| Background and ObjectiveWith the increasing of bone defects caused by orthopedic diseases and traumas,the clinical demand for bone implants continues to rise.Titanium alloy is one of the most important bone implant materials.However,the elastic modulus of titanium alloy is much higher than the human bone,so it is easy to produce stress shielding effect.Meanwhile,the lack of biological activity makes titanium alloy difficult to form a solid osseointegration between the implant and bone tissue,affecting the long-term stability after implantation.In order to overcome the above problems,the porous titanium alloy(Ti6A14V)scaffold was prepared by 3D printing,and the bioactive Sr-CaP coating was prepared by hydrothermal method,in order to reduce the elastic modulus of the implant,reduce the stress shielding,promote the growth of osteocytes and improve the osseointegration level of the implant.Method and result1.The Ti6A14V porous scaffold was prepared by 3D printing technology,and its elastic modulus was 5.19 GPa,which can effectively reduce the stress shielding.Sr-CaP active coating was prepared on the scaffold by hydrothermal method.The cytotoxicity of CaP coating with different Sr content was studied,and the optimum Sr content(10%)was selected.The 10%Sr-Ca/P coating has the following physical and chemical properties:the coating is uniform and the main elements are Ca,P and Sr;The main phase structure of the coating is CaHPO4;The coating has good hydrophilicity;The bonding stress between the coating and the substrate is 15.18MPa,which meets the standard of clinical use.The corrosion resistance of titanium scaffold is improved after modification.The release of Ca2+,Sr2+and Ti4+of the coating does not affect biosafety.2.mBMSCs were used to study the osteogenic effect of 10%Sr-Ca/P-Ti6A14V scaffold in vitro and explore the related osteogenic signaling pathway.CCK8,live and death staining and adhesion experiments showed that 10%Sr-Ca/P-Ti6Al4V scaffold had good cytocompatibility and without cytotoxicity.The results of ALP and alizarin red staining showed that 10%Sr-CaP-Ti6A14V scaffold could significantly improve the osteogenic ability of mBMSCs.Meanwhile,qRT-PCR and Western Blot results showed that 10%Sr-CaP-Ti6A14V scaffold significantly increased the gene expression levels of ALP,OCN,OPN,RUNX-2 and COL I,indicating that Sr doping significantly improved the bioactivity of CaP coating,and gave it good osteogenic ability in vitro.The protein expression of AKT and PI3K was further studied.The results showed that before the inhibition of PI3K,the expression of p-PI3K and p-AKT was significantly increased in the 10%Sr-CaP-Ti6Al4V group,compared to Ti6A14V and CaP-Ti6Al4V group.After the inhibition of PI3K,the expression of p-PI3K and p-AKT proteins in the group of 10%Sr-CaP-Ti6A14V scaffold was inhibited,suggesting that Sr ions released from 10%Sr-CaP-Ti6A14V scaffold promoted osteogenic differentiation through the PI3K/AKT signaling pathway.3.To verify the osteogenic effect of 10%Sr-CaP-Ti6A14V in vivo,the New Zealand rabbit femoral defect model was used for in vivo experiment.Micro-CT and tissue section showed that the new bone mass in Ti6A14V scaffold,CaP-Ti6A14V scaffold and 10%Sr-CaP-Ti6A14V scaffold showed an increasing relationship,and the doping of strontium could futher improve the osteogenic property of the scaffold.The push-out test of the scaffold confirmed that the 10%Sr-CaP-Ti6Al4V scaffold needed more greater pressure to be pushed out,which showed that the 10%Sr-CaP-Ti6A14V scaffold was more closely integrated with the bone tissue,and more bone tissue extended into the scaffold.ConclusionThe porous structure constructed by 3D printing titanium alloy material and the surface modification of Sr-CaP coating not only reduce the shielding effect and achieve personalized design,but also overcome the biological inertia of titanium scaffold to form a firm bone integration between the implant and bone tissue. |
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