Monodispersed sirolimus-loaded PLGA microspheres with a controlled degree of drug-polymer phase separation for drug-coated implantable medical devices and subcutaneous injection

Monodispersed sirolimus (SRL)-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres with a diameter of 1.8, 3.8 and 8.5 μm were produced by high-throughput microfluidic step emulsification - solvent evaporation using single crystal silicon chips consisted of 540-1710 terraced microchannels with a depth of 2, 4, or 5 μm arranged in 10 parallel arrays. Uniformly sized droplets were generated over 25 h across all channels. Nearly 15% of the total drug was released by the initial burst release during an accelerated drug release testing performed at 37 °C using a hydrotropic solution containing 5.8 M N,N-diethylnicotinamide. After 24 h, 71% of the drug was still entrapped in the particles. The internal morphology of microspheres was investigated by florescence microscopy using Nile Red as a selective fluorescent stain with higher binding affinity toward sirolimus. By increasing the drug loading from 33 wt% to 50 wt%, the particle morphology evolved from homogeneous microspheres, in which the drug and polymer were perfectly mixed, to patchy particles, with amorphous drug patches embedded within a polymer matrix to anisotropic patchy Janus particles. Janus particles with fully segregated drug and polymer regions were achieved by pre-saturating the aqueous phase with organic solvent which decreased the rate of solvent evaporation and allowed enough time for complete phase separation. This approach to manufacturing drug-loaded monodisperse microparticles can enable the development of more effective implantable drug delivery devices and improved methods for subcutaneous drug administration, which can lead to better therapeutic treatments.