Bioactivity Of Coatings Research Articles

Ti3C2Tx MXene-functionalized Hydroxyapatite/Halloysite nanotube filled poly– (lactic acid) coatings on magnesium: In vitro and antibacterial applications

Magnesium (Mg) stands out in temporary biomaterial applications due to its biocompatibility, biodegradability, and low Young's modulus. However, controlling its corrosion through next-generation polymer-based functional coatings is crucial due to the rapid degradation behavior of Mg. In this study, the function of 2D lamellar Ti3C2Tx (MXene) in Hydroxyapatite (HA) and Halloysite nanotube (HNT) hybrid coatings in biodegradable poly– (lactic acid) (PLA) was investigated. The morphological and structural characterizations of the coatings on Mg were revealed through HRTEM, XPS, SEM-EDX, XRD, FTIR, and contact angle analyses/tests. Electrochemical in vitro corrosion tests (OCP, PDS, and EIS-Nyquist) were conducted for evaluate corrosion resistance under simulated body fluid (SBF) conditions. The bioactivity of the coatings in SBF have been revealed in accordance with the ISO 23,317 standard. Finally, antibacterial disk diffusion tests were conducted to investigate the functional effect of MXene in coatings. It has been determined that the presence of MXene in the coating increased not only surface wettability (131°, 85°, 77°, and 74° for uncoated, pH, PHH, and PHH/MXene coatings, respectively) but also increased corrosion resistance (1857.850, 42.357, 1.593, and 0.085 × 10–6, A/cm2 for uncoated, pH, PHH, and PHH/MXene coatings, respectively). It has been proven that the in vitro bioactivity of PLA-HA coatings is further enhanced by adding HNT and MXene, along with SEM morphologies after SBF. Finally, 2D lamellar MXene-filled coating exhibits antibacterial behavior against both E. coli and S. aureus bacteria.

The microstructural features and corrosion behavior of Hydroxyapatite/ZnO nanocomposite electrodeposit on NiTi alloy: Effect of current density

In the present study, hydroxyapatite/ZnO nanocomposite coatings were developed on NiTi superelastic alloy via pulse electrodeposition technique under three different current densities. The morphological observations (FESEM) indicated that under 6 mA/cm2, a compact, uniform composite layer could form, whereas lower or higher current densities resulted in non-uniform, porous coatings with uneven distribution of nanoparticles. XRD and FTIR studies revealed that pure hydroxyapatite was not achieved below 6 mA/cm2. Topographic features (AFM) were assessed and demonstrated a continuous rise in roughness parameters as current density increased. The corrosion behavior was investigated through potentiodynamic polarization as well as impedance spectroscopy techniques. According to the extracted data, the porosity and non-uniformity of coatings formed under 3 and 9 mA/cm2 caused a detrimental effect on the corrosion resistance of surfaces. The layer obtained under 6 mA/cm2 showed resistance (Rc) which was almost two times greater than those deposited under 3 and 9 mA/cm2 current densities. Last but not least, the bioactivity of coatings was evaluated in simulated body fluid. It was observed that more compact deposits offered more active sites for apatite nucleation, resulting in refined cauliflower-like grains. Accordingly, it can be asserted that the best composite coating was achieved under 6 mA/cm2 current density.

