Zirconia Surface Research Articles

The effect of surface material, roughness and wettability on the adhesion and proliferation of Streptococcus gordonii, Fusobacterium nucleatum and Porphyromonas gingivalis☆

Dental implants are inevitably exposed to bacteria in oral cavity. Understanding the colonization of bacteria on implant surface is necessary to prevent bacteria-related inflammation surrounding dental implants. The purpose of this study was to investigate the effect of surface properties on biofilm formation on the implant surface. One early colonizer, Streptococcus gordonii (S. gordonii), and two late colonizers, Fusobacterium nucleatum (F. nucleatum) and Porphyromonas gingivalis (P. gingivalis), were grown on the titanium and zirconia surfaces with two types of surface roughness for 24 and 72h. Each bacterial biofilm on specimens was quantified using crystal violet assay and observed by scanning electron microscopy. S. gordonii formed more biofilm on the titanium surface than zirconia at the same roughness and more biofilm on the rough surface than smooth one of the same materials at 24 and 72h of incubation. F. nucleatum adhered on all the surfaces at 24h and proliferated actively on the surfaces except smooth zirconia at 72h. P. gingivalis proliferated vigorously on the surfaces at 72h while it scarcely adhered at 24h. There was no consistent correlation between contact angle and biofilm formation of the three bacteria. The three bacteria proliferated most on the rough titanium surface and least on the smooth zirconia surface. In addition, the proliferation was affected by the bacterial species as well as the surface properties.

Effect of thickness of externally characterized stains on optical properties of high-translucency zirconia.

There is insufficient information about the effects of the thickness of externally characterized stains or glazes on CIELAB color parameters and the translucency parameter (TP) of 5mol% yttria partially stabilized zirconia (5Y-PSZ). The present study evaluated the effect of a thickness reduction of the externally characterized or glazed layer on its CIE2000 color parameters and TP00 of 5Y-PSZ. Twenty-eight specimens were sectioned from 5Y-PSZ blanks. Three brands of powdered stains (namely VI, SH, and IV) and a glaze (GL) were used to extrinsically stain the specimen surfaces (n = 7 per group). After measuring the final thickness and color, specimens of each group were carefully ground and finally polished. The reduced thickness was carefully controlled in decrements of 0.02mm on the characterized stains or glazed layers at each reduction cycle until the surface of the un-stained zirconia was exposed. The CIELAB color parameters of specimens were measured using a spectrophotometer. Subsequently, differences in lightness (∆L'), chroma (∆C'), and hue (∆H'), and TP00 values and color differences (ΔE00) were calculated using the CIEDE2000 formula to determine differences between the specimen and the un-stained zirconia at each reduction cycle. A paired-samples t-test, two-way mixed-design analysis of variance, and Pearson correlation coefficient were used to analyze the data (α = 0.05). There were no significant differences in lightness, chroma, hue, or TP00 values before or after glazing or after each reduction cycle of the glazed layer. Mean ΔE00 values ranged between 20.94 and 33.55 after applying the externally characterized stains. With a decreased thickness of the characterized stain layer, there were observed that significant decreases in ∆L', ∆H', ∆C', and ΔE00, and significant increases in TP00. Increasing the thickness of externally characterized stains decreased the lightness and caused the alternation of chroma and hue, whereas these phenomena were not observed in the glazed group. There was a slight change of CIE2000 color parameters and TP00 when the thickness of the characterized layer exceeded 0.06mm. The application and thickness of externally characterized stains can sensitively affect CIE2000 color parameters and translucency of 5Y-PSZ.

