The work aims to employ graphene nanosheets (GNS) to simultaneously enhance the mechanical properties, wear resistance, corrosion resistance, and hemocompatibility of hydroxyapatite (HA) coatings while preserving their excellent bioactivity. To improve the interfacial bonding between the coating and the substrate, Ti-6Al-4V substrates were firstly pretreated by electrical discharge machining milling (EDM-milling) to construct a microstructured surface characterized by uniformly distributed discharge craters. In addition, a novel composite powder with a "spherical HA core-sheet-like GNS surface decoration" architecture was designed, enabling the spatial pre-distribution of GNS prior to plasma spraying. This design promoted the preferential enrichment of GNS at the lamellar interfaces of the coating, thereby regulating the thermal behavior and spreading characteristics of molten droplets as well as the interlamellar bonding structure. Atmospheric plasma spraying (APS) was subsequently employed to fabricate pure HA coatings and GNS/HA composite coatings containing 1.5, 2.0, and 2.5wt.% GNS on the pretreated Ti-6Al-4V substrates. The phase composition, microstructure, crystallinity, microhardness, bond strength, tribological behavior, electrochemical corrosion resistance, in vitro mineralization ability, hemocompatibility, and antibacterial activity of the coatings were systematically characterized. Scanning electron microscopy (SEM) revealed that the incorporation of GNS significantly improved the surface quality of the coating, with the 2.0wt.% GNS/HA coating exhibiting the smoothest and most uniform surface morphology. Owing to the high thermal conductivity of GNS, the fluidity of molten HA was enhanced, leading to the formation of a characteristic "hand-in-hand" interlamellar structure that improved load transfer between adjacent splats. Meanwhile, the unique surface microstructure produced by EDM-milling markedly strengthened the mechanical interlocking between the coating and the substrate. Cross-sectional observations further demonstrated that GNS incorporation significantly increased coating densification. X-ray diffraction (XRD) analysis confirmed that GNS effectively suppressed the high-temperature decomposition of HA and refined the crystallite size. As a result, the microhardness of the 2.0wt.% GNS/HA coating increased from 193.96HV for the pure HA coating to 230.50HV, representing an improvement of approximately 18.9%, while the bond strength increased by 26.2%. The toughening mechanisms of the GNS/HA coatings were mainly attributed to crack bridging, crack deflection, crack propagation inhibition, crack filling, and the pull-out or tearing of GNS. Tribological tests conducted in simulated body fluid (SBF) demonstrated that the GNS/HA composite coatings exhibited substantially lower coefficients of friction than the pure HA coating under normal loads ranging from 10 to 30 N, with the maximum reduction approaching 20%. Among all coatings, the 2.0wt.% GNS/HA coating exhibited the best wear resistance, accompanied by significantly reduced wear-track width and depth. This improvement was primarily attributed to the formation of a carbon-rich tribofilm with solid-lubricating capability, which originated from the exfoliation and subsequent adhesion of fine GNS fragments onto the worn surface during sliding. The formation of this tribofilm was further verified by energy-dispersive X-ray spectroscopy (EDS) mapping, which showed that the carbon content within the wear track increased from 1.51wt.% to 2.76wt.%. Electrochemical measurements demonstrated that the incorporation of GNS shifted the corrosion potential toward more positive values and significantly reduced the corrosion current density. Specifically, the corrosion current density of the 2.0wt.% GNS/HA coating decreased from 8.071×10-6 A/cm2 to 2.087×10-6 A/cm2. Furthermore, GNS incorporation remarkably enhanced the surface wettability of the coatings, reducing the water contact angle from 62° to 8.5°. After immersion in simulated body fluid for 7 days, the surfaces of the 2.0 and 2.5wt.% GNS/HA coatings were completely covered with honeycomb-like bone-like apatite, indicating accelerated in vitro mineralization. The 2.0wt.% GNS/HA coating also exhibited excellent hemocompatibility, with a hemolysis ratio as low as 0.33% and a low degree of platelet activation, thereby effectively delaying blood coagulation. In addition, the GNS/HA composite coatings showed pronounced antibacterial activity against both Escherichia coli and Staphylococcus aureus. The synergistic effect of EDM-milling surface pretreatment and the incorporation of 2.0wt.% GNS significantly enhanced the mechanical performance, wear resistance, corrosion resistance, and biological properties of plasma-sprayed HA coatings, providing a promising strategy for the development of high-performance bioactive coatings for orthopedic implants.
