Biocompatibility of hydroxyapatite coatings deposited by pulse electrodeposition technique on the Nitinol superelastic alloy

Electrochemical deposition multi-walled carbon nanotube coatings on the surface of Ti6Al4V alloy for enhancing its biotribological properties

Ti6Al4V alloys have potential applications as bone implants. However, their poor biotribological performances affected the service life. In this work, carboxylic multi-walled carbon nanotubes (CMWNT) coatings were grafted on the surface of Ti6Al4V alloys by electrochemical deposition for enhancing the biotribological properties. The CMWNT coatings showed lower coefficient of friction and wear rates, with the reduction of wear rates of 6% in dry condition and 90% under simulated body fluid (SBF) lubrication. This result might be ascribed to the transfer of friction behavior from sliding friction to rolling friction. In addition, the tribological regularity of CMWNT coating with the frequency and load were discussed. Under dry friction, with the increase of frequency and the decrease of normal load, the COF of the CMWNT coating decreased. In SBF lubrication, the COF decreased and the wear rate increased with the increase of frequency. Moreover, the excellent anti-wear properties were observed at the below of 10 N. These findings indicate that the CMWNT coating has an excellent protective effect on titanium alloy, and has a certain application potential in the biomedical field.

Properties of Coatings Based on Calcium Phosphate and Their Effect on Cytocompatibility and Bioactivity of Titanium Nickelide

Coatings based on calcium phosphate with thicknesses of 0.5 and 2 μm were obtained by high-frequency magnetron sputtering on NiTi substrates in an argon atmosphere. The coating was characterized using X-ray diffraction, scanning electron microscopy, atomic force microscopy, and in vitro cytocompatibility and bioactivity studies. A biphasic coating of tricalcium phosphate (Ca₃(PO₄)₂) and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) with a 100% degree of crystallinity was formed on the surface. The layer enriched in calcium, phosphorus, and oxygen was observed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Scanning electron microscopy showed that the surface structure is homogeneous without visible defects. The 2 µm thick coating obtained by sputtering with a deposition time of 4 h and a deposition rate of 0.43 µm/h is uniform, contains the highest amount of the calcium phosphate phase, and is most suitable for the faster growth of cells and accelerated formation of apatite layers. Samples with calcium phosphate coatings do not cause hemolysis and have a low cytotoxicity index. The results of immersion in a solution simulating body fluid show that NiTi with the biphasic coating promotes apatite growth, which is beneficial for biological activity.

Biomimetic Hydroxyapatite Composite Coatings with a Variable Morphology Mediated by Silk Fibroin and Its Derived Peptides Enhance the Bioactivity on Titanium

Various modifications performed on titanium alloy surfaces are shown to improve osteointegration and promote the long-term success of implants. In this work, a bioactive nanostructured hydroxyapatite (HA) composite coating with a variable morphology mediated by silk fibroin (SF) and its derived peptides (Cs) was prepared. Numerous experimental techniques were used to characterize the constructed coatings in terms of morphology, roughness, hydrophilicity, protein adsorption, in vitro biomineralization, and adhesion strength. The mixed protein layer with different contents of SF and Cs exhibited different secondary structures at different temperatures, effectively mediating the electrodeposited HA layer with different characteristics and finally forming proteins/HA composite coatings with versatile morphologies. The addition of Cs significantly improved the hydrophilicity and protein adsorption capacity of the composite coatings, while the electrodeposition of the HA layer effectively enhanced the adhesion between the composite coatings and Ti surface. In the in vitro mineralization experiments, all the composite coatings exhibited excellent apatite formation ability. Moreover, the composite coatings showed excellent cell growth and proliferation activity. Osteogenic induction experiments revealed that the coating could significantly increase the expression of specific osteogenic markers, including ALP, Col-I, Runx-2, and OCN. Overall, the proposed modification of the Ti implant surface by protein/HA coatings had good potential for clinical applications in enhancing bone induction and osteogenic activity of implants.

