Microarc Calcium Phosphate Research Articles

Study of tribological characteristics of micro-arc calcium phosphate coatings on titanium

Tribological characteristics of implants, such as wear resistance and friction coefficient, play a critical role in ensuring their durability and functionality when interacting with surrounding tissues. These parameters influence the implant's ability to withstand mechanical loads and minimize wear throughout its service life. Minimizing friction between the implant and biological tissues not only helps prevent mechanical damage but also reduces the risk of inflammatory reactions, ensuring better biological compatibility. In this study, calcium phosphate coatings were obtained using the micro-arc oxidation method with different duty cycle of current to investigate their tribological characteristics. The coatings deposited on titanium had a structure with volcano-like formations with pores ranging from 66 to 98 micrometers. The thickness of the coatings varied from 74.3 to 100 micrometers depending on the conditions during microarc oxidation. Tribological tests were conducted using a ball-on-flat setup with reciprocating motion. The coatings were subjected to tribological tests against SHX15 steel under normal loads of 5 and 20 N. Depending on the applied load, the friction coefficients of the coatings ranged from 0.029 to 0.034 at 5 N and from 0.9 to 1.26 at 20 N. Analysis of wear parameters and micrographs of worn surfaces indicate that the mode with a pulse current duty cycle of 17.3% during micro-arc oxidation allows for the production of titanium surface coatings with high wear resistance.

Effect of ultraviolet irradiation or diffuse discharge plasma on structure and surface electrical charge of micro-arc calcium phosphate coatings

The studies of the effect of ultraviolet (UV) irradiation and plasma of a runaway electron preionized diffuse discharge (REP DD) post-treatments on the surface structure and electrical charge of the micro-arc oxidation (MAO) coatings were performed. The UV irradiation and plasma treatment did not effect on the morphology, roughness and thickness of the MAO coatings. However, these post-treatments led to formation of the small fraction of the crystalline CaHPO4phase in the X-ray amorphous structure of the coatings. Moreover, the UV and REP DD plasma treatments increased the electrostatic potential (EP) negative values from –85 mV to –126 mV of the coatings in the following order: MAO < MAO/UV (for 5 min) < MAO/Plasma (with 10,000 pulses) < MAO/UV (for 20 min) < MAO/Plasma (with 80,000 pulses).

Gene Expression Regulation and Secretory Activity of Mesenchymal Stem Cells upon In Vitro Contact with Microarc Calcium Phosphate Coating.

The manufacture of biomaterial surfaces with desired physical and chemical properties that can directly induce osteogenic differentiation without the need for biochemical additives is an excellent strategy for controlling the behavior of mesenchymal stem cells (MSCs) in vivo. We studied the cellular and molecular reactions of MSCs to samples with a double-sided calcium phosphate (CaP) coating and an average roughness index (Ra) of 2.4–4.6 µm. The study aimed to evaluate the effect of a three-dimensional matrix on the relative mRNA expression levels of genes associated with the differentiation and maturation of MSCs toward osteogenesis (RUNX2, BMP2, BMP6, BGLAP, and ALPL) under conditions of distant interaction in vitro. Correlations were revealed between the mRNA expression of some osteogenic and cytokine/chemokine genes and the secretion of cytokines and chemokines that may potentiate the differentiation of cells into osteoblasts, which indicates the formation of humoral components of the extracellular matrix and the creation of conditions supporting the establishment of hematopoietic niches.

Effect of UV irradiation and diffuse plasma on surface properties of micro-arc calcium phosphate coatings

The influence of UV irradiation or plasma of runaway electron preionized diffuse discharge (REP DD) post-modification on the surface properties of the calcium phosphate (CaP) coatings formed by the micro-arc oxidation (MAO) method was investigated. The formed MAO-coatings had porous structure and rough surface morphology with incorporation of spheroidal structural elements with inner pores. It was showed that the UV irradiation or REP DD post-treatment of the MAO-coatings led to the decrease of the coating contact angels with water from 20 to 0 or to 7 degrees, respectively. However, the free surface energy of the coatings did not change after post-treatments and equalled to 74±1 mJ·m−2. The polar component of the free surface energy of the all types of the coatings exceeded almost 5–6 times the dispersion component that indicated the presence of strong polar bonds on the coating surface, e. g. OH- and PO4-groups.

