Development of hydroxyapatite coatings on laser textured 316 LSS and Ti-6Al-4V and its electrochemical behavior in SBF solution for orthopedic applications

The current work focused on the development of hydroxyapatite (HAP) coating on laser textured metallic implants using electrophoretic deposition. HAP was synthesized by sol-gel technique and its phase purity and surface morphology were confirmed by FT-IR, XRD and SEM analysis. 316 L SS and Ti-6Al-4V metal implants were polished and the surface was modified using Nd-YAG laser operating at a pulse interval of 10 ns at various overlapping rate of 0%, 25% and 50%. The laser treated surface was characterized for its surface roughness using surface profilometry and surface morphology. The surface roughness of the metallic implants was increased by increase in the overlapping rate. The prepared HAP powder was electrophoretically deposited on bare and laser textured Ti-6Al-4V and 316 L stainless steel followed by vacuum sintering at 300 °C for 2 h. Scratch analysis results showed an improvement in adhesion strength for the HAP coatings on laser treated specimens than untreated metal. Corrosion efficiency of the coated samples was studied in SBF solution using EIS and potentiodynamic polarization studies. The result from the corrosion experiments proved increased corrosion resistance property of laser textured coated samples when compared to bare alloy due to higher adhesion of HAP coating on the metal surface.     

Osseointegration of sputtered SiC-added hydroxyapatite for orthopaedic applications

Over the last few years, a trend in medical applications is to find solutions for metallic implants using coatings that can improve bioactivity and osseointegration. The goal of this study was to obtain and investigate sputtered hydroxyapatite coatings enriched with SiC to enhance the bioactivity and osseointegration of Ti alloys used in orthopaedic applications. The films were characterized in terms of phase composition, roughness, corrosion resistance in a synthetic body fluid (SBF) and in vitro biocompatibility with MG 63 osteoblast-like cells. All of the investigations were conducted using XRD, AFM, cell viability assays and proliferation tests. The results revealed that the addition of SiC had a positive influence on the properties of the sputtered hydroxyapatite. The addition of SiC led to an improvement in coating adhesion and corrosion resistance in an SBF solution over the HAP coating. All of the coatings presented cell viability values over 90%, revealing their suitability for medical applications.     

Hydroxyapatite coating on selectively passivated and sensitively polymer-protected surgical grade stainless steel

Surgical grade stainless steel (316L SS) is a widely used implant material in orthopedic surgeries. However, the release of metallic ions evidenced from the 316L SS implants in vivo conditions is a big challenge. In order to minimize the release of metallic ions, coating the 316L SS implant with a biocompatible material like hydroxyapatite [HAP, Ca₁₀(PO₄)₆(OH)₂] is one of the suitable methods. In this paper, the hydroxyapatite coating on borate passivated through poly-ortho-phenylenediamine (PoPD)-coated 316L SS by a dip coating method has been reported. The coatings were characterized by electrochemical techniques such as potentiodynamic polarization, electrochemical impedance spectroscopy, and cyclic voltammetry. Surface characterization studies of the coatings such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were also carried out. The leach out characteristics of the coatings was determined at the impressed potential. The mechanical property of the coatings was evaluated by Vicker’s microhardness test. The Cr-rich passive film formed underneath the PoPD layer showed a higher protective efficiency. The ability to form apatite on the post-passivated PoPD-coated 316L SS specimen was examined by immersing it in the simulated body fluid. The enhanced corrosion resistivity of the HAP coating on the post-passivated PoPD-coated 316L SS was due to an effective barrier of PoPD followed by the passive film underneath the PoPD.     