In Ukrainian

The aim of the research is the development of compositions and technology for obtaining bioactive glass-ceramic calcium phosphate-silicate coatings on titanium for dental prosthetics, to find the relationship between the structural parameters of the calcium phosphate-silicate coatings surface on titanium with their bioactivity. The structure of the material was studied by means of petrographic analysis (microscope Mi-2e) and X-ray phase analysis (DRON-3M). Solubility and bioactivity of coatings were evaluated in solutions: distilled water (GOST R 31576-2012), SBF (ISO 23317:2012), 10 % albumin solution. The surface free energy was determined by the Owens-Wendet-Rebel-Kaebel method. The surface microrelief of the coatings was assessed by the mean arithmetic deviation of the profile Ra (Surtronic 3+ profilometer). The surface layer structure was investigated by X-ray fluorescence (SPRUT spectrometer-analyzer) and X-ray spectral (PEM Tesla 3 LMU + oxygen spectrometer Oxford X-max 80 mm) methods. The behavior of stem cells on the coatings surface was investigated by fluorescence microscopy (Carl Zeiss Axio Observer Z1). Criteria were selected of model glass synthesis and the model glasses were melted. Glass-ceramic coatings for titanium were applied by slip technology and synthesized under conditions of short-term low-temperature heat treatment. It has been found that the model glasses, after heat treatment, are characterized by behaviour of a volumetric fine-disperced (crystals ≤ 1 μm) crystallization of calcium phosphate - HAP and FAP (Σ ≈ 24÷44 % by volume). The possibility of spontaneous adsorption of proteins on the coatings surface has been confirmed due to the provision of coating parameters: SEM ≈ 65 mJ/m 2 , R a ≈ 3.5 μm and the presence of through pores with a diameter of 10÷100 μm. The changes in the structure and composition of the coatings surface after ageing in SBF have been studied for 1 month period. It has been found that the provision for these model glasses of a set of indicators, namely: solubility in distilled water (30 days) - 0.89 wt. %; ion yield of Ca 2+ is 0.26 wt. % and groups [PO 4 ] 3 – -0.162 wt. %, pH ~ 7.3, is sufficient for the formation of precursors of hydroxyapatite on the coatings surface in vitro. Gradual displacement (build-up) of the coatings surface layers (due to the dissolution of the coating and deposition of the SBF components) was found within the boundaries up to 6.7 μm and the apatite-like layer was formed in 28 days of soaking. These structural and chemical transformations of the surface of glass-ceramic coating form a durable apatite-like layer for 35 days period under in vitro conditions. The formation of this layer creates conditions for increasing the area of mesenchymal stem cell spacing on the coatings surface and allows their use in the creation of bioengineering design with stem cells (in vivo).

Growth characteristics and properties of micro-arc oxidation coating on SLM-produced TC4 alloy for biomedical applications

Titanium alloy produced by selective laser melting (SLM) requires surface treatment to improve its bioactivity. In this study, Micro-arc oxidation (MAO) was applied on TC4 alloy produced by SLM with a homogeneous coating of microporous TiO2 and significant amounts of Ca and P. The microstructure, thickness, roughness, and composition of the MAO coating with different oxidation times were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD), respectively. The adhesion strength of the MAO coating was obtained by scratch testing. The corrosion behavior of the MAO coatings was evaluated by potentiodynamic polarization test and electrochemical impedance spectroscopy. The bioactivity of the coatings was carried out by immersion test in simulated body fluid (SBF). The results showed that the thickness of the MAO coatings, roughness and pore size gradually increase as a function of the oxidation time, which at the same time increases the rutile phase constituent. The coating prepared by 15 min exhibited the best adhesive strength, which mainly consists of TiO2, CaO, CaHPO4 and Ca3(PO4)2. The corrosion resistance and bioactivity of MAO coatings could be improved by changing the oxidation time, and MAO coating formed at 15 min has the best corrosion resistance and bioactivity. The whole MAO process on SLM-produced TC4 alloy can be divided into four stages through “anodic oxidation → film puncturing → micro-arc oxidation → arc light stage” according to voltage change and microstructure evolution. In addition, a large amount of grain boundary interfacial area in SLM-produced TC4 alloy may participate in the MAO reaction to form a large number of discharge channels and share the total energy to decline energy density.

The study of electrodeposition of hydroxyapatite-ZrO2-TiO2 nanocomposite coatings on 316 stainless steel