Evaluation of Zirconia Surface Roughness after Different Surface Treatment with Sandblasting, Hydrofluoric Acid Etching, and Combination Treatment

Zirconia is one of the materials used in prosthetic restoration because of its better physical, mechanical, chemical, and biological properties. The surface treatment for zirconia can be mechanical, with grinding, sandblasting, and laser or chemically, with silane and etching. The combination of chemical and mechanical surface treatment can increase the surface roughness so that the bonding with the resin cement also increases. The study aims to examine the zirconia surface roughness after different surface treatments. This study used 25 zirconia samples in 10x10x2 mm square-shaped, divided into five groups. Group 1 treats sandblasting as a control. Group 2 sandblasting then etching with 9.5% hydrofluoric acid at 25°C for 60 minutes. Group 3 sandblasting then etching with 9.5% hydrofluoric acid at 100°C for 1 minute. Group 4 etching with 9.5% hydrofluoric acid at 25°C for 60 minutes. Group 5 etching with 9.5% hydrofluoric acid at 1000C for 1 minute. The samples were cleaned with an ultrasonic cleaner and tested using a profilometer. The data test by using the ANOVA test and T-test. The highest surface roughness was the combination of sandblasting with 9.5% hydrofluoric acid etching at 25°C for 60 minutes. The lowest was 9.5% hydrofluoric acid etching at 100°C for 1 minute. ANOVA statistical analysis with a p-value <0.05 ((8.4051 x 10-12) indicates that the test was significant. The result of this study was the combination of surface treatments resulted in higher surface roughness. Duration of the etching time affected the increase of zirconia surface roughness.

Zirconia surface polymer grafting via dopamine-assisted co-deposition and radical photopolymerization

Zirconia surfaces were functionalized by polymer grafting according to a simple and successful two-steps procedure. In the first step, the initiator bearing a N,N-dimethyl amine group was grafted on the surface by co-deposition with dopamine. Secondly, different monomers such as styrene, methyl methacrylate, 2-hydroxyethylmethacrylate, 2,2,2-trifluoroethyl methacrylate and styrene sulfonate were polymerized on the surface using photochemical activation. The efficiency of the two steps, initiator grafting and photopolymerization, were checked by several analytical techniques including X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE) and water contact angle measurements. Theses characterizations highlighted the surface chemical change after each step and the possibility to modulate surface hydrophilicity and hydrophobicity by grafting-from polymerizations.

Wettability and frictional properties on zirconia surfaces irradiated by femtosecond laser

This study aimed to explore the wettability and tribological performance of zirconia surface by laser irradiating. To investigate the effect of laser parameters, zirconia samples were divided into two groups according to laser power and scanning pitch. The surfaces were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and goniometer. Microcracks were observed from SEM in the laser-irradiated area. The XRD results in turn indicated that the tetragonal → monoclinic (t→m) phase transformation led to microcracks formation. The contact angles (CAs) results demonstrated that the effect of laser powers on wettability was more than that of scanning pitch. With moderate laser power, it is possible to induce micro/nano morphology with best wettability. Hardness tests and friction tests were further performed to investigate the effect of laser irradiation on mechanical properties. The results indicated that the hardness of laser-irradiated showed a slightly increase, expect for the case of the percentage of m phase exceed 50 %. Meanwhile, laser irradiation can slightly reduce the coefficient of friction (COF) of dry friction and increase the COF of wet friction. For wet friction, laser-irradiated microstructure can effectively enhance the adhesion of bone to zirconia. This work may offer a simple method to produce surfaces with controlled wettability and phase transformation by selecting appropriate laser parameters to promote the adhesion of bone to zirconia.

A Novel Approach for Micro-Antenna Fabrication on ZrO2 Substrate Assisted by Laser Printing for Smart Implants

The use of Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) in medicine has rapidly expanded over the past decade, driven by its advantageous properties, showing potential to overcome titanium alloy in implant fabrication. The release of metal ions and the aesthetic problems of titanium alloy implants are the main reasons for this trend. In addition to meeting expectations regarding its properties, an implant must possess intrinsic capacities such as auto-diagnostic and auto-treatment. Thus, based on the concept of smart implants, this work proposes a hybrid approach for printing a part of the communication system of a zirconia implant by resorting to laser technology, aiming to endow the implant with intrinsic capacities. Therefore, the antenna was designed and then printed on the zirconia surface. The laser was applied as a versatile tool, whether for preparing the surface of the material in a subtractive way, by creating the micro-cavity, or for printing the silver-based antenna in an additive way through laser technology. The silver powder was used as the conductor material of the antenna. The results revealed that the antenna is capable of communicating from inside the body with the outside world without needing to have an exterior antenna attached to the skin.