Key words
electrical discharge machining milling /
atmospheric plasma spraying /
graphene nanosheet-reinforced hydroxyapatite coating /
bonding strength /
biocompatibility
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References
[1] FERGUSON R J, PALMER A J, TAYLOR A, et al.Hip Replacement[J]. The Lancet, 2018, 392(10158): 1662-1671.
[2] ABD-ELAZIEM W, DARWISH M A, HAMADA A, et al.Titanium-Based Alloys and Composites for Orthopedic Implants Applications: A Comprehensive Review[J]. Materials & Design, 2024, 241: 112850.
[3] NISAR S S, ARUN S, CHOE H C.Plasma Electrolytic Oxidation Coatings on Femtosecond Laser-Treated Ti- 6Al-4V Alloy for Bio-Implant Use[J]. Surface and Coatings Technology, 2023, 464: 129553.
[4] WU S L, LIU X M, YEUNG K W K, et al. Surface Nano-Architectures and Their Effects on the Mechanical Properties and Corrosion Behavior of Ti-Based Orthopedic Implants[J]. Surface and Coatings Technology, 2013, 233: 13-26.
[5] KE D X, VU A A, BANDYOPADHYAY A, et al.Compositionally Graded Doped Hydroxyapatite Coating on Titanium Using Laser and Plasma Spray Deposition for Bone Implants[J]. Acta Biomaterialia, 2019, 84: 414-423.
[6] KUMAR A, BISWAS K, BASU B.On the Toughness Enhancement in Hydroxyapatite-Based Composites[J]. Acta Materialia, 2013, 61(14): 5198-5215.
[7] LAHIRI D, SINGH V, KESHRI A K, et al.Carbon Nanotube Toughened Hydroxyapatite by Spark Plasma Sintering: Microstructural Evolution and Multiscale Tribological Properties[J]. Carbon, 2010, 48(11): 3103-3120.
[8] FANG L M, LENG Y, GAO P.Processing and Mechanical Properties of HA/UHMWPE Nanocomposites[J]. Biomaterials, 2006, 27(20): 3701-3707.
[9] MITTAL M, NATH S K, PRAKASH S.Improvement in Mechanical Properties of Plasma Sprayed Hydroxyapatite Coatings by Al2O3 Reinforcement[J]. Materials Science and Engineering: C, 2013, 33(5): 2838-2845.
[10] ZAKERI M, HASANI E, TAMIZIFAR M.Mechanical Properties of TiO2-Hydroxyapatite Nanostructured Coatings on Ti-6Al-4V Substrates by APS Method[J]. International Journal of Minerals, Metallurgy, and Materials, 2013, 20(4): 397-402.
[11] FU L, KHOR K A, LIM J P.Effects of Yttria-Stabilized Zirconia on Plasma-Sprayed Hydroxyapatite/Yttria- Stabilized Zirconia Composite Coatings[J]. Journal of the American Ceramic Society, 2002, 85(4): 800-806.
[12] JAGADEESHANAYAKA N, AWASTHI S, JAMBAGI S C, et al.Bioactive Surface Modifications through Thermally Sprayed Hydroxyapatite Composite Coatings: A Review of Selective Reinforcements[J]. Biomaterials Science, 2022, 10(10): 2484-2523.
[13] ZHANG Y, NAYAK T R, HONG H, et al.Graphene: A Versatile Nanoplatform for Biomedical Applications[J]. Nanoscale, 2012, 4(13): 3833.
[14] BARADARAN S, MOGHADDAM E, BASIRUN W J, et al.Mechanical Properties and Biomedical Applications of a Nanotube Hydroxyapatite-Reduced Graphene Oxide Composite[J]. Carbon, 2014, 69: 32-45.
[15] NAYAK T R, ANDERSEN H, MAKAM V S, et al.Graphene for Controlled and Accelerated Osteogenic Differentiation of Human Mesenchymal Stem Cells[J]. ACS Nano, 2011, 5(6): 4670-4678.
