Investigation of the self-assembly of CS and PCL copolymers with different molecular weights in water solution by coarse-grained molecular dynamics simulation

Abstract

Coarse-grained molecular dynamics (CGMD) simulation was employed to investigate how stable chondroitin sulfate-graft-polycaprolactone (CS-PCL, CP) copolymers self-assemble into micelles in an aqueous environment. Three types of CP containing low (2.4%), medium (6.3%), and high (18.7%) PCL contents (denoted L-CP, M-CP, and H-CP, respectively) in which PCL molecules consisting of 63 monomers were grafted onto each CS molecule consisting of 120 monomers were considered. L-CP and M-CP were found to display spheroidal micellar structures, while H-CP presented a rod-like structure, in agreement with previous experimental observations. In addition, the entanglement of the PCL segment increased as its molecular weight was increased. The number density distribution profiles of PCL, CS, and water molecules indicated that there were a few water molecules between the PCL core of the micelle and the water solution surrounding the micelle (in the micelle layer immediately above the core), and the number density of water in the CP micelle increased as the PCL content decreased. Using the radius of gyration, the three-dimensional conformations of the micelles were explored. When the number of CP chains was 3, H-CP adopted a long nanorod form, whereas L-CP and M-CP were roughly nanospherical. When the number of CP chains was increased beyond 3, however, the structure of L-CP changed from a nanosphere to a nanodisk. Finally, the slope of the mean square displacement profile was greatest when the molecular weight of the PCL segment was lowest, indicating that the mobilities of the CS and PCL segments are highest in L-CP. The self-diffusion coefficients of the CS and PCL segments decreased as the number of PCL segments grafted increased. Graphical abstract Morphologies of H-CP micelle.