In this research pure HA and HA-ZrO2-TiO2 nanocomposite coatings (named HZT coatings) were successfully synthesized by merging two usual electroplating methods. In order to deposit pure HA coating a particular saline solution of Calcium and Phosphate was prepared with pH = 4.2, thermodynamically rich of hydroxyapatite. XRD and FTIR studies prove the synthesis of hydroxyapatite during electrodeposition process. To synthesize composite coatings with rational molar ratios of composite agents to matrix, two different concentrations of ZrO2-TiO2 suspensions were added to Ca-P solution at the pH = 4.2 and electrodeposition process done similar to pure HA sample. XRD, FTIR and FESEM (EDS) analyses prove that composite coatings electrodeposited successfully too. The effect of ZrO2-TiO2 composite agents on the characteristics of the coatings were investigated using X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), Field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy. Polarization test was carried out to evaluate corrosion behavior of the coatings. In-vitro test was done in SBF solution and bioactivity of coatings was evaluated using FESEM observation.Adding ZrO2-TiO2 nanoparticles makes different changes in the coating specifications. In composite coatings hydroxyapatite has higher crystallinity (92%) rather than pure HA (80%). FESEM observations reveal new morphologies of electrodeposited HA, such as micro-nanorods of HA formed in composite coatings that are not mentioned before in the literature. EDS results show that adding more nanoparticles to the solution results in more nanoparticles deposition in composite coating.The minimum corrosion current density (icorr.) of coatings was for HZT2 composite coating equal to 0.01 μA/cm2 while icorr. of bare substrate was 1.5 μA/cm2 (it means that icorr. of composite coating is 0.007 icorr. of bare substrate.). As a result of nanoparticles addition, porosity is decreased from 46% for HA coating to 6% for HZT2 coating. EIS results show that corrosion resistance of coating increased as a result of adding nanoparticles and HZT2 coating has largest charge transfer resistance among the prepared coatings.The FE-SEM observations suggest that the coatings would demonstrate bioactive behavior because natural hydroxyapatite (deposits formed during immersion) is formed during immersion.

Electrophoretic deposition of tetracycline hydrochloride loaded halloysite nanotubes chitosan/bioactive glass composite coatings for orthopedic implants

Electrophoretic deposition (EPD) was used to apply bioactive multifunctional composite coatings with antibacterial substances on stainless steel AISI 316L (SS). Tetracycline hydrochloride (TCN) loaded halloysite nanotubes were co-deposited with chitosan and bioactive glass (BG) particles to produce composite coatings. SEM/EDX, XRD, and FTIR analyses were performed to characterize the composition and microstructure of coatings. The release of tetracycline hydrochloride (TCN) in phosphate buffered saline (PBS) was investigated by UV spectrometry, and measurements indicated the release of around 54% of the drug within 14days of immersion in PBS. Furthermore, to determine that the bioactivity of coatings had not been adversely influenced, simulated body fluid (SBF) bioactivity tests were performed. The formation of hydroxyl carbonate apatite on the surface of the coatings was confirmed after 3days. The ability of coatings to prevent bacterial growth was tested using E. coli as gram-negative and S. aureus as gram-positive bacteria. Results showed improved bactericidal effect of TCN-containing coatings compared to non-TCN loaded coatings. The corresponding amount of TCN loaded in EPD coatings supported cell viability and proliferation of MG-63 cells for up to 3days. Fluorescence images of MG-63 cells showed evidence of cell growth in islands on the coated surface. The surface roughness of the coating loaded with halloysite nanotubes supported cell adhesion and proliferation. Additionally, the wettability value of the coatings confirmed a moderately hydrophilic surface, which is suitable for bone regenerative applications. Improved corrosion resistance compared to the pure stainless steel (SS) substrate was confirmed. The adhesion between coatings and substrates was tested by the tape test, and the result showed sufficient adhesion of the coatings to be handled without detachment. In all, the new coating system has potential for applications in orthopedics.

Effect of phosphate additives on the microstructure, bioactivity, and degradability of microarc oxidation coatings on Mg-Zn-Ca-Mn alloy

Calcium phosphate coatings were prepared on the surface of self-designed Mg-Zn-Ca-Mn alloy using microarc oxidization technology. To characterize the microstructures, cross-section morphologies, and compositions of the coatings, the authors used scanning electron microscopy equipped with an energy-disperse spectrometer, x-ray diffraction, and Fourier transform infrared spectroscopy. Potentiodynamic polarization in the simulated body fluid (SBF) was used to evaluate the corrosion behaviors of the samples. An SBF immersion test was used to evaluate the coating bioactivity and degradability. After the immersion tests, some bonelike apatite formed on the coating surfaces indicate that bioactivity of the coatings is excellent. The coating prepared in electrolyte containing (NaPO3)6 had slower degradation rate after immersion test for 21 days.