Controlled surface modification of Ti6Al4V using biomimetic mineralization via thermo-chemical route improves bioactivity

Ti alloy (Ti6Al4V) sheets were bio-activated by a two-step thermo-chemical treatment followed by biomimetic mineralization. The samples were then characterized by standard techniques and evaluated of their mechanical properties, electrochemical corrosion potential and biological performance. The intermediate layer corresponding to thermo-chemical treatment displayed anatase TiO₂ peaks and the final bio-mineralization resulted in a globular hydroxyapatite (HAP) layer. Thermo-chemical treatment yielded a two-fold increase (98.79% increment) in microhardness value, whereas, the biomimetically activated samples showed a very small decrease in the same owing to their ceramic behavior. The surface hydrophobicity of the bio-activated surface was found reduced significantly, might assist to facilitate improved cell adhesion. Electrochemical corrosion measurements exhibited an increase in corrosion potential and decrease in current density of the samples, suggested increased corrosion resistant. The surface coating on the Ti6Al4V sheet also demonstrated enhanced cytocompatibility as no toxic effect of the samples could be perceived to human keratinocyte cell line (HaCaT). Similarly, the samples showed higher hemocompatibility and enhanced bactericidal activity. Our study concluded that the surface coating of Ti6Al4V sheets significantly improved corrosion resistance and bioactivity of the substrates, which can be applied for various biomedical applications.     

Micro-arc oxidation of bioceramic coatings containing eggshell-derived hydroxyapatite on titanium substrate

In the present study eggshells-derived hydroxyapatite (EHA) coatings were successfully produced on Ti6Al4V substrates using micro-arc oxidation process (MAO) at various concentrations of EHA (i.e. 1, 1.5 and 2 g/L) in an electrolyte consisting of tri-sodium orthophosphate. The attributes of the coatings were determine by X-ray diffraction, attenuated total reflectance-fourier transform infrared spectroscopy, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The adhesion strength was evaluated using micro scratch tester, while the corrosion behavior of the MAO-coated substrates in phosphate buffer solution was determined by an electrochemical method. The results showed that as the EHA concentration increased, this was accompanied by a reduction in the porosity due to the formation of a dense and thick coating layer. This has also resulted in an increased in the surface roughness and degree of crsytallinity of the HA phase. The MAO-coated substrate prepared with 1.5 g/L EHA concentration exhibited a well-formed coating layer with improved adhesive strength and excellent corrosion resistance. The mechanism of EHA-coating formation as well as the enhanced corrosion resistance of the coated substrates were discussed. This research shows the viability of using calcium-rich waste eggshells to produce phase pure HA suitable for coating on Ti6Al4V substrate using MAO method.     

Multifunctional hybrid coating on titanium towards hydroxyapatite growth: Electrodeposition of tantalum and its molecular functionalization with organophosphonic acids films

Titanium and its alloys are base materials used in the dental and orthopaedic fields owing to suitable intrinsic properties: good biocompatibility, high corrosion resistance and excellent mechanical properties. However, the bonding between titanium and bone tissue is not always strong enough and can become a critical problem. In this context, the two main objectives of this paper are the increase of the corrosion resistance and the improvement of the hydroxyapatite (HAp) growth. The surface modification considered here is achieved in three main steps and consists in the elaboration of different inorganic and organic coatings. The first step is the elaboration of electrodeposition of tantalum on the titanium oxide film of a titanium substrate. The second step is the modification of the tantalum oxide coating with organophosphonic acids. The last step is the nucleation and growth of HAP on the outermost layer of the system by immersion in a simulated body fluid. The hybrid coating tantalum oxide/organophosphonic acids/molecular layer is shown to be promising for orthopaedic implants.     

电接触件用T2紫铜表面功能性镀银层的制备与表征

在电接触件用T2紫铜表面制备了功能性镀银层。参照相关标准并使用扫描电镜、表面粗糙度测量仪、回路电阻测试仪和盐雾试验机,对镀银层进行了表征。结果表明:镀银层具有银白色金属光泽,与基体的结合力较好;镀银层表面非常平整,表面粗糙度约为0.16um,镀银使T2紫铜试样的表面粗糙度和接触电阻分别降低了12%和11%;镀银后的T2紫铜试样表现出较好的耐盐雾腐蚀性。     

Electrophoretic deposition of biomimetic zinc substituted hydroxyapatite coatings with chitosan and carbon nanotubes on titanium

In this study, a biomimetic method was used to prepare hydroxyapatite (HAP) and zinc substituted HAP (ZnHAP) nanoparticles, in which silk fibroin was used as template. The morphology of HAP is rod-like, while ZnHAP changes to wrinkled sheets. HAP and ZnHAP nanoparticles were used to coat titanium by EPD with additional chitosan and multiwalled carbon nanotubes. Phase composition, morphology and structure were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared and Raman spectroscopy. The results showed that the composite coatings containing HAP and ZnHAP had homogeneous morphology and good apatite formation ability. The ZnHAP composite coating possessed class 5B adhesive strength using tape test. Furthermore, the ZnHAP composite coating had better corrosion resistance compared to the HAP composite coatings.     

