Polymer Prolate Spheroids, Ellipsoids, and Their Assemblies at Interfaces-Current Status and Perspectives

Most nanoparticles and microparticles used as carriers of bioactive compounds are spherical in shape. Such particles are the easiest to obtain, as many processes spontaneously minimize the surface energy of the objects produced. However, in recent years, scientists have turned their attention to non-spherical particles in the hope of obtaining particles that interact with their environment in a tailored manner. The production of such particles should be easy and reproducible. The best candidates are spheroids produced by various methods. The most often used is the linear transformation of spheres during processes that preserve constant particle volume. The typical process consists of stretching a polymer matrix filled with spherical particles. The article delivers a critical overview of methods, discussing their advantages and disadvantages. A list of presented methods also includes the preparation of spheroids by polymer solution emulsification-solvent evaporation, controlled dispersion polymerization, electrohydrodynamic jetting, adsorption of amphiphilic copolymers on solid particles, and copolymer self-organization processes, as well as microfluidic methods, deformation of spherical particles into spheroids by irradiation, and phase microseparation. A special section is devoted to the self-organization of the particles at the phase boundaries. Eventually, the preparation and selected properties of two-dimensional and three-dimensional assemblies of spheroidal particles, particularly the preparation of a quasi-nematic colloidal crystal, are discussed.