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Preparation of hydroxyapatite-containing titania coating on titanium substrate by micro-arc oxidation
Abstract
Hydroxyapatite-containing titania coatings on titanium substrates were formed by micro-arc oxidation (MAO) in electrolyte containing calcium acetate monohydrate (CH3COO)2Ca·H2O) and sodium phosphate monobasic dihydrate (NaH2PO4·2H2O) using a pulse power supply. Scanning electron microscopy (SEM) with Energy dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD) were employed to characterize the microstructure, elemental composition and phase components of the coatings. The coatings were rough and porous, without apparent interface to the titanium substrates. All the oxidized coatings contained Ca and P as well as Ti and O, and the porous coatings were made up of anatase, rutile and hydroxyapatite. Such MAO films are expected to have significant applications as artificial bone joints and dental implants.
... With this relatively new technique, it is also possible to grow a thick, rough and porous TiO 2 layer as well as to incorporate chemical species (such as calcium and phosphorus from the electrolyte) that enhance the biocompatibility. In this respect, MAO of titanium-based materials is generally conducted in alkaline electrolytes containing sodium carbonate, sodium phosphate, acetate monohydrate, and β-glycerophosphate disodium salt pentahydrate [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. ...
... These micro-plasma discharges modify the oxide layer by inducing complex high temperature reactions between the metal surface and the electrolyte [26,27]. In this respect, formation of surface oxides with different characteristics has been reported for titanium based metals after the MAO process, depending on the compositions of the metal and/or electrolyte as well as the electrical parameters (voltage and current) and the exposure time of the process [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. ...
... There are many works in the literature concluding the beneficial effect of calcium and phosphorus containing formations on the bioactivity of the TiO 2 layers [11][12][13][14][15][16][17][18][19][20][21][22][23][24] as confirmed by the SBF tests conducted in the present study (Figs. 3 and 4). Since hydroxyapatite has a composition similar to that of bone, deposition of hydroxyapatite during SBF tests is generally assumed as a primary indicator of a bioactive surface, which leads to good bonding between the implant and the bone [25]. ...
In the present study, the in-vitro biological responses of two competitive titanium alloys (Ti6Al4V and Ti6Al7Nb) were investigated after modifying their surfaces by the micro-arc oxidation (MAO) process conducted in a (CH3COO)2Ca·H2O and Na3PO4 containing electrolyte under identical electrical parameters and exposure time. After the process, the surfaces of the alloys were covered with a thick (approx. 10 μm) TiO2 layer exhibiting different characteristics. The oxide layer of the Ti6Al4V alloy was porous and contained hydroxyapatite precipitates whereas the oxide layer of the Ti6Al7Nb alloy showed a more grainy appearance and contained calcium titanate precipitates. Simulated body fluid (SBF) and cell culture tests were conducted to compare the biological performance of the alloys. Even though oxidized alloys exhibited somewhat similar response in SBF tests, the number of SAOS-2 cells attached to the oxide layer of the Ti6Al4V alloy was greater than that of the Ti6Al7Nb alloy.Research Highlights► Ca and P incorporated rough TiO2 layers were generated on Ti6Al4V and Ti6Al7Nb. ► TiO2 were in the form of anatase and rutile. ► Formation of TiO2 layers by the MAO process enhanced the bioactivity. ► After MAO, SAOS-2 cells had higher rate of attachment on Ti6Al4V than Ti6Al7Nb. ► In original state cell attchment on Ti6Al7Nb was higher than on Ti6Al4V.
... The other methods such as electrophoretic deposition may produce highly crystalline coatings, which are difficult to resorb in the body (Gross & Berndt, 1994). Recently, it was reported that hydroxyapatite-containing titania coating on titanium or titanium alloy was prepared by micro-arc oxidation (MAO) technique ( Barrere et al., 2002;Chen et al., 2006; Fu et al., 2002;Han et al., 2003;Wei et al., 2009;Ni et al., 2008). The obtained coating has a porous surface and exhibits perfect biocompatibility and biological activity, which is essential for orthopaedic and dental metallic implant materials. ...
... It was reported by almost all investigators that the oxide film formed using MAO on titanium surface exhibited a porous microstructure with SEM. The holes which were regarded as discharge channels of micro-arc in electrolyte were relatively well separated and homogrneously distributed over the surface ( Chen et al., 2006;Han et al., 2002aHan et al., , 2002bHan et al., , 2003Li et al., 2004;Ni et al., 2008). Theoretically speaking (Akin et at., 2001;Dunn et al., 1993), this micro-porous morphology of the implant surface is beneficial to bone tissue growth and enhanced anchorage of implant to bone; furthermore, a porous surface may be valuable for bioactive constituents such as growth factors or bone morphogenic proteins and has the function of an enhanced cell proliferation. ...
... Theoretically speaking (Akin et at., 2001;Dunn et al., 1993), this micro-porous morphology of the implant surface is beneficial to bone tissue growth and enhanced anchorage of implant to bone; furthermore, a porous surface may be valuable for bioactive constituents such as growth factors or bone morphogenic proteins and has the function of an enhanced cell proliferation. The cross-sections of the oxide layers formed with different oxidation time showed that there was no obvious discontinuity between the film and the underlying substrate, which indicated that the film could be tightly adhered to the substrate ( Han et al., 2002aHan et al., , 2002bHan et al., , 2003Ni et al., 2008). The morphological difference such as diameter of the pores and the thickness of the film associated with electrolyte concentration, discharge voltage and treatment time, have been found by many investigators ( Li et al., 2004;Han et al., 2002aHan et al., , 2003Kuromoto et al., 2007;Yao et al. 2008). ...
... Plasma electrolytic oxidation (PEO), also known as micro-arc oxidation [1][2][3][4][5][6][7][8][9][10], is one of the most effective, though energy consuming, surface treatment methods. It still offers challenging topics for researchers to reveal the mechanisms, which underlie the coating formation kinetics and determine their structure and properties [11]. ...
... It still offers challenging topics for researchers to reveal the mechanisms, which underlie the coating formation kinetics and determine their structure and properties [11]. Not only light metals and alloys such as aluminum [3,[12][13][14][15][16][17][18][19], titanium [2,[8][9][10][20][21][22][23][24][25][26], magnesium [5,[27][28][29][30][31][32][33], but even steel [34][35][36][37][38][39] can be successfully treated by this method. PEO-coatings results from the plasma microdischarges action on the surface of materials and typically consist of oxidized elements of the metal/alloy and the components of the electrolyte [31,32]. ...
The paper presents results of the study aimed at assessing the effect of duty cycle (D) during plasma electrolytic oxidation (PEO) on morphology, composition, and protective properties of the coatings produced on 5754 aluminum alloy in a mixed electrolyte. It is shown that increasing the duty cycle of a microsecond current pulses leads to a decrease of porosity and an increase of thickness of the PEO-layers, which are composed of γ-Al2O3, β-Al2O3, AlPO4, and Al2Mo3C. This improved the barrier properties and microhardness of the coating. The Young's modulus increased with an increase of the quantity of electricity due to the changes of morphological and chemical structure of the coatings. The PEO-coatings produced at a higher duty cycle and longer oxidation time are more wearproof as compared to ones formed at a shorter oxidation time and lower D values. The obtained data allowed confirming the hypothesis on phase formation mechanism.
... [148][149][150] It is known that the formation of stoichiometric HA can be directly influenced by electrolyte pH during MAO processing. 56,[151][152][153] According to previous studies, the pH of the HA coating stabilizes at 4.2 and 6.0 in the aqueous electrolyte and water system. 98,101 Deposition of HA can be achieved in multiple layers with the influence of ultra-fine scattering by MAO. ...
... The biphasic Ca-P granules on the coating surface were 55-95 nm in diameters after § 10% of its duty cycle. Ni et al. 56 investigated the effects of different electrolytes such as sodium phosphate monobasic dehydrate (NaH 2 PO 4 2H 2 O) and calcium acetate monohydrate ((CH 2 COO) 2 Ca) on the Ca-P coating. Their study reported that an electrolyte solution containing 0.06 mol/L sodium phosphate monobasic dehydrate and 0.13 mol/L calcium acetate monohydrate resulted in the formation of coatings with an average pore size of 5 mm. ...
