Encapsulation of Curcumin in Polystyrene-Based NanoparticlesDrug Loading Capacity and Cytotoxicity

Nanoparticles made of amphiphilic block copolymers are commonly used in the preparation of nano-sized drug delivery systems. Poly­(styrene)–block–poly­(acrylic acid) (PS–PAA) copolymers have been proposed for drug delivery purposes; however, the drug loading capacity and cytotoxicity of PS–PAA nanoparticles are still not fully recognized. Herein, we investigated the accumulation of a model hydrophobic drug, curcumin, and its spatial distribution inside the PS–PAA nanoparticles. Experimental methods and atomistic molecular dynamics simulations were used to understand the molecular structure of the PS core and how curcumin molecules interact and organize within the PS matrix. The hydrophobic core of the PS–PAA nanoparticles consists of adhering individually coiled polymeric chains and is compact enough to prevent post-incorporation of curcumin. However, the drug has a good affinity for the PS matrix and can be efficiently enclosed in the PS–PAA nanoparticles at the formation stage. At low concentrations, curcumin is evenly distributed in the PS core, while its aggregates were observed above ca. 2 wt %. The nanoparticles were found to have relatively low cytotoxicity to human skin fibroblasts, and the presence of curcumin further increased their biocompatibility. Our work provides a detailed description of the interactions between a hydrophobic drug and PS–PAA nanoparticles and information on the biocompatibility of these anionic nanostructures which may be relevant to the development of amphiphilic copolymer-based drug delivery systems.