The Influence of pH Value on the Microstructure and Properties of Strontium Phosphate Chemical Conversion Coatings on Titanium.

Strontium (Sr) is a trace element in the human body that can promote bone formation and inhibit bone absorption. A conversion coating of strontium phosphate (Sr-P) on the surface of titanium (Ti) can improve its biological properties and has many potential applications in the fields of dentistry and orthopedics. In the present study, Sr-P coatings with SrHPO4 and Sr3(PO4)2 crystals on Ti are prepared by a phosphate chemical conversion (PCC) treatment and the effect of pH values on the properties of the Sr-P coatings is researched. The results prove that the phase composition, morphology, and corrosion resistance of the coated Ti vary according to the pH values of the PCC solution. The morphology of the conversion deposition on Ti changes from plat-like to cluster-like and then to homogeneous microcrystals as the pH value changes from 2.50 to 3.25. Only discrete SrHPO4 crystals are generated on the substrate at lower pH values, while relatively stable Sr3(PO4)2 and SrHPO4 crystals grow and subsequently form an integrated coating on the Ti as the pH exceeds 2.50. The cross-sectional morphologies and bonding strength of different coatings are also researched. The corrosion resistance of coated Ti improves compared with that of bare Ti because of the Sr-P coatings with a Sr3(PO4)2 phase. In addition, it is indicated that the Sr-P coatings on Ti can improve the adhesion and differentiation of BMSCs.

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.

Effect of Substrates Performance on the Microstructure and Properties of Phosphate Chemical Conversion Coatings on Metal Surfaces.

Phosphate chemical conversion (PCC) technology has attracted extensive attention for its ability to regulate the surface properties of biomedical metals. However, titanium (Ti)-based alloys exhibit inertia because of the native passive layer, whereas zinc (Zn)-based alloys show high activity in acidic PCC solutions. The substrate performance affects the chemical reaction in the phosphating solution, which further leads to diversity in coating properties. In this work, the zinc-phosphate (ZnP) coatings are prepared on Ti alloy (TA) and Zn alloy (ZA) substrates using the PCC method, respectively. The coatings prepared herein are detected by a scanning electron microscope (SEM), X-ray diffractometer (XRD), laser scanning confocal microscope (LSCM), universal testing machine, contact angle goniometer, and electrochemical workstation system. The results show that the substrate performance has little effect on the phase composition but can significantly affect the crystal microstructure, thickness, and bonding strength of the coatings. In addition, the ZnP coatings improve the surface roughness of the substrates and show good hydrophilicity and electrochemical corrosion resistance. The formation mechanism of the ZnP coating is revealed using potential-time curves, indicating that the metal-solution interfacial reaction plays a dominant role in the deposition process.

Engineered Niobium Carbide MXenzyme-Integrated Self-Adaptive Coatings Inhibiting Periprosthetic Osteolysis by Orchestrating Osteogenesis-Osteoclastogenesis Balance.

Periprosthetic osteolysis induced by the ultrahigh-molecular-weight polyethylene (UHMWPE) wear particles is a major complication associated with the sustained service of artificial joint prostheses and often necessitates revision surgery. Therefore, a smart implant with direct prevention and repair abilities is urgently developed to avoid painful revision surgery. Herein, we fabricate a phosphatidylserine- and polyethylenimine-engineered niobium carbide (Nb2C) MXenzyme-coated micro/nanostructured titanium implant (PPN@MNTi) that inhibits UHMWPE particle-induced periprosthetic osteolysis. The specific mechanism by which PPN@MNTi operates involves the bioresponsive release of nanosheets from the MNTi substrate within an osteolysis microenvironment, initiated by the cleavage of a thioketal-dopamine molecule sensitive to reactive oxygen species (ROS). Subsequently, functionalized Nb2C MXenzyme could target macrophages and escape from lysosomes, effectively scavenging intracellular ROS through its antioxidant nanozyme-mimicking activities. This further achieves the suppression of osteoclastogenesis by inhibiting NF-κB/MAPK and autophagy signaling pathways. Simultaneously, based on the synergistic effect of MXenzyme-integrated coatings and micro/nanostructured topography, the designed implant promotes the osteogenic differentiation of bone mesenchymal stem cells to regulate bone homeostasis, further achieving advanced osseointegration and alleviable periprosthetic osteolysis in vivo. This study provides a precise prevention and repair strategy of periprosthetic osteolysis, offering a paradigm for the development of smart orthopedic implants.

Calcium-Zinc Phosphate Chemical Conversion Coating Facilitates the Osteointegration of Biodegradable Zinc Alloy Implants by Orchestrating Macrophage Phenotype.

Zinc (Zn) alloys provide a new generation for orthopedic applications due to their essential physiological effects and promising degradation properties. However, excessive release of Zn ions (Zn2+ ) during degradation and the severe inflammatory microenvironment are not conducive to osseointegration, which is determined by the characteristics of the implant surface. Therefore, it is essential to modulate the release rate of Zn alloys by surface modification technology and endow them with anti-inflammatory and osteogenic effects. In this study, two kinds of phosphate chemical conversion (PCC) coatings with different compositions and morphological structures are prepared, namely Zn-P (with disk-like crystals) and Ca-Zn-P (with lamellar crystals). Although all the PCC-coated Zn implants have low cytotoxicity, Ca-Zn-P show better osteoimmunomodulation effects in several aspects: the induction of the M2-phenotype macrophage polarization and thus promotion of osteogenesis in vitro; the regulation of the bone immune microenvironment which is conducive to tissue regeneration and osseointegration in vivo; and the release of ions (through PI3K/AKT and Wnt signaling pathways) and the morphological structures (through RhoGTPase signaling pathways) act as possible mechanisms of M2 polarization. The Ca-Zn-P coating can be considered to provide new insights into bone immunomodulation and osseointegration.

Zinc-Doping Induces Evolution of Biocompatible Strontium-Calcium-Phosphate Conversion Coating on Titanium to Improve Antibacterial Property.

Implant-associated infections (IAI) remains a common and devastating complication in orthopedic surgery. To reduce the incidence of IAI, implants with intrinsic antibacterial activity have been proposed. The surface functionalization and structure optimization of metallic implants can be achieved by surface modification using the phosphate chemical conversion (PCC) technique. Zinc (Zn) has strong antibacterial behavior toward a broad-spectrum of bacteria. Herein, Zn was incorporated into strontium-calcium-phosphate (SrCaP) coatings on titanium (Ti) via PCC method, and the influence of its doping amount on the phase, microstructure, antibacterial activity, and biocompatibility of the composite coating was researched. The results indicated that traces of Zn doping produced grain refinement of SrCaP coating with no significant effect on its phase and surface properties, while a higher Zn content induced its phase and microstructure transformed into zinc-strontium-phosphate (SrZn2(PO4)2). SrCaP-Zn1 and SrCaP-Zn4 represented trace and high content Zn-doped coatings, respectively, which exhibited a similar bacterial attachment for a short time but showed inhibition of biofilm formation after continuous incubation up to 24 h. The killing rates of SrCaP-Zn1 coating for Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) reached 61.25% and 55.38%, respectively. While that data increased to 83.01% and 71.28% on SrCaP-Zn4 coating due to the more-releasing Zn2+. Furthermore, in vitro culture of MC3T3-E1 cells proved that the Zn-doped coatings also possessed excellent biocompatibility. This study provides a new perception for the phase and microstructural optimization of phosphate coatings on implant surfaces, as well as fabricating promising coatings with excellent biocompatibility and antimicrobial properties against IAI.

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.