Bioactive hydroxyapatite/graphene composite coating and its corrosion stability in simulated body fluid
Graphical abstract
Introduction
Carbon nanomaterials with two-dimensional (2D) morphologies as a single layer of sp2-hybridized carbon atoms packed in a honeycomb form, known as graphene (Gr), have been reported recently. The extraordinary electrical, thermal, and mechanical properties (e.g., tensile strength 130 GPa and Young’s modulus 0.5–1 TPa) and very high specific surface area (up to 2630 m2 g−1) have drawn great attention as a reinforcement in the composite field of material science [1], [2], [3]. Graphene materials possess physical properties identical to those of carbon nanotubes (CNTs) but have a larger surface area. It has been reported that inclusion of Gr into polymer or ceramic matrices leads to remarkable improvements in the properties of the host materials [1]. Furthermore, graphene nanosheets (GNSs), formed by several layers of Gr with a thickness of up to 100 nm [4], are much easier to produce than other graphene materials and successfully use as nanofillers for polymers [5], metals [6], and ceramics [3], [7] to produce composites with exceptional mechanical properties.
Biomaterials used in orthopedic surgery usually encounter complex service environments and therefore require versatile performances from the materials [8]. As a major player in orthopedic surgery, synthetic hydroxyapatite (Ca10(PO4)2(OH)2, HAP), chemically similar to bone mineral, has been developed in various forms and shapes. Metallic implants, such as Ti and its alloys, have insufficient biocompatibility and lack bioactivity, which means they usually cease to function over the long term because of wear, disease, or injury [8], [9] or release metallic ions with a high potential to corrode in their biological environments [9]. HAP provides bioactivity, biocompatibility and an ability to initiate osteogenesis, but on the other side it lacks good mechanical properties. Because of its poor mechanical properties, such as an intrinsic brittleness, low fracture toughness (0.8–1.2 MPa), low flexural strength (<140 MPa), and wear resistance [10], the main focus of HAP research has been to improve its mechanical performance by combining it with various reinforcements.
The focus of the latest published research has been the fabrication of Gr or its derivatives to create reinforced HAP biocomposites because of the exciting findings regarding the biological performance of Gr [8]. Nonetheless, the mechanical properties of hydroxyapatite limit its use in the regeneration of various parts of the bone systems, especially those under significant mechanical tension. The incorporation of Gr or its derivatives as reinforcing materials in HAP composites has been studied and reported using in situ synthesis [11], [12], spark plasma sintering (SPS) [13], biomimetic mineralization [14], [15], chemical vapor deposition [16], and electrospinning [17]. The general idea of using Gr as nanofiller is to minimize the brittleness of HAP and gain an improved composite. Any reinforcement material for HAP should not only significantly improve the mechanical properties, but also retain HAP’s original biocompatibility. Latest published reports on graphene materials aimed to demonstrate that crack deflection is more effective for sheet-like reinforcement than for tubular-like reinforcement, suggesting that Gr exhibits a more pronounced toughening effect on brittle materials than do carbon nanotubes (CNTs) [18]. Also, reports on CNTs cytotoxicity in organic environments are disconcerting [19]. Unlike CNTs, Gr is synthesized in relatively pure ways and is therefore expected to show little cytotoxicity, since few metallic catalyst particles are associated with its production [20]. Also, recent reports have discussed the qualities of Gr and Gr-based composites, including low toxicity toward human osteoblasts [21], excellent antibacterial properties [22], and its potential to initialize apatite mineralization [23]. Therefore, our aim was to explore the potential of implementing Grs as HAP reinforcement for load-bearing orthopedic applications.
Electrophoretic deposition (EPD) is a special colloidal processing technique widely used to apply bioactive ceramic or composite coatings on various metal surfaces, such as Ti and its alloys, stainless steel, and CoCr alloys, for orthopedic applications with improved osteoconductivity, bioactivity, biocompatibility, and corrosion resistance. EPD emerged as the method of choice due to its many advantages (e.g., high deposition rate) and good control of deposition parameters that affect coating thickness, crystallinity, and desirable uniformity even on substrates of complex shape [24], [25], [26], [27], [28], [29], [30]. Briefly, factors influencing the EPD process are electrical conditions (voltage and time) and parameters related to suspension (particle charging, solid loading, dispersants, suspension viscosity, particle size distribution). According to the proposed mechanism [31], the deposition process occurs in several steps. Charged particles attract oppositely charged ions (counterions) around the particles. In the case of cataphoretic deposition, positively charged particles migrate toward the cathode. The rate of migration that the particles can achieve depends on the applied electric field, suspension viscosity, particle radius and particle charge. Because the particles are close enough to the cathode, attractive forces dominate, and coagulation/deposition occurs. The primary process is OH− ion generation and hydrogen evolution on the cathode by H2O discharge, followed by electrocoagulation of the ceramic particles at the cathode surface by neutralization of positively charged groups with electrochemically generated OH− ions. Evolved hydrogen on the cathode goes out through the coating, leaving vacancies inside the deposited film and causing its porous structure.
In this study, the novel hydroxyapatite/graphene (HAP/Gr) composite was electrodeposited on Ti using the EPD process to obtain uniform bioactive coating with improved mechanical strength and favorable corrosion stability in simulated body fluid (SBF).