Calcium phosphate (Ca-P) based composites have attracted great attention in the scientific community over the last decade for the development of biomedical applications. Among such Ca-P-based structures, carbonate apatite (CA) and hydroxyapatite (HA) materials have received much attention in the clinical and biomedical fields, mainly because of their unique biological characteristics. These characteristics can promote the biocompatibility of implant materials and osseointegration between the implant and host bone. Various studies have been carried out on the fabrication of Ca-P coatings on orthopedic and dental implants using the micro-arc oxidation (MAO) process; however, there has not been a comprehensive review of the control of MAO parameters to achieve an optimal coating structure. This article presents a critical analysis of the synthesis techniques that have been adopted for the fabrication of Ca-P-based coatings on both commercially pure titanium (CP-Ti) and biomedical grade Ti alloys. Moreover, this work elucidates the influence of MAO processing parameters such as electrolyte concentration, pH value, voltage, and time on the crystal structure and surface morphology of Ca-P coatings. It is shown that the surface thickness, crystal structure, and surface morphology of Ca-P coatings directly influence their biocompatibility.
... Cross-sectional images (Figure 9) also indicated that highly-ordered nano-channels were perpendicular to the substrate, and a compact layer can be observed between the nanopore arrays and the substrate. Besides, the addition of PO 3− 4 in the electrolyte further improved the cellular performance [92,93]. Moreover, A well-defined micro-/nano-morphology can also be acquired by this HCA technique in electrolytes, such as Cu(NO 3 ) 2 , Zn(NO 3 ) 2 , (Na 3 PO 4 + Ca(NO 3 ) 2 + Na 2 SiO 3 ) and (Na 3 PO 4 + AgNO 3 + Na 2 SiO 3 ), which will extend its application. ...
... Cross-sectional images (Figure 9) also indicated that highly-ordered nano-channels were perpendicular to the substrate, and a compact layer can be observed between the nanopore arrays and the substrate. Besides, the addition of PO 3− 4 in the electrolyte further improved the cellular performance [92,93]. Moreover, A well-defined micro-/nanomorphology can also be acquired by this HCA technique in electrolytes, such as Cu(NO3)2, Zn(NO3)2, (Na3PO4 + Ca(NO3)2 + Na2SiO3) and (Na3PO4 + AgNO3 + Na2SiO3), which will extend its application. ...
Ti and its alloys are the most commonly-used materials for biomedical applications. However, bacterial infection after implant placement is still one of the significant rising complications. Therefore, the application of the antimicrobial agents into implant surfaces to prevent implant-associated infection has attracted much attention. Scientific papers have shown that inorganic antibacterial metal elements (e.g., Ag, Cu, Zn) can be introduced into implant surfaces with the addition of metal nanoparticles or metallic compounds into an electrolyte via micro-arc oxidation (MAO) technology. In this review, the effects of the composition and concentration of electrolyte and process parameters (e.g., voltage, current density, oxidation time) on the morphological characteristics (e.g., surface morphology, bonding strength), antibacterial ability and biocompatibility of MAO antimicrobial coatings are discussed in detail. Anti-infection and osseointegration can be simultaneously accomplished with the selection of the proper antibacterial elements and operating parameters. Besides, MAO assisted by magnetron sputtering (MS) to endow Ti-based implant materials with superior antibacterial ability and biocompatibility is also discussed. Finally, the development trend of MAO technology in the future is forecasted.
... The literature contains many proposals for the preparation of HA coatings, including plasma spraying, sol gel synthesis, pulsed laser deposition, and electrochemical reaction [17][18][19][20][21]. Various studies have shown that microarc oxidation (MAO) also provides an effective approach for the deposition of biomedical coatings. In the MAO process, the high-voltage micro-arc discharge events raise the specimen surface instantaneously to a temperature of 2000-3000 °C, causing the surface to melt and regenerate as a thin layer of porous bioactive and biocompatible ceramic material with a high level of wear and corrosion resistance [22][23][24][25][26][27]. Notably, the MAO process is performed via immersion in an electrolytic bath, and is thus ideally suited to the surface treatment of complex shaped implants. ...
... For the electrolyte with the lowest F content (0%), the solution contains only Ca(CH 3 COO) 2 ·H 2 O and NaH 2 PO 4 ·2H 2 O. Thus, the coating surface has only HA, A-TiO 2 and R-TiO 2 phases (i.e., no FA). The authors in [24,28] showed that as the MAO anodizing voltage or discharge duration time increases, the intensity of the R-TiO 2 phases increases, while that of the A-TiO 2 phases decreases. Furthermore, as the applied voltage or discharge duration time is further increased, the A-TiO 2 and R-TiO 2 phases are gradually replaced by HA phase. ...
Fluorapatite (FA) has better chemical and thermal stability than hydroxyapatite (HA), and has thus attracted significant interest for biomaterial applications in recent years. In this study, porous bioceramic layers were prepared on pure titanium surfaces using a micro-arc oxidation (MAO) technique with an applied voltage of 450 V and an oxidation time of 5 min. The MAO process was performed using three different electrolyte solutions containing calcium fluoride (CaF2), calcium acetate monohydrate (Ca(CH3COO)2·H2O), and sodium phosphate monobasic dihydrate (NaH2PO4·2H2O) mixed in ratios of 0:2:1, 1:1:1, and 2:0:1, respectively. The surface morphology, composition, micro-hardness, porosity, and biological properties of the various MAO coatings were examined and compared. The results showed that as the CaF2/Ca(CH3COO)2·H2O ratio increased, the elemental composition of the MAO coating transformed from HA, A-TiO2 (Anatase) and R-TiO2 (Rutile); to A-TiO2, R-TiO2, and a small amount of HA; and finally A-TiO2, R-TiO2, CaF2, TiP2O5, and FA. The change in elemental composition was accompanied by a higher micro-hardness and a lower porosity. The coatings exhibited a similar in vitro bioactivity performance during immersion in simulated body fluid for 7–28 days. Furthermore, for in initial in vitro biocompatibility tests performed for 24 h using Dulbecco’s Modified Eagle Medium (DMEM) supplement containing 10%Fetal bovine serum, the attachment and spreading of osteoblast-like osteosarcoma MG63 cells were found to increase slightly with an increasing CaF2/Ca(CH3COO)2·H2O ratio. In general, the results presented in this study show that all three MAO coatings possess a certain degree of in vitro bioactivity and biocompatibility.
... In particular, when an applied voltage is increased beyond a certain point, micro-arcs are generated as a result of the dielectric breakdown of the surface TiO 2 layer, whereupon Ti ions in the Ti implant and OH ions in the electrolyte move in opposite directions very quickly to form TiO 2 again. Furthermore, bioactive materials or antibiotics can be incorporated into the coating layer during the MAO process by tailoring the composition of the electrolyte solu- tion [6,7,12,13] . For example, Ca and P ions have been incorporated successfully into the TiO 2 layer using an electrolyte solution containing Ca and P sources, which resulted in a considerable improvement in the osseointegration ability of the implant in vivo tests [6,12,13]. ...
... Furthermore, bioactive materials or antibiotics can be incorporated into the coating layer during the MAO process by tailoring the composition of the electrolyte solu- tion [6,7,12,13] . For example, Ca and P ions have been incorporated successfully into the TiO 2 layer using an electrolyte solution containing Ca and P sources, which resulted in a considerable improvement in the osseointegration ability of the implant in vivo tests [6,12,13]. In addition, these incorporated Ca and P ions can be crystallized to form hydroxyapatite (HA) or other calcium phosphate phases using a hydrothermal treatment141516. ...
Micro-arc oxidation (MAO) is commonly used to modify the surface of Ti-based medical implants with a bioactive and porous titanium oxide (TiO(2)) layer. This study reports a novel method of incorporating hydroxyapatite (HA) within the TiO(2) layer by coupling MAO with an electrophoretic deposition (EPD) process. A HA-incorporated, porous TiO(2) layer was produced successfully on the Ti substrate using the EPD-coupled MAO treatment, as confirmed by electron microscopy observations. Addition of ethanol to the electrolyte solution containing the fine HA particles was essential to reduce the level of gaseous emission on the anode, which obstructs the attachment of HA particles. In vitro cellular assays showed that the incorporation of HA significantly improved the osteoblastic activity on the coating layer.
... However, increase in the concentration of electrolyte CaCl 2 may reduce the adhesive strength. Ni et al [22] established a relationship between pore size and concentration of (CH 3 COO) 2 CaH 2 O and NaH 2 PO 4 2H 2 O of the aqueous electrolyte. Our previous study [23] showed that titanium MAO in phosphoric acid electrolytes at pH ∼ 3-1 is promising from the point of view to obtain bioactive coatings. ...
