Anodizing/Anaphoretic Electrodeposition of Nano-Calcium Phosphate/Chitosan Lactate Multifunctional Coatings on Titanium with Advanced Corrosion Resistance, Bioactivity, and Antibacterial Properties

Material and technique fundamentals of nano-hydroxyapatite coatings towards biofunctionalization: a review

Hydroxyapatite (HAp) nanocoatings on titanium alloys (e.g. Ti6Al4V) have been used for prosthetic orthopaedic implants in recent decades because of their osseointegration, bioactivity, and biocompatibility. HAp is brittle with low mechanical strength and poor adhesion to metallic surfaces, which limits its durability and bioactivity. Surface modification techniques have alleviated the imperfections in biomaterials by coating the substrate. Several methods for improving the characteristics of implants, such as physical vapour deposition, the thermal spray method, the sol-gel method, microarc oxidation, and electrochemical deposition methods, have been discussed in this review. These processes provide mechanical strength without sacrificing biocompatibility and may lead to the development of new ideas for future research. This review discusses various selective additives, including carbon allotropes, ceramic materials, metallic materials, and multiple materials, to enhance tribological characteristics, biocompatibility, wear resistance, and mechanical strength. This review focuses on the fabrication of nano-HAps as coatings using selective deposition methods with controlled deposition parameters, paying special attention to recent developments in bone tissue engineering. This report is organized in such a way that it may inspire further research on surface modifications during medical treatment. The present review may help prospective investigators understand the importance of surface modifications for obtaining excellent implantation performance.

Zn-doped CaP coating equips Ti implants with corrosion resistance, biomineralization, antibacterial and immunotolerant activities

INTRODUCTION

Chronic inflammation leading to implant failure present major challenges in orthopedics, dentistry, and reconstructive surgery. Titanium alloys, while widely used, often provoke inflammatory complications. Zinc-doped calcium phosphate (CaP) coatings offer potential to enhance implant integration by improving corrosion resistance, bioactivity, and immunocompatibility.

OBJECTIVES

The objective of the study was to develope novel coating composition based on zinc-doped CaP coatings on Ti64 alloy implants that for the first time combines improved corrosion resistance, antibacterial properties and principally improved compatibly with the innate immunity primarily due to the proper programming of resident tissue macrophages to promote long-term implant acceptance.

METHODS

Ti64 substrates were coated with CaP and Zn-doped CaP using the microarc oxidation (MAO) technique. The adhesion between substrate and coatings are investigated by the progressive scratch test. The corrosion resistance and bioactivity were evaluated through electrochemical tests and simulated body fluid immersion. RNA sequencing was used to assess inflammatory responses in human primary macrophages. Antibacterial efficacy was tested against Escherichia coli and Staphylococcus aureus.

RESULTS

Zn addition significantly increased the adhesion of the coatings to Ti64 alloy, doubling up the critical load (from 4 N to 11 N). Zn-doped CaP coatings demonstrated enhanced corrosion resistance and increased biomineralization. RNA sequencing revealed that Zn addition suppressed inflammatory and promoted tolerogenic macrophage programming. Most pronounced effects was compensatory effect Zi on the CaP-supressed oxidative phosphorylation and lysosomal pathways in healing macrophages, and by upregulation of metallothioneins. Zn-doped coatings also exhibited superior antibacterial efficacy, reducing E. coli and S. aureus colonization by 99 % and 90 %, respectively.

CONCLUSION

Zinc-doped CaP coatings on Ti64 implants significantly improved corrosion resistance, bioactivity, and antibacterial performance. We developed advanced multifunctional biomaterial equipped with beneficial anti-inflammatory and tissue integrative programming of innate immunity providing principal advantages for the long-term implant integration and reducing the implant failure risks.