In Vitro Corrosion and Cytocompatibility Properties of Nano-Whisker Hydroxyapatite Coating on Magnesium Alloy for Bone Tissue Engineering Applications

We report here the successful fabrication of nano-whisker hydroxyapatite (nHA) coatings on Mg alloy by using a simple one-step hydrothermal process in aqueous solution. The nHA coating shows uniform structure and high crystallinity. Results indicate that nHA coating is promising for improving the in vitro corrosion and cytocompatibility properties of Mg-based implants and devices for bone tissue engineering. In addition, the simple hydrothermal deposition method used in the current study is also applicable to substrates with complex shapes or surface geometries.     

Comparative study of the hydroxyapatite coatings prepared with/without substrate bias

The aim of this paper is to prepare the hydroxyapatite by Ion Beam Assisted Deposition and to investigate in terms of its elemental and phase composition, roughness and in vitro corrosion resistance. The coatings were prepared with and without applying bias on substrate, in order to find the effect of bias on the chemical, structural, morphological and anti-corrosive properties. The biased coatings exhibited Ca/P ratio closer to the value of the stoichiometric HAP (1.67). The phase composition is not affected by the bias evolution. The adhesion of both coatings is still satisfactory for biomedical applications, irrespective of the bias. Hydroxyapatite deposited without bias presented the best corrosion resistance in SBF at 37 °C, probably due to its smooth surface and low porosity. Moreover, this coating proved to have the highest protection ability at the SBF corrosive attack.     

A comprehensive review on the preparation and application of calcium hydroxyapatite: A special focus on atomic doping methods for bone tissue engineering

Hydroxyapatite (HAP) has been considered to be one of the most preferred scaffold materials among many in the last decade for the bone tissue engineering. Be it prosthetic implants, scaffolds or artificial bone cement, hydroxyapatite has received highest attraction among all due to its chemical and physical properties similar to that of human bone. Although it can be used in the bone tissue engineering as the original composition; for enhancing its different properties relevant to in vivo applications, the calcium in HAP may also be replaced by other atomic dopants depending on usage. Here, we review various HAP coating agents and methods, their merits and demerits. We also review various HAP doping materials, including both cationic as well as anionic materials. We discuss the effects and usage of substitution of hydroxyapatite and their subsequent usage in both bone tissue engineering and maxillofacial surgeries. We consider various research articles published in recent times to accomplish detailed discussion on the subject.     

Fabrication of corrosion resistant, bioactive and antibacterial silver substituted hydroxyapatite/titania composite coating on Cp Ti

The present work is aimed at developing a bioactive, corrosion resistant and anti bacterial nanostructured silver substituted hydroxyapatite/titania (AgHA/TiO₂) composite coating in a single step on commercially pure titanium (Cp Ti) by plasma electrolytic processing (PEP) technique. For this purpose 2.5 wt% silver substituted hydroxyapatite (AgHA) nanoparticles were prepared by microwave processing technique and were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM) methods. The as-synthesized AgHA particles with particle length ranging from 60 to 70 nm and width ranging from 15 to 20 nm were used for the subsequent development of coating on Cp Ti. The PEP treated Cp Ti showed both titania and AgHA in its coating and exhibited an improved corrosion resistance in 7.4 pH simulated body fluid (SBF) and 4.5 pH osteoclast bioresorbable conditions compared to untreated Cp Ti. The in vitro bioactivity test conducted under Kokubo SBF conditions indicated an enhanced apatite forming ability of PEP treated Cp Ti surface compared to that of the untreated Cp Ti. The Kirby-Bauer disc diffusion method or antibiotic sensitivity test conducted with the test organisms of Escherichia coli (E. coli) for 24 h showed a significant zone of inhibition for PEP treated Cp Ti compared to untreated Cp Ti.     

