| Objective:The treatment cycle of bone defect is long,and it takes at least 3 months to form a more mature bone tissue.In the process of healing and repair,angiogenesis precedes bone formation,and the early formation of blood vessels plays an important role in the later osteogenic differentiation.In the current clinical treatment,it has been recognized by many researchers by promoting early angiogenesis and accelerating bone tissue regeneration.The aim of this study is to prepare microspheres with core-shell structure by coaxial electrostatic spray of PLGA and SF.This drug delivery system combines with the treatment mode of bone defect,and encapsulates the angiogenic drug tetramethylpyrazine and icariin in the shell and nuclear layer of the microsphere,respectively.By releasing tetramethylpyrazine and icariin in turn,increasing the local accumulation of angiogenic drugs and osteogenic drugs,promoting the early angiogenesis of bone defects and later osteogenesis,so as to achieve the purpose of treatment.Methods:In this study,PLGA and SF were dissolved in HFIP organic solvent as shell solution and nuclear layer solution,respectively.SF/PLGA core-shell microspheres were prepared by coaxial electrostatic spray,and the optimal preparation parameters were found by single factor control variable method.Tetramethylpyrazine and icariin were added into shell solution and nuclear layer solution respectively,and core-shell drug-loaded microspheres were prepared under the optimal preparation parameters.The morphology and core-shell structure of the microspheres were characterized by SEM and LSCM.The physical properties,drug loading properties,in vitro degradation and drug release were studied.CCK-8 method was used to evaluate the cytocompatibility of unloaded microspheres and drug loaded microspheres by detecting the proliferation and toxicity of BMSCs and HUVECs.Results:1.By exploring the effects of various parameters on the morphology of the core-shell microspheres,the optimal concentration ratio of PLGA and SF solution for the preparation of the core-shell microspheres is 4%(w/v): 1%(w/v),and the optimal process parameters are: receiving distance 20 cm,applied voltage 12.5k V,shell flow rate1 m L/h,core flow rate 0.1m L/h.Characterized by SEM,it was found that the no-loaded core-shell microspheres and drug-loaded microspheres prepared under these conditions had smooth surface and good monodisperse particle size.The existence of core-shell structure of microspheres was indirectly proved by LSCM.2.The contact angles of drug-loaded microspheres and drug-loaded microspheres were measured: the contact angles of drug-loaded microspheres and drug-loaded microspheres were(124.5 ± 1.49)° and(78.24 ± 3.94)° respectively.The water absorption of unloaded microspheres and drug-loaded microspheres were calculated: the results were(87.30 ± 5.51)% and(112.87 ± 6.82)%,respectively.The entrapment efficiency and drug loading rate of tetramethylpyrazine and icariin in core-shell microspheres were(45.3 ±3.13)% and(0.314 ± 5.62)%,(65.5 ± 2.67)% and(0.13 ±4.47)%,respectively.3.The results of in vitro degradation experiments showed that at the initial stage of degradation,the microsphere matrix swelled by water absorption,pores began to appear on the surface of the shell and expanded into pieces,and the loose and porous nuclear layer was exposed,and gradually collapsed and broken into small blocks and powders.until it disappears completely.4.The results of drug release experiment in vitro showed that the drug release performance of drug-loaded microspheres was stable,and with the gradual degradation of SF and PLGA in core-shell layer,tetramethylpyrazine loaded in shell layer and icariin loaded in core layer were sequentially released.In the third month,the release of tetramethylpyrazine from the shell reached nearly 90%,and the release of icariin from the nuclear layer reached 80%,and the drug release was still in progress.5.The cell experiment in vitro showed that the cell proliferation rate of the drug-loaded microsphere group was higher than that of the unloaded microsphere group in 5 days,because the angiogenic drugs loaded on the shell of the drug-loaded microsphere were released in the early stage.Therefore,the proliferation effect of HUVECs group was significantly higher than that of BMSCs group(P<0.05).There was no significant difference in cell proliferation between the empty microsphere group and the blank control group,indicating that the microsphere had no cytotoxicity.There was no inhibitory effect on cell proliferation(P>0.05).Both empty core-shell microspheres and drug-loaded core-shell microspheres had good cytocompatibility.Conclusion:In summary,SF/PLGA core-shell microspheres with round and smooth surface and uniform particle size were prepared by coaxial electrostatic spray,and the optimal preparation parameters were obtained.Combined with the treatment mode of bone defect,this study successfully constructed a core-shell microsphere drug delivery system with tetramethylpyrazine in shell and icariin in nuclear layer.Compared with empty microspheres,the addition of drugs changed its hydrophilicity.In vitro experiments,the drug-loaded microspheres with high drug entrapment efficiency and drug loading rate showed slow drug release for up to three months,and had good biodegradability and cytocompatibility.Therefore,the research and preparation of this drug delivery system with double step release has potential application value and clinical significance in the treatment of bone defects and biomedical applications. |
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