Preparation And Characterization Of Multilayer Core-shell-structured Bioceramic Composite Microspheres

The regeneration and repair of the pathological bone defect is still a great challenge in clinic. The spherical particles exhibit good flowability and fully interconnected pore network in the closed packed sphere systems, so that the bioceramic microsperes are favorable for conducting and enahncing bone regeneration.Herein, a facile, convenient, and versatile approach to fabricate multilayer core-shell-structured bioceramic microspheres is developed. This strategy is based on a general fluid controlling system and free separation mechanism through a coaxially aligned multi-capillary terminal. As expected, the bioceramic microspheres exhibit core-shell architectures, and the biphasic bioceramic compositions and bioceramic interface is obviously distinguished by SEM observation and energy dispersive X-ray (EDX) microanalysis. The critical factor in influencing slurry bead size is the drying process, and meanwhile increasing sintering temperature leads to reduction of bead size, but the spherical morphology is maintained well after high-temperature sintering. To probe the early-stage bio-dissolution and biologically active ion release behavior, an immersion test release is investigated in Tris buffer at 37℃ for the double-shell bioceramic spheres with different core and shell chemical compositions. As expected, the bioceramic microspheres with β-TCP external shell layer show a slower weight loss and inorganic ion release than those with β-CaSiO3 external shell layer.When monodisperse polystyrene (PS) microbeads (～15μm) are pre-mixed into the shell bioceramic slurry, the tailorable porous structures can be introduced into the different shell layers after sintering treatment. The results of in vitro degradation exhibited that the porous microstructures have a great influence on the rate of degradation.In order to show great potential in the fabrication of multilayer bioceramic microspheres with tunable composition distribution in different layers, we also employ the 13-93 BG and dilute magnesium doping into CaSi phase to demonstrate the universtal potential of the systems. The SEM micrographs with progressively increasing magnifications confirmed that the 13-93 BG could be distributed in any layer of the double-shell, core-shell-strcutured spheres, similar to the other two CaP or CaSi phases. In addition, the experimental results of the weight loss and ion release show great differences among bioceramic microspheres with different components in different shell or core layers.In conclusion, this new strategy has been demosntrated to readily fabricate a variety of multilayer core-shell-structured porous bioceramic microspheres for a range of applications such as tissue engineering and drug delivery.