The micro-arc oxidation method has been used to obtain calcium-phosphate coatings on titanium surface, expected to have bioactive properties. The effect of the pulse current duty cycle and voltage of micro-arc oxidation on the morphology, elemental and phase composition of the coating has been studied. Decrease in the pulse duty cycle during micro-arc oxidation results in the formation of flake, spheroidal and lamellar structures. It has been shown that the Ca/P ratio and surface roughness of the coating increases regardless of the pulse duty cycle with increase of applied voltage. Depending on the application mode, the Ca/P ratio and the roughness of calcium phosphate coatings ranged from 0.44 to 0.67 and from 4.2 to 6.8 μm, respectively. It was found that change of the pulse current duty cycle and increase of the voltage up to 600 V results in the formation of the main crystalline phases Ca(H2PO4)2(H2O) and CaPO3(OH) in the coatings.
... After 10 min of PEO treatment the coating formed in the electrolyte with a Ca/P ratio of 5 had significantly enhanced bioactivity, with a HA layer formed after 1 week of immersion in SBF, whereas 4 weeks of immersion in SBF solution was required for the formation of a HA layer on the coating formed in the electrolyte with a Ca/P ratio of 2. Mohedano et al. [300] studied the effect of treatment duration on coating stoichiometry and discovered that after 90 s of PEO the Ca/P ratio in the coating was far from that of the electrolyte, while after 600 s of treatment it became nearly equal to it. However, Ca and P content, and thus the Ca/P ratio, does not appear to change significantly for treatment times exceeding 10 minutes, meaning only morphology or phase composition might be altered in these cases [301] (although these times are specific to the electrolyte and current density being used). The applied signal is also an important factor to consider. ...
The plasma electrolytic oxidation is an innovative method for the surface treatment of titanium and its alloys. This review provides an overview of the historical development of the process and summarizes the current state of the art. The chemical as well as the electro- and plasma-chemical basics of the layer forming mechanisms, which comprises the substrate/electrolyte interface before discharge initiation and the different types and stages of plasma electrolytic discharge phenomena are explained within the context of titanium-based materials. How these phenomena can be influenced by the use of suitable electrolytes and controlled by the electrical regime is described. Subsequently, the microstructures and composition of the layers are described in detail, and the properties for specific applications are then discussed. The resistance of a PEO coating to corrosive environments, tribological factors, and alternating mechanical stress is viewed critically, and the extensive functional properties such as physiological compatibility, photocatalytic activity, and decorative properties are revealed. Finally, examples of various practical applications in the medical engineering, aviation, automotive, and environmental technology fields, as well as other branches of industry, are presented.
... No obvious discontinuity is observed among the three layers, indicating that the composite coating can be tightly adhered to the substrate. Such MAO films are expected to have significant applications as artificial bone joints and dental implants [22]. stretching mode of CO 2− 3 group at 1450 cm −1 , but the characteristic OH bands of hydroxyapatite at 3560 cm −1 are not clearly visible, indicating that carbonate incorporated to apatite and formed a carbonate apatite. ...
... Cross-sectional images (Fig.9) also indicated that highly-ordered nano-channels were perpendicular to the substrate, and a compact layer can be observed between the nanopore arrays and the substrate. Besides, the addition of PO4 3-in the electrolyte further improved the cellular performance [92,93]. Moreover, A well-defined micro/nano-morphology can also be acquired by this HCA technique in electrolyte such as Cu(NO3)2, Zn(NO3)2, (Na3PO4 + Ca(NO3)2 + Na2SiO3), and (Na3PO4 + AgNO3 + Na2SiO3), which will extend its application. ...
Ti and its alloys are the most commonly used materials for biomedical applications. However, bacterial infection after implant placement is still one of the significant rising complications. Therefore, the application of the antimicrobial agents into implant surfaces to prevent implant-associated infection has attracted lots of attention. Scientific papers have shown that inorganic antibacterial metal element (e.g. Ag, Cu, Zn) can be introduced to implant surfaces with the addition of metal nanoparticles or metallic compounds into electrolyte via micro-arc oxidation (MAO) technology. In this review, the effects of the composition and concentration of electrolyte and process parameters (e.g. voltage, current density, oxidation time) on morphological characteristics (e.g. surface morphology, bonding strength), antibacterial ability and biocompatibility of MAO antimicrobial coating were discussed in detail. Anti-infection and osseo-integration can be simultaneously accomplished with the selection of the proper antibacterial elements and operating parameters. Besides, MAO assisted by magnetron sputtering (MS) to endow Ti-based implant materials with superior antibacterial ability and biocompatibility was also discussed. Finally, the development trend of MAO technology in the future was forecasted.
... Among the calcium phosphate compounds, hydroxyapatite (HAP) is the most valuable one because of its potential use in bone tissue engineering and also because it exhibits excellent osteoinductivity. 1 The relevance of HAP in load-bearing implants is constrained because of the typical fragility with small fracture toughness. 2 Generally, HAP can be combined with different varieties of natural polymers, synthetic polymers, and graphene family materials. 3 The graphene family nanomaterials include several graphene derivatives, such as few-layered graphene, graphene oxide (GO), reduced graphene oxide, ultrathin graphite, and graphene nanosheets that were used in various biomedical applications. ...
Presently, tissue engineering approaches have been focused toward finding new potential scaffolds with osteoconductivity on bone-disease-affected cells. This work focused on the cisplatin (CDDP)-loaded graphene oxide (GO)/hydroxyapatite (HAP)/chitosan (CS) composite for enhancing the growth of osteoblast cells and prevent the development of osteosarcoma cells. The prepared composites were characterized for the confirmation of composite formation using Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction techniques. A flowerlike morphology was observed for the GO/HAP/CS-3/CDDP composite. UV-vis spectroscopy was used to observe the controlled release of CDDP from the GO/HAP/CS-3/CDDP composite, and 67.34% of CDDP was released from the composite over a time period of 10 days. The GO/HAP/CS-3/CDDP nanocomposites showed higher viability in comparison with GO/HAP/CS-3 on MG63 osteoblast-like cells and higher cytotoxicity against cancer cells (A549). The synthesized composite was found to show enhanced proliferative, adhesive, and osteoinductive effects on the alkaline phosphatase activity of osteoblast-like cells. Our results suggested that the CDDP-loaded GO/HAP/CS-3 nanocomposite has an immense prospective as a bone tissue replacement in the bone-cancer-affected tissues.
... Since the electric parameters of the MAO process also provide incorporation of the anions in the electrolyte into developing coating, the composition of the coating is governed by the composition of the electrolyte used [21]. There are many reports in the literature describing fabrication of biocompatible compounds and/or antibacterial agents containing MAO coatings on titanium and its alloys upon addition of calcium/phosphorus and/or silver containing chemicals into the electrolyte [18,[23][24][25][26][27][28][29][30][31]. More specifically, multi-layer MAO coatings consisting of Ag containing HA layer over a micro-porous, thick and adherent TiO 2 layer have been reported [16,17]. ...
This study has been carried out to optimise the silver (Ag) content of the coating synthesised on commercially pure titanium (Cp–Ti, Grade 4) for biomedical applications by micro-arc oxidation (MAO) process. The MAO process has been conducted in electrolytes containing silver acetate (AgC2H3O2) at different concentrations between 0 and 0·002 mol L⁻¹. When compared to the base electrolyte, coatings synthesised in ≥0·001 mol L⁻¹ AgC2H3O2 added electrolytes exhibited an antibacterial efficiency of 99·98% against Staphylococcus aureus (S. aureus). Detailed examination revealed that the presence of 0·001 mol L⁻¹ AgC2H3O2 in the electrolyte resulted in incorporation of 1·14 wt-% Ag into fabricated coating consisting mainly of outer hydroxyapatite (HA) and inner titanium oxide (TiO2) layers. In comparison to the Ag-free coating, 1·14 wt-% Ag in the coating lowered the proliferation of SAOS-2 cells, which still tended to grow at a relatively low rate with increasing culturing time.
... The micro-pores present on the PEO surface are useful as a depot for bone morphogenic proteins or growth factors which in turn enhances the cell proliferation. In an attempt to improve the bioactivity of the titanium, Ni et al. [7] developed hydroxyapatite containing PEO coating by using Ca and P containing electrolyte. Simka et al. [8] reported an increased bioactivity of Ti alloy by incorporating Ca and P species into the PEO coating. ...
Titania coating was produced on commercially pure titanium by a pulsed DC plasma electrolytic oxidation (PEO) process in an aqueous electrolyte containing 5 g/l trisodium orthophosphate and 2 g/l potassium hydroxide. Four different PEO coatings were fabricated with two different duty cycles (10% and 95%) and two different current frequencies (50 Hz and 1000 Hz) while maintaining a constant current density and process time of 150 mA/cm2 and 8 min, respectively. The phase composition, roughness, thickness, surface morphology and cross-sectional microstructure of the coating were assessed using X-ray diffraction (XRD), optical profilometer, eddy current thickness gauge and scanning electron microscope (SEM). The scratch resistance of the coating was assessed by a scratch test. The corrosion behaviour of the coating was studied in a Kokubo 7.4 pH simulated body fluid (SBF) solution by open circuit potential (OCP) measurement, potentiodynamic polarisation (PDP) and electrochemical impedance spectroscopy (EIS) with equivalent circuit modelling and EIS curve fitting. Among the coatings, the coating produced at 10% duty-50 Hz frequency had a lower thickness, poor corrosion resistance (icorr, 1.9 × 10-4 mA/cm2) and poor scratch resistance (Lc, 15 N) while the coating produced at 95% duty-1000 Hz frequency showed higher corrosion resistance (icorr, 3.3 × 10-6 mA/cm2), higher scratch resistance (Lc, 26 N) and had a dense coating. The coating with highest corrosion resistance also showed good wettability (contact angle, 61 ± 3 °) and apatite forming ability under bioactivity test.
... Indeed, some investigators [1,6,11,59,60] used NaOH or NH 3 ·H 2 O to establish of a basic pH of~9-11. Surprisingly enough, HA is successfully produced in neutral or even acidic electrolytes [7,36,56,58]. Hydroxyapatite is generally considered stable in aqueous systems at pH N 4.2 [63]. However, there are reports of its solubility in water even at pH 6 (see, for example, [64]). ...
Hydroxyapatite (HA) is a bioactive material that is widely used for improving the osseointegration of titanium dental implants. Titanium can be coated with HA by various methods, such as chemical vapor deposition (CVD), thermal spray, or plasma spray. HA coatings can also be grown on titanium surfaces by hydrothermal, chemical, and electrochemical methods. Plasma electrolytic oxidation (PEO), or microarc oxidation (MAO), is an electrochemical method that enables the production of a thick porous oxide layer on the surface of a titanium implant. If the electrolyte in which PEO is performed contains calcium and phosphate ions, the oxide layer produced may contain hydroxyapatite. The HA content can then be increased by subsequent hydrothermal treatment. The HA thus produced on titanium surfaces has attractive properties, such as a high porosity, a controllable thickness, and a considerable density, which favor its use in dental and bone surgery. This review summarizes the state of the art and possible further development of PEO for the production of HA on Ti implants.
... It is worth while mentioning that the anodic part of plasma electrolysis (e.g., PEO treatment) does not show this behavior, and sparking begins at a constant value of applied voltage and is not dependent on DC or AC source for a given electrolytic system. [106][107][108][109] The mechanism of CPE can be described by linear increase of current due to an increase in applied voltage. After reaching specific value of applied potential (break down potential), random sparks will form on the surface of substrate. ...
Cathodic plasma electrolytic (CPE) techniques are new groups of coating processes, which can be used for fabrication of nanostructured layers on surface of a wide range of metallic substrates. The most exciting visible feature of these atmospheric-based plasma techniques is continuous sparking on processed surface inside an electrolyte. Unlike the anodic part of plasma electrolysis (usually known as plasma electrolytic oxidation (PEO) or micro arc oxidation (MAO)), which is commonly used for oxidation of light metals/alloys such as aluminum, titanium and magnesium, CPE techniques can clean and coat different metals and alloys such as steel, copper, and light metals/alloys with formation of wide range of nanostructures including complex carbides, carbonitrides, intermetallics, and even oxides. It has been observed that the properties of obtained layers depend on the characteristics of achieved nanostructures such as average size, distribution and average coordination number of nanocrystallites. Furthermore, the properties of the processed surface can be tailored by tailoring the nanostructure characteristics. There is limited literature available on the mechanism of CPE and its connection to the morphology of nanostructured layers. This article addresses the two important aspects of CPE, namely characterization of nanostructured layers and mechanism of cathodic plasma electrolysis, which are reviewed in accordance to the morphology of fabricated nanostructures.
... Various materials and coatings are currently used for implants (Ratner et al., 2004). It has been repeatedly suggested that PEO coatings offer promise for these purposes, particularly on titanium alloys (Schreckenbach et al., 1999;Sul, 2003;Koegler and Griffith, 2004;Tang et al., 2004;Li et al., 2004Li et al., , 2005Liu et al., 2005;Lee et al., 2006;Chen et al., 2006;Wei et al., 2007;Ni et al., 2008). ...
The adhesion of bovine chondrocytes and human osteoblasts to three titania-based coatings, formed by plasma electrolytic oxidation (PEO), was compared to that on uncoated Ti-6Al-4V substrates, and some comparisons were also made with plasma sprayed hydroxyapatite (HA) coatings. This was done using a centrifuge, with accelerations of up to 160,000 g, so as to induce buoyancy forces that created normal or shear stresses at the interface. It is shown that, on all surfaces, it was easier to remove cells under normal loading than under shear loading. Cell adhesion to the PEO coatings was stronger than that on Ti-6Al-4V and similar to that on HA. Cell proliferation rates were relatively high on one of the PEO coatings, which was virtually free of aluminium, but low on the other two, which contained significant levels of aluminium. It is concluded that the Al-free PEO coating offers promise for application to prosthetic implants.
In this review paper, different methods of hydroxyapatite‐based coatings on external fixation pins with improvement in the adhesion strength are explained. Different coating methods such as dip coating, surface‐induced mineralization, plasma spraying, physical vapor deposition magnetron sputtering, micro‐arc oxidation, electrophoretic deposition, chemical vapor deposition, ion beam assisted deposition, sol‐gel dip coating, pulsed laser deposition, and electrohydrodynamic coating are investigated. The micro‐arc oxidation method showed high degradation delaying of the substrate with a high‐voltage electrolyte solution. Moreover, controlling the coating porosity by applying the gas is a good feature of the physical vapor deposition magnetron sputtering method. The comparison of the hydroxyapatite (HA) coatings method showed that the plasma spraying method leads to better coating features between the coating methods on the implant pins.
Zinc oxide nanoflakes were synthesized using the wet precipitation method from aqueous solutions of zinc nitrate and sodium hydroxide. The obtained materials were characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and nitrogen adsorption–desorption methods. The presence of sodium lauryl sulfate in the preparation of zinc oxide resulted in thinner, larger size, and higher specific surface area nanoflakes. The saturated adsorption capacities of zinc oxide nanoflakes for HCN, NO 2 , and SO 2 were 216 mg g –1 , 81 mg g –1 , and 38 mg g –1 , respectively. These results suggest that the material is a potential candidate for the removal of these toxic gases.
Ti6-Al-4V and pure titanium substrates were subjected to two-step plasma electrolytic oxidation (hybrid PEO coating) and alkali treatment. Electrochemical properties of the hybrid PEO coatings were studied in SBF solution and it was revealed that electrochemical behavior of the samples were correlated to discharge behavior of second step and its effect on compactness of first layer. If discharges are intensified corrosion performance of the existing layer deteriorates while lowering of discharge intensity of second step will result in modification of existing layer and hence improves corrosion performance. Electrochemical and microstructural tests were carried out after alkali treatment and it was found that after alkali-treatment the surface became nano-flaky, phase composition of oxide layer was not changed, and the chemical composition was slightly changed due to dissolution in NaOH solution. After 2 weeks of immersion, surface of samples were fully covered by HA. XPS and FTIR studies confirmed that hydroxyl groups were formed on the surface of oxide film which found to be responsible for enhanced bioactivity of the samples. Superior bioactivity of PEO oxide film on CP-Ti samples were correlated to presence of anatase and its lower point of zero charge, compared to rutile phase. It was also revealed that the surficial porosities favored formation of HA nuclei and hence improve bioactivity. A novel graphical method is developed for estimation of porosity of PEO oxide films, which helps to predict bioactivity behavior of oxide films. It was found that the area under graph of Nyquist admittance plot is inversely proportional to the porosity of HPEOs. It was revealed that the first peak at high-frequency range of electrolyte resistance corrected Bode-Phase plots can be considered as the upper limit of frequency for the proposed graphical method. The results of estimations of graphical method show good compatibility with image analysis method.
