Superior biocompatibility and osteogenic efficacy of micro-arc oxidation-treated titanium implants in the canine mandible

An investigational time course study of titanium plasma spray on osseointegration of PEEK and titanium implants: an in vivo ovine model

BACKGROUND CONTEXT

Methods to improve osseointegration of orthopedic spinal implants remains a clinical challenge. Materials composed of poly-ether-ether-ketone (PEEK) and titanium are commonly used in orthopedic applications due to their inherent properties of biocompatibility. Titanium has a clinical reputation for durability and osseous affinity, and PEEK offers advantages of a modulus that approximates osseous structures and is radiolucent. The hypothesis for the current investigation was that a titanium plasma spray (TPS) coating may increase the rate and magnitude of circumferential and appositional trabecular osseointegration of PEEK and titanium implants versus uncoated controls.

PURPOSE

Using an in vivo ovine model, the current investigation compared titanium plasma-sprayed PEEK and titanium dowels versus nonplasma-sprayed dowels. Using a time course study of 6 and 12 weeks postoperatively, experimental assays to quantify osseointegration included micro-computed tomography (microCT), biomechanical testing, and histomorphometry.

STUDY DESIGN/SETTING

In-vivo ovine model.

METHODS

Twelve skeletally mature crossbred sheep were equally randomized into postoperative periods of 6 and 12 weeks. Four types of dowel implants-PEEK, titanium plasma-sprayed PEEK (TPS PEEK), titanium, and titanium plasma-sprayed titanium (TPS titanium) were implanted into cylindrical metaphyseal defects in the distal femurs and proximal humeri (one defect per limb, n=48 sites). Sixteen nonoperative specimens (eight femurs and eight humeri) served as zero time-point controls. Half of the specimens underwent destructive biomechanical pullout testing and the remaining half quantitative microCT to quantify circumferential bone volume within 1 mm and 2 mm of the implant surface and histomorphometry to compute direct trabecular apposition.

RESULTS

There were no intra- or perioperative complications. The TPS-coated implants demonstrated significantly higher peak loads at dowel pullout at 6 and 12 weeks compared with uncoated controls (p<.05). No differences were observed across dowel treatments at the zero time-point (p>.05). MicroCT results exhibited no significant differences in circumferential osseointegration between implants within 1 mm or 2 mm of the dowel surface (p>.05). Direct appositional osseointegration of trabecular bone based on histomorphometry was higher for TPS-coated groups, regardless of base material, compared with uncoated treatments at both time intervals (p<.05).

CONCLUSIONS

The current in vivo study demonstrated the biological and mechanical advantages of plasma spray coatings. TPS improved histological incorporation and peak force required for implant extraction.

CLINICAL SIGNIFICANCE

Plasma spray coatings may offer clinical benefit by improving biological fixation and osseointegration within the first 6 to 12 weeks postoperatively- the critical healing period for implant-based arthrodesis procedures.

Synergistic Amelioration of Osseointegration and Osteoimmunomodulation with a Microarc Oxidation-Treated Three-Dimensionally Printed Ti-24Nb-4Zr-8Sn Scaffold via Surface Activity and Low Elastic Modulus

Biomaterial scaffolds, including bone substitutes, have evolved from being primarily a biologically passive structural element to one in which material properties such as surface topography and chemistry actively direct bone regeneration by influencing stem cells and the immune microenvironment. Ti-6Al-4V(Ti6Al4V) implants, with a significantly higher elastic modulus than human bone, may lead to stress shielding, necessitating improved stability at the bone-titanium alloy implant interface. Ti-24Nb-4Zr-8Sn (Ti2448), a low elastic modulus β-type titanium alloy devoid of potentially toxic elements, was utilized in this study. We employed 3D printing technology to fabricate a porous scaffold structure to further decrease the structural stiffness of the implant to approximate that of cancellous bone. Microarc oxidation (MAO) surface modification technology is then employed to create a microporous structure and a hydrophilic oxide ceramic layer on the surface and interior of the scaffold. In vitro studies demonstrated that MAO treatment enhances the proliferation, adhesion, and osteogenesis capabilities on the scaffold surface. The chemical composition of the MAO-Ti2448 oxide layer is found to enhance the transcription and expression of osteogenic genes in bone mesenchymal stem cells (BMSCs), potentially related to the enrichment of Nb2O5 and SnO2 in the oxide layer. The MAO-Ti2448 scaffold, with its synergistic surface activity and low stiffness, significantly activates the anti-inflammatory macrophage phenotype, creating an immune microenvironment that promotes the osteogenic differentiation of BMSCs. In vivo experiments in a rabbit model demonstrated a significant improvement in the quantity and quality of the newly formed bone trabeculae within the scaffold under the contact osteogenesis pattern with a matched elastic modulus. These trabeculae exhibit robust connections to the external structure of the scaffold, accelerating the formation of an interlocking structure between the bone and implant and providing higher implantation stability. These findings suggest that the MAO-Ti2448 scaffold has significant potential as a bone defect repair material by regulating osteoimmunomodulation and osteogenesis to enhance osseointegration. This study demonstrates an optional strategy that combines the mechanism of reducing the elastic modulus with surface modification treatment, thereby extending the application scope of β-type titanium alloy.