Mesoporous Bioactive Glass Nanolayer‐Modified Zirconia Coatings on Ti‐6Al‐4V with Improved In Vitro Bioactivity

The bioactivity of coatings on alloy implants plays critical roles in the fast osteointegration and maintenance of a long‐term life span of the implants. The aim of this study is to incorporate nanopores and bioactive components into the plasma‐sprayed coatings by constructing nanopores and bioactive elements on the surface of coatings and further improve their in vitro bone‐forming activity. In this study, mesoporous bioactive glasses (MBG) were used for modifying the surface of ZrO2 coatings on Ti‐6Al‐4V by spin‐coating methods. The result shows that MBG nanolayer has been successfully coated on the surface of ZrO2 coatings. The MBG‐modified ZrO2 coatings have improved apatite‐mineralization ability and stable bonding strength. In addition, the attachment, proliferation, alkaline phosphate activity, and bone‐related gene expression of rabbit bone marrow stromal cells on MBG‐ZrO2 coating were also enhanced as compared with conventional bioactive glass‐modified ZrO2 coatings and pure ZrO2 coatings. The results indicated that MBG‐modified ZrO2 coatings on Ti alloy are promising for orthopedic application.

Bioactive and Antibacterial Ag-AgCl-TiO<sub>2</sub> Coating on Titanium Implants

In this work, Ag-AgCl-TiO2 coating was fabricated on titanium substrates to obtain an implant material having excellent antibacterial property and bioactivity. The coating was investigated by scanning electron microscopy and X-ray diffraction. The bioactivity of coatings was examined by simulated body fluid soaking test. To verify the susceptibility of implant material surface to bacterial adhesion, S. aureus (Sau), E. coli (Eco), K. pneumoniae (Kpn), P. Aeruginosa (Pae), four types of major pathogen were chosen for in vitro antibacterial analyses. The results showed that Ag-AgCl-TiO2 coating had excellent antibacterial property and bioactivity.

INVESTIGATION OF BORON INFLUENCE ON THE STRUCTURE AND PROPERTIES OF MULTICOMPONENT NANOSTRUCTURED TiCaPCON COATINGS

Multicomponent nanostructured TiCaPCON–B coatings with 7,4–15,0 at.% of boron were obtained by magnetron sputtering. It was shown that all elements were uniformly distributed over the coating thickness. The TiCaPCON–B coatings revealed a dense columnar structure with a column width less than 80 nm. It was found that the introduction of boron changed the phase composition of the coatings, but had no significant effect on their morphology. The base of the TiCaPCON–B coatings consisted of free carbon and Ti(C, N), TiB 2 , BN phases. The study of mechanical properties revealed that the coatings had a relatively high hardness (20–24 GPa) and low Young’s modulus (213–231 GPa). The coatings exhibited hydrophilic properties within the 24-hour exposure to air. Depending on the boron content in the coating, its rate of release into normal saline was 17–24 mkg/(l·сm 2 ·day). In vitro biological studies showed 30–40 % improvement in bioactivity of coatings containing 12,7–15,0 at.% of boron as compared with titanium.

Bioactive, nanostructured Si-substituted hydroxyapatite coatings on titanium prepared by pulsed laser deposition.

The aim of this work was to deposit silicon-substituted hydroxyapatite (Si-HAp) coatings on titanium for biomedical applications, since it is known that Si-HAp is able to promote osteoblastic cells activity, resulting in the enhanced bone ingrowth. Pulsed laser deposition (PLD) method was used for coatings preparation. For depositions, Si-HAp targets (1.4 wt % of Si), made up from nanopowders synthesized by wet method, were used. Microstructural and mechanical properties of the produced coatings, as a function of substrate temperature, were investigated by scanning electron and atomic force microscopies, X-ray diffraction, Fourier transform infrared spectroscopy, and Vickers microhardness. In the temperature range of 400-600°C, 1.4-1.5 µm thick Si-HAp films, presenting composition similar to that of the used target, were deposited. The prepared coatings were dense, crystalline, and nanostructured, characterized by nanotopography of surface and enhanced hardness. Whereas the substrate temperature of 750°C was too high and led to the HAp decomposition. Moreover, the bioactivity of coatings was evaluated by in vitro tests in an osteoblastic/osteoclastic culture medium (α-Modified Eagle's Medium). The prepared bioactive Si-HAp coatings could be considered for applications in orthopedics and dentistry to improve the osteointegration of bone implants.

