| The inconvenience to people`s life caused by traumatic accidents and other reasons,it is crucial to prepare and reconstruct new bone repair materials.Hydroxyapatite（HA）,tricalcium phosphate（β-TCP）and other materials with good biocompatibility and osteoconduction are widely studied.Whitlockite（WH）as the main inorganic constituents in bones and teeth has excellent biocompatibility and bone induction.The components of WH are composed of Ca2+、PO43-ions,which contribute to the transformation of WH into bone-like HA in vivo and in vitro.Moreover,Mg2+plays an importat role in bone metabolism and regeneration.Therefore,WH is a promising bone tissue engineering materials.The inorganic minerals in human bone including minute quantities of rare earth elements（REEs）,it`s of great significance to control the release of rare earth in vivo because of the“Hormesis”effect on cells.With the chemical precipitation and high temperature solid phase methods to prepared WH,cerium-doped whitlockite（Ce-WH）and gadolinium-doped whitlockite（Gd-WH）podwers,respectively.The correspond nanohybrid scaffolds were fabricated by compositing the powders with chitosan（CS）with the help of freeze-dried method.The phase structure and morphologies were characterized by dint of XRD,FESEM,EDS,FTIR and TEM.The mechanical properties of the scaffolds and ions release testing characterized by electronic universal testing and ICP,respectively.In addition,the mechanism of the influence of rare earth elements in bone scaffold materials on biocompatibility and osteoinductivity was revealed based on the result of cell experiemnts and in vivo experiments.The scaffolds fabricated by freeze-drying method with pore sizes of approximately 300μm have a three dimensional interconnected macropores,which benefits the spread and adhesion of cells and the transporting of nutrients and waste products.Besides,the mechanical properties show that the scaffolds can meet the requirements of mechanical properties of bone material.The Ce-WH particles in the Ce-WH/CS scaffold were prepared by chemical precipitation method with the size of10-50 nm.The lattice parameters and morphologies were changed after doping of Ce3+.The particles were distributed throughout the CS films or attached to the surface of CS film.While,Gd-WH powders in Gd-WH/CS scaffold with the particles of200-300 nm obtained by high temperature solid phase method.Ion release tests show that the rare earth ions have the sustained release effect of the degradation of the scaffolds and its release concentration within the appropriate range,which in favor of cell growth and new boneformation.hADSCs cell experiments indicate that all the scaffolds have excellent biocompatibility and capacity on cell spread,adhension and proliferation.What`s more,cells growth in the scaffold doped with rare earth elements much better than the control group.Cell viability experiments in vitro exhibited that when the concentration of rare earth ions kept in the range of 0-10μM have no cytotoxic effect on cells.If the dose of the rare earth ions arrived at over 100μM,the cell viability of the hADSCs decreased gradually with the increasing culture time.Experiments on the repair of skull defects in mice showed that new bone produced in Ce-WH/CS and WH/CS group arrived at 20.03±4.19%and 4.91±1.53%,respectively.Besides,much more new bone formed in Gd-WH/CS than WH/CS group.They are reached at24.20±7.10%and 4.16±1.69%,respectively.Therefore,the scaffolds doped with rare earth elements had excellent osteoinductivity and bone regeneration and mineralization capacity.The in vivo experiments demonstrated that unlike activating of SMAD signaling pathway of Ce-WH/CS scaffolds,Gd-WH/CS scaffolds can improve the expression of the osteogenic-related genes,such as OCN,OSX and COL1A1,and new bone formation by the activating of GSK3βsignaling pathway.In conclusion,the rare earth doped WH/CS nanohybrid scaffolds provide a promising platform for bone regeneration. |
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