[16] YOON H H, BHANG S H, KIM T, et al.Dual Roles of Graphene Oxide in Chondrogenic Differentiation of Adult Stem Cells: Cell-Adhesion Substrate and Growth Factor-D elivery Carrier[J]. Advanced Functional Materials, 2014, 24(41): 6455-6464.
[17] GUO Y T, YAN X J, YANG Y N, et al.Graphene Oxide/Hydroxyapatite Composite Coatings on Additively Manufactured NiTi Alloy for Biomedical Applications[J]. Ceramics International, 2024, 50(1): 2479-2489.
[18] MOHAMMADIPOUR E, GHORBANI M. Characterization, Mechanical, Corrosion, and in Vitro Apatite-Formation Ability Properties of Hydroxyapatite-Reduced Graphene Oxide Coatings on Ti6Al4V Alloy by Plasma Electrolytic Oxidation[J]. Journal of Materials Research and Technology, 2024, 33: 441-457.
[19] PERES E A B, BARBOSA W T, LINHARES D V, et al. In Situ Synthesis of Hydroxyapatite/Graphene Nanocomposites by Solution Combustion: Influence of the Reducing Reaction[J]. Ceramics International, 2025, 51(25): 44020-44028.
[20] REN J, ZHANG X G, CHEN Y.Graphene Accelerates Osteoblast Attachment and Biomineralization[J]. Carbon Letters, 2017, 22: 42-47.
[21] HUSSAIN S, SABIRUDDIN K, PATIDAR P, et al.In Vitro Bioactivity and Biocompatibility Behaviour of Atmospheric Plasma Sprayed Indian Clam Seashell Derived Hydroxyapatite Coating on Ti-Alloy[J]. Journal of Alloys and Compounds, 2024, 976: 173132.
[22] SINGH A, SINGH G, CHAWLA V.Influence of Post Coating Heat Treatment on Microstructural, Mechanical and Electrochemical Corrosion Behaviour of Vacuum Plasma Sprayed Reinforced Hydroxyapatite Coatings[J]. Journal of the Mechanical Behavior of Biomedical Materials, 2018, 85: 20-36.
[23] MIA M, DHAR N R.Effects of Duplex Jets High-Pressure Coolant on Machining Temperature and Machinability of Ti-6Al-4V Superalloy[J]. Journal of Materials Processing Technology, 2018, 252: 688-696.
[24] 于鹏程, 李丽, 刘宪福, 等. 等离子喷涂制备石墨烯增强羟基磷灰石复合涂层及其性能研究[J]. 电镀与涂饰, 2025, 44(9): 94-101.
YU P C, LI L, LIU X F, et al.Preparation of Graphene- Reinforced Hydroxyapatite Composite Coating by Plasma Spraying and Study on Its Properties[J]. Electroplating & Finishing, 2025, 44(9): 94-101.
[25] MUKHERJEE B, ASIQ RAHMAN O S, ISLAM A, et al. Plasma Sprayed Carbon Nanotube and Graphene Nanoplatelets Reinforced Alumina Hybrid Composite Coating with Outstanding Toughness[J]. Journal of Alloys and Compounds, 2017, 727: 658-670.
[26] CHENG X J, WU H, ZHANG L, et al.Hydroxyl Migration Disorders the Surface Structure of Hydroxyapatite Nanoparticles[J]. Applied Surface Science, 2017, 416: 901-910.
[27] BAI Y, CHI B X, MA W, et al.Suspension Plasma-Sprayed Fluoridated Hydroxyapatite Coatings: Effects of Spraying Power on Microstructure, Chemical Stability and Antibacterial Activity[J]. Surface and Coatings Technology, 2019, 361: 222-230.
[28] HOSSAIN M S, UDDIN M N, SARKAR S, et al.Crystallographic Dependency of Waste Cow Bone, Hydroxyapatite, and Β-Tricalcium Phosphate for Biomedical Application[J]. Journal of Saudi Chemical Society, 2022, 26(6): 101559.
[29] OVERGAARD S, BROMOSE U, LIND M, et al. The Influence of Crystallinity of the Hydroxyapatite Coating on the Fixation of Implants: MECHANICAL AND HISTOMORPHOMETRIC RESULTS[J]. The Journal of Bone and Joint Surgery British Volume, 1999, 81-B(4): 725-731.
