Controlled Release of Ropivacaine from Single-Armed (1-PCL) and Four-Armed PCL (4-PCL) Microspheres

Sustained release of anesthesia has shown great promise in the treatment of chronic pain in patients. In this research, we used neutralized ropivacaine as an anesthesia and poly(ε-caprolactone) (PCL) with different architectures to systematically study how these architectures affect the release of ropivacaine. After optimizing the parameters of the preparation of microspheres, ropivacaine-loaded 1-PCL microspheres and 4-PCL microspheres were obtained. Fourier Transform infrared spectra (FT-IR) and X-ray diffraction spectra (XRD) confirmed that ropivacaine was encapsulated within the microsphere rather than inserted on the surface of the microsphere. Ropivacaine was found to be buried deeper in the 1-PCL microsphere than in the 4-PCL microsphere. In vitro release assay revealed that small crystalline grains interfered with ropivacaine release in 4-PCL microspheres during the initial release period, but then two kinds of microspheres showed a similar ropivacaine release rate. We basically proved that the architecture of PCL has a negligible effect on ropivacaine release. Cell proliferation test revealed that the release of products from the microspheres resulted in insignificant toxicity towards mammalian cells.