.0, no control over TMR-D release was observed by PCBCL-PEG-PCBCL hydrogel.

Conclusion: PCBCL-PEG-PCBCL hydrogel provides depot release of macromolecules at physiological conditions. This release can be triggered through changes in the temperature or pH.