Bioactive Surface of Zirconia Implant Prepared by Nano-Hydroxyapatite and Type I Collagen

Zirconia, with its excellent mechanical strength and esthetics, has a growing potential for applications in dentistry and orthopedics. However, in order for zirconia to have a high affinity with bone tissue, the bioactivity of the surface must be further increased. In order to increase the bioactivity of zirconia, research was conducted to make a porous support or to fill the porous structure with nano-hydroxyapatite (nHA). In this case, there is a risk that physically filled nHA could be released depending on the living environment. In this study, nHA and type I collagen were introduced to the zirconia surface by chemical covalent bonding to increase bioactivity and ensure safety in the body. The chemical reaction of the surface was confirmed by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FT-IR) spectroscopy. In addition, the biological activity was evaluated by examining the cytotoxicity and bone formation ability of the modified zirconia using osteoblasts. As a result, it was found that the bioactivity of the zirconia surface was greatly improved by immobilizing nHA and type I collagen.

Early bone formation around immediately placed two-piece tissue-level zirconia implants with a modified surface: an experimental study in the miniature pig mandible

PurposeTo histologically examine early bone formation around transmucosal implants and to evaluate the influence of surface characteristics on early peri-implant bone healing using a miniature pig model. For this, commercially available dental implants with a rough zirconia (YTZP) surface were compared to surface-modified Ti control implants at 4 and 8 weeks after placement.MethodsImmediately following the extraction of six mandibular premolars, 20 two-piece, tissue-level, screw-shaped YTZP implants (Patent™ Standard Zirconia Implant ø4.1 × 11 mm) with a modified rough blasted before sintering surface were inserted in four adult miniature pigs. In addition, four titanium (Ti) tissue-level implants (Straumann® Standard RN ø4.1 × 10 mm Roxolid®) with a moderate surface (SLActive®), one per animal, were placed as control implants. A histological analysis was performed on the hard tissues after 4 and 8 weeks of transmucosal healing.ResultsThe results show a high rate of osseointegration of the test YTZP dental implants at 4 and 8 weeks following insertion. At 4 weeks, a bone-to-implant contact ratio (BIC) of 73.7% (SD ± 16.8) for the test implants (n = 10) and 58.5% for the first control implant was achieved. The second control implant had to be excluded from analysis. At 8 weeks, a BIC of 82.4% (SD ± 16.9) for the test implants (n = 9) and 93.6% (SD ± 9.1) (n = 2) for the control implant was achieved. No statistical difference was observed comparing 4 and 8 weeks YTZP data (p = 0.126).ConclusionsThe results indicate a predictable osseointegration of immediate zirconia implants with a modified YTZP implant surface and a high degree of BIC present at 4 weeks following insertion. After 8 weeks of healing both the zirconia implants and the Ti implants show a BIC indicating full osseointegration. Further studies involving a larger sample size with more time points are needed to confirm these results.

Effect of Elemental Doping on the Adsorption Behavior and the Mechanism of Hydrogen Adsorption on the Zirconium Surface

This study used the Monte Carlo (MC) and density functional theory (DFT) methods to simulate the adsorption process of a H atom on element (vacancy, Cr, Sn, and Fe)-doped Zr(0001) surfaces and further analyzed the adsorption site distribution, adsorption energy, charge transfer, and electronic structure, etc. of the doped zirconium surface model. Simulated results indicated that (i) although the doping of vacancy, Cr, Sn, and Fe had a significant effect on the adsorption site distributions of the H atom on the Zr(0001) surface, they showed completely different distribution patterns. (ii) Vacancy doping promoted the adsorption of the H atom on the Zr(0001) surface. The H atom would penetrate the zirconium matrix along the vacancy and then occupy the octahedral gap stably. On the contrary, the doping of Cr, Sn, and Fe inhibited Zr(0001) surface hydrogen uptake in the order of Fe > Cr > Sn, where the effect of Sn could be negligible. (iii) Fe doping had the greatest effect on the chemical reaction mechanism of H adsorption on the Zr(0001) surface, which significantly converted the chemical reaction from Zr–H- to Fe–H-dominated, while Cr doping caused the formation of the Cr–H and Zr–H coaction mechanism, and Sn doping had almost no effect on the mechanism of H adsorption on the Zr(0001) surface.

