Core–shell biopolymer microspheres for sustained drug release

In this work, a core–shell biopolymer microsphere comprising a carvedilol-loaded yeast cell wall polysaccharides core surrounded by a silk fibroin shell layer is developed to eliminate the risks of using synthetic polymers for drug encapsulation on human health and to avoid burst release and to prolong the release time. Transmission electron microscopy, Fourier-transform infrared, confocal laser scanning microscope, and phase contrast microscopy analysis indicate that yeast treated with Tris–HCl containing cetyltrimethylammonium bromide, EDTA, and NaCl could provide much larger space for host drug as compared to plasmolyzed cells because the former can help maintain the original shape of yeast cells. In addition, its permeability barrier is significantly altered and nucleus becomes pyknotic. In contrast, plasmolyzed cells can hardly maintain the rigidity and integrity of their cell walls and will finally end up with cell fragments. SEM observation reveals that the carvedilol-loaded cells maintain very similar shape and size before and after coating with 0.1% silk fibroin. In vitro release studies show that a drug delivery system using the carvedilol-loaded cells can achieve a sustained drug release up to 20 days probably due to the electrostatic interaction between the positively charged carvedilol and the negatively charged yeast cells at the pH 7.4 and to the stability of the yeast cell helped by silk fibroin that provides an effective diffusion barrier. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41782.