Structural evaluation of brushite/gelatine coatings on graphite substrate Ľ. Medvecký ⁎, R. Štulajterová, R. Bureš Institute of Materials Research of SAS, Watsonova 47, 043 53 Kosice, Slovakia abstract article info Article history: Received 14 January 2009 Accepted in revised form 7 June 2009 Available online 13 June 2009 Keywords: Biomaterials Calcium phosphate Electrochemical deposition Coatings Graphite Brushite is one of the most frequently formed products of the electrochemical deposition. It has shown excellent biological behaviour of calcium phosphate coatings on carbon composites. Calcium phosphate coatings were obtained by the electrochemical deposition from the solution of calcium and phosphate ions at pH = 2.4 and with 0.2 or 1 wt.% gelatine addition. Graphite substrate was used as cathode and Pt basket as anode. Electrochemical deposition of brushite/gelatine composite layer was carried out at current densities from 5 to 20 mA/cm 2 . Coatings were examined before and after annealing at 850 °C in Ar. The large channels were observed in coatings at higher concentrations of gelatine and high current densities in microstructure. The adhesive strength of thin brushite/gelatine coating was around 7 MPa. Linear dependence of deposit weight increase with electrolysis time was observed. Similarly, the gelatine content in coating rose linearly with gelatine concentration in electrolyte. After annealing of coatings at 850 °C in argon, the brushite was transformed to hydroxyapatite and CaO, the size of the needle-like brushite particles decreased and small spherical or regular shaped particles of CaO were formed. The weak bonding of thermal treated brushite/ gelatine deposits to graphite was found. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Carbonaceous materials with ordered crystalline, amorphous gra- phitic or mixed structure in the form of carbon fibres/carbon [1,2], carbon or carbon fibre/polymer composites [3], graphite, diamond like carbon or calcium phosphate/carbon nanotubes coatings on metal substrates [4–7] are applied as hard and soft tissue implants because of their exceptional mechanical (flexural and fatigue strength, hardness, etc.) [8–11], tribological properties [12] and biocompatibility [13–16]. The deposition of calcium phosphates (e.g. hydroxyapatite, brushite, etc.) on implants significantly enhances their biocompat- ibility and bioactivity. Brushite is one of the most frequently formed products of the electrochemical deposition on metal substrates from aqueous solutions of calcium and phosphates at room temperature and it is strong bonded to the surface of metal substrate. It can be consequently transformed to hydroxyapatite using the hydrothermal treatment usually at higher pH values and temperatures [17–20]. On graphite substrates, the hydroxyapatite (HA) deposition was mainly examined. It has shown excellent biological behaviour of calcium phosphate coatings on carbon composites and carbon fabric clothes [21,22]. Hydroxyapatite/chitosan composite film preparation method based on the electrophoretic deposition of chemically precipitated HA nanoparticles and electrochemical deposition of chitosan or chitosan- heparine was studied [23–25]. It was established that the deposit composition can be varied by the change of the concentration of HA nanoparticles in the chitosan solutions. An electrodeposit process was used to form a layer of calcium phosphates on the surface of carbon fibres and results showed that composite reinforced by carbon fibres with a layer of β-tricalcium phosphate coatings exhibited significantly better biomechanical properties by changing the surface properties of carbon fibres [26]. A thick, uniform and crack-free HA coating was obtained by electrophoretic deposition of submicron HA powders using repeated deposition method [27]. Calcium phosphate deposits on carbon substrate in the form of pure HA or HA carbonate were produced by electrocrystallization from Ca(NO 3 ) 2 and NH 4 H 2 PO 4 solutions at pH=5.5 and at temperatures of 60 or 85 °C [28]. Gelatine was successfully utilized for the preparation of very fine nanocrystalline hydroxyapatite and gelatine–hydroxyapatite nanocom- posites [29]. Ti6Al4V substrate was coated with the HA/gelatine gel using the dip-coating method and composite layer was sintered at elevated temperatures [30]. The rise in adhesion strength of electro- chemically prepared hydroxyapatite coating on Ti substrate was found after a small addition of vinyl acetate to electrolyte that shows the possibility to improve the calcium phosphate layer bonding to substrate by simultaneous electrochemical precipitation of calcium phosphate particles and organic polymers or substances [31]. The electrochemical formation and properties of gelatine/brushite coatings on graphite or carbon substrates has not been studied yet whereas this method allows the simple and very fast deposition of more bioactive brushite layers (in comparison with for example hydroxyapatite) on carbonaceous materials and their composites. In addition to the good adhesion of gelatine/brushite coatings to substrate, another advantage of this Surface & Coatings Technology 203 (2009) 3754–3762 ⁎ Corresponding author. E-mail address: lmedvecky@imr.saske.sk (Ľ Medvecký). 0257-8972/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2009.06.016 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat