Ability of zirconia double coated with titanium and hydroxyapatite to bond to bone under load-bearing conditions

Recent Strategies to Combat Infections from Biofilm-Forming Bacteria on Orthopaedic Implants

Biofilm-related implant infections (BRII) are a disastrous complication of both elective and trauma orthopaedic surgery and occur when an implant becomes colonised by bacteria. The definitive treatment to eradicate the infections once a biofilm has established is surgical excision of the implant and thorough local debridement, but this carries a significant socioeconomic cost, the outcomes for the patient are often poor, and there is a significant risk of recurrence. Due to the large volumes of surgical procedures performed annually involving medical device implantation, both in orthopaedic surgery and healthcare in general, and with the incidence of implant-related infection being as high as 5%, interventions to prevent and treat BRII are a major focus of research. As such, innovation is progressing at a very fast pace; the aim of this study is to review the latest interventions for the prevention and treatment of BRII, with a particular focus on implant-related approaches.

A novel coating layer on zirconia using modified zinc phosphatizing method

Yttria doped ZrO₂ was deposited using an acidic zinc phosphatizing solution and the hydrothermal treatment. The coating was analyzed using a field emission-scanning electron microscope (FE-SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). A piston on three balls (ISO 6872) was used for the measurement of biaxial flexural strength. MC3T3-E1 cells attachment was evaluated by SEM, and cell proliferation were assessed using MTS assay™. SEM images confirmed that the zinc phosphate coating layer was successfully prepared and fully covered the surface. The measured adhesive strength of the coating was 79.11 MPa. In vitro cell study indicated that the coated sample had better cell morphology and proliferation. XRD and EDS analysis revealed that the crystalline coating structure indexed as zinc phosphate (hopeite) and the substrate was assigned as zirconia. The flexural strength test showed that the strength of zirconia before and after hydrothermal treatment was not affected.

Time-dependent efficacy of combination of silver-containing hydroxyapatite coating and vancomycin on methicillin-resistant Staphylococcus aureus biofilm formation in vitro

OBJECTIVE

We developed a silver-containing hydroxyapatite (Ag-HA) coating to prevent periprosthetic joint infection (PJI). Methicillin-resistant Staphylococcus aureus (MRSA) is the main PJI-causing bacteria. Previously, we had reported the combined effect of Ag-HA coating and vancomycin (VCM) on MRSA biofilm formation 24 h after MRSA inoculation. In this study, we investigated the time-dependent efficacy of Ag-HA coating and VCM on MRSA biofilm formation on Ti discs in vitro by three-dimensional confocal laser scanning microscopic analysis.

RESULTS

For the Ti VCM and HA VCM groups, the total biofilm volumes per area at 96 h after MRSA inoculation were significantly larger than those at 48 h after MRSA inoculation, respectively (p < 0.001). In contrast, for the Ag-HA VCM group, the total biofilm volume per area at 96 h was significantly smaller than that at 48 h (p < 0.0001). Moreover, 96 h after MRSA inoculation, the total biofilm volume per area of the Ag-HA VCM groups was significantly smaller than those of the Ti VCM and HA VCM groups (p < 0.0001). Thus, the combination of Ag-HA and VCM might be useful for the prevention of MRSA-associated PJI.

The combination of silver-containing hydroxyapatite coating and vancomycin has a synergistic antibacterial effect on methicillin-resistant Staphylococcus aureus biofilm formation

Aims

Biofilm formation is intrinsic to prosthetic joint infection (PJI). In the current study, we evaluated the effects of silver-containing hydroxyapatite (Ag-HA) coating and vancomycin (VCM) on methicillin-resistant Staphylococcus aureus (MRSA) biofilm formation.

Methods

Pure titanium discs (Ti discs), Ti discs coated with HA (HA discs), and 3% Ag-HA discs developed using a thermal spraying were inoculated with MRSA suspensions containing a mean in vitro 4.3 (SD 0.8) x 10⁶ or 43.0 (SD 8.4) x 10⁵ colony-forming units (CFUs). Immediately after MRSA inoculation, sterile phosphate-buffered saline or VCM (20 µg/ml) was added, and the discs were incubated for 24 hours at 37°C. Viable cell counting, 3D confocal laser scanning microscopy with Airyscan, and scanning electron microscopy were then performed. HA discs and Ag HA discs were implanted subcutaneously in vivo in the dorsum of rats, and MRSA suspensions containing a mean in vivo 7.2 (SD 0.4) x 10⁶  or 72.0 (SD 4.2) x 10⁵  CFUs were inoculated on the discs. VCM was injected subcutaneously daily every 12 hours followed by viable cell counting.

Results

Biofilms that formed on HA discs were thicker and larger than those on Ti discs, whereas those on Ag-HA discs were thinner and smaller than those on Ti discs. Viable bacterial counts in vivo revealed that Ag-HA combined with VCM was the most effective treatment.

Conclusion

Ag-HA with VCM has a potential synergistic effect in reducing MRSA biofilm formation and can thus be useful for preventing and treating PJI.

Cite this article:Bone Joint Res. 2020;9(5):211–218.

Biomechanical Evaluation of Nano-Zirconia Coatings on Ti-6Al-7Nb Implant Screws in Rabbit Tibias

The clinical success of dental implants can be improved by achieving optimum implant properties, such as their biomechanical and surface characteristics. Nano-structured coatings can play an important role in improving the implant surface. The purpose of the present study was to determine the most appropriate conditions for electrophoretic deposition (EPD) of nano-zirconia coatings on Ti-6Al-7Nb substrates and to evaluate the structural and biomechanical characteristics of these deposited coatings on the dental implants. EPD was used with different applied voltages and time periods to obtain a uniform layer of nano-zirconia on Ti-6Al-7Nb samples. The coated samples were weighed and the thickness of the product layer was measured. Surface analysis was performed by using optical microscopical examination, scanning electron microscope and X-ray diffraction phase analysis. For in vivo examination, 48 screw-designed implants (24 uncoated and 24 nano-zirconia coated) were implanted in both tibiae of 12 white New Zealand rabbits and evaluated biomechanically after 4- and 12-week healing intervals. Results revealed that the use of different conditions for EPD affected the final coating film properties. Increasing the applied voltage and coating time period increased the deposited nano-zirconia film thickness and weight. By selecting the appropriate coating conditions, and analyzing scanning electron microscopical examination and XRD patterns, this technique could produce a thin and continuous nano-zirconia layer with a uniform thickness of the Ti-6Al-7Nb samples. Mechanically, the nano-zirconia-coated implants showed a highly statistically significant difference in removal torque values, while histologically these coated implants enhanced and promoted osseointegration after 4 and 12 weeks of healing, compared with the uncoated ones. In conclusion, EPD is an effective technique for providing a high quality nano-zirconia coating film on dental implant surfaces. Moreover, the osseointegration of these coated dental implants is improved compared with that of uncoated ones.

Bioactive-hybrid-zirconia implant surface for enhancing osseointegration: an in vivo study

Background

Zirconia is characterized by a hard, dense, and chemically inert surface which requires additional surface treatments in order to enhance osseointegration. The proposed hypothesis of the study was that combination of a nano-porous surface infiltrated with a bioactive material may enhance osseointegration of zirconia implants.

Methods

Custom-made zirconia implants (3.7 mm × 8 mm) were designed, milled, and sintered according to manufacturer recommendations. All implants received selective infiltration etching (SIE) technique to produce a nano-porous surface. Surface porosities were either filled with nano-hydroxy apatite particle- or platelet-rich plasma while uncoated surface served as a control (n = 12, α = 0.05). New surface properties were characterized with mercury porosimetry, XRD analysis, SEM, and EDX analysis. Implants were inserted in femur head of rabbits, and histomorphometric analysis was conducted after healing time to evaluate bone–implant contact percentage (BIC%).

Results

Selective infiltration etching produced a nano-porous surface with interconnected surface porosities. Mercury porosimetry revealed a significant reduction in total porosity percent after application of the two coating materials. XRD patterns detected hexagonal crystal structure of HA superimposed on the tetragonal crystal phase of zirconia. Histomorphometric analysis indicated a significantly higher (F = 14.6, P < 0.001) BIC% around HA–bioactive–hybrid surface (79.8 ± 3%) and PRP-coated surface (71 ± 6 %) compared to the control (49 ± 8%).

Conclusions

Bioactive–hybrid–zirconia implant surface enhanced osseointegration of zirconia implants.

