Formation of micro/nanoparticles and microspheres from polyesters by dispersion ring-opening polymerization

The micro/nanoparticles and microspheres of polyesters derived from the heterocyclic monomers of lactide (L,L or D,L), ε-caprolactone, and glycolide have received significant interest as drug carriers for biomedical applications. This review focuses on the recent advances in the study of polyester-based micro/nanoparticles and microspheres derived from the dispersion ring-opening polymerization (ROP) of heterocyclic monomers, and/or self-assembly of polyester macromolecules, and/or dialysis of polyester solution in water-miscible organic solvents against water. The dispersion polymerization of heterocyclic monomers in the presence of non-polar miscible solvents and amphiphilic polymer surfactant leads to the formation of polyester particles with a narrower size distribution. The use of the polymer surfactant is crucial in controlling the diameter, morphology, and stability of the polyester particles formed during the ROP. The polymer surfactant acts as a stabilizer and is bound to the polyester particles strongly and irreversibly to control the size and morphology of polyester microspheres. The properties of polyester particles are varied by controlling the number average diameter and diameter polydispersity index. Hence, in this article, we review different synthetic strategies developed for the formation of polyester based particles with controlled diameter of distribution and the factors influencing its formation such as structure of the polymer surfactant, critical micelle concentration of the surfactant, type of radical initiator/monomer used, reaction parameters, etc. The article also describes methods developed for transforming the polyester microspheres into the water for better biocompatibility and encapsulation of bioactive compounds, drugs, and proteins into the polyester particles and their potential release at the targeted specific site are reviewed.