Effect of Nitrogen Doping and Oxygen Vacancy on the Oxygen Reduction Reaction on the Tetragonal Zirconia(101) Surface

In this study, we investigated the role of defects in promoting the oxygen reduction reaction (ORR) of a zirconia-based cathode, which is motivated by the need for a stable and active electrocatalyst for proton exchange membrane fuel cells. A defective catalyst was modeled by a tetragonal ZrO2(101) slab introduced with oxygen vacancies and nitrogen dopants, and the structure of the ORR intermediates was exhaustively computed from first principles. As is typical of oxides, various adsorption structures with slightly different energies were obtained. Therefore, we obtained the free energy profile for the ORR and established that the energy barrier of the rate-determining step, or the removal of OH*, is comparable to (or only slightly lower than) that of the pristine surfaces, indicating that defects play only a minor role in enhancing the ORR activity. The measured enhancement in the ORR current could be ascribed to the enhanced carrier supply, which may be attributed to the formation of a gap state or change in the potential profile, or to other factors so far overlooked. The results of the first-principles study provide a significant insight for experimentalists to develop optimal cathode materials.

Effect of hot etching with HF on the surface topography and bond strength of zirconia

Zirconia has occupied an increasingly important role in oral clinical applications in recent years. However, how to achieve the ideal bonding effect of zirconia is a significant problem that needs to be solved urgently in oral clinics. Hot etching treatment of zirconia is a hot spot of current research, but it is still unclear about the optimal acid solution and the effect of hot etching on the surface topography and bond strength of zirconia. This study evaluated the effect of hot etching with HF and HCl on the surface topography, roughness, crystalline phase, zirconia/resin cement interfacial evaluation and shear bond strength of zirconia. The results showed that the hot etching groups produced completely different topographical changes on the surface of zirconia than the sandblasting group. Obvious interfacial cracks were observed in the sandblasting group. The HF hot etching group achieved the highest roughness values (78.17 ± 4.94 nm) and the highest shear bond strength (25.09 ± 4.09 MPa). Compared with HCl, hot etching with HF could achieve more uniform and dense porous morphology, greater roughness and shear bond strength. Moreover, there were no prominent zirconia/resin cement interfacial cracks and crystal phase transformations on the surface of zirconia.

Effect of Increased Powder-Binder Adhesion by Backbone Grafting on the Properties of Feedstocks for Ceramic Injection Molding.

The good interaction between the ceramic powder and the binder system is vital for ceramic injection molding and prevents the phase separation during processing. Due to the non-polar structure of polyolefins such as high-density polyethylene (HDPE) and the polar surface of ceramics such as zirconia, there is not appropriate adhesion between them. In this study, the effect of adding high-density polyethylene grafted with acrylic acid (AAHDPE), with high polarity and strong adhesion to the powder, on the rheological, thermal and chemical properties of polymer composites highly filled with zirconia and feedstocks was evaluated. To gain a deeper understanding of the effect of each component, formulations containing different amounts of HDPE and or AAHDPE, zirconia and paraffin wax (PW) were prepared. Attenuated total reflection spectroscopy (ATR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and rotational and capillary rheology were used for the characterization of the different formulations. The ATR analysis revealed the formation of hydrogen bonds between the hydroxyl groups on the zirconia surface and AAHDPE. The improved powder-binder adhesion in the formulations with more AAHDPE resulted in a better powder dispersion and homogeneous mixtures, as observed by SEM. DSC results revealed that the addition of AAHDPE, PW and zirconia effect the melting and crystallization temperature and crystallinity of the binder, the polymer-filled system and feedstocks. The better powder--binder adhesion and powder dispersion effectively decreased the viscosity of the highly filled polymer composites and feedstocks with AAHDPE; this showed the potential of grafted polymers as binders for ceramic injection molding.

