Drug releasing behavior of hybrid micelles containing polypeptide triblock copolymer.

We report a new type of hybrid polymeric micelles for drug delivery applications. These micelles consist of PLGA (PLGA: poly(l-glutamic acid)) and PEG (PEG: polyethylene glycol) mixed corona chains. In acidic condition, PLGA undergoes a transformation from water-soluble random coils to water-insoluble alpha-helix, leading to microphase separation in micelle coronas and formation of PEG channels. These channels connect the inner core and the outer milieu, accelerating the diffusion of drugs from micelles. The micelles were prepared through a co-micellization of PLGA-b-PPO-b-PLGA (PPO: poly(propylene oxide)) and PEG-b-PPO in water. During the self-assembly, the PPO blocks of both block copolymers aggregated into cores that were surrounded by mixed corona chains of PLGA and PEG blocks. We confirmed this structure by using a number of characterization techniques including nuclear magnetic resonance spectroscopy, zeta potential, circular dichroism, and dynamic light scattering. We also performed molecular dynamics (MD) simulations to verify the models of the hybrid micelle structure. One advantage of the hybrid micelles as drug carriers is their tunable release rate without sacrificing colloidal stability. The rate can be tuned by either micelle structures such as the composition of the mixture or external parameters such as pH.