Modified Titanium Surface with Nano Amorphous Calcium Phosphate@Chitosan Oligolactate as Ion Loading Platform with Multifunctional Properties for Potential Biomedical Application

Titanium (Ti) is widely used in medical and dental implants. Calcium phosphate (CPs) coatings enhance Ti implants' osteoinductive properties, and additives further improve these coatings. Recently, a nano amorphous calcium phosphate (nACP) coating decorated with chitosan oligolactate (ChOL) and selenium (Se) showed immunomodulatory effects. This study investigates the surface morphology, composition, bioactivity, mechanical properties, and Se-release mechanism of the nACP@ChOL-Se hybrid coating on Ti substrates. Amorphous calcium phosphate (ACP) was synthesized, and the nACP@ChOL-Se hybrid coating was deposited on Ti substrates using in situ anaphoretic deposition. Physico-chemical characterization was used to analyze the surface of the coating (scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy). The distribution of Se within the coating was examined with energy-dispersive X-ray spectroscopy (EDS). Bioactivity was evaluated in simulated body fluid (SBF), and adhesion was tested using a scratch test method. In vitro testing determined the release mechanism of Se. SEM images illustrated the surface morphology, while AFM provided a detailed analysis of surface roughness. XRD analysis revealed structural and phase composition, and EDS confirmed Se distribution within the coating. The coating exhibited bioactivity in SBF and showed good adhesion according to the scratch test. In vitro testing uncovered the release mechanism of Se from the coating. This study successfully characterized the surface morphology, composition, bioactivity, and Se-release mechanism of the nACP@ChOL-Se hybrid coating on Ti substrates, offering insights for developing immunomodulatory coatings for medical and dental applications.

Synergetic effect of essential oils and calcium phosphate nanoparticles for enhancement the corrosion resistance of titanium dental implant

Calcium phosphate (CaPO4) coating is one of various methods that is used to modify the topography and the chemistry of Ti dental implant surface to solve sever oral problems that result from diseases, accidents, or even caries due to its biocompatibility. In this work, anodized (Ti-bare) was coated by CaPO4 prepared from amorphous calcium phosphate nanoparticles (ACP-NPs) and confirmed the structure by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) techniques. Ti-bare was coated by prepared CaPO4 through the casting process, and the morphology of Ti/CaPO4 was characterized by scanning electron microscope (SEM) where the nano-flakes shape of CaPO4 and measured to be 60 ~ 80 nm was confirmed. The stability of Ti-bare and coated Ti/CaPO4 was studied in a simulated saliva solution using electrochemical impedance spectroscopy (EIS) and linear polarization techniques to deduce their corrosion resistance. Furthermore, three essential oils (EO), Cumin, Thyme, and Coriander, were used to stimulate their synergistic effect with the CaPO4 coat to enhance the corrosion resistance of Ti implant in an oral environment. The fitting EIS parameters based on Rs [RctC]W circuit proved that the charge transfer resistance (Rct) of Ti/CaPO4 increased by 264.4, 88.2, and 437.5% for Cumin, Thyme, and Coriander, respectively, at 2% concentration.

Octacalcium Phosphate-Laden Hydrogels on 3D-Printed Titanium Biomaterials Improve Corrosion Resistance in Simulated Biological Media

The inflammatory-associated corrosion of metallic dental and orthopedic implants causes significant complications, which may result in the implant's failure. The corrosion resistance can be improved with coatings and surface treatments, but at the same time, it might affect the ability of metallic implants to undergo proper osteointegration. In this work, alginate hydrogels with and without octacalcium phosphate (OCP) were made on 3D-printed (patterned) titanium alloys (Ti Group 2 and Ti-Al-V Group 23) to enhance their anticorrosion properties in simulated normal, inflammatory, and severe inflammatory conditions in vitro. Alginate (Alg) and OCP-laden alginate (Alg/OCP) hydrogels were manufactured on the surface of 3D-printed Ti substrates and were characterized with wettability analysis, XRD, and FTIR. The electrochemical characterization of the samples was carried out with open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). It was observed that the hydrophilicity of Alg/OCP coatings was higher than that of pure Alg and that OCP phase crystallinity was increased when samples were subjected to simulated biological media. The corrosion resistance of uncoated and coated samples was lower in inflammatory and severe inflammatory environments vs. normal media, but the hydrogel coatings on 3D-printed Ti layers moved the corrosion potential towards more nobler values, reducing the corrosion current density in all simulated solutions. These measurements revealed that OCP particles in the Alg hydrogel matrix noticeably increased the electrical charge transfer resistance at the substrate and coating interface more than with Alg hydrogel alone.