Fabrication and characterization of hybrid coating on Mg–Zn–Ca Mg alloy for enhanced corrosion and degradation resistance as medical implant

Magnesium (Mg)-based alloys have appealing properties as promising implants for medical applications. However, their clinical applications are hindered due to the rapid corrosion and degradation rate in the physiological environment. In this investigation, we reported a novel interfacial engineering approach for the fabrication of polymer/ceramic hybrid coating on Mg–Zn–Ca Mg alloy. Firstly, hydroxyapatite (HA) coating was fabricated on the Mg–Zn–Ca sample followed by an alkali treatment that was performed in 1 M NaOH solution at 60 °C. Finally, polycaprolactone (PCL) coating was synthesized using a dip-coating approach on the top of the HA-coated Mg–Zn–Ca specimen. Microhardness test and adhesion test revealed that PCL/HA hybrid coating significantly improved mechanical properties and enhanced biointerface property between the substrate and coating. The immersion tests showed that the hybrid coating considerably slowed down the degradation in the simulated body fluid (SBF) solution. In addition, in vitro electrochemical investigations confirmed that PCL/HA coating significantly improved corrosion resistance and greatly reduced corrosion rate by about 10 times compared to HA coating and about 900 times to untreated Mg–Zn–Ca sample. Moreover, cytotoxicity assessment exhibited PCL/HA hybrid coating enhanced biocompatibility and bioactivity due to adopting a suitable interfacial engineering approach.     

Preparation,scratch adhesion and anti-corrosion performance of TiO2-MgO-BHA coating on Ti6Al4V implant by plasma electrolytic oxidation technique

Bovine hydroxyapatite (BHA) (from cortical bone), was selected as the main electrolyte for plasma electrolytic oxidation (PEO) on Ti6Al4V implant. The prepared PEO coatings were examined by X-ray diffraction, field emission scanning electron microscope and energy-dispersive X-ray spectroscopy. The surface roughness, adhesion strength, wettability, surface energy and corrosion behaviour of the film were also investigated. The results show that the oxide layer (26 μm) formation on the Ti6Al4V was rough and porous. The micro-pores were filled with anatase TiO₂, cubic MgO and hexagonal BHA particles. The porous structures and the compound particles were mainly composed of Mg, O, Ca, P, Ti, Na and Al. Unlike previous coatings produced from calcium and phosphorus inorganic solutions, the coating formation from a newly developed bovine bone-derived HA electrolyte revealed an additional MgO phase in the coating layer. Moreover, higher amount of single phase hexagonal crystalline BHA phase with a Ca/P ratio of 1.1 was achieved with a single PEO process. A film-to-substrate adhesion strength of 1862.24 mN and scratch hardness of about 4.1 GPa was achieved from this method. The TiO₂/MgO/BHA film exhibited better wettability, higher surface energy and superior corrosion resistance compared to the bare Ti6Al4V substrate.     

Improvement in bioactivity and corrosion resistance of Ti by hydroxyapatite deposition using ultrasonic mechanical coating and armoring

In the present work, nanostructured hydroxyapatite (HA)-containing coating was prepared on a Ti surface by ultrasonic mechanical coating and armoring (UMCA). A Ti plate was pre-coated with HA slurry, followed by UMCA, which was achieved by high-frequency ZrO₂ ball bombardment. The UMCA process comprised several cycles of pre-coating and ball bombardment, providing high amounts of HA and good coating adhesion. The coating mainly consisted of nano-HA particles (less than 10 nm) and a small amount of Ti. Furthermore, the deformation structures of the Ti surface region were characterized in a nanocrystalline layer with a grain size of 50–200 nm. Additionally, the coating exhibited improved bioactivity and corrosion resistance in Hanks’ balanced salt solution than the Ti surface. Furthermore, the in vitro cytotoxicity test assessed that the HA-containing coating was non-cytotoxic.     

