Thermoplastic elastomers based on lactide and caprolactone: The influence of chain microstructure on surface topography and subsequent interaction with cells

Abstract

Surface biophysical properties of biomaterials, including surface topography and roughness, determine the interaction of a biomaterial with the surrounding cells, tissues and organs once implanted in the human body. Herein, the surface topography of thermoplastic copolymers based on lactide and caprolactone showing elastomeric behaviour was modulated by precisely controlling the chain microstructure (i.e., distribution and length of the repetitive units within the polymeric chain). The synthesized copolymers were subjected to different thermal treatments from the melt, leading to polymeric films with various surface textures and roughness values. Copolymers synthesized with triphenyl bismuth as a catalyst, with a more random distribution of the repetitive units, showed limited crystallization capability. Accordingly, only the copolymer with higher amount of l-lactide (i.e., 80 wt%) subjected to an isothermal treatment from the melt at 70 °C was able to crystallize, and spherulites of around 7 μm were discernible by atomic force microscopy. In contrast, the copolymers synthesized with stannous octoate, which had a more blocky nature, showed axialitic crystalline domains at the submicron-to nanoscale when subjected to an isothermal treatment from the melt at 50 °C, whereas well-defined spherulites of sizes up to 14 μm were obtained at 70 °C. Human fibroblast showed a more elongated morphology when seeded on those samples having higher roughness values and larger spherulites, whereas they had a more spread morphology when seeded on the amorphous, smooth surfaces. As concluded from the present study, by precisely controlling the chain microstructure of the synthesized copolymers, a wide variety of surface topographies can be obtained, which has a clear impact on the way the biomaterial interacts with cells. This opens the possibility to study the influence of surface biophysical properties on more complex cell processes in the future, including inflammatory or foreign body response processes.