Polyvinylpyrrolidone–polycaprolactone block copolymer micelles as nanocarriers of anti-TB drugs

A range of polyvinylpyrrolidone–polycaprolactone diblock copolymers with varying chain lengths were synthesized by Atom Transfer Radical Polymerisation (ATRP) using bromo-polycaprolactone as macroinitiator and copper(I) bromide/bipyridine catalytic system. The copolymers self-assembled in solution into core–shell micelles with sizes varying from 150 to 205 nm and critical micelle concentration of the order of 10⁻⁵ to 10⁻⁶ M. Front line anti-Tuberculosis drugs Rifampicin (RIF), Pyrazinamide (PZA) and Isoniazid (INH) were successfully encapsulated within the micelle hydrophobic core singly or in dual combination. The effect of length of hydrophobic and hydrophilic segments on drug loading, micelle size and drug release was investigated. Determination of binding constants showed that RIF binds more strongly to the micelle core than PZA and INH, leading to highest drug loading content. All drugs were released in vitro (PBS solution at 37 °C) in a sustained manner with zero-order kinetics and followed the order INH > PZA > RIF.