Synthesis and characterization of hydroxyapatite/carboxylic acid functionalized MWCNTS composites and its triple layer coatings for biomedical applications

Introduction

Achievement of bioactive coatings on metallic implant surface with higher adhesive strength and corrosive resistance was one of the main challenges for the current biomaterial researchers. Hydroxyapatite was one of the promising bioactive ceramic which can be applied as a coating on the metallic substrate due to its similarity with the human bone.

Composition and Crystallization of Hydroxyapatite Coating Layer Formed by Electron Beam Deposition

To improve the biocompatibility of Ti-based metal implants, a hydroxyapatite (HA) coating layer was formed on the surface by electron-beam deposition. The dissolution rate of the coating layer was strongly dependent on the layer's calcium/phosphorus (Ca/P) ratio. Layers with a Ca/P ratio close to that of crystalline HA (Ca/P = 1.67) showed good stability in a physiologic saline solution. When the layer was crystallized by heat treatment in air at temperatures between 400° and 500°C, the stability was enhanced further while maintaining good interfacial bonding strength with the substrate. Preliminary in vivo tests on rabbits indicated that heat treatment and the resultant enhancement in stability are beneficial for bone attachment to the implants.     

Effects of powder size and metallic bonding layer on corrosion behaviour of plasma-sprayed Al2O3-13% TiO2 coated mild steel in fresh tropical seawater

This study focuses on the effects of powder size and Ni–Al bonding layer on the electrochemical behaviour of plasma-sprayed Al₂O₃-13% TiO₂ coating in fresh tropical seawater. The presence of the metallic bonding layer reduces the coating porosity and increases the surface roughness for both microparticle and nanoparticle coatings. The nanoparticle exhibits better corrosion rate of 1.9×10⁻⁶ mmpy compared to the microparticle coating, with a corrosion rate of 3.05×10⁻⁶ mmpy. However, the presence of the metallic bonding layer increases the corrosion rate for both micro and nanoparticle coatings. The corrosion mechanism for the coating with and without the metallic bonding layer is discussed in detail.     

Electrochemical characterization of hydroxyapatite coatings on HNO3 passivated 316L SS for implant applications

Type 316L SS play a key role in the bone replacement surgery due to its excellent mechanical features, availability at low cost and ease of fabrication. However it fails miserably in vivo conditions due to corrosion-related problems. Hence an alternative method on the development of hydroxyapatite (HAP) coatings has been elucidated to impart corrosion resistance of the base metal and ensure biocompatibility of the ceramic on the metal surface. This also could not match the implant at the host site due to the continuous interaction of hostile environment with the implant and results in the dissolution of both ceramic and metal. An artificially induced passive layer on the metal surface prior to coating may improve the nature of implant on the resistance to corrosion. In the present study, the effect of HNO₃ treatments on 316L SS and the coatings on passivated 316L SS is being explored. Electrochemical studies involving cyclic anodic polarization experiments and impedance analysis in Ringer's solution were done to determine the corrosion resistance of the coatings. The leach out characteristics of the coatings was determined at the impressed potential. The results have indicated the efficiency of HAP coatings on HNO₃-treated surface.     

Characterization and corrosion behavior of plasma sprayed calcium silicate reinforced hydroxyapatite composite coatings for medical implant applications

Titanium and its alloys are widely used for medical implant applications, but their corrosion in the physiological environment leads to the discharge of metal ions, which can trigger severe health issues. In the present study, calcium silicate reinforced hydroxyapatite (HA-CS) coatings were deposited on the Ti6Al4V substrate by using atmospheric plasma spray (APS) process with an aim to improve the corrosion resistance and bioactivity. The coatings were prepared by varying the weight percentage (wt %) of calcium silicate (CS) reinforcement in hydroxyapatite (HA) as Ha/x CS (x = 0, 10, 20 wt %). The SEM analysis of the pure HA coating revealed the presence of surface microcracks, whereas HA-CS coatings displayed the crack-free surface morphology. The corrosion investigation revealed that with the progressive increment of CS content in HA coating, the corrosion resistance of HA-CS coatings improved. In addition, surface roughness, porosity, microhardness and crystallinity increased with the increase of CS content in HA. The findings of this study indicate that the development of plasma sprayed HA-CS coatings is a promising approach to improve the performance of Ti6Al4V alloy for medical implant applications.