Recent Advances on Development of Hydroxyapatite Coating on Biodegradable Magnesium Alloys: A Review

The wide application of magnesium alloys as biodegradable implant materials is limited because of their fast degradation rate. Hydroxyapatite (HA) coating can reduce the degradation rate of Mg alloys and improve the biological activity of Mg alloys, and has the ability of bone induction and bone conduction. The preparation of HA coating on the surface of degradable Mg alloys can improve the existing problems, to a certain extent. This paper reviewed different preparation methods of HA coatings on biodegradable Mg alloys, and their effects on magnesium alloys’ degradation, biocompatibility, and osteogenic properties. However, no coating prepared can meet the above requirements. There was a lack of systematic research on the degradation of coating samples in vivo, and the osteogenic performance. Therefore, future research can focus on combining existing coating preparation technology and complementary advantages to develop new coating preparation techniques, to obtain more balanced coatings. Second, further study on the metabolic mechanism of HA-coated Mg alloys in vivo can help to predict its degradation behavior, and finally achieve controllable degradation, and further promote the study of the osteogenic effect of HA-coated Mg alloys in vivo.

Electrodeposited Hydroxyapatite-Based Biocoatings: Recent Progress and Future Challenges

Hydroxyapatite has become an important coating material for bioimplants, following the introduction of synthetic HAp in the 1950s. The HAp coatings require controlled surface roughness/porosity, adequate corrosion resistance and need to show favorable tribological behavior. The deposition rate must be sufficiently fast and the coating technique needs to be applied at different scales on substrates having a diverse structure, composition, size, and shape. A detailed overview of dry and wet coating methods is given. The benefits of electrodeposition include controlled thickness and morphology, ability to coat a wide range of component size/shape and ease of industrial processing. Pulsed current and potential techniques have provided denser and more uniform coatings on different metallic materials/implants. The mechanism of HAp electrodeposition is considered and the effect of operational variables on deposit properties is highlighted. The most recent progress in the field is critically reviewed. Developments in mineral substituted and included particle, composite HAp coatings, including those reinforced by metallic, ceramic and polymeric particles; carbon nanotubes, modified graphenes, chitosan, and heparin, are considered in detail. Technical challenges which deserve further research are identified and a forward look in the field of the electrodeposited HAp coatings is taken.

A review on hydroxyapatite coatings for the biomedical applications: experimental and theoretical perspectives

The production of hydroxyapatite (HAP) composite coatings has continuously been investigated for bone tissue applications during the last few decades due to their significant bioactivity and osteoconductivity.

The morphological effect of nanostructured hydroxyapatite coatings on the osteoinduction and osteogenic capacity of porous titanium

Weak osteogenic activity affects the long-term fixation and lifespan of titanium (Ti) implants. Surface modification along with a built-in porous structure is a highly considerable approach to improve the osteoinduction and osseointegration capacity of Ti. Herein, the osteoinduction and osteogenic activities of electrochemically deposited (ED) nanoplate-like, nanorod-like and nanoneedle-like hydroxyapatite (HA) coatings (named EDHA-P, EDHA-R, and EDHA-N, respectively) were evaluated in vitro and in vivo by comparison with those of acid/alkali (AA) treatment. The results revealed that the apatite forming ability of all nanostructured EDHA coatings was excellent, and only 12 h of soaking in SBF was needed to induce a complete layer of apatite. More serum proteins adsorbed on EDHA-P than others. In cellular experiments, different from those on EDHA-R and EDHA-N, the cells on EDHA-P presented a polygonal shape with lamellipodia extension, and thus exhibited a relatively larger spreading area. Furthermore, EDHA-P was more favorable for the enhancement of the proliferation and ALP activity of BMSCs, and the up-regulation of OPN gene expression. Based on the good biological performance in vitro, EDHA-P was selected to further evaluate its osteoinduction and osteogenic activities in vivo by comparison with AA treatment. Interestingly, a greater ability of ectopic osteoinduction was observed in the EDHA-P group compared to that in the AA group. At the osseous site, EDHA-P promoted more bone on/ingrowth, and had a higher area percentage of newly formed bone in the bone-implant interface and inner pores of the implants than in the AA group. Thus, a nanoplate-like HA coating has good potential in improving the osteoinductivity and osteogenic activity of porous Ti implants in clinical applications.

Influence of low modulus Co-Zr alloys surface modification on protein adsorption and MC3T3-E1, NIH3T3 and RAW264.7 cell behaviour

Three types of Co-xZr (x = 5, 7.5, and 10 wt.%) were treated with hydroxyapatite (HA) and used as an object to investigate the effect of HA coating on the surface and biocompatibility of Co-xZr alloys. And the protein adsorption and the subsequent biological behaviour of osteoblast, fibroblast and macrophages were also investigated. The surface microstructure and wettability were assessed by scanning electron microscopy (SEM) and static angle profilometer. To evaluate the biocompatibility of Co-xZr and Co-xZr-HA, we quantified plasma proteins adsorption by bicinchoninic acid assay (BCA), cytotoxicity and cell proliferation by cell counting kit-8 (CCK-8) and scanning electron microscopy (SEM). The results indicated that Co-xZr-HA alloy surfaces were more hydrophilic and had higher affinity to plasma proteins. Higher protein concentrations were found adsorbed onto Co-7.5Zr-HA and Co-10Zr-HA alloys. Cytotoxicity analysis indicated that HA coating improved the biocompatibility of Co-xZr alloys. Furthermore, the comparable results of co-incubation of Co-xZr-HA alloys with cells reveal cellular attachments to HA surfaces. HA was successfully formed on Co-xZr alloys and modified the surface structure and biocompatibility of the alloys. Co-10Zr-HA and Co-7.5Zr-HA had the most favourable properties and cytocompatibility, and therefore can be potentially used for dental implants.

Calcium Phosphate Based Bioactive Ceramic Layers on Implant Materials Preparation, Properties, and Biological Performance

Calcium phosphate based bioactive ceramics (CPCs) can be successfully applied as implant coatings since they are chemically similar to the inorganic constituent of hard tissues (bones, teeth). Nowadays, in orthopedic surgeries, it is still common to use metallic implants. However, the biological response of the human body to these foreign materials can be adverse, causing the failure of implant materials. This disadvantage can be avoided by bioactive coatings on the surface of implants. CPCs can be prepared by different routes that provide coatings of different quality and properties. In our paper, we compared the morphological, chemical, and biological properties of CPC coatings prepared by the pulse current electrochemical method. The size and thickness of the pulse current deposited platelets largely depended on the applied parameters such as the length of ton and the current density. The decrease in the ton/toff ratio resulted in thinner, more oriented platelets, while the increase in current density caused a significant decrease in grain size. The higher pH value and the heat treatment favored the phase transformation of CPCs from monetite to hydroxyapatite. The contact angle measurements showed increased hydrophilicity of the CPC sample as well as better biocompatibility compared to the uncoated implant material.

Electrodeposited Biocoatings, Their Properties and Fabrication Technologies: A Review

Coatings deposited under an electric field are applied for the surface modification of biomaterials. This review is aimed to characterize the state-of-art in this area with an emphasis on the advantages and disadvantages of used methods, process determinants, and properties of coatings. Over 170 articles, published mainly during the last ten years, were chosen, and reviewed as the most representative. The most recent developments of metallic, ceramic, polymer, and composite electrodeposited coatings are described focusing on their microstructure and properties. The direct cathodic electrodeposition, pulse cathodic deposition, electrophoretic deposition, plasma electrochemical oxidation in electrolytes rich in phosphates and calcium ions, electro-spark, and electro-discharge methods are characterized. The effects of electrolyte composition, potential and current, pH, and temperature are discussed. The review demonstrates that the most popular are direct and pulse cathodic electrodeposition and electrophoretic deposition. The research is mainly aimed to introduce new coatings rather than to investigate the effects of process parameters on the properties of deposits. So far tests aim to enhance bioactivity, mechanical strength and adhesion, antibacterial efficiency, and to a lesser extent the corrosion resistance.