Section snippets
Materials
For synthesis of nanosized HAP powder, we used a modified chemical precipitation method that required the reaction of calcium oxide (obtained by aerobic calcination of CaCO3 for 5 h at 1000 °C) and phosphoric acid, according to our previously reported protocol [32], [33]. The final suspension was spray-dried at 120 ± 5 °C into granulated powder. Ti from Aldrich (foil, thickness 0.25 mm, 99.7% trace metals basis) was used as a substrate for electrophoretic deposition of HAP/Gr coatings. Ti samples
Surface morphology and microstructure analysis
The surface morphology of the HAP/Gr composite coating after air drying is shown in Fig. 1a. Compared to the pure HAP coating (Fig. 1b), the HAP/Gr composite coating had fewer cracks and no peeling off the Ti surface in the macroscopic observation. The microscopic view revealed that both HAP/Gr composite (Fig. 1a) and pure HAP (Fig. 1b) coatings on Ti foils displayed micro-cracks. However, these SEM images, taken under the same magnification (1000×), indisputably revealed that fewer cracks
Conclusions
Bioactive HAP/Gr composite coating was successfully produced by the EPD technique on a Ti substrate. FE-SEM images of the coating surfaces revealed indisputably fewer cracks in the HAP/Gr coating than in the pure HAP coating. According to XPS analysis, the calculated Ca/P ratio of 1.58 for the HAP/Gr coating is greater than the Ca/P ratio for the pure HAP coating of 1.50 and closer to the stoichiometric value. The total weight loss for the HAP/Gr coating was 5.28 wt.%, confirming the greater
Acknowledgements
This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Project number: 2013R1A1A2A10063466). This research was also financed by the Ministry of Education, Science and Technological Development, Republic of Serbia, contract No. III 45019. The authors would like to thank Dr. Maja Vukašinović-Sekulić, Faculty of Technology and Metallurgy, University of Belgrade, for
References (63)
- et al.
In situ deposition of hydroxyapatite on graphene nanosheets
Mater. Res. Bull.
(2013) - et al.
Synthesis of few-layer graphene over gold nanoclusters supported on MgO
Carbon
(2012) - et al.
A tough graphene nanosheet/hydroxyapatite composite with improved in vitro biocompatibility
Carbon
(2013) - et al.
Toughening of zirconia/alumina composites by the addition of graphene platelets
J. Eur. Ceram. Soc.
(2012) - et al.
Recent advances in graphene based polymer composites
Prog. Polym. Sci.
(2010) - et al.
Graphene–aluminum nanocomposites
Mater. Sci. Eng. A
(2011) - et al.
The beneficial effect of graphene nanofillers on the tribological performance of ceramics
Carbon
(2013) - et al.
Hydroxyapatite/graphene-nanosheet composite coatings deposited by vacuum cold spraying for biomedical applications: inherited nanostructures and enhanced properties
Carbon
(2014) - et al.
Mechanical properties and biomedical applications of a nanotube hydroxyapatite-reduced graphene oxide composite
Carbon
(2014) - et al.
Carbon nanotube reinforced hydroxyapatite composite for orthopedic application: a review
Mater. Sci. Eng. C
(2012)
Graphene substrates promote adherence of human osteoblasts and mesenchymal stromal cells
Carbon
Electrophoretic deposition: from traditional ceramics to nanotechnology
J. Eur. Ceram. Soc.
Electrophoretic deposition of carbon nanotube–ceramic nanocomposites
J. Eur. Ceram. Soc.
Electrodeposition of hydroxyapatite coating on AZ91D magnesium alloy for biomaterial application
Mater. Lett.
Electrochemical synthesis of nanosized monetite powder and its electrophoretic deposition on titanium
Colloid Surf. A
The effect of lignin on the structure and characteristics of composite coatings electrodeposited on titanium
Prog. Org. Coat.
Antifungal activity of Ag: hydroxyapatite thin films synthesized by pulsed laser deposition on Ti and Ti modified by TiO2 nanotubes substrates
Appl. Surf. Sci.
FT-IR and XRD investigations on sintered fluoridated hydroxyapatite composites
J. Mol. Struct.
One-pot synthesis of graphene/hydroxyapatite nanorod composite for tissue engineering
Carbon
Large reversible capacity of high quality graphene sheets as an anode material for lithium-ion batteries
Electrochim. Acta
Characterization of a calcium phosphate–TiO2 nanotube composite layer for biomedical applications
Mater. Sci. Eng. C
Synthesis and properties of hydroxyapatite-containing porous titania coating on ultrafine-grained titanium by micro-arc oxidation
Acta Biomater.
Raman, infrared and XPS study of bamboo phytoliths after chemical digestion
Spectrochim. Acta A
Preparation and antibacterial activity of silver nanoparticles-decorated graphene composites
J. Supercrit. Fluids
Electrophoretic deposition of carbon nanotube-reinforced hydroxyapatite bioactive layers on Ti–6Al–4V alloys for biomedical applications
Ceram. Int.
Nano-scratch and fretting wear study of DLC coatings for biomedical application
Diamond Relat. Mater.
Thermoluminescence properties of graphene–nano ZnS composite
J. Lumin.
Bone-like apatite layer formation on hydroxyapatite prepared by spark plasma sintering (SPS)
Biomaterials
Corrosion studies on electrochemically deposited PANI and PANI/epoxy coatings on mild steel in acid sulfate solution
Prog. Org. Coat.
EIS and differential capacitance measurements onto single crystal faces in different solutions: Part I: Ag(1 1 1) in 0.01 M NaCl
J. Electroanal. Chem.
Bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid
Mater. Lett.
Cited by (173)
Corrosion evaluation of AZ91D Mg alloy coated with HA, thermal reduced GO and MgF<inf>2</inf> in simulated body fluid
2023, Diamond and Related MaterialsNanocomposites for anticorrosive application
2023, Nanocomposites-Advanced Materials for Energy and Environmental AspectsInfluence of graphene oxide and carbon nanotubes on physicochemical properties of bone cements
2023, Materials Chemistry and Physics