The effects of the applied voltage on the morphology, composition and corrosion behaviour of Ti7Cu5Sn coated were investigated. At applied voltages lower than 250 V, the composite coatings consist of anatase-TiO2, rutile-TiO2, DCPD(CaHPO4·2H2O) and a small amount of amorphous calcium phosphate phase. When the applied voltage is increased, the ceramic coatings transform from DCPD (CaHPO4·2H2O) to HA (Ca10(PO4)6(OH)2, 300 V), and new phases of Ca2P2O7, CaTiO3 and TCP(Ca3(PO4)2) form at 350 V. The passive current densities at body potential are one order of magnitude lower than that of the uncoated sample, indicating better corrosion resistance. The MAO film is a tri-layer system: a compact inner layer, a mesosphere porous oxide layer, and an outer layer.
In the present study, a novel TiO2-based coating containing nanosized hydroxyapatite (n-HA) and Silver particles has been formed on commercially available Ti-6Al-4V (Grade 5) and Ti-pure (Grade 2) alloy substrates by the Plasma Electrolytic Oxidation (PEO) technique. The coating deposition were provided in an aqueous solution of disodium hydrogen phosphate containing suspended hydroxyapatite nanoparticles and potassium hydroxide under a pulsed bipolar current mode with controlled duty cycle. Inclusion of antimicrobial silver particles were possible from a separate technological operation in AgNO3 aqueous solution by the principle of photocatalysis at TiO2 surface under ultraviolet treatment. The surface morphology of the formed coatings has been examined by Scanning Electron Microscopy (SEM), while the element composition of the coatings has been determined by Energy Dispersive X-ray analysis (EDS). The presence of HA nanoparticles within the formed coatings has been analyzed by Fourier 66 Bioaktywne powłoki przeciwdrobnoustrojowe na wyrobach medycznych do implantacji... Dzhurinskiy Dmitry. 2018. "Bioaktywne powłoki przeciwdrobnoustrojowe na wyrobach medycznych do implantacji nałożone przez plazmowe utlenianie elektrolityczne". Obróbka Plastyczna Metali XXIX (1): 65-76. Transform Infrared Spectroscopy (FTIR). The results indicate that the formed PEO coatings exhibit a porous network structure with embedded n-HA and Ag particles uniformly distributed over the entire surface of the coatings. The PEO-formed TiO2:n-HA:Ag layers can be used as a bioactive biomimetic coating with antimicrobial properties to enhance surface bioactivity, osseointegration and biochemical stability in implantable medical devices.
A porous hydroxyapatite (HA)-incorporated TiO2 coating has been deposited on the titanium substrate using a plasma electrolytic oxidation coupled with electrophoretic deposition (PEO-EPD). Potassium titanium(iv) oxalate is decomposed by micro arcs generated on the anode producing TiO2 while HA particles have been simultaneously deposited on anode during EPD process. Hydroxyapatite and TiO2 particles have been coagulated into roundish conglomerates with the average diameter in a range of 200-600 nm. The microstructure, as well as elemental and phase composition of the coatings have been examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), glow discharge optical emission spectroscopy (GDOES), fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). XRD has showed that the coatings are composed mainly of HA, rutile and anatase phases. The composition and surface morphologies are not strongly dependent on the applied voltages. The amount of HA deposited into the coating increases with increasing the applied voltage. The wear resistance of PEO-EPD coatings has been assessed using tribological tests. The bioactivity of the obtained coatings has been investigated in a simulated blood fluid.
High current anodization (HCA) is a novel strategy to fabricate micro/nano-textured surface with TiO2 mesoporous arrays (MNT-TMAs) on biomedical titanium (Ti) and its alloys. However, our previous study shows that the structure prepared in AgNO3 electrolyte has severe cytotoxicity because of the incorporation of Ag into the surface. The present work tries to prepare MNT-TMAs on Ti surfaces in Cu(NO3)2 electrolyte to eliminate the side effect of Ag. Our results show that the unique structure can be generated in a wide range of Cu(NO3)2 concentrations (1.0 to 12.0 g/l). The increase of Cu(NO3)2 concentration has little influence on its micromorphology but decreases the diameter of mesopores. Good interfacial strength is observed. The resultant surface possesses good cytocompatibility because of the absence of toxic Cu in the coatings. Addition of Na3PO4 into the electrolyte has little influence on its microstructure, but can further improve the cytocompatibility due to the incorporation of P into the surface. Good cytocompatibility and interfacial strength render the technique promising in surface modification of implant materials.
Microarc oxidation (MAO) coatings with a rich calcium and phosphorus composition are prepared on the titanium surface in Ca2+ and PO43- ion electrolytes; the surface is then treated with a hydrothermal method in order to obtain the hydroxyapatite (HA). The effects of the different voltage of MAO and hydrothermal treatment (neutral water used) on the surface morphology, phase composition, properties of the coatings and biologically active property are investigated. The results show that the MAO coatings are composed mainly of anatase TiO2 and that the pore size, surface roughness, thickness, hydrophilic property and corrosion resistance of the MAO coatings strongly depend on the voltage. Furthermore, the proportion of anatase and rutile TiO2, content of HA and cell proliferation are affected by the hydrothermal treatment (neutral water used). As a result, the MAO and hydrothermal treatment coatings obtain a better hydrophilic property, richer calcium and phosphorus content, favored higher cell proliferation. The oxide films on titanium are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thickness gauge and polarization curves, respectively. In addition, the methyl thiazole tetrazolium (MTT) assay is used to explore the cell proliferation assay.
The mineralization behavior of the petal-like apatite/TiO2 coating, which was prepared by micro-arc oxidation (MAO) on the surface of the commercially pure titanium, was studied in simulated body fluid (SBF). The results showed that the bone-like apatite formed on the surface of the petal-like apatite layer as early as 12 h immersion in SBF. In the early immersion stage, the petal-like apatite dissolved fast into the SBF, which promoted the nucleation of the bone-like apatite, and then the nucleus of apatite grew by consuming the Ca and P ions in the SBF. It was proposed that the formation of the apatite layer on the surface of the petal-like apatite/TiO2 composite coating in SBF followed the dissolution-precipitation mechanism.
The aim of this study is to explore porous titanium inner-pore wall modification by plasma electrolytic oxidation, with the emphasis on the structural characteristics of the anodized films (including morphology, phase component, element composition and chemical species), and to evaluate the apatite-forming ability of PEO-treated porous titanium in a simulated body fluid (SBF).
Hydroxyapatite is a commonly known biocompatible and bioactive material employed in the field of medicine. Many of these properties depend on the particle size, grain size distribution and micro structural defects. Keggin is a mesoporous structured compound which can stack the biomolecules into it. We have successfully formed Hydroxyapatite by coprecipitation method over aluminium Keggin. The formation of the hydroxyapatite has been confirmed with XRD and the particle size has been calculated by using Scherrer formula. The organic bands have been studied with the FTIR bands and SEM images show the morphological properties of the Hydroxyapatite. EDX graph gives the chemical compositions.
In recent years, calcium phosphate-base composites, such as hydroxyapatite (HA) and carbonate apatite (CA) have been considered desirable and biocompatible coating layers in clinical and biomedical applications such as implants because of the high resistance of the composites. This review focuses on the effects of voltage, time and electrolytes on a calcium phosphate-base composite layer in case of pure titanium and other biomedical grade titanium alloys via the plasma electrolytic oxidation (PEO) method. Remarkably, these parameters changed the structure, morphology, pH, thickness and crystallinity of the obtained coating for various engineering and biomedical applications. Hence, the structured layer caused improvement of the biocompatibility, corrosion resistance and assignment of extra benefits for Osseo integration. The fabricated layer with a thickness range of 10 to 20 μm was evaluated for physical, chemical, mechanical and tribological characteristics via XRD, FESEM, EDS, EIS and corrosion analysis respectively, to determine the effects of the applied parameters and various electrolytes on morphology and phase transition. Moreover, it was observed that during PEO, the concentration of calcium, phosphor and titanium shifts upward, which leads to an enhanced bioactivity by altering the thickness. The results confirm that the crystallinity, thickness and contents of composite layer can be changed by applying thermal treatments. The corrosion behavior was investigated via the potentiodynamic polarization test in a body-simulated environment. Here, the optimum corrosion resistance was obtained for the coating process condition at 500 V for 15 min in Ringer solution. This review has been summarized, aiming at the further development of PEO by producing more adequate titanium-base implants along with desired mechanical and biomedical features.
The strength of adhesion at the cell-substrate interface is an important parameter in the design of many prosthetic implant material surfaces, due to the desire to create and maintain a strong implant-tissue bond. This study focuses on the mechanical strength of the interface and the ease of cell removal from ceramic coatings using normal and shear forces, but also looks at cell proliferation rates on the same series of surfaces.
This systematic study of cell proliferation and adhesion has been carried out on a series of oxide coated Ti6Al4V based substrates with a range of surface morphologies and chemistries. Oxide coatings were formed using Plasma Electrolytic Oxidation (the PEO process).
