Preparation And Characterization Of Core-shell-structured Bioceramic Microspheres With Adjustable Degradability

It is still a great challenge in some clinical critical-sized bone repair due to mechanical damage or bone tumor resection. To find the ideal artificial materials for promoting bone regeneration and repair becomes the key research direction in the biomaterial science field. Thus, it is of specific significance to fabricate the highly bioactive materials with tailored degradation rate to match the rate of new bone regeneration.It is well known that the bioactive inorganic materials mainly include Ca-phosphate (CaP) ceramics and self-setting cements, bioactive glasses (BG) and glass-ceramics (BGC). It is generally agreed that the CaP ceramics have similar composition to the natural bone mineral, whereas they have low fracture strength and biodegrade slowly. Studies have proved that beta-tricalcium phosphate (P-Ca3(PO>4)2;(β-TCP) is bioactive and wollastonite (CaSiO3; CaSi) has a good biodegradable capacity. The degradation rate of these materials is respectively slower and faster than the rate of new bone regeneration. Due to the unique biodegradable properties of CaSi and β-TCP, we design the cor-shell-structured, spherical (hollow) CaSi@β-TCP or β-TCP@CaSi composite ceramics with adjustable degradability. The novel compositional distribution and microstructure of the biphasic bioceramic microspheres certainly will be of great significance in the study of bone regeneration and repair in situ.The experimental results and correlative conclusions are presented as follows:1. A series of hollow bioceramic microspheres with two or three shell layers were fabricated via alginate microsphere template and layer-by-layer coating technique. The Na2SiO3-alginate mixture hydrosol beads were firstly injected into the Ca(NO>3)2aqueous solution under mild stirring to form calcium silicate hydrate-coated alginate microspheres. The composite microspheres were dispersed into the beta-tricalcium phosphate (β-TCP)-containing alginate hydrosol and wollastonite (CaSiO3)-containing alginate hydrosol in turn while gently stirring. The microspheres were filtered, dried in vacuum and finally calcined at850℃for2h to obtain the multi-shell hollow bi-phase ceramic microspheres.2. In order to improve the mechanical properties of the microspheres, we adopted a novel microsphere preparative technique with a coaxial needle. We prepared bi-phase bioceramic microspheres with core-shell structure. Firstly, we prepared beta-tricalcium phosphate (β-TCP)-containing alginate hydrosol and wollastonite (CaSiO3)-containing alginate hydrosol. Then, the two hydrosol were put into different injectors and were injected at the same time into the Ca(NO3)2aqueous solution under mild stirring to form microspheres with core-shell structure. Finally, The microspheres were filtered, dried and finally calcined to obtain the bi-phase ceramic microspheres.In summary, the microspheres with multi-shell or core-shell structure were successfully prepared via an alignate-template and layer-by-layer coating technique. The microspheres were stable in morphology and structure. Besides, we can control the composition of different shells to control the rate of degradation. In the way, we can prepare scafford by the microspheres’close-pack which has interconnected channel. As the shell degrades, the channel spans with ion group freed into the microenvironment which is good for osteoblast migration, angiogenesis and new bone is reconstruction. The idea of the design of the multi-shell microsphere with adjustable degradability and high bioactivity is of great academic value, and the microspheres are hoped to used as drug carriers and artificial bone materials.