Tailorable Degradation of pH-Responsive All-Polyether Micelles: Unveiling the Role of Monomer Structure and Hydrophilic-Hydrophobic Balance

Abstract

Polymeric micelles have been widely used as ideal drug-delivery vehicles with unique advantages. However, fine tuning of the degradation rates of micelles over a wide time frame remains challenging. Herein, we designed and synthesized a novel pH-responsive, hydrophobic epoxide monomer, tetrahydrofuranyl glycidyl ether (TFGE), carrying an acetal group as a cleavable linkage. The hydrolysis kinetics of TFGE was carefully evaluated with representative functional epoxide monomers, such as 1-ethoxyethyl glycidyl ether and tetrahydropyranyl glycidyl ether, via in situ H-1 NMR spectroscopy and quantum mechanical calculations. Interestingly, the hydrolysis kinetics and the associated energy barrier were closely related not only to the cyclic/acyclic structure of the monomers but also to their hydrophobicity. Subsequently, a series of amphiphilic block copolymers (mPEG-b-PTFGE) were synthesized via anionic ring-opening polymerization and the self-assembled polymeric micelles were evaluated with respect to critical micelle concentration, encapsulation efficiency, drug release, and cell viability. Most notably, the release kinetics of the model compound from polymeric micelles exhibited a different trend, confirming the critical role of hydrophobicity in governing the pH-responsive hydrolysis of the polymeric micelles. This study provides new insights applicable to the design of functional monomers for tailoring the release profiles of polymeric micelles for smart drug delivery.