The characteristic and osteogenic effect of a nanoporous coating of zirconia implant

Zirconia ceramics have become increasingly used as dental implant material which is mainly due to their “tooth-like” color, superior biocompatibility, and excellent mechanical properties. However, the bio-inertness of the zirconia surface limits its use for a wider range of clinical applications. To enhance the surface bioactivity, a combination of magnetron sputtering, and anodization has in the present study been used to deposit a homogeneous nano-porous coating (ZrNP) on the zirconia surface (forming ZrO 2 /ZrNP with a ZrNP pore diameter of 20–30 nm, and a ZrNP layer thickness of ∼2 μm). EDS and XRD analysis showed that the distribution of the surface chemical components, as well as the crystalline structure of the zirconia (ZrO 2 ), remained unchanged. On the other hand, the hydrophilicity of the ZrO 2 /ZrNP surface became significantly improved (as compared with a control group). In addition, the bond strength of the coating was decreased as a result of the anodization treatment. Moreover, both the Zr and ZrNP nanolayers exhibited improved proliferation and osteogenic properties in the in vitro cell experiment. Also, the ZrNP nanolayer was found to promote the biocompatibility and osteogenic ability to the largest extent. The ZrNP nanolayer did also provide numerous adhesion sites for MC3T3-E1 whereby the cell morphology could be enhanced. Additionally, the nano porous ZrNP layer improved the new bone formation around the zirconia implant and did robustly enhance the push out bond strength, thereby indicating the best osteointegration ability. In conclusion, a nano porous zirconium layer has been found to be very promising for the improvement of the bioactivity of the zirconia implant material.

Effect of Sandblasting with Fluorapatite Glass-ceramic Powder and Chemical Primers/Adhesives on Shear Bond Strength of Indirect Repairing Composite to Zirconia.

To investigate the effect of sandblasting with fluorapatite glass-ceramic (FGC) powder on zirconia surface roughness, crystallinity, and shear bond strength (SBS) of indirect repairing composite to zirconia using different primers/adhesives. Zirconia blocks were treated as follows: no treatment (control group), blasting with 30-μm silica-coated alumina (CoJet group), and blasting with FGC powder (FGC group). The surface topography, silica content, roughness, and crystallinity of treated zirconia surfaces were analyzed by a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), an optical profilometer, and X-ray diffraction (XRD), respectively. Four primers/adhesives (Monobond Plus, Calibra Silane, Futurabond M+, and Scotchbond Universal) were compared to bond precured resin composite to zirconia groups using Multilink Automix resin cement. Bonded specimens were thermocycled for 10,000 cycles and tested in SBS and the modes of failure were recorded. The effect of different surface treatments and primers/adhesives on SBS results were statistically analyzed using two-way ANOVA and Bonferroni post-hoc tests (α=0.05). Both CoJet and FGC groups showed rough surfaces with a higher content of silica in FGC, but less monoclinic crystals, compared to the CoJet group. The highest mean SBS was found in the FGC group treated with Monobond Plus compared to CoJet and Control groups. Adhesive failure was predominant in control groups, while combined failure was found in the CoJet and FGC groups regardless of the primers/adhesives employed. Sandblasting zirconia with FGC powder increased SBS of resin composite to zirconia with lower monoclinic phase transformation compared to CoJet sand. Monobond Plus reported the highest means of SBS values compared to other primers/adhesives.

