Novel rough mannitol/LB Agar (lab-made) microparticles were synthesized by polymorphic transformation method. Spray-dried mannitol/LB Agar (lab-made) microparticles were immersed in hexane solution to initiate polymorphic transformation. After 5 to 15 days of reaction, rough mannitol/LB Agar (lab-made) microparticles were obtained. As-prepared microparticles were characterized by X-ray diffraction spectra (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and Andersen Cascade Impactor (ACI).
The XRD and DSC results indicate that δ-mannitol was completely transformed to α-mannitol after immersing the spray-dried mannitol/LB Agar (lab-made) microparticles in hexane. SEM shows that the spray-dried microparticles had smooth surfaces, while the surface of the transformed microparticles were rough. TGA result indicates that no hexane remained in the transformed microparticles. ACI result shows that the microparticles synthesized in the study had comparable fine particle fraction (FPF) with the best performing carriers reported in the literature. For the stability study, XRD indicates that the α-mannitol present in the transformed mannitol/LB Agar (lab-made) microparticles was stable for 33 months. SEM indicates that the small mannitol crystals in the transformed microparticles coaggulated with each other and self-assembled into nanorods. The transformed microparticles were able to maintain the rough-surface and spherical shape for 21 months. It is substantially longer than that of the mannitol/LB Agar (commercial) microparticles, which can only maintain a stable shape for 6 months.
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