Cells were seeded at a low concentration onto substrates and proliferation monitored for up to three weeks. The same cell concentrations were seeded on samples for adhesion testing. These were cultured for a few days to ensure well established adhesion of viable cells. The normal and shear strength of osteoblasts (bone cells) and chondrocytes (cartilage cells) adhered to these substrates was measured using accelerated negative buoyancy within an ultracentrifuge.
The variation in proliferation rates on, and adhesive strengths to, the range of coatings, is discussed and related to morphological and chemical differences in the coatings. A comparison is made between the normal and shear strengths of the cell-coating bonds and the differences between the behaviour of the two cell types discussed.
Micro-arc oxidation (MAO) is commonly applied to modify the surface of titanium (Ti)-based medical implants with a bioactive and porous Ti oxide (TiO2) coating. The study reports a new method of incorporating hydroxyapatite (HA) within the TiO2 coating by MAO and alkali heat treatment (AHT) in the solution containing Ca ion and P ion. The morphology, composition and phase composition of the coatings were analyzed with scanning electron microscopy with energy-dispersive X-ray spectrometer and X-ray diffraction. Surface topography and roughness of the coatings were investigated by atomic force microscopy operated in the tapping mode. The results showed that TiO2-based coatings were obtained on pure Ti by MAO with an electrolyte containing Ca ion and P ion; the prepared MAO coatings were mainly composed of Ca, P, O and Ti. AHT transformed Ca and P to HA crystals. In conclusion, the TiO2/HA composite coatings can be obtained on the surface of pure Ti by MAO and AHT, and the addition of Ca ion and P ion to the AHT solution contributed to the formation of HA.
Polycrystalline and dispersed hydroxyapatite (HAP) nanoparticles were successfully prepared via a simple precipitation method with the aid of a new capping agent based on Schiff base compounds. After that, a composite of chitosan (CT), graphene oxide (GO) and HAP nanoparticles was synthesized by a freeze-drying method. The as-produced Schiff base, HAP nanoparticles, and CT/GO/HAP nanocomposite were analysed by several techniques including FTIR, SEM, HR-TEM, and XRD. In addition, the in vitro bioactivity of HAP nanoparticles and the CT/GO/HAP nanocomposite was evaluated by soaking them in simulated body fluid (SBF). By monitoring the changes of chemical composition of the SBF solutions, it was concluded that more Ca and P ions were released from the CT/GO/HAP nanocomposite compared to the pure HAP nanoparticles, indicating a high bioactivity of the nanocomposite. The SEM images showed that the formation and growth of apatite on the surfaces of the products increased after immersion for 14 days in SBF.
In this work, crystalline hydroxyapatite (HAP) nanorods were first prepared by a simple precipitation method in the presence of a new capping agent based on Schiff base compounds, and then composite of polyethylene glycol (PEG), graphene oxide (GO), and the HAP nanorods was synthesized by freeze-drying method. X-ray diffraction patterns indicated that poor crystalline HAP powders produced in the absence of Schiff base were highly agglomerated. In addition, in vitro bioactivity of the produced HAP nanorods and PEG/GO/HAP nanocomposite was evaluated by soaking the products in simulated body fluid (SBF). The chemical composition of the SBF solutions was analyzed by inductively coupled plasma-optical emission spectrometry, and it was found that more Ca and P were released from the nanocomposite compared to the pure HAP nanorods, indicating high bioactivity of the nanocomposite. In addition, it was observed that the growth of new apatite on the surface of the nano-sized materials increased after immersion for 14 days in the SBF solution.
It is believed that the excellent biological performance of a titanium implant is a result of its passivating nature, forming of a whole titanium oxide layer on the implant. There are increasing evidences that the titanium oxide layer is decisive for a good contact of an orthopedic implant to its surrounding tissue. And numerous reports reveal that the titanium oxide can be activated by chemical or physical procedures. In this article, based on the mechanisms and mode of action, they are classified into four categories, including doping of inorganic components, light exciting, interface engineering, and external electric field programming. The exploration and design on light exciting and interface engineering procedures are most worth receiving further illuminations since these kinds of processes are promising in fabrication of coatings with selective or "smart" biological activity.
Two types of ceramic coatings on commercially pure titanium for dental implant applications with different Ca/P ratios in the range from 1.5 to 4.0, and two different thicknesses (∼5 and ∼15μm) were examined with the aim of underpinning the effect of coating composition, thickness and microstructure on the corrosion behavior and hydroxyapatite forming ability in SBF.
Bioactive coatings were formed on Ti by plasma electrolytic oxidation (PEO). The composition, structure, and morphology of the materials were characterized before and after the immersion in simulated body fluid solution (SBF) at 37°C for up to 4 weeks. All the materials were screened with respect to metal ion release into SBF.
Only thick PEO coating with overstoichiometric Ca/P ratio of 4.0 exhibited capacity to induce the precipitation of hydroxyapatite over the short period of 1 week. Long term Ti(4+) ion release from all PEO-coated materials was 2-3 times lower than from the uncoated Ti. Metal ion release is attributed mostly to chemical dissolution of the coating at initial stages of immersion.
The long term stability was greater for thin PEO coating with overstoichiometric Ca/P ratio of 2.0, which exhibited ∼95ngcm(-2) of Ti(4+) ions release over 4 weeks. Thin PEO coatings present economically more viable option.
TiO2 nanopowders have been synthesized from a peroxotitanium solution chemical bath route. The variation of H+ concentrations of the reaction solutions was measured during the course of the synthesis. X-ray diffraction analysis and transmission electron microscope observation showed that peroxotitanium concentration can affect the crystal type and morphology of the TiO2 nanopowders. The particle size of TiO2 nanopowders prepared from 0.1 mol L−1 peroxotitanium is 7.7 nm. The specific surface area of this nanopowder is 250 m2 g−1. Thermogravimetric analysis showed that the TiO2 nanopowder dried at 80 °C for 24 h contains 11% water.
Ti-based implant materials have specific complications associated with their applications because of their unsatisfactory bioactivity. Hence, a surface which displays selective biointeractivity, i.e., enhancing the bioactivity of material but inhibiting pathogenic microbial adhesion, would be highly desirable. The aim of the present study was to investigate the effects of the haloid ions on the bioactivity of Ti oxide film via the micro-arc oxidation (MAO). After MAO treatment, scanning electron microscopy (SEM) and X-ray diffraction (XRD) results showed the titanium surfaces were covered by porous titania of anatase and/or rutile. In simulated body fluid, titanium treated with MAO could induce apatite formation on its surface. SEM and energy dispersive X-ray spectroscopy (EDX) showed there were some particles covered, and the Ca/P, Si, and haloid ions deposited on the surfaces of MAO groups. Our results showed that induction of apatite-forming ability on titanium metal and co-deposition of TiO2 film and haloid ions could be attained by MAO. So it is believed that MAO is an effective way to prepare bioactive titanium and the haloid ions may not have an effect on the bioactivity of the TiO2 film, which can be applied to transcutaneous implant.
Ti-6Al-4V was hydrothermal treated in the solution of sodium dihydrogen phosphate after the process of Micro-arc oxidization (MAO). The phase, composition morphology and biocompatibility of the coatings are characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS). It was found that the adding of sodium dihydrogen phosphate in the hydrothermal solution can help optimal HA growth condition. Inside certain limits, higher concentration of sodium dihydrogen phosphate do not provide a more competitive HA growth condition. The samples treated by such process performance a good bioactivity. Many HA crystals formed after 0.5 day, and HA crystals were formed all through the film after 1 day.
Microwave (MW) processing has been studied as an alternative method of hydroxyapatite (HA) based composite coatings on commercially pure titanium (CPTi) to enhance the bioactivity for orthopaedic and dental implant applications. The coating was formed by processing CPTi metal packed in HA and at 800W microwave power for 22min. The composition of the coating was found to be TiO2 (rutile) as major phase along with HA as minor phase. The MW absorption of non-stoichiometric TiO2 layer, which was grown during the initial hybrid heating, resulted in sintering of apatite particles interfacing them. The non-stoichiometric nature of TiO2 was evident from the observed mid-gap bands in ultraviolet–visible diffusive reflectance (UV–VIS-DR) spectrum. The lamellar α structure of the substrate suggests that the processing temperature was above β transus of CPTi (1155K). The oxygen stabilized α phase whose thickness increased with microwave processing time, was likely to be the reason for the increase in Young's Modulus and hardness of the substrate. The coating induced apatite precipitation in bioactivity test. The osteoblast cell adhesion test demonstrated cell spreading which is considered favourable for cell proliferation and differentiation. Thus, in situ composite coating of titania and HA on CPTi was obtained by a simple one-step process.
