Microfluidic Supported Emulsion Polymerization and In Situ Assemblies for Synthesis of Size and Shape-Tunable Soft Polymer Nanoparticles

Polymer particles are promising nanoscale materials for a wide range of applications in the field of biomedicine, sensing, and labeling. Controlled structural aspects of the polymer nanoparticles such as size, shape, surface topology, morphology, internal softness, interior cross-linking, and core composition determine their impact on the cargo loading capacity and controlled/sustained release, the possibility of endocytosis, and degradability during their biomedical application. The designed interfacial features, on the other side, such as stimuli-responsive surfaces, wrinkling, surface porosity, shell-layer swellability, layer-by-layer surface functionalization, surface charge, surface roughness, and textures regulate nanoparticles’ interfacial interactions, controlled assembly, movement and collision, and compatibility with the surroundings like a solvent and biological environments. These characteristics define polymer nanoparticles’ overall properties/functions based on homogeneity, stability, interfacial tension, and minimization of the surface energy barrier. If nanoparticles are not uniform in their size or shape, the resultant outcome may be significantly lower directly related to the concept of the structure-function relationship. Therefore, a key requirement is to produce well-defined and uniform polymer nanoparticles with controlled characteristics. However, because polymers are amorphous (or semi-crystalline), flexible, and soft materials, controlling their structural/interfacial features through the single-step process is a challenge. The microfluidic reaction strategy can provide the platform for homogeneous mixing of reactants and the production of uniform particles with controlled assemblies. Here, the state-of-the-art fundamental characteristics of the polymer nanoparticles are presented through experimental results. We have applied a semi-microfluidic approach where initial emulsification has been formed inside the microfluidic channel and the completion of polymerization together with their in-situ assemblies realized externally. In the case of utilizing molecular surfactants, the spherical polymer nanoparticles between the size range of 50 nm and 500 nm were obtained. Besides, we observed that the application of polyionic polyelectrolytes was the key driving force for initiating the in-situ assemblies of the growing polymer nanoparticles during polymerization to form the anisotropic structures. In this way, we created the library of the shape-controlled polymer nanoparticles in the form of ellipsoidal, dumbbell, elongated chain-like, branched-shape, and flower-shaped polymer nanoparticles.