Phase stability and rapid consolidation of hydroxyapatite–zirconia nano-coprecipitates made using continuous hydrothermal flow synthesis

A rapid and continuous hydrothermal route for the synthesis of nano-sized hydroxyapatite rods co-precipitated with calcium-doped zirconia nanoparticles using a superheated water flow at 450°C and 24.1 MPa as a crystallizing medium is described. Hydroxyapatite and calcium-doped zirconia phases in the powder mixtures could be clearly identified based on particle size and morphology under transmission electron microscopy. Retention of a nanostructure after sintering is crucial to load-bearing applications of hydroxyapatite-based ceramics. Therefore, rapid consolidation of the co-precipitates was investigated using a spark plasma sintering furnace under a range of processing conditions. Samples nominally containing 5 and 10 wt% calcium-doped zirconia and hydroxyapatite made with Ca:P solution molar ratio 2.5 showed excellent thermal stability (investigated using in situ variable temperature X-ray diffraction) and were sintered via spark plasma sintering to >96% sintered densities at 1000°C resulting in hydroxyapatite and calcium-doped zirconia as the only two phases. Mechanical tests of spark plasma sintering sintered samples (containing 10 wt% calcium-doped zirconia) revealed a three-pt flexural strength of 107.7 MPa and Weibull modulus of 9.9. The complementary nature of the spark plasma sintering technique and continuous hydrothermal flow synthesis (which results in retention of a nanostructure even after sintering at elevated temperatures) was hence showcased.

Osteoconductivity of thermal-sprayed silver-containing hydroxyapatite coating in the rat tibia

A silver-containing hydroxyapatite (Ag-HA) coating has been developed using thermal spraying technology. We evaluated the osteoconductivity of this coating on titanium (Ti) implants in rat tibiae in relation to bacterial infection in joint replacement.

At 12 weeks, the mean affinity indices of bone formation of a Ti, an HA, a 3%Ag-HA and a 50%Ag-HA coating were 97.3%, 84.9%, 81.0% and 40.5%, respectively. The mean affinity indices of bone contact of these four coatings were 18.8%, 83.7%, 77.2% and 40.5%, respectively. The indices of bone formation and bone contact around the implant of the 3%Ag-HA coating were similar to those of the HA coating, and no significant differences were found between them (bone formation, p = 0.99; bone contact, p = 0.957). However, inhibition of bone formation was observed with the 50%Ag-HA coating.

These results indicate that the 3%Ag-HA coating has low toxicity and good osteoconductivity, and that the effect of silver toxicity on osteoconductivity depends on the dose.

In vitro and in vivo biocompatibility of graded hydroxyapatite-zirconia composite bioceramic

To obtain bioceramics with good osteoinductive ability and mechanical strength, graded hydroxyapatite-zirconia (HA-ZrO(2)) composite bioceramics were prepared in this work. The biocompatibility of the bioceramics was investigated in vitro based on acute toxicity and cytotoxicity tests and hemolysis assay. Results showed the studied graded HA-ZrO(2) had little toxicity to mouse and L929 mouse fibroblasts. Also, hemolysis assay indicated a good blood compatibility of the bioceramics. Based on the results of in vitro tests, animal experiments were performed on white New Zealand rabbits by implantation into hip muscles and femur. It was found that the graded HA-ZrO(2) composite bioceramics exhibited superior osteoinductive ability, which may be a promising bioceramics implant.

Two Human Hydroxyapatite-Coated Dental Implants Retrieved After a 14-Year Loading Period: A Histologic and Histomorphometric Case Report

BACKGROUND

Controversy over the long-term clinical effectiveness of hydroxyapatite (HA)-coated dental implants still persists, despite numerous clinical studies documenting high survival rates. Concerns about the degradation of the coating over the years have been raised; it has been speculated that resorption of the HA could produce a space between the implant and the bone with a resultant mechanical instability.

METHODS

Two HA-coated implants were retrieved due to a fracture of the abutment screws after a loading period of 14 years and were treated to obtain thin ground sections for histologic evaluation.

RESULTS

At low-power magnification, it was possible to observe that the HA coating was in contact with mature bone. No gaps or connective fibrous tissue was found at the implant-bone interface. No epithelial downgrowth was present. No acute or chronic inflammatory cell infiltrate was present at the implant-bone interface. No foreign body reaction was present in the peri-implant tissues. Some osteocytes were in direct contact with the coating. For implant 1, the percentage of bone-titanium contact was 25% +/- 2.1%, and the percentage of bone-HA contact was 35% +/- 1.4%. The total bone-implant contact was approximately 60%. The HA coating appeared to be resorbed in 46% +/- 3.2% of the implant perimeter, especially in the coronal portions of the implant. For implant 2, the mean percentage of bone-HA contact was 13% +/- 1.8%, and the mean percentage of bone-titanium contact was 15% +/- 2.3%. The total bone-implant contact was approximately 28%. The HA coating appeared to be resorbed for a mean of 68% +/- 4.1% of the implant perimeter, especially in the coronal portion of the implant.

CONCLUSIONS

No acute or chronic inflammatory cell infiltrate was present in the peri-implant tissues. No signs of coating infection, fatigue, or failure were observed in two specimens. The HA coating may not be susceptible to degradation or dissolution under long-term function.