Bioactivity and mechanical properties of bioactive glass coatings fabricated by flame spraying

In this study, bioactive glass powders were synthesized from four different types of oxides (SiO2, P2O5, CaO and MgO). These oxides were mixed, melted and milled to produce two materials of 31SiO2–11P2O5-(58-x)-CaO–xMgO, where the values x=0 and x=2 describe powders P0 and P2, respectively. The powders were sieved to obtain a particle size distribution of 8.8–66.2μm for P0 and 5.1–61.6μm for P2. The powders were flame sprayed onto AISI 316L stainless steel and Ti6Al4V alloy substrates using a modified Terodyn 2000 (Eutetic-Castolín) gun. The flame-forming gas was a mixture of O2–C2H2 (38/22L/min). The microstructure of the powders and the obtained coatings was examined by SEM. X-ray diffraction (XRD) was used to identify the crystalline phases in the powders and coatings. The hardness and fracture toughness of the coatings were determined by Vickers micro-indentation tests. According to the feedstock powder, the substrate material and thermal spraying parameters, the microhardness of the coatings was between 4.1±0.5 and 5.2±0.6GPa, and their fracture toughness was between 4.6±0.9 and 6.6±1.1MPa·m1/2. The bioactivity of coatings was evaluated from hydroxyapatite layer produced in their surface by exposure with simulated body fluid (SBF) during 1, 9 and 15days. The hydroxyapatite layer was characterized by X-ray diffraction and SEM-EDS.

Wetting and in vitro bioactivity of laser processed CaP coating with presence and variation of SiO2 on Ti–6Al–4V

Calcium phosphate bioceramic and SiO2–CaP bioceramic composite coatings were prepared on Ti–6Al–4V substrates by laser cladding method. Surface energy components were calculated and the wettability of the coatings in simulated body fluid (SBF) was investigated. In vitro bioactivity of the coatings were performed by immersing in SBF and analysed for the precipitation of hydroxyapatite (HA). The effects of SiO2 content on the wettability and in vitro bioactivity of the bioceramic composite coatings were investigated. The surface energy values increased as the percentage of SiO2 in the coating precursor increased, resulting in decrease in contact angle with SBF for improved wettability. X-ray diffraction results indicated that after immersion in SBF for more than three days, 17 wt-%SiO2–CaP and 25 wt-%SiO2–CaP samples possessed highly intense peaks of HA than 100 wt-%CaP sample. Furthermore, in vitro bioactivity assays show that the SiO2–CaP bioceramic composite coatings possess a higher HA precipitation rate than CaP coating and Ti–6Al–4V control.

Apatite Formation on Surface of Plasma-Sprayed TiO<sub>2</sub> Coating by Sulfuric Acid Treatment

TiO2 coatings on titanium alloy substrates were prepared by atmospheric plasma spraying using commercial nano-powders and followed by H2SO4 treatment. The bioactivity of coatings was evaluated by the simulated body fluid soaking test. Scanning electron microscopy and energy-dispersive X-ray spectrometry were used to characterize the surface morphologies and phase composition of the coating before and after soaking in simulated body fluid. The results obtained indicate that H2SO4-treated TiO2 coating can induce a bone-like apatite formation on its surface, however, no apatite appears on the surface of as-sprayed TiO2 coatings. The acid concentration and treated time affected the bioactivities of TiO2 coatings.

Plasma-sprayed wollastonite 2M/ZrO 2 composite coating

Wollastonite 2M/ZrO 2 composite coatings in different proportions were deposited onto Ti–6Al–4V substrates using plasma spraying. The tensile adhesion test (TAT) specified by ASTM C 633-79 was used to measure the tensile bonding strength of the coating. The bioactivity of coatings was evaluated using a simulated body-fluid soaking test. The results obtained showed that the composite coatings have a lamellar structure with alternating wollastonite 2M and ZrO 2 phases. The Vickers microhardness of composite coatings increases with increasing ZrO 2 content . Carbonate-containing hydroxyapatite (CHA) was formed on the surface of the wollastonite 2M and wollastonite 2M/ZrO 2 composite coatings soaked in simulated body fluid, but was not formed on the surface of the ZrO 2 coatings after immersion. This indicates that wollastonite 2M and W7Z3 and W3Z7 coatings have very good bioactivity. In addition, a silica-rich layer appeared at the interface of CHA and wollastonite 2M and W7Z3 coatings, but is absent in the case of the W3Z7 coating. The ZrO 2 in the composite coatings may decrease the dissolution rate of the coating in simulated body fluid compared to pure wollastonite 2M coatings.