Effect of Reaction Temperature on the Microstructure and Properties of Magnesium Phosphate Chemical Conversion Coatings on Titanium

Magnesium phosphate (MgP) has garnered growing interest in hard tissue replacement processes due to having similar biological characteristics to calcium phosphate (CaP). In this study, an MgP coating with the newberyite (MgHPO₄·3H₂O) was prepared on the surface of pure titanium (Ti) using the phosphate chemical conversion (PCC) method. The influence of reaction temperature on the phase composition, microstructure, and properties of coatings was systematically researched with the use of an X-ray diffractometer (XRD), a scanning electron microscope (SEM), a laser scanning confocal microscope (LSCM), a contact angle goniometer, and a tensile testing machine. The formation mechanism of MgP coating on Ti was also explored. In addition, the corrosion resistance of the coatings on Ti was researched by assessing the electrochemical behavior in 0.9% NaCl solution using an electrochemical workstation. The results showed that temperature did not obviously affect the phase composition of the MgP coatings, but affected the growth and nucleation of newberyite crystals. In addition, an increase in reaction temperature had a great impact on properties including surface roughness, thickness, bonding strength, and corrosion resistance. Higher reaction temperatures resulted in more continuous MgP, larger grain size, higher density, and better corrosion resistance.

Interleukin-4 assisted calcium-strontium-zinc-phosphate coating induces controllable macrophage polarization and promotes osseointegration on titanium implant

Titanium (Ti) and its alloys are believed to be promising scaffold materials for dental and orthopedic implantation due to their ideal mechanical properties and biocompatibility. However, the host immune response always causes implant failures in the clinic. Surface modification of the Ti scaffold is an important factor in this process and has been widely studied to regulate the host immune response and to further promote bone regeneration. In this study, a calcium-strontium-zinc-phosphate (CSZP) coating was fabricated on a Ti implant surface by phosphate chemical conversion (PCC) technique, which modified the surface topography and element constituents. Here, we envisioned an accurate immunomodulation strategy via delivery of interleukin (IL)-4 to promote CSZP-mediated bone regeneration. IL-4 (0 and 40 ng/mL) was used to regulate immune response of macrophages. The mechanical properties, biocompatibility, osteogenesis, and anti-inflammatory properties were evaluated. The results showed that the CSZP coating exhibited a significant enhancement in surface roughness and hydrophilicity, but no obvious changes in proliferation or apoptosis of bone marrow mesenchymal stem cells (BMMSCs) and macrophages. In vitro, the mRNA and protein expression of osteogenic related factors in BMMSCs cultured on a CSZP coating, such as ALP and OCN, were significantly higher than those on bare Ti. In vivo, there was no enhanced bone formation but increased macrophage type 1 (M1) polarization on the CSZP coating. IL-4 could induce M2 polarization and promote osteogenesis of BMMSCs on CSZP in vivo and in vitro. In conclusion, the CSZP coating is an effective scaffold for BMMSCs osteogenesis, and IL-4 presents the additional advantage of modulating the immune response for bone regeneration on the CSZP coating in vivo.

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A chemical conversion calcium-strontium-zinc-phosphate (CSZP) coating is prepared on titanium.

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The CSZP coating exhibits micellar lamellar crystal morphology in micro-nano scale.

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The CSZP coating has an optimal topography and element composition for osteogenesis.

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Interleukin-4 assisted CSZP coating can obtain better osteoimmunomodulation properties.

Microstructural characterization and film-forming mechanism of a phosphate chemical conversion ceramic coating prepared on the surface of 2A12 aluminum alloy

Phosphate chemical conversion (PCC) ceramic coatings on the surface of 2A12 aluminum alloy substrate have been fabricated by a simple and inexpensive chemical conversion process in CrO₃–NaF–H₃PO₄ solution. Microstructure characterization showed that the average diameter of micro-pores and the thickness of the PCC ceramic coating were about 50 nm and 4 μm, respectively, and the ceramic coating was compact and uniform when the conversion time was 60 min. Meanwhile, we found that the PCC ceramic coating mainly consisted of AlPO₄, AlOOH, AlF₃, and a few amorphous phases (CrPO₄ and CrOOH) via EDS, XRD, XPS analyses. TG-DSC results indicated that the PCC ceramic coatings had excellent thermal stability. Significantly, the adhesion strength (178.55 N) between the PCC ceramic coatings and 2A12 Al substrate was remarkably improved owing to the strong chemical bond between the PCC ceramic coating and 2A12 Al substrate and the increase of surface roughness. Furthermore, a lower corrosion current density (1.382 × 10⁻⁷ A cm⁻²) and a higher corrosion inhibition efficiency (99.91%) confirmed that PCC ceramic coatings had fantastic corrosion resistance because of the presence of crystalline AlPO₄/AlF₃/AlOOH and amorphous CrPO₄/CrOOH as a barrier layer. Additionally, a possible film-forming mechanism of the PCC ceramic coating was proposed during the chemical conversion process, which could be divided into four stages: dissolution of 2A12 aluminum substrate and hydrogen evolution; crystallization of insoluble phosphates and formation of an amorphous phase; growth of insoluble phosphates and dissolution of PCC ceramic coatings; growth and dissolution of PCC coatings to dynamic equilibrium.

Phosphate chemical conversion (PCC) ceramic coatings on the surface of 2A12 aluminum alloy substrate have been fabricated by a simple and inexpensive chemical conversion process in CrO₃–NaF–H₃PO₄ solution.

In-situ preparation of scholzite conversion coatings on titanium and Ti-6Al-4V for biomedical applications

A scholzite (CaZn₂(PO₄)₂·2H₂O) coating was prepared in situ on commercially pure titanium (cpTi) and Ti-6Al-4V (Ti64) substrates using the chemical conversion technology, and its phase composition and microstructure, as well as mechanical, chemical and biological properties were investigated to explore potential applications as a bioactive coating on bone implants. It is indicated that the coating consists mainly of monoclinic scholzite crystals with nano-thick laminar morphology. The crystals on cpTi aggregate to flower-like particles with the diameter of 5-10μm, while form a network structure homogeneously on Ti64. The scratch test shows that the interfacial bonding strength between the coatings and substrates is higher than 40N. Electrochemical measurements indicate that the corrosion behavior of the coatings is not inferior compared with that of oxide film on substrates. MG63 osteoblast-like cells show good adherence and significantly proliferation and differentiation characteristics on the scholzite coated cpTi and Ti64 (p<0.05) in in-vitro cell tests, demonstrating the cytocompatibility of Ti is significantly improved by the scholzite coating. It is suggested that the scholzite coating might be a promising option in hard tissue replacements for early osteogenesis.

Formation mechanism and properties of fluoride–phosphate conversion coating on titanium alloy

Formation mechanism of fluoride–phosphate conversion coating on titanium alloy.