A difference between F4 and F5/F6 is that the core-shell structures of the latter can be clearly seen in the projection of the core from the shell. This is thought FHPI molecular weight to be associated with the increase of drug content, which makes the nanofibers brittle. The higher contents of quercetin in the shell of fibers F5 and F6 made them easier to fracture, and thus the core projects a little from the shell after breaking. TEM images of fibers F2, F4, F5, and F6 are shown in Figure 5. The uniform contrast of F2 suggests that the quercetin is distributed in the EC matrix at the molecular level, with no aggregates (Figure 5a). Fibers F4, F5, and F6 have evident core-shell structures (Figure 5b,c,d).

Except for the heterogeneous region in the shell of F6 (see Figure 5d), no nanoparticles were observed in the three core-shell fibers, indicating uniform structures. The heterogeneous region in Figure 5d may be the result of a migration of the core components to the shell, or phase separation may have happened within the shell due to the high quercetin content in F6. Figure 5 TEM images. (a) F2, (b) F4, (c) F5, and (d) F6. Physical state of quercetin XRD analyses were conducted to determine the physical status of

the drug in the nanofibers. Quercetin, a yellowish green powder to the naked eye, comprises polychromatic crystals in check details the form of prisms or needles. The crystals exhibit a rough surface under cross-polarized light (Figure 6a). The data in Figure 6b show the presence of numerous distinct Bragg reflections in the XRD pattern of pure quercetin, demonstrating

its existence as a crystalline material. The PVP and EC diffraction patterns Chorioepithelioma exhibit a diffuse background with two diffraction haloes, showing that the polymers are amorphous. The patterns of fibers F2, F4, F5, and F6 show no Bragg reflections, instead consisting of diffuse haloes. Hence, the composite nanofibers are amorphous, and quercetin is not present as a crystalline material in the fibers. Figure 6 Physical form investigation. (a) Crystals of quercetin viewed under cross-polarized light and (b) XRD patterns of the raw materials and nanofibers. These results concur with the SEM and TEM observations. No crystalline features are observed for any of the nanofibres. The heterogeneous region in Figure 5d is thus thought unlikely to be because of the recrystallization of quercetin, but most probably this anomaly comprises a composite of the drug and PVP with a higher concentration of quercetin than its surroundings. In vitro drug release profiles The in vitro drug release profiles of the four different nanofibers are given in Figure 7. As anticipated, the monolithic nanofibers F2 (containing only quercetin and EC) exhibited a sustained release AZD2281 nmr profile as a result of the poor water solubility of quercetin and the insolubility of EC. In contrast, the core-shell fibers F4, F5, and F6 showed an initial burst release of 31.7%, 47.2%, and 56.