Ultrasonicate-assisted preparation of eumelanin-loaded nano/microparticles based on polylactide stereocomplex

The utilization of ultrasonication in the preparation of polymeric nano/microparticles has attracted vast attention due to its simplicity with low cost and high energy efficiency. The occurrence of acoustic cavitation generated by the ultrasonication process can enhance droplet disintegration, allowing the improved stability of emulsions. In this study, eumelanin-loaded nano/microparticles were prepared by employing polylactide stereocomplex (sc-PLA) formed by blending of poly(D-lactide-caprolactone-D-lactide), P(DLA-b-CL-b-DLA), triblock copolymer with linear poly(L-lactide), PLLA. The particles were prepared through an oil in water emulsion (O/W) technique followed by a solvent evaporation. The effect of ultrasonication on the encapsulation efficiency and physicochemical properties of the nano/microparticles was evaluated. The results showed that ultrasonication treatment could control nano/microparticles' shape, size, and size distribution, which enhanced the particle stability and the entrapment efficiency of eumelanin. Particle size distribution of ultrasound-assisted nano/microparticles was in a range of 0.38–135 μm, while those without ultrasonication had a broader distribution from 0.38–153 μm. Higher zeta potential was also observed in the ultrasound-assisted nano/microparticles, reflecting their higher suspension stability. The ultrasonication treatment led to higher eumelanin encapsulation efficiency (46.6%) with higher thermal stability and crystallinity, promoted by the formation of higher contents of the stereocomplex crystallites. The results confirm that ultrasonicate-assisted emulsification can be effectively used to fabricate the functional eumelanin-loaded nano/microparticles.