Early osseointegration of micro-arc oxidation coated titanium alloy implants containing Ag: a histomorphometric study

BACKGROUND

This study aimed to evaluate bone response to micro-arc oxidation coated titanium alloy implants containing Ag.

METHODS

144 titanium alloy implants were prepared by machine grinding and divided into three treatment groups as following, SLA group: sand-blasting and acid-etched coating; MAO group: micro-arc oxidation without Ag coating; MAO + Ag group: micro-arc oxidation containing Ag coating. Surface characterization of three kind of implants were observed by X-ray diffraction, energy dispersive X-ray spectrometer, scanning electron microscopy, High Resolution Transmission Electron Microscope and roughness analysis. The implants were inserted into dog femurs. 4, 8 and 12 weeks after operation, the bone response to the implant to the bone was evaluated by push-out experiment, histological and fluorescent labeling analysis.

RESULTS

MAO + Ag group consisted of a mixture of anatase and rutile. Ag was found in the form of Ag₂O on the surface. The surface morphology of MAO + Ag group seemed more like a circular crater with upheaved edges and holes than the other two groups. The surface roughness of MAO and MAO + Ag groups were higher than SLA group, but no statistical difference between MAO and MAO + Ag groups. The contact angles in MAO + Ag group was smallest and the surface free energy was the highest among three groups. The maximum push-out strength of MAO and MAO + Ag groups were higher than SLA group at all time point, the value of MAO + Ag group was higher than MAO group at 4 and 8 weeks. Scanning electron microscopy examination for the surface and cross-section of the bone segments and fluorescent labeling analysis showed that the ability of bone formation and osseointegration in MAO + Ag group was higher than that of the other two groups.

CONCLUSION

The micro-arc oxidation combination with Ag coating is an excellent surface modification technique to posse porous surface structure and hydrophilicity on the titanium alloy implants surface and exhibits desirable ability of osseointegration.

Osteogenic activity and antibacterial ability on titanium surfaces modified with magnesium-doped titanium dioxide coating

Aim: To improve the bioactivity and antibacterial activity of titanium (Ti) implants. Materials & methods: Magnesium (Mg)-doped titanium dioxide microporous coatings (Mg-TiO₂) were prepared on the surface of Ti implants by plasma electrolytic oxidation. Results: Ti surfaces were covered with porous Mg-TiO₂, and Mg was evenly distributed throughout the coating. Mg-TiO₂ could not only promote osteoblast adhesion, proliferation and differentiation but also inhibit the colonization and growth of Staphylococcus. In addition, Mg-TiO₂ may promote osteogenesis through the ERK/c-Fos signaling pathway as well as the early osseointegration of Ti implants. Conclusion: Mg-TiO₂ has both osteogenic and antibacterial effects and thus presents important theoretical significance and clinical potential.

In Vivo Osseointegration Performance of Titanium Dioxide Coating Modified Polyetheretherketone Using Arc Ion Plating for Spinal Implant Application

Polyetheretherketone (PEEK), which has biomechanical performance similar to that of human cancellous bone, is used widely as a spinal implant material. However, its bioinertness and hydrophobic surface properties result in poor osseointegration. This study applies a novel modification method, arc ion plating (AIP), that produces a highly osteoblast compatible titanium dioxide (TiO₂) coatings on a PEEK substrate. This PEEK with TiO₂ coating (TiO₂/PEEK) was implanted into the femurs of New Zealand white male rabbits to evaluate its in vivo performance by the push-out test and histological observation. Analytical results show that AIP can prepare TiO₂ coatings on bullet-shaped PEEK substrates as implant materials. After prolonged implantation in rabbits, no signs of inflammation existed. Newly regenerated bone formed more prominently with the TiO₂/PEEK implant by histological observation. The shear strength of the bone/implant interface increases as implantation period increases. Most importantly, bone bonding performance of the TiO₂/PEEK implant was superior to that of bare PEEK. The rutile-TiO₂ coatings achieved better osseointegration than the anatase-TiO₂ coatings. Therefore, AIP-TiO₂ can serve as a novel surface modification method on PEEK for spinal interbody fusion cages.

