| The success of a biomedical implant is mainly governed by the interaction of implant-surface and bone cells that encourage the osseointegration process,long-lasting stability,and excellent antibacterial properties of an implant.Calcium hydroxyapatite(HA)is broadly used as a well-known bioceramic coating material for orthopedic and dental clinical applications,which support the bone tissue generation.Single and binary doped calcium apatite has been extensively focused as it improves the osteoconductive characteristic for orthopedic and dental implants applications.The present study aims to examine the function of the two significant biological cations,Zn2+,and Sr2+ when co-doped in the structure of hydroxyapatite(HA).Six samples with different Zn2+and Sr2+ concentrations were prepared by a hydrothermal process that includes the addition of Zn2+and Sr2+containing precursors to replace Ca2+partially in the HA structure.The obtained nanomaterials were examined via XRD,ICP,FTIR,Raman spectroscopy,FESEM,TEM,and TGA for the investigation and confirmation of co-doping,crystallinity,phase purity,lattice parameters,elemental compositions,particle morphology,and thermal stability respectively.Interestingly the Zn2+substitution increase with Sr2+co-doping and the apatite structure going disappear up to 20%Zn10%Sr or 10%Zn20%Sr in the solution.Furthermore,in vitro cell viability even at high Zn2+concentration(up to 10%),MC3T3-E1 cells proliferated at a high rate on co-substituted HA materials,confirming that Sr2+offset the cytotoxic effect of Zn2+and increased the biocompatibility of the material.Moreover,the antibacterial effects of co-substituted HA against pathogen bacterial strains(E.coil and S.aureus)were also significantly increased.Overall results demonstrated that HA co-substituted by Zn2+and Sr2+at(10%Zn10%Sr-HA)is a potential material for hard tissue scaffolds.Recently the use of strontium and zinc-containing HA as an excellent biomaterial has been reported.In vitro studies have demonstrated that(Sr and Zn)-HA encourages osteoblast response,new bone formation,and increased the antibacterial properties.In order to expand the usage to the load-bearing applications,like hip replacement,it has been proposed that the material can be used in the form of a coating on the implant surface.In the current work,we reported a preliminary study of plasma sprayed(Sr,Zn)-HA coating biocompatibility on the titanium alloy(Ti-6Al-4V)substrate.Sr2+ and Zn2+ co-substituted HA coating at different concentrations were produced on the metallic substrates.All substituted coating showed excellent bonding strength with the substrate.The bioactivity and apatite layer formation on the substituted HA coating was evaluated in vitro via immersion in SBF.After immersion 5%Zn10%Sr-HA and 10%Zn10%Sr-HA coating revealed the great capability to persuade the apatite layer configuration on the coating surface,however,10%Zn5%Sr-HA coating inhabited the apatite layer formation even after 21 days of immersion.The cell material interaction on the surfaces of the substituted coating was examined through culturing MC3T3-E1 cell and compared with pure HA coating which is extensively used in dentistry and orthopedics.All substituted HA coating indicates a higher dissolution rate in SBF,protein adsorption ability,and significantly higher biocompatibility than pure HA coating.However,the 10%Zn5%Sr-HA coating shows cytotoxicity which is confirmed by cell proliferation,cell adhesion,and ALP activity,even some dead cells,and poor cellular morphologies were also found on the coating surface.The antibacterial properties of substituted HA coating were tested against gram-negative Escherichia coli,all substituted HA coating demonstrates excellent antibacterial ability against bacterial colonization.The addition of Sr2+ to the Zn-HA coating effectively decreases the thermal instability,cytotoxicity,and increased the performance as compared to HA coating.From the above results,it is indicated that 5%Zn10%Sr-HA and 10%Zn 10%Sr-HA coating have good mechanical strength,bioactivity,biocompatibility,and antibacterial properties in vitro.In order,to reduce the effect and contents of co-doping on the chemistry of nanopowder and increase the biocompatibility,mechanical strength the coating was further heat treated.Implant-related infections are a major concern in total joint prostheses,occurring up to 3%in operations.In this work,5%Zn2+was added in HA to offset bacterial activity,and 5%Sr2+ was also incorporated as a binary dopant to reduce the cytotoxic effect of Zn2+.The nano-sized HA powder was synthesized by the hydrothermal method and then heat-treated at 600? for 4 hours.The heat-treated powder was plasma sprayed on the titanium alloy Ti-6Al-4V substrate.The addition of dopants did not significantly influence the physical and mechanical properties of the coating.However,the cytocompatibility,antimicrobial,and contact angle properties statistically enhanced.Moreover,the(Sr,Zn)-HA coating was post-heat treated at 500 and 600? for 3 hours.X-ray diffraction confirmed that after heat treatment phase purity and crystallinity increased,and residual stress decreased.Mechanical stability was evaluated by adhesive bond strength,and the results showed that after heat-treatment bonding strength increased from 26.81±2.93 to 29.84±3.62 and 34.66±2.57 MPa,at 500 0 C and 600 0 C respectively.Similar to the mechanical property,antibacterial activities and biological functions are also significantly improved.More interestingly,it was also observed that the Zn2+ions released from the coating depend on Ca2+,P,and Sr2+ions while Ca2+,P,and Sr2+ions relied on heat treatment temperatures.However,(Sr,Zn)-HA coating at 600?demonstrates cytotoxic effects on MC3T3-E1 cells,characterized by poor cellular morphology on the coating surface and ultimately,cell death.The doping of Sr2+with Zn2+,therefore,can offset the cytotoxic effects and enhanced biological performance.All the outcomes of this study signify that,(Sr,Zn)-HA coating heat-treated at 500 0 C showed not only excellent mechanical and biological performance but also enhanced the antibacterial properties. |
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