Optimizing organic electrosynthesis through controlled voltage dosing and artificial intelligence

Organic electrosynthesis can transform the chemical industry by introducing electricity-driven processes that are more energy efficient and that can be easily integrated with renewable energy sources. However, their deployment is severely hindered by the difficulties of controlling selectivity and achieving a large energy conversion efficiency at high current density due to the low solubility of organic reactants in practical electrolytes. This control can be improved by carefully balancing the mass transport processes and electrocatalytic reaction rates at the electrode diffusion layer through pulsed electrochemical methods. In this study, we explore these methods in the context of the electrosynthesis of adiponitrile (ADN), the largest organic electrochemical process in industry. Systematically exploring voltage pulses in the timescale between 5 and 150 ms led to a 20% increase in production of ADN and a 250% increase in relative selectivity with respect to the state-of-the-art constant voltage process. Moreover, combining this systematic experimental investigation with artificial intelligence (AI) tools allowed us to rapidly discover drastically improved electrosynthetic conditions, reaching improvements of 30 and 325% in ADN production rates and selectivity, respectively. This powerful AI-enhanced experimental approach represents a paradigm shift in the design of electrified chemical transformations, which can accelerate the deployment of more sustainable electrochemical manufacturing processes.

Effect of Ta2O5 content on the osseointegration and cytotoxicity behaviors in hydroxyapatite-Ta2O5 coatings applied by EPD on superelastic NiTi alloys

In the present study, the different contents of tantalum pentoxide (Ta₂O₅: 10, 15, 20 and 30 wt%) nanoparticles were introduced into the natural hydroxyapatite (nHA) coating structure on NiTi substrate through electrophoretic deposition (EPD) method. The phase compositions of coatings were perused before and after the sintering at 800 °C for 1 h by XRD. The incorporation of 30wt%Ta₂O₅ into nHA matrix induced the formation of undesirable soluble Ca₃(PO₄)₂ phase in composite coating. The FESEM images showed that the density of continuous nHA coating increased by compositing with Ta₂O₅. The maximum adhesion strength of 28.3 ± 0.7 MPa accomplished from the nHA-20 wt%Ta₂O₅ composite coating. The Ni ions concentration measurement results from the passivated-NiTi with nHA and nHA-(10, 15 and 20)wt%Ta₂O₅ coatings during 30 days of immersion in PBS clarified the positive role of Ta₂O₅ in decreasing the Ni leaching due to the lowering the open porosities of nHA structure. The biological response of the coating surfaces was assessed in vitro by cell culturing and MTS assay. By considering the morphology and density of adsorbed cells on each coating, the improved biocompatibility of nHA coating in the presence of Ta₂O₅ was justified by scrutinizing the surface roughness, wettability and charge. The highest cell attachment and proliferation on nHA-20 wt%Ta₂O₅ coating was related to owning the lowest roughness, wetting angle of 34^o ± 0.5 and the highest negative surface charge density. Also, the concentration of the highest negative charge density on nHA-20 wt%Ta₂O₅ coating surface in the SBF solution caused to the enhancement of the amount of the apatite nuclei through providing more sites to calcium absorption.

A Comparative Study on the Direct and Pulsed Current Electrodeposition of Cobalt-Substituted Hydroxyapatite for Magnetic Resonance Imaging Application