Oxide based ceramic conversion layers containing Ca and P were prepared on AZ91D Mg alloy by plasma electrolytic oxidation technique in Na 2SiO3 and NaOH systems respectively. The conversion layers prepared in both systems were porous and grey white. The doping of Ca decreased the porosity of the conversion layers in Na2SiO3 system, while increasing the porosity of and the microcracks of the conversion layers in NaOH system. The conversion layer prepared in NaOH system was composed of MgO, and the one prepared in Na2SiO3 system was composed of Mg2SiO4 and MgO; P and Ca only existed in the form of amorphous state in the conversion layer. The doping of Ca decreased the relative content of P while increasing the relative content of Ca in both conversion layers. The ceramic conversion layers in both systems improved the corrosion resistance of the AZ91D Mg alloy in 0·9%NaCl solution by one or two orders of magnitude.
A Plasma electrolytic oxidation (PEO) process was used to produce bioactive coatings on Ti. PEO coatings with Ca/P atomic ratio of 1.7 and 4.0 were fabricated and characterized with respect to their morphology, composition, and microstructure. AC and DC electrochemical tests were used to evaluate the effect of (i) organic additives (amino acids, proteins, vitamins, and antibiotics) in alpha-minimum essential medium (α-MEM) on electrochemical stability of noncoated and PEO-coated Ti and (ii) coating composition, microstructure, and corrosion behavior on the cell response in α-MEM. PEO-coated Ti showed higher corrosion resistance than the noncoated Ti in MEM with and without organic additives by an order of magnitude. The corrosion resistance in α-MEM decreased with time for nonmodified Ti and increased for PEO-coated Ti; the latter was because of the adsorption of the proteins in the coating pores which increased the diffusion resistance. The presence of Ca and P in titanium oxide coating at the Ca/P ratio exceeding that of any stoichiometric Ca-P-O and Ca-P-O-H compounds facilitates faster osteoblast cell adhesion. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.
This study attempts to enhance the osseointegration of titanium implants by adopting a micro-arc treatment (MAT) capable of replacing calcium (Ca) with different percentages of strontium (Sr) in order to fabricate strontium-containing hydroxyapatite (Sr-HAp) coatings. Sr, regarded as a significant therapy promoting bone mass and bone strength, has a dual mechanism, enhancing osteoblast differentiation and inhibiting osteoclast differentiation. This study also investigates how Sr content affects the microstructure of and osteoblast/osteoclast growth on the coatings. Experimental results indicate that an increase in the Sr content in the electrolyte bath results in a greater degree of Sr substitution at Ca sites within the HAp phase, facilitating the formation of Sr-HAp coatings with Sr fully solid soluble in the HAp phase. Irrespective of the Sr content, most coatings are similar in porous morphology and pore size. Additionally, the Sr-HAp coating shows higher osteoblast compatibility than raw titanium metal and the HAp coating. Moreover, cell adhesion and proliferation after 48 h was greater than that after 4 h, indicating that Sr can stimulate osteoblast adhesion and proliferation. Further, Sr significantly inhibits osteoclast differentiation when the Sr-HAp coatings exceed 38.9 at.% Sr.
This article describes the preparation and analysis of macroporous TiO2 films on Ti surfaces, for application in bone tissue–Ti implant interfaces. These TiO2 bioceramic films have a macroporous structure consisting of monodisperse, three-dimensional, spherical, interconnected pores adjustable in the micron size range. Micron-sized polystyrene (PS) bead templates are used to precisely define the pore size, creating macroporous TiO2 films with 0.50, 16, and 50 μm diameter pores, as shown by scanning electron microscopy. X-ray photoelectron spectroscopy shows the films to be predominantly composed of TiO2, with ∼10% carbon. X-ray diffraction reveal rutile as the main phase when fired to the optimal temperature of 950°C. Preliminary experiments find that the in vitro proliferation of human bone-derived cells (HBDC) is similar on all three pore sizes. However, higher [3H]thymidine incorporation by the HBDC is observed when they are grown on 0.50- and 16-μm pores compared to the 50-μm pores, suggesting an enhanced cell proliferation for the smaller pores. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 57: 588–596, 2001
The present paper reports on the production of oxide coatings on an aluminium alloy by microplasma oxidation and on their properties. The surface characteristics of the coatings were determined by surface and structural analytical techniques, i.e. SEM and X-ray diffraction. Thermo-analysis of the coatings was evaluated by means of differential scanning calorimetry and thermogravimetric analyses. It was ascertained that the coatings with a mixture of crystallised γ-Al2O3 and α-Al 2O3 have significant microhardness, good electric resistance and good thermostability.
A porous hydroxylapatite-containing titania film was prepared by a electrochemical oxidation method, i.e. micro-arc oxidation (MAO). During the oxidation treatment, the titanium sample was immersed in electrolytic solution containing calcium acetate monohydrate and sodium biphosphate dihydrate by using a pulse power supply. The thickness, phase, composition and morphology of the oxide coating were monitored with X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS). The thickness of the MAO film was about 20 μm and the coating was porous and uneven, without apparent interface to the titanium substrates. The coating formed in the Ca- and P-containing solution with MAO contained Ca and P along with Ti and O. The Ca/P ratio on the surface is 1.63, while that in the interface is 0.51. XRD showed that the porous coating was made up of anatase, rutile and hydroxyapatite. Such MAO films are expected to have significant medical applications as dental implants and artificial bone joints.
In order to optimize the production regime for effective coatings of required thickness on Ti6Al4V surface, a comparative study was made on the kinetics of ceramic coatings growth, and was associated with the evolution of microstructure and phase composition during microarc oxidation (MAO) under constant voltage and constant current density regime, respectively, using an Ac pulse power supply in Na2SiO3–KOH–(NaPO3)6 solution. The thickness of the resulting coatings was measured using a coating thickness gauge based on eddy principle. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to characterize the microstructure and phase composition of the coatings. The results show that as treatment time increases, the coating grows in an exponential function accompanied by a gradually decaying current density for constant voltage control mode (U=500 V), For constant density control mode (J=60 mA/cm2), voltage increases rapidly up to a relatively stable value and the coating grows linearly; compared with the constant voltage mode, the coating grows faster. Phase composition and microstructure evolution during MAO process are almost independent of control mode. With increasing treatment time, the predominant phase composition varies from anatase to rutile, which indicates that phase transformation of anatase into rutile occurs in the duration of oxidizing process. Meanwhile, the size of micropores existing on the coating surface increases and thus the surface becomes much coarser.
Pretreatment of titanium by implantation of P and Ca is of interest in order to improve the quality of hydroxyapatite coatings used to enhance its biocompatibility. A near surface implantation of high doses of calcium results in an oxidation of the modified layer and the formation of CaO. By post-implantation annealing also Ca4Ti3O10 is formed. For deeper calcium implantations, precipitation of the metastable hexagonal modification of calcium has been observed instead of the cubic equilibrium phase. By high dose implantation of phosphorus, the implanted layer becomes partly amorphized. This hinders the reaction with oxygen during implantation and room temperature aging. The thickness of the surface oxide corresponds to the native oxide layer. For high dose double implantation with both elements, due to the strong swelling effect and the incorporation of oxygen, the second implant is shifted to the surface, if the energies are chosen so that the profiles should be overlapping by implantation into pure titanium. No indication for compound formation besides calcium oxide has been found as a result of the implantation.
Titanium alloys have been used with some success in several bioimplant applications. However, they can suffer certain disadvantages, such as poor osteoinductive properties and low corrosive-wear resistance. Attempts to overcome the first of these drawbacks have involved coating the metal with the bioceramic material hydroxyapatite (HA), a primary component of bone and a very good osteoinductor. Since TiO2 coatings are also known to be effective as chemical barriers against the in-vivo release of metal ions from the implants, a double layer HA–TiO2 coating on titanium alloys with HA as the top layer and a dense TiO2 film as the inner layer should possess a very good combination of bioactivity, chemical stability and mechanical integrity.This paper describes efforts to improve implant biocompatibility and durability by applying a hybrid treatment of micro-arc discharge oxidation (MDO) and electrophoretic deposition. The most common structural titanium alloy (Ti-6Al-4V) was used as the substrate material. A phosphate salt solution and an HA powder aqueous suspension were used as the electrolyte for micro-arc oxidation and the solution for HA electrophoretic deposition, respectively. It is shown that a relatively thick and hard TiO2 coating can be produced by anodic micro-arc oxidation of titanium, and an HA coating incorporated on top of the TiO2 layer can simultaneously be formed using a combination of plasma electrolysis and electrophoresis, with the suspension held at high values of pH.X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) have been used to investigate the microstructure and morphology of the coatings. The adhesive strength between the coating and substrate has been assessed using scratch adhesion testing. The corrosion resistance of the specimens was examined using potentiodynamic tests in a buffered physiological solution. The results indicate that a hybrid combination of micro-arc oxidation and electrophoretic deposition can provide a phase-pure HA top layer and anticorrosive TiO2 interlayer, which should show good mechanical and biochemical stability in the corrosive environment of the human body.
