| At present,titanium alloy implants are the commonly used bone implants clinically.For enhancing the bone integration,they need to be coated with bioactive materials.Previous research has shown that plasma sprayed bioactive calcium silicate(Ca-Si)coatings on Ti-based alloys are the potential biomaterials for orthopedic implant application due to the combination between the great bioactivity of bioceramics and the excellent mechanical properties of Ti-based alloys.However,the fast degradation of Ca-Si biomaterials,attenuating their physicochemical properties and biological activities,would lead to implant loosening and poor osseointegration.Consequently,it is very significant to improve their chemical stability.Currently,most studies improve the chemical stability of Ca-Si biomaterials by changing network modifiers and replacing Ca ions with other metal cations.But the excessive release of doped metal ions may result in cytotoxicity.Considering this point,we prepared to change the network formers and replace Si with B to form more stable compounds with complicated network structures.B is an essential nutrient element for humans,and it has been shown to be beneficial for osteoporosis and arthritis alleviation,would healing,and immune response.Especially in recent years,the boom in the osteoimmunology renders boron promising nutrient element which promotes osteogenesis and inhibit inflammation.Based on the above background,in this work,boron incorporated calcium silicate ceramic powder(Ca11Si4B2O22,B-CS)was firstly prepared by high temperature solid method and then the B-CS coating was successfully developed on Ti substrates by atmospheric plasma spraying technique.The physical and chemical properties of the powder and coating are systematically studied.Next,we investigated the effects of the B-CS coating on osteogenic differentiation of osteogenic cells,immune response of macrophages as well as angiogenic potential of HUVECs,and the potential mechanisms of the corresponding actions were also explored.As is known,bone has the natural hierarchical surfaces with different scales of structure features.From the viewpoint of biomimics,we can construct microstructures with different scales on the implant surface to enhance its bioactivity.Therefore,how to combine nanostructure and boron into calcium silicate coatings and develop novel implant materials are also one of the emphases for our research in this paper.The main results obtained were summarized as follows:(1)The B-CS powder was successfully obtained through optimizing the sintering temperatures by high temperature solid method with the main phase of ?-Ca11Si4B2O22.The B content in the powder was about 2.36 wt%,which was slightly lower than the stoichiometric B content.Then the B-CS coating was successfully developed on Ti substrates by atmospheric plasma spraying technique.The B-CS coating presented had a rough surface and good wettability and boned well with Ti substrates with a higher bond strength than HA coatings.It had apatite-mineralization ability and possessed enhanced chemical stability than the CaSiO3 coating.After the spraying,a phase transition of Ca11Si4B2O22 from ? to ? phase had happened.There was amorphous phase existing in the coating,where lots of grains of less than 500 nm size distributed.Besides,the coating had amounts of lamellar structures formed by the stacking and assembling of thin layers with a thickness of about 100 nm.After the heat treatment,the amorphous regions were transformed into lots of crystalline regions ranging from 10 to 50 ?m.And every crystalline region contained many fine dendritic crystals with a length of 10~50 ?m and a width of less than 1 ?m.Every fine dendritic crystal was formed by the stacking of thin layers with a thickness of about 100 nm and was perpendicular to thin layers.It could be observed that after the heat treatment,there was lots of clusters composed of columnar crystals with a diameter of 100 nm on the fracture surface.(2)The B-CS coating had good biocompatibility and promoted the spread,attachment and proliferation of osteoblasts.Moreover,it obviously stimulated the secretion of Col I & ALP and ECM mineralization,and significantly upregulated the mRNA expression of osteogenic genes(Runx2,Osterix,BSP,OPN,OCN,BMP2,VEGF)of BMSCs.It had good osteogenesis-promoting capability and could regulate osteogenesis by BMP2 signaling pathway.Besides,the B-CS coating decreased the M1 polarization and switched M1 to M2 phenotype via restraining the TLR signaling pathway,resulting in the decrease of pro-inflammatory cytokines(iNOS,IL-1?,IL-6,TNF-?,OSM)as well as increase of anti-inflammatory factors(IL-10,IL-1ra).Moreover,osteoclastogenic genes(TRAP,RANK,MSCF,MMP9)of macrophages were also downregulated,inhibiting the osteoclastogenesis.The B-CS coating showed good immunomodulatory properties and could create benefical microenvironment for following osteogenesis.In addition,B-CS coating extracts presented good angiogenic potentials.They promoted the HUVECs migration and enhanced in vitro tubule formation.They can also increase secretion of VEGF and NO production,and significantly upregulate the expression of angiogenic genes VEGF,bFGF and their receptors and finally stimulate the proangiogenesis of HUVECs by regulating Akt pathway.In summary,the B-CS coating showed excellent biological properties and may be a promising candidate for orthopedic applications.(3)In this study,we have successfully developed nanostructured boron incorporated calcium silicate coatings(B-CS)with various amounts of boron(B)on Ti substrates by combining plasma spraying technique and hydrothermal treatment process.The coatings had various nanostructures including nanoflake-like,nanoleaf-like and nanoplate-like structures.After the hydrothermal treatment,the amorphous phase in the coating almost disappeared and nanostructured coatings presented better chemical stabilities.Nanostructured B-CS coatings possessed good surface wettability and controllable B ion releases.Among them,S1 exhibited good biocompatibility and significantly increased the protein adsorption and stimulate the focal adhesion formation and cytoskeleton extensions of BMSCs.Besides,S1 coatings,exhibiting the highest levels of Col I secretion and calcium deposition as well as least fat droplet,could significantly stimulate the osteogenic differentiation of BMSCs by activating BMP2 signaling pathway and the focal adhesion kinase pathway.In addition,nanostructured B-CS coatings could also downregulate the expression of M1 macrophage surface markers and the pro-inflammatory cytokines,and present anti-inflammatory activities by inhibiting the TLR signaling pathway.The coating extracts of S1 exhibited good angiogenic functions.They promoted the HUVECs migration and increased in vitro tubule formation.They can also stimulate secretion of VEGF and NO production,and significantly upregulate the expression of angiogenic genes(VEGF,bFGF,bFGFR,eNOS)and finally enhance the proangiogenesis of HUVECs.The present study suggests that nanostructured B-CS coatings,especially S1,showed good biological effects and might be highly promising candidate for orthopedic applications.Meanwhile,it also indicated that the combination of plasma spraying technique and hydrothermal treatment process is an effective strategy for design and modification of biomaterials with nanostructures and specific functional elements. |
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