Effects of dextran sulfate and gelation conditions on simvastatin encapsulation in chitosan-coated alginate microspheres

摘要

Introduction: Simvastatin is a promising drug candidate for the treatment of wear particle-induced implant aseptic loosening due to its anti-inflammatory property as well as its ability to stimulate bone growth and inhibit bone resorption. Chitosan-coated alginate microspheres have been used as a drug delivery system for simvastatin. However, simvastatin encapsulation has been limited, mainly due to its leakage during microsphere synthesis. Therefore, the objective of the present study was to increase simvastatin encapsulation in chitosan-coated alginate microspheres by adding dextran sulfate to the alginate solution and/or varying the gelation conditions used for the microsphere synthesis (e.g., volume of gelation medium, curing time, and addition of simvastatin in the gelation medium). Materials and Methods: Simvastatin was activated and complexed with 2-hydroxypropyl-β-cyclodextrin (HP-βCD), as previously described, to increase its solubility in alginate. The simvastatin-HP-βCD solution (containing 26 mM simvastatin) was then mixed with the alginate solution containing dextran sulfate at different concentrations, followed by extrusion in a 60-mL solution of 5% (w/v) CaCl_2-0.1 % (w/v) chitosan using a customized extrusion pump (final concentrations in the microspheres: 3% [w/v] alginate, and 0.5,1.5 or 2.5% [w/v] dextran sulfate). After 15-min curing time, the synthesized microspheres were dissolved in 1 M NaOH, followed by centrifugation and UV absorbance measurement of the supernatant at 238 nm to measure simvastatin encapsulation efficiency (EE). Finally, the effects of the gelation medium volume (60,30 and 20 mL), curing time (15 and 5 min), and the addition of simvastatin in the gelation medium (0.263 mM based on maximum solubility) were determined using microspheres containing the previously optimized dextran sulfate concentration (giving maximum EE). Statistical analysis was performed using one-way ANOVA and Tukey Kramer tests. p＜0.05 was considered significant Results and Discussion: Dextran sulfate at 1.5% (w/v) significantly increased simvastatin EE, up to 14.0% (p＜0.001) (Table 1). This increase may be due to a denser polymer matrix resulting from electrostatic interactions between the anionic alginate-dextran sulfate mixture with the cationic chitosan. The lower concentration of dextran sulfate (0.5% [w/v]) did not have any effect, and the higher concentration (2.5% [w/v]) significantly decreased simvastatin EE (p=0.009), likely because of the increase in the initial polymer solution viscosity limiting the extrusion procedure. The volume of the gelation medium and the curing time did not affect simvastatin EE. However, the 5-min gelation time led to a higher variability in the EE results. Finally, simvastatin EE significantly increased up to 22.4% when simvastatin was added to the gelation medium (p=0.001), likely because of a decrease in the diffusion of simvastatin out of the microspheres. Conclusion: The addition of dextran sulfate (at a final concentration of 1.5% [w/v] in the microspheres) and the addition of simvastatin in the gelation medium led to an increase in simvastatin EE in chitosan-coated alginate microspheres. Future studies include the analysis of simvastatin release kinetics from the synthesized microspheres.