Effects Of Magnetic Liquid Metal Scaffolds With Dynamic Stiffness On Osteogenic Differentiation Of MSCs And Bone Repair

Stiffness of bone tissue engineering scaffold is one of the important factors affecting the osteogenic differentiation of stem cells and bone regeneration.a biomimetic matrix stiffness has a positive effect on bone regeneration.Recently,a variety of scaffolds with static stiffness matching bone tissue were applied to bone repair,but these studies neglected the microenvironment of bone repair is highly dynamic.From callus formation to tissue mineralization,the stiffness of the defect site increases continuously,so the scaffolds with static stiffness are difficult to provide an ideal biomimetic mechanical microenvironment,and the scaffolds with dynamic stiffness are obviously more attractive than those with static stiffness.This study prepared magnetic liquid metal（MLM）scaffolds based on galinstan and magnetic silica particles（Fe@SiO₂）.The MLM scaffolds could realize dynamic stiffness change by changing the magnetic field intensities.Then the effect of MLM scaffold with dynamic stiffness on osteogenic differentiation of mesenchymal stem cells（MSCs）was investigated.Furthermore,porous magnetic liquid metal（PMLM）scaffolds were obtained by using polyethylene glycol 8000 particles as pore-forming agent.The effect of PMLM scaffolds with dynamic stiffness on bone repair of rabbit femoral condyle defect was evaluated in vivo.The main contents and results of this research are as follows:（1）Galinstan and Fe@SiO₂ were prepared to synthesize MLM scaffold.The results showed that MLM scaffolds had good hydrophilicity,which was conducive to cell adhesion and growth.Acute hemolysis test showed that MLM scaffolds had good blood compatibility.By adjusting the magnetic field intensity from 0 to 0.4 T,the stiffness of the MLM scaffolds could increase from 3.58±0.48 MPa to 14.32±0.97 MPa.（2）MSCs were cultured on the MLM scaffolds,and 0 T magnetic field was applied in1-5 days,0.1 T magnetic field was applied in 6-10 days,0.2 T magnetic field was applied in 11-15 days,and 0.4 T magnetic field was applied in 16-20 days to realize the dynamic change of stiffness.MLM scaffolds had good cell compatibility.Further experiments showed that the variation of the stiffness of the MLM scaffold with dynamic stiffness could affect the cell spreading of MSCs.Meanwhile,the activity of alkaline phosphatase（ALP）and calcium deposition were also enhanced,and the expressions of osteogenic related genes ALP,osteopontin（OPN）and osteocalcin（OC）were significantly up-regulated,which promoted the early and late osteogenic differentiation of MSCs.（3）PMLM scaffolds were prepared by using polyethylene glycol 8000 particles of325-380μm size as pore-forming agent.When the magnetic intensities increased from 0to 0.4 T,the stiffness of the PMLM scaffolds could vary from 0.99±0.11 MPa to 1.94±0.15 MPa.A rabbit femoral condyle defect model was established and PMLM scaffold was implanted at the defect site,and the stiffness of the scaffold was regulated by external magnetic field.The effect of dynamic stiffness PMLM on bone regeneration in vivo was evaluated by X-ray and histology.The results showed that compared with the static stiffness group,the PMLM scaffold with dynamic stiffness significantly promoted bone integration and bone regeneration.To sum up,this study successfully prepared MLM and PMLM scaffolds with dynamic stiffness,and proved the role of dynamic stiffness scaffolds in promoting osteogenic differentiation of MSCs and bone regeneration in vivo.Compared with the static stiffness,scaffolds with dynamic stiffness could promote osteogenic differentiation of MSCs in vitro and bone regeneration in vivo more effectively.The results of this study will provide a meaningful theoretical reference for the application of liquid metal in bone repair.