Titania-based films on titanium were formed by micro-arc oxidation in electrolytic solutions containing sodium carbonate, sodium phosphate, acetate monohydrate and β-glycerophosphate disodium salt pentahydrate using a pulse power supply. The morphology, elemental composition and phase components of the films were investigated as a function of the electrolytes composition and the applied voltage (in the range of 200–500 V). In vitro bioactivity of the films was evaluated in a most commonly used simulated body fluid as proposed by Kokubo et al. The results showed that the films were porous with 1–8 μm pores and nano-crystallized, without apparent interface to the titanium substrates. The phase components of the films could be anatase, rutile, CaTiO3, β-Ca2P2O7 and α-Ca3(PO4)2, strongly depending on the electrolytes composition and the applied voltage. The pore size and the content of Ca and P tended to increase with the applied voltage. Among the prepared titania-based films, only the film containing CaTiO3, β-Ca2P2O7 and α-Ca3(PO4)2 could induce an apatite layer on its surface, exhibiting bioactivity. The bioactive response of the micro-arc oxidized films to the structural factors and the apatite-induced mechanism were discussed.
Nanocrystalline titania films were synthesized by micro-arc oxidation of titanium substrates in an electrolytic solution using a pulsed power supply. X-ray diffraction (XRD) indicated that the deposited films consisted of a high crystalline anatase phase. Field emission scanning electron microscopy (FESEM) showed that the films were macro-porous with 1–2 μm pores and the matrix was composed of 10–20 nm grains. The adhesion–tension test showed that the films had an adhesive strength of 20±2MPa. Such firmly adhesive, porous and nanocrystalline anatase films are expected to have significant applications as orthopaedic/dental implants and catalysts.
Weight-saving materials are becoming increasingly important, especially in the automotive and aerospace industries. Design engineers would thus like to make more extensive use of light metals such as aluminium, titanium, magnesium and their alloys; however, these materials tend to have poor wear resistance. Previous treatments and coatings applied to aluminium alloys, for example by traditional processes such as hard anodising and thermal spraying, have suffered from the low load support from the underlying material and/or insufficient adhesion, which reduces their durability. Also, although TiN-, CrN- or DLC-coated aluminium alloys (using various PVD methods) can achieve a high surface hardness, in practice they often exhibit poor performance under mechanical loading, since the coatings are usually too thin to protect the substrate from the contact conditions.In the work reported here, a plasma electrolysis technique known as micro-arc discharge oxidation (MDO) was investigated; thick and hard oxide ceramic layers were fabricated on BS Al-6082 aluminium alloy by this method. The phase composition and microstructure of the MDO coatings were investigated by XRD, SEM and EDX analyses. A number of adhesion and tribological sliding and impact wear tests were also performed. It was found that Al–Si–O coatings with a hardness of up to 2400 HV and with excellent wear resistance and load support could be formed. The thickness of the coatings significantly influenced the mechanical properties. In terms of tribological performance, the thicker coatings performed best in sliding, scratch and impact tests whilst thin coatings were also surprisingly effective in both impact and low-load sliding. Coatings of intermediate thickness provided relatively poor performance in all tribological tests.
A novel method has been developed to attach, retain, and release antibiotics from titanium based materials. This technique consists of forming porous surface coatings by anodizing and using the surface chemical properties of the oxide coatings to attach antibiotics. Coatings with pores in the size range 0.1-0.5 micron have been formed in acid solutions. The attachment and retainment of gentamicin sulfate, a cationic antibiotic, to the coatings has been investigated using microbiological methods. In vitro test results have shown that the duration of antimicrobial activity on the surface of anodized materials is dependent on the porosity and isoelectric point of the coatings. Using microporous oxide coatings formed in phosphoric acid solutions, it has been found that antimicrobial activity could be retained for more than 2 weeks.
Bond coats for plasma-sprayed hydroxyapatite (HAp) coatings on Ti-6A1-4V hip endoprotheses are being developed for improved in vivo performance. Bond coat powders consisting of (i) CaO-stabilized zirconia, (ii) a eutectic composition of titania and non-stabilized zirconia, and (iii) titania were applied by atmospheric plasma spraying (APS) to Ti-6A1-4V-coupons and 100 microm-thick Ti-6A1-4V foils. Subsequently, a thick layer of HAp was sprayed onto the thin bond coats. Peel tests on Ti-6A1-4V foil/bond coat/HAp top coat assemblies revealed that titania and titania/ zirconia bond coats increased the peel adhesion strength in a statistically significant way from 22 N m(-1) (HAp without a bond coat) to >42 and 32 N m(-1), respectively. Microstructural investigations by SEM on cross-sections of coatings leached in simulated body fluid for up to 28 days led to the conclusion that the chemically very stable bond coats act as an improved chemical barrier against in vivo release of metal ions from the implant, as well as an improved adhesive bond by development of very thin well-adhering reaction layers, presumbly composed of perovskite, calcium dititanate, and/or calcium zirconate.
The aim of the present study is to investigate bone tissue reactions to various surface oxide properties, in particular to different surface oxide chemistry of oxidized titanium implants (grade 1). One control and three test screw-shaped implant groups were prepared. Controls were turned implants. Test implants, i.e. S implants, P implants and Ca implants were by the micro-arc oxidation (MAO) method. The surface characterizations were performed with X-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning electron microscopy, X-ray diffractometry and TopScan 3D. Eighty implants were inserted in the femora and tibiae of ten mature New Zealand white rabbits for 6 weeks. The removal torque values (RTQ) showed significant differences between S implants and controls (p=0.022), Ca implants and controls (p=0.0001), Ca implants and P implants (p=0.005) but did not show significant differences between the others (p>0.05). In addition, the bone to metal contact (BMC) around the entire implants demonstrated 186% increase in S implants, 232% increase in P implants and 272% increase in Ca implants when compared to the paired control groups. Based on the comparative analysis of the surface characteristics resulting different bone responses between all groups, it was concluded that surface chemistry and topography separately or together play important roles in the bone response to the oxidized implants.
The surface of a titanium (Ti) implant was modified by micro-arc oxidation (MAO) treatment. A porous layer was formed on the Ti surface after the oxidation treatment. The phase and morphology of the oxide layer were dependent on the voltage applied during the oxidation treatment. With increasing voltage, the roughness and thickness of the film increased and the TiO(2) phase changed from anatase to rutile. During the MAO treatment, Ca and P ions were incorporated into the oxide layer. The in vitro cell responses of the specimen were also dependant on the oxidation conditions. With increasing voltage, the ALP activity increased, while the cell proliferation rate decreased. Preliminary in vivo tests of the MAO-treated specimens on rabbits showed a considerable improvement in their osseointegration capability as compared to the pure titanium implant.
Biomimetic apatite coatings on micro-arc oxidized titania films were investigated and their apatite-inducing ability was evaluated in a simulated body fluid (1.0 SBF) as well as in a 1.5 times concentrated SBF (1.5 SBF). Titania-based films on titanium were prepared by micro-arc oxidation at various applied voltages (250-500 V) in an electrolytic solution containing beta-glycerophosphate disodium salt pentahydrate (beta-GP) and calcium acetate monohydrate (CA). Macro-porous, Ca- and P-containing titania-based films were formed on the titanium substrates. The phase, Ca and P content, morphology, and thickness of the films were strongly dependent on the applied voltage. In particular, Ca- and P-containing compounds such as CaTiO3, beta-Ca2P2O7 and alpha-Ca3(PO4)2 were produced at higher voltages (>450 V). When immersed in 1.0 SBF, a carbonated hydroxyapatite was induced on the surfaces of the films oxidized at higher voltages (>450 V) after 28 days, which is closely related to the Ca- and P-containing phases. The use of 1.5 SBF shortened the apatite induction time and apatite formation was confirmed even on the surface of the films oxidized at 350 V, which suggests that the incorporated Ca and P in the titania films play a similar role to the Ca- and P-containing compounds in the SBF.