[30] ZHANG L, LIU W W, YUE C G, et al.A Tough Graphene Nanosheet/Hydroxyapatite Composite with Improved in Vitro Biocompatibility[J]. Carbon, 2013, 61: 105-115.
[31] YOURDKHANI M, PASINI D, BARTHELAT F.Multiscale Mechanics and Optimization of Gastropod Shells[J]. Journal of Bionic Engineering, 2011, 8(4): 357-368.
[32] CHAE K, JANG W Y, PARK K, et al. Antibacterial Infection and Immune-Evasive Coating for Orthopedic Implants[J]. Science Advances, 2020, 6(44): eabb0025.
[33] MENZIES K L, JONES L.The Impact of Contact Angle on the Biocompatibility of Biomaterials[J]. Optometry and Vision Science, 2010, 87(6): 387-399.
[34] LI M, LIU Q, JIA Z J, et al.Graphene Oxide/ydroxyapatite Composite Coatings Fabricated by Electrophoretic Nanotechnology for Biological Applications[J]. Carbon, 2014, 67: 185-197.
[35] SHI Z M, LIU M, ATRENS A.Measurement of the Corrosion Rate of Magnesium Alloys Using Tafel Extrapolation[J]. Corrosion Science, 2010, 52(2): 579-588.
[36] YIGIT O, DIKICI B, SENOCAK T C, et al.One-Step Synthesis of Nano-Hydroxyapatite/Graphene Nanosheet Hybrid Coatings on Ti6Al4V Alloys by Hydrothermal Method and Their In-Vitro Corrosion Responses[J]. Surface and Coatings Technology, 2020, 394: 125858.
[37] ZADPOOR A A.Relationship between in Vitro Apatite- Forming Ability Measured Using Simulated Body Fluid and in Vivo Bioactivity of Biomaterials[J]. Materials Science and Engineering: C, 2014, 35: 134-143.
[38] CLAVIJO-MEJÍA G A, HERMANN-MUÑOZ J A, RINCÓN- LÓPEZ J A, et al. Bovine-Derived Hydroxyapatite Coatings Deposited by High-Velocity Oxygen-Fuel and Atmospheric Plasma Spray Processes: A Comparative Study[J]. Surface and Coatings Technology, 2020, 381: 125193.
[39] ZHANG Q Y, CHEN J Y, FENG J M, et al.Dissolution and Mineralization Behaviors of HA Coatings[J]. Biomaterials, 2003, 24(26): 4741-4748.
[40] KIM H M, HIMENO T, KOKUBO T, et al.Process and Kinetics of Bonelike Apatite Formation on Sintered Hydroxyapatite in a Simulated Body Fluid[J]. Biomaterials, 2005, 26(21): 4366-4373.
[41] SHANKAR D, JAMBAGI S C.Improvements in Bioactivity, Blood Compatibility, and Wear Resistance of Thermally Sprayed Carbon Nanotube Reinforced Hydroxyapatite-Based Orthopedic Implants[J]. Tribology International, 2024, 197: 109809.
[42] WEBER M, STEINLE H, GOLOMBEK S, et al.Blood- ontacting Biomaterials: In Vitro Evaluation of the Hemocompatibility[J]. Frontiers in Bioengineering and Biotechnology, 2018, 6: 99.
[43] GROTH T, KLOSZ K, CAMPBELL E J, et al.Protein Adsorption, Lymphocyte Adhesion and Platelet Adhesion/ctivation on Polyurethane Ureas Is Related to Hard Segment Content and Composition[J]. Journal of Biomaterials Science, Polymer Edition, 1995, 6(6): 497-510.
[44] TZONEVA R, HEUCHEL M, GROTH T, et al.Fibrinogen Adsorption and Platelet Interactions on Polymer Membranes[J]. Journal of Biomaterials Science, Polymer Edition, 2002, 13(9): 1033-1050.
[45] AKHAVAN O, GHADERI E.Toxicity of Graphene and Graphene Oxide Nanowalls Against Bacteria[J]. ACS Nano, 2010, 4(10): 5731-5736.
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