Assessment of osteoinduction using a porous hydroxyapatite coating prepared by micro-arc oxidation on a new titanium alloy

Surface modification and material improvement is now an important way to improve the osseointegration between bone and uncemented prothesis. The purpose of this study was to investigate the bone ingrowth potential of porous hydroxyapatite (HA) coatings prepared by micro-arc oxidation (MAO) on Ti-3Zr-2Sn-3Mo-25Nb, a new titanium alloy. HA-coated specimens were implanted in the left proximal femoral medullary canal of beagles for 4, 12, and 24 weeks, and uncoated specimens were implanted in the right as a control. The surface morphology and phase composition were investigated with environmental scanning electron microscopy and X-ray diffractometry. The bone ingrowth was assessed by histomorphometry. A pull-out test was performed to assess the mechanical performance of the bone-implant interface. A porous coating was well prepared on the new titanium alloy by using the MAO method. The bone-to-implant contact was significantly higher for the HA-coated group compared to that in the uncoated group. Mechanical tests showed that the HA-coated group had significantly higher maximum force at the bone-implant interface compared to the uncoated specimens. MAO is a suitable coating approach for this new titanium alloy. The HA coating prepared by this approach can significantly promote bone ingrowth and the mechanical performance of the bone-implant interface.

Antibacterial property, angiogenic and osteogenic activity of Cu-incorporated TiO2 coating

Numerous efforts have been made to modify the surface topography and chemical composition of biomedical implants in order to enhance the antibacterial ability and the osteointegration between implants and surrounding bone tissue. In the present work, copper-incorporated TiO₂ coatings were fabricated by combining micro-arc oxidation and hydrothermal treatment together to functionalize the surface of Ti implants. The as-prepared surfaces exhibited a hierarchical structure comprising nanoneedles nearly perpendicular to the microrough surface of the TiO₂ coating. The Cu-loaded TiO₂ coating possessed strong antimicrobial ability against Gram-negative Escherichia coli. In vitro cytocompatibility evaluation suggests that no significant cytotoxicity appeared on the Cu-incorporated TiO₂ coating. Furthermore, the addition of the copper element could stimulate the expression of angiogenic genes, including the hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) in rat bone marrow stem cells (BMSCs). Moreover, they tended to undergo osteogenic differentiation, indicated by the up-regulation expression of osteogenic markers and the higher level of alkaline phosphatase activity. This study provides insight for the surface modification of biomedical Ti-based implants. To the best of our best knowledge, this is a successful attempt for the first time to combine micro-arc oxidation and hydrothermal treatment to introduce copper nutrient element to functionalize Ti-based implant surfaces with enhanced angiogenesis potential, osteostimulation and antimicrobial properties that can better meet clinical needs.

Significance of calcium phosphate coatings for the enhancement of new bone osteogenesis--a review

A systematic analysis of results available from in vitro, in vivo and clinical trials on the effects of biocompatible calcium phosphate (CaP) coatings is presented. An overview of the most frequently used methods to prepare CaP-based coatings was conducted. Dense, homogeneous, highly adherent and biocompatible CaP or hybrid organic/inorganic CaP coatings with tailored properties can be deposited. It has been demonstrated that CaP coatings have a significant effect on the bone regeneration process. In vitro experiments using different cells (e.g. SaOS-2, human mesenchymal stem cells and osteoblast-like cells) have revealed that CaP coatings enhance cellular adhesion, proliferation and differentiation to promote bone regeneration. However, in vivo, the exact mechanism of osteogenesis in response to CaP coatings is unclear; indeed, there are conflicting reports of the effectiveness of CaP coatings, with results ranging from highly effective to no significant or even negative effects. This review therefore highlights progress in CaP coatings for orthopaedic implants and discusses the future research and use of these devices. Currently, an exciting area of research is in bioactive hybrid composite CaP-based coatings containing both inorganic (CaP coating) and organic (collagen, bone morphogenetic proteins, arginylglycylaspartic acid etc.) components with the aim of promoting tissue ingrowth and vascularization. Further investigations are necessary to reveal the relative influences of implant design, surgical procedure, and coating characteristics (thickness, structure, topography, porosity, wettability etc.) on the long-term clinical effects of hybrid CaP coatings. In addition to commercially available plasma spraying, other effective routes for the fabrication of hybrid CaP coatings for clinical use still need to be determined and current progress is discussed.

Effects of irradiation on osteoblast-like cells on different titanium surfaces in vitro

The aim of this study was to investigate the effects of irradiation on adhesion ability, proliferation, and differentiation of MC3T3-E1 cells on microarc oxidation (MAO) titanium surfaces and polished titanium (PT) surfaces. MC3T3-E1 cells were exposed to a single dose at 2, 4, 6, 8, or 10 Gy using a (60) Co source, with tissue culture polystyrene plates chosen as controls. On all surfaces, irradiation resulted in a dose-dependent decrease in cellular proliferation. At 4 Gy dose, the cell proliferation of cells decreased by 17.8% on MAO and 18.6% on PT surfaces, respectively, compared with nonirradiated controls. Cells exposed to 8 Gy dose showed significant inhibition in collagen secretion and osteogenesis-related genes expression (OSX, COL-Iα1, and OCN). In contrast, irradiation increased cell adhesion to three surfaces dose dependently. It was also demonstrated that cells on MAO surface showed higher adhesion and collagen secretion than on PT surface at different radiation doses. This study revealed the effects of irradiation on osteoblasts in vitro on two titanium surfaces. MAO surface could be used in dental implants in irradiated bone due to enhanced adhesion ability and collagen secretion in osteoblasts.