Fabrication And Characterization Of PLA/β-TCP/Si Microsphere-based Scaffold For Bone Repair

The autogeneic graft is still the gold standard for bone reconstruction, however there are not enough donors available and the patient have to suffer from the required surgery. There are also problems for allograft and xenograft since it is likewise difficult to obtain those materials due to low availability, as well as the risk of disease transfer and morbidity. Therefore, the development of biomimetic materials with similar structural and chemical properties to those of natural bone became one of the hottest topics in bone engineering. So far, different bone reconstruction materials have been developed in the world, however, the properties of those materials need to be improved further for using in clinic. With the developing of modern bionic technologies, it is necessary to fabricate the novel biomimetic bone materials with suitable properties for clinical applications.As previously discovered, silicate is one of the necessary nutritional components for vertebrate. It deposits on the site within the body where the sclerocytes reside and proliferate, therefore promotes the growth of bone. If the silicate level is very low in vertebrate, it could cause growth deformation of bone.Siliceous sponge has a skeleton of silica, termed spicule, which is enzymatically synthesized by silicatein/enzyme under ambient temperature, pressure and near-neutral pH condition. The recombinant technology of silicatein had been developed by Prof. Miiller’s group from the University of Mainz, Germany, so it is possible to use the biomineralization mechanism of siliceous sponge spicules for the biomimetic applications. They demonstrated by experiments that biosilica can stimulate the growth of SaOS-2cells greatly, so biosilica-based bionic material is a potential bone repairing material with distinguished properties.In the paper, we fabricated a silicate-based microsphere scaffold which will be used as the carrier of silicatein for a bone substitution material. Selecting suitable concentrations of PLGA (poly-lactide-co-glycolide acide,75:25), large and uniform particle size of PLGA microspheres, termed PLGA/β-TCP/Si microsphere, were prepared by water/oil/water (W/O/W) double emulsification method. The PLGA microspheres consist of10%β-TCP (B-tricalcium phosphate) and10%silicate. Addition of a certain amount of PLGA/β-TCP/Si microspheres into a cylindrical stainless steel mold and addition of75%N-methyl-2-pyrrolidone (NMP; water solution) biolinker, the microsphere-based scaffolds were assembled.The microstructure of the PLGA/B-TCP/Si microspheres and microsphere-based scaffolds were studied by scanning electron microscopy (SEM). We found that the surface of microsphere and microsphere-based scaffolds are porous. This property is a proposition for cells to remain there and to proliferate. During the16days’culture of PLGA/B-TCP/Si microspheres in physiological saline, silicon ion released out of the PLGA/β-TCP/Si microspheres slowly, and hence no burst release. The accumulated release amount of silicon ion is about10%during this period studied. Because β-TCP and silicate are trapped into the PLGA/β-TCP/Si microspheres, the degradation rate of the PLGA scaffolds made by the PLGA/Si and PLGA/β-TCP/Si microspheres was increased. The cytotoxicity of PLGA/β-TCP/Si microsphere-based scaffold was evaluated using a extraction method as follows. The scaffold was incubated in McCoy’s5A medium (15%serum) at37℃while rotating at a rate of90rpm for24hours to get the extraction solution as the medium used for the cultivation of SaOS-2cells. After24hours, SaOS-2cells still grow well, that means there is no toxicity for the PLGA/β-TCP/Si microsphere-based scaffold. Furthermore, the scaffolds incubated with SaOS-2cells overnight were cultured for one week, and it was found that SaOS-2cells grew likewise well together with the PLGA/β-TCP/Si microsphere-based scaffold showing that this material is biocompatible. This scaffold can be used as a carrier of bioactive materials or factors to be used as bone substitution material.In conclusion, a series of tests were performed to assess the physico-chemical properties and biological properties of PLGA/β-TCP/Si microsphere-based scaffold. It is confirmed that this scaffold material is a3D scaffold material with porous structure and distinguished properties (biocompatible, biodegradable, moldable and hardening in situ). We propose that PLGA/β-TCP/Si microsphere-based scaffold can be used as biomedical bone substitution material and might have the potential to be used widely in clinic.