Hydroxyapatite has excellent biocompatibility and osteo-conductivity and, as the main inorganic component of human bones and teeth, is commonly used for bone repair. Its original characteristics can be changed by metal ion substitution. Cobalt ions can act as hypoxia-inducible factors and accelerate bone repair. At the same time, cobalt has paramagnetic properties and is often used in the study of medical imaging and target drugs. Through the introduction of cobalt ions, the unique hydroxyapatite has better biological activity and positioning of medical images. Herein, cobalt-substituted hydroxyapatite (CoHA) was synthesized on the surface of a titanium plate by electrochemical deposition and changes in the power output mode to explore the impact on CoHA. Electrochemical deposition with a pulse current significantly improved the productivity and uniformity of CoHA on the surface of titanium. CoHA show paramagnetic characteristics by a superconducting quantum interference device (SQUID). Resulting smaller particle size and circular morphology improves the magnetic strength of CoHA. Magnetic resonance imaging (MRI) of CoHA showed significant image contrast effect at low concentrations. The calculated particle relaxation rate was higher than other common MRI contrast agents. Biocompatibility of CoHA powder was evaluated using the human osteosarcoma cell line (MG63) which confirmed that CoHA is not cytotoxic and can promote cell growth and extracellular matrix mineralization. With the release of cobalt ions, CoHA was found to be significantly good in repression E. coli indicating about than 95% reduction in bacterial growth. The as-synthesized CoHA has a low degree of crystallinity, highly sensitive image contrast effect, and good bioactivity, and may have potential applications in bone repair and MRI.

Effect of employing ultrasonic waves during pulse electrochemical deposition on the characteristics and biocompatibility of calcium phosphate coatings

In the present work, we investigated the effect of employing ultrasonic waves during pulse electrochemical deposition on surface topography, chemical composition and biocompatibility of calcium phosphate (Ca-P) coatings. The SEM and 3D AFM images showed that the anodized titanium surface was covered with the uniform and refined size of plate-like Ca-P crystals, when the ultrasonic treatment of the electrolyte with power of 60 W was carried out during deposition. In contrast, for the Ca-P; 0 W coating applied under only the magnetic stirring of the electrolyte, the microstructure was non-uniform and some Ca-P crystals with the larger size were randomly observed in different regions, causing a rougher surface. The FTIR results also revealed that employing the ultrasound increases the deposition of a coating involved in only the most stable Ca-P phase of carbonated hydroxyapatite (CHA). However, in the absence of ultrasound, besides the prominent phase of CHA, some less stable Ca-P phases like octa calcium phosphate (OCP) and brushite were also formed in the Ca-P; 0 W coating. The Ca-P; 60 W coating showed the higher ability for apatite biomineralization after a 7-day immersion in the simulated body fluid (SBF). This coating also provided a better surface for the cellular activity, as compared to the Ca-P; 0 W coating.

Biocompatibility assessment of graphene oxide-hydroxyapatite coating applied on TiO2 nanotubes by ultrasound-assisted pulse electrodeposition

In this study, the ultrasound-assisted pulse electrodeposition was introduced to fabricate the graphene oxide (GO)-hydroxyapatite (HA) coating on TiO₂ nanotubes. The results of the X-ray diffraction (XRD), Fourier Transform Infrared spectroscope (FTIR), Transmission Electron Microscope (TEM) and micro-Raman spectroscopy showed the successful synthesis of GO. The Scanning Electron Microscope (SEM) images revealed that in the presence of ultrasonic waves and GO sheets a more compact HA-based coating with refined microstructure could be formed on the pretreated titanium. The results of micro-Raman analysis confirmed the successful incorporation of the reinforcement filler of GO into the coating electrodeposited by the ultrasound-assisted method. The FTIR analysis showed that the GO-HA coating was consisted predominantly of the B-type carbonated HA (CHA) phase. The pretreatment of the substrate and incorporation of the GO sheets into the HA coating had a significant effect on improving the bonding strength at the coating-substrate interface. Moreover, the results of the fibroblast cell culture and 3‑(4,5‑dimethylthiazolyl‑2)‑2, 5‑diphenyltetrazolium bromide (MTT) assay after 2 days demonstrated a higher percentage of cell activity for the GO-HA coated sample. Finally, the 7-day exposure to simulated body fluid (SBF) showed a faster rate of apatite precipitation on the GO-HA coating, as compared to the HA coating and pretreated titanium.