Modification of titanium surface via Ag-, Sr- and Si-containing micro-arc calcium phosphate coating

The current research is devoted to the study of the modification of the titanium implants by the micro-arc oxidation with bioactive calcium phosphate coatings containing Ag or Sr and Si elements. The coatings’ microstructure, phase composition, morphology, physicochemical and biological properties were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). Ag-containing and Sr-Si-incorporated coatings were formed in alkaline and acid electrolytes, respectively. The formation of the coatings occurred at different ranges of the applied voltages, which led to the significant difference in the coatings properties. The trace elements Ag, Sr and Si participated intensively in the plasma-chemical reactions of the micro-arc coatings formation. Ag-containing coatings demonstrated strong antibacterial effect against Staphylococcus aureus AТСС 6538-P. MTT in vitro test with 3T3-L1 fibroblasts showed no cytotoxicity appearance on Sr-Si-incorporated coatings.

Nanoscale Electrical Potential and Roughness of a Calcium Phosphate Surface Promotes the Osteogenic Phenotype of Stromal Cells.

Mesenchymal stem cells (MSCs) and osteoblasts respond to the surface electrical charge and topography of biomaterials. This work focuses on the connection between the roughness of calcium phosphate (CP) surfaces and their electrical potential (EP) at the micro- and nanoscales and the possible role of these parameters in jointly affecting human MSC osteogenic differentiation and maturation in vitro. A microarc CP coating was deposited on titanium substrates and characterized at the micro- and nanoscale. Human adult adipose-derived MSCs (hAMSCs) or prenatal stromal cells from the human lung (HLPSCs) were cultured on the CP surface to estimate MSC behavior. The roughness, nonuniform charge polarity, and EP of CP microarc coatings on a titanium substrate were shown to affect the osteogenic differentiation and maturation of hAMSCs and HLPSCs in vitro. The surface EP induced by the negative charge increased with increasing surface roughness at the microscale. The surface relief at the nanoscale had an impact on the sign of the EP. Negative electrical charges were mainly located within the micro- and nanosockets of the coating surface, whereas positive charges were detected predominantly at the nanorelief peaks. HLPSCs located in the sockets of the CP surface expressed the osteoblastic markers osteocalcin and alkaline phosphatase. The CP multilevel topography induced charge polarity and an EP and overall promoted the osteoblast phenotype of HLPSCs. The negative sign of the EP and its magnitude at the micro- and nanosockets might be sensitive factors that can trigger osteoblastic differentiation and maturation of human stromal cells.

Formation of a Surface Charged Microarc Coatings Modified by Boehmite Nanoparticles

Investigations of microarc calcium phosphate (CaP) boehmite-containing biocoatings on the pure titanium (Ti) alloy were presented. There were discovered relationships of coating properties (morphology, elemental and phase composition, zeta-potential, wettability) on the boehmite deposition parameters. A variation of the modification parameters of boehmite nanoparticles deposition allowed producing hydrophilic boehmite-containing CaP coatings with the roughness of 2.2-3.1 μm and nanoscale morphology. The influence of boehmite nanoparticles on the surface zeta-potential of the coating was found.

Cell-IQ visualization of motility, cell mass, and osteogenic differentiation of multipotent mesenchymal stromal cells cultured with relief calcium phosphate coating.

The Cell-IQ continuous surveillance system allowed us to establish the following changes in a 14- day culture in vitro: a twofold suppression of the directional migration of multipotent mesenchymal stromal cells of human adipose tissue (MMSC-AT) towards the samples with a microarc calcium phosphate (CP) coating from synthetic hydroxyapatite; a tenfold decrease in the cell mass on the interphase with the samples, which was accompanied by a slight reduction in the expression of membrane determinants of stromal stem cells; and an enhancement of their osteogenic differentiation (osteocalcin secretion and mineralized matrix formation) on the 21st day of the study. Calcium phosphate particles, but not the calcium and phosphorus ions, may trigger the phenotypic transformation of the MMSC-AT behavior in vitro.

Modification of Calcium Phosphate Microarc Coatings Surface by Boehmite Nanoparticles

The surface modification of microarc calcium phosphate coatings by boehmite nanoparticles deposition was studied. The powder of aluminium nitride AlN was deposited on the microarc calcium phosphate coatings, and then the hydrolysis reaction was initiated. The boehmite (AlO(OH)) was formed as a result of the reaction. The influence of boehmite nanoparticles deposition on the properties of calcium phosphate microarc coatings (i.e. the morphology, elemental and phase composition, wettability) was studied. Experimental results show that the introduction of boehmite nanoparticles affects the surface morphology and wettability of the coating.