Molybdate and Phosphate Cross-Linked Chitosan Films for Corrosion Protection of Hot-Dip Galvanized Steel

Environmentally friendly and sustainable methods to protect hot-dip galvanized (HDG) steel from corrosion are extensively studied. Films of the biopolymer polyelectrolyte chitosan were ionically cross-linked in this work with the well-known corrosion inhibitors phosphate and molybdate. Layers on this basis are presented as components in a protective system and could, e.g., be applied in pretreatments similar to a conversion coating. For the preparation of the chitosan-based films, a procedure involving sol-gel chemistry and wet-wet application was utilized. Homogeneous films of few micrometers thickness were obtained on HDG steel substrates after thermal curing. Properties of chitosan-molybdate and chitosan-phosphate films were compared with purely passive epoxysilane-cross-linked chitosan, and pure chitosan. Delamination behavior of a poly(vinyl butyral) (PVB) weak model top coating studied by scanning Kelvin probe (SKP) showed an almost linear time dependence over >10 h on all systems. Delamination rates were 0.28 mm h^-1 (chitosan-molybdate) and 0.19 mm h^-1 (chitosan-phosphate), ca. 5% of a non-cross-linked chitosan reference and slightly higher than of the epoxsyilane cross-linked chitosan. Immersion of the treated zinc samples over 40 h in 5% NaCl solution yielded a 5-fold increase of the resistance in the chitosan-molybdate system, as evidenced by electrochemical impedance spectroscopy (EIS). Ion exchange of electrolyte anions with molybdate and phosphate triggers corrosion inhibition, presumably by reaction with the HDG surface as well described in the literature for these inhibitors. Thus, such surface treatments have potential for application, e.g., in temporary corrosion protection.

Immunomodulatory Effects Mediated by Nano Amorphous Calcium Phosphate/Chitosan Oligosaccharide Lactate Coatings Decorated with Selenium on Titanium Implants

The aim of this work is in situ anodization/anaphoretic deposition of a nano amorphous calcium phosphate (ACP)/chitosan oligosaccharide lactate (ChOL) multifunctional hybrid coating decorated with selenium (Se) on a titanium substrate and in vivo investigation of its immunomodulatory and anti-inflammatory effect. Investigating phenomena at the implant-tissue interface of interest for controlled inflammation and immunomodulation was also the aim of the research. In our earlier research, we designed coatings based on ACP and ChOL on titanium with anticorrosive, antibacterial and biocompatible properties, while in the presented results we show that selenium addition makes this coating an immunomodulator. The immunomodulatory effect of the novel hybrid coating is characterized by the examination of the functional aspects in the tissue around the implant (in vivo): proinflammatory cytokines' gene expression, M1 (iNOS) and M2 (Arg1) macrophages, fibrous capsule formation (TGF-β) and vascularization (VEGF). The EDS, FTIR and XRD analyses prove the formation of a ACP/ChOL/Se multifunctional hybrid coating on Ti and the presence of Se. A higher M2/M1 macrophage ratio in the ACP/ChOL/Se-coated implants compared to pure titanium implants (a higher level of Arg1 expression) is noted at all time points examined (after 7, 14 and 28 days). Lower inflammation measured by gene expression of proinflammatory cytokines IL-1β and TNF, lower expression of TGF-β in the surrounding tissue and higher IL-6 expression (solely at day 7 post-implantation) is noted in presence of the ACP/ChOL/Se-coated implants.

