Effect And Mechanism Of Sinusoidal Electromagnetic Field Combined With Tissue Engineering Technology To Accelerate Bone Regeneration

Objective:The repair of critical-sized bone defects is always a challenging problem.Electromagnetic fields(EMFs),used as a physiotherapy for bone defects,have been suspected to cause potential hazards to human health due to the long-term exposure.To optimize the application of EMF while avoiding its adverse effects,a combination of EMF and tissue engineering techniques is critical.Furthermore,a deeper understanding of the mechanism of action of EMF will lead to better applications in the future.Methods:In this research,the porous composite scaffolds were fabricated by 3D printing using polycaprolactone(PCL)and hydroxyapatite(HA)as raw materials,and the scaffolds modified with polydopamine were used as cell carriers.CCK-8 kit and Live/Dead staining kit were used to determine the biocompatibility of the scaffolds.Then the morphology and distribution of cells on the PCL/HA scaffold were observed under scanning electron microscope(SEM)and confocal microscope. Subsequently,bone marrow mesenchymal stem cells(BMSCs)seeded on 3D-printed scaffolds were treated with sinusoidal EMF in vitro.The osteogenic ability of BMSCs was detected by staining,PCR,Western Blot,immunofluorescence staining and other methods.In the animal experiments,the spinal fusion model was constructed by removing the tail vertebral disc of rats and implanting the cell-scaffold.At the same time,another group of rats were used to construct a critical-sized calvarial defect model with a diameter of 5.5mm.The bone tissue regeneration was observed and analyzed by imaging and histological methods.In addition,the molecular and cellular mechanisms by which EMFs regulate BMSCs were explored with various approaches to gain deeper insight into the effects of EMFs.Results:PCL/HA scaffolds modified by polydopamine possess not only good mechanical properties but also excellent biocompatibility.BMSCs can grow healthily on the scaffolds.In addition,EMF does not affect the morphology and proliferation of cells.The cell-scaffolds treated with EMF successfully accelerated caudal intervertebral fusion and the repair of critical-sized calvarial defects in vivo. Further studies revealed that EMF could not directly induce the differentiation of BMSCs but improved the sensitivity of BMSCs to BMP signals by upregulating the quantity of specific BMP(bone morphogenetic protein)receptors.Once these receptors receive BMP signals from the surrounding milieu,a cascade of reactions is initiated to promote osteogenic differentiation via the BMP/Smad signaling pathway.Moreover,the cytokines secreted by BMSCs treated with EMF can better facilitate osteogenesis,angiogenesis and osteoimmunomodulation which play fundamental roles in bone regeneration.Conclusion:In summary,PCL/HA scaffolds with polydopamine surface modification have good mechanical properties and biocompatibility.EMF(15 Hz,0.3 m T)combined with tissue engineering successfully accelerated intervertebral fusion and the repair of critical-sized calvarial defects in rats.EMF can promote the osteogenic potential of BMSCs and enhance the paracrine function of BMSCs to facilitate bone regeneration.These findings highlight the profound impact of EMF on tissue engineering and provide a new strategy for the clinical treatment of bone defects.