Structure and properties of micro-arc calcium phosphate coatings on pure titanium and Ti–40Nb alloy

The microstructure, physical and mechanical, and chemical properties of micro-arc calcium phosphate (CaP) coatings deposited under different process voltages in the range of 150–400 V on the commercially pure titanium (Ti) and Ti–40%Nb (Ti–40Nb) (mass fraction) alloy were investigated by the SEM, TEM, XRD and EDX methods. The coating thickness, roughness, and sizes of structural elements were measured and showed similar linear character depending on the process voltage for the coatings on both substrates. SEM results showed the porous morphology with spherical shape structural elements and rough surface relief of the coatings. XRD and TEM studies exhibited the amorphous structure of the CaP coating. With increasing the process voltage to 300–400 V, the crystalline phases, such as CaHPO4 and β-Ca2P2O7, were formed onto the coatings. The annealing leads to the formation of complex poly-phase structure with crystalline phases: CaTi4(PO4)6, β-Ca2P2O7, TiP2O7, TiNb(PO4)3, TiO2, NbO2, and Nb2O5. The applied voltage and process duration in the ranges of 200–250 V and 5–10 min, respectively, revealed the coating formed on Ti and Ti–40Nb with optimal properties: thickness of 40–70 μm, porosity of 20%–25%, roughness (Ra) of 2.5–5.0 μm, adhesion strength of 15–30 MPa, and Ca/P mole ratio of 0.5–0.7.

Modulating effect of matrices with calcium phosphate coating on cytotoxicity of strontium ranelate and ibandronic acid in vitro.

Strontium ranelate (29 μg/ml) and ibandronic acid (50 μM) produced a cytotoxic effect on rat bone marrow myelokaryocytes in vitro. Strontium ranelate increased the number of myelokaryocytes with signs of necrosis, ibandronic acid increased the number of apoptotic and necrotic cells in the 9-day 2D culture of bone marrow cells on the plastic surface of the wells of culture plates. Co-culturing of the bone marrow with 3D matrices with microarc calcium phosphate coating that simulated bone mineral matrix increased intracellular ROS concentration, but abolished the cytotoxic effect of these drugs.

Structure and Properties of Microarc Calcium Phosphate Coatings on the Surface of Titanium and Zirconium Alloys

Regularities of the formation of calcium phosphate coatings on the surface of titanium and zirconium alloys formed by the method of microarc oxidation are investigated. The scheme of deposition of the calcium phosphate coating in microarc discharges is suggested that explains the difference in the morphology, microstructure, and properties of coatings on the surface of titanium and zirconium alloys. It is demonstrated that coatings on the surface of titanium and zirconium alloys have different structures, phase compositions, and physicomechanical properties due to different electrophysical characteristics of metal (titanium and zirconium) substrates, disperse β-Nb particles, and passivating oxide films on their surfaces.

Artificial Niches for Stromal Stem Cells as a Potential Instrument for the Design of the Surface of Biomimetic Osteogenic Materials

A relationship between the topography of rough calcium phosphate surfaces having osteogenic niche-reliefs and the electrostatic potential of these surfaces as a possible instrument to control stromal stem cells has been investigated. The in vitro culture of human lung prenatal stromal cells on nanostructured/ultrafine-grained VT1.0 titanium alloy plates with bilateral rough calcium phosphate (CaP) microarc coating was used. It was established that the amplitude of the electret CaP surface potential linearly increased with increasing area of valleys (sockets), and the negative charge is formed on the socket surface. The area of alkaline phosphatase staining (the marker of osteoblast maturation and differentiation) of adherent CD34 – CD44 + cells increases linearly with increasing area of artificial microterritory (socket) of the CaP surface occupied with each cell. The negative electret potential in valleys (sockets) of microarc CaP coatings can be the physical mechanism mediating the influence of the surface topography on osteogenic maturation and differentiation of cells in vitro. This mechanism can be called “niche-potential” and can be used as an instrument for biomimetic modification of smooth CaP surfaces to strengthen their integration with the bone tissue.

Hybrid Method for the Formation of Biocomposites on the Surface of Stainless Steel Implants

This study reports a hybrid method which allows the formation of biocomposites on stainless steel implants. The main idea of the method is to create multilayer coatings consisting of titanium primer layer and a microarc calcium-phosphate coating. The titanium layer is deposited from plasma of continuous vacuum-arc discharge, and calcium-phosphate coating is formed by the microarc oxidation technique. The purpose of the hybrid method is to combine the properties of good strength stainless steel with high bioactivity of calcium-phosphate coating. This paper describes the chemical composition, morphology characteristics, adhesion and the ability of the formed biocomposites to stimulate the processes of osteoinduction. It is expedient to use such biocomposites for implants which carry heavy loads and are intended for long-term use, e.g. total knee endoprosthesis.