In Situ Facile Synthesis of Low-Cost Biogenic Eggshell-Derived Nanohydroxyapatite/Chitosan Biocomposites for Orthopedic Implant Applications

In situ facile synthesis and the characterization of nanohydroxyapatite/chitosan (nHAP/CS) biocomposites were investigated for examining their potential applications in orthopedic implant technology. Firstly, the bare nHAP, europium-doped hydroxyapatite (Eu-nHAP), yttrium-doped hydroxyapatite (Y-nHAP), and Eu- and Y-codoped hydroxyapatite (Eu,Y-nHAP) nanoparticles were synthesized by the wet precipitation technique using biowaste-eggshell-derived calcium oxide powders. Then, through ultrasonication using the nanohydroxyapatite/chitosan mixtures (molar ratio = 1:2), the nHAP/CS, Eu-nHAP/CS, Y-nHAP/CS, and Eu,Y-nHAP/CS biocomposites were fabricated. Among them, Eu,Y-nHAP/CS showed higher cell viability (94.9%), higher solubility (pH = 7.6 after 21 days), and greater antibacterial activity than those of the other composites. In addition, Eu,Y-nHAP/CS exhibited improved mechanical properties compared with the other composites. For example, the nanoindentation test displayed the Eu,Y-nHAP/CS-coated 316L stainless steel implant to possess a higher Young's modulus value (9.24 GPa) and greater hardness value (300.71 MPa) than those of the others. The results indicate that the biomass-eggshell-derived Eu,Y-doped nHAP is of good use for orthopedic implant applications.

Antibacterial Coatings for Titanium Implants: Recent Trends and Future Perspectives

Titanium and its alloys are widely used as implant materials for biomedical devices owing to their high mechanical strength, biocompatibility, and corrosion resistance. However, there is a significant rise in implant-associated infections (IAIs) leading to revision surgeries, which are more complicated than the original replacement surgery. To reduce the risk of infections, numerous antibacterial agents, e.g., bioactive compounds, metal ions, nanoparticles, antimicrobial peptides, polymers, etc., have been incorporated on the surface of the titanium implant. Various coating methods and surface modification techniques, e.g., micro-arc oxidation (MAO), layer-by-layer (LbL) assembly, plasma electrolytic oxidation (PEO), anodization, magnetron sputtering, and spin coating, are exploited in the race to create a biocompatible, antibacterial titanium implant surface that can simultaneously promote tissue integration around the implant. The nature and surface morphology of implant coatings play an important role in bacterial inhibition and drug delivery. Surface modification of titanium implants with nanostructured materials, such as titanium nanotubes, enhances bone regeneration. Antimicrobial peptides loaded with antibiotics help to achieve sustained drug release and reduce the risk of antibiotic resistance. Additive manufacturing of patient-specific porous titanium implants will have a clear future direction in the development of antimicrobial titanium implants. In this review, a brief overview of the different types of coatings that are used to prevent implant-associated infections and the applications of 3D printing in the development of antibacterial titanium implants is presented.

Electrochemical Behaviour of Ti and Ti-6Al-4V Alloy in Phosphate Buffered Saline Solution

The electrochemical behavior of commercially pure titanium (CP Ti) and Ti-6Al-4V (Grade 5) alloy in phosphate buffered saline solution (PBS, pH = 7.4) at 37 °C (i.e., in simulated physiological solution in the human body) was examined using open circuit potential measurements, linear and potentiodynamic polarization and electrochemical impedance spectroscopy methods. After the impedance measurements and after potentiodynamic polarization measurements, the surface of the samples was investigated by scanning electron microscopy, while the elemental composition of oxide film on the surface of each sample was determined by EDS analysis. The electrochemical and corrosion behavior of CP Ti and Ti-6Al-4V alloys is due to forming a two-layer model of surface oxide film, consisting of a thin barrier-type inner layer and a porous outer layer. The inner barrier layer mainly prevents corrosion of CP Ti and Ti-6Al-4V alloy, whose thickness and resistance increase sharply in the first few days of exposure to PBS solution. With longer exposure times to the PBS solution, the structure of the barrier layer subsequently settles, and its resistance increases further. Compared to Ti-6Al-4V alloy, CP Ti shows greater corrosion stability.