A simple AI-enabled method for quantifying bacterial adhesion on dental materials

Purpose Measurement of bacterial adhesion has been of great interest for different dental materials. Various methods have been used for bacterial counting; however, they are all indirect measurements with estimated results and therefore cannot truly reflect the adhesion status. This study provides a new direct measurement approach by using a simple artificial intelligence (AI) method to quantify the initial bacterial adhesion on different dental materials using Scanning Electron Microscope (SEM) images. Materials and Methods Porphyromonas gingivalis (P.g.) and Fusobacterium nucleatum (F.n.) were used for bacterial adhesion on dental zirconia surfaces, and the adhesion was evaluated using SEM images at time points of one, seven, and 24 h(s). Image pre-processing and bacterial area measurement were performed using Fiji software with a machine learning plugin. The same AI method was also applied on SEM with Streptococcus mutans (S.m.) inoculated PMMA nano-structured surface at 1, 24, 72, and 168 h(s), and then further compared with the CLSM method. Results For both P.g. and F.n. initiation adhesion on zirconia, a new linear correlation (r2 > 0.98) was found between bacteria adhered area and time, such that: For S.m. on PMMA surface, live/dead staining CLSM method and the newly proposed AI method on SEM images were strongly and positively associated (Pearson's correlation coefficient r > 0.9), i.e. both methods are comparable. Conclusions SEM images can be analyzed directly for both morphology and quantifying bacterial adhesion on different dental materials’ surfaces by the simple AI-enabled method with reduced time, cost, and labours.

Cytokines Activate JAK-STAT Signaling Pathway in MG-63 Cells on Titanium and Zirconia.

Although titanium has been traditionally used as the gold standard for dental implants, recent years have seen the widespread application of zirconia implants given their superiority with regards to reduced bacterial adhesion, inflammation and cellular-interaction in terms of bio-compatibility. The JAK–STAT signaling pathway plays an important role in bone remodeling and formation. The aim of the study was to investigate the activation of the JAK–STAT pathway through different cytokines in osteoblast-like cells (MG-63) on zirconia in comparison to titanium discs. IFN-γ induced the very strong activation of STAT1 protein, IFN-α activated both STAT1 and STAT3 molecules, IL-6 activated STAT3 and IL-4 induced the activation of STAT6 on both surfaces. The activation of STAT proteins was confirmed by western blot, immunofluorescence and flow cytometry using phospho-specific anti-STAT antibodies, which recognize only phosphorylated STAT proteins. The incubation of MG-63 cells with IFN-γ caused the upregulation of MHC class I and class II proteins when MG-63 cells were grown on zirconia and titanium discs. In sum, the present study shows that the JAK–STAT pathway is activated in MG-63 cells when they are incubated on titanium or zirconia surfaces.

Enhanced osteogenic activity of titania-modified zirconia implant by ultraviolet irradiation.

Zirconia is a superior implant material owing to its high mechanical strength, durable corrosion resistance, superior aesthetic effect and excellent biocompatibility. However, the bioactivity of zirconia surfaces remains a great challenge for implant osseointegration. A titania (TiO2) coating was innovatively synthesized on the surface of zirconia by infiltration in a suspension of zirconium oxychloride and titania for dense sintering. Subsequently, the coating was subjected to ultraviolet (UV) light to enhance the biological inertness of zirconia. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and contact angle analysis were conducted to confirm the surface characteristics. Afterwards, in vitro assessments of cell adhesion, proliferation and osteogenic differentiation of MC3T3-E1 cells were performed. Zirconia samples were implanted into rat femurs to assess biocompatibility and host tissue response in vivo. Micro-CT evaluation and histological testing were conducted. After UV irradiation, the content of hydroxyl groups and hydrophilicity of TiO2-modified zirconia were significantly increased. The results of in vitro experiments showed that TiO2-modified zirconia subjected to UV light could promote cell proliferation and spreading, enhance ALP activity and the degree of mineralization, and upregulate osteogenesis-related genes. Furthermore, in vivo assessments confirmed that UV-irradiated TiO2-modified zirconia implants maximized the promotion of osseointegration. TiO2-modified zirconia after UV treatment will have broad clinical application prospects in improving the osseointegration of zirconia implants.

Effect of Non-Thermal Plasma Treatment of Contaminated Zirconia Surface on Porphyromonas gingivalis Adhesion and Osteoblast Viability.

Plasma treatment on a zirconia surface prevents bacterial contamination and maintains osteoblast activity. To assess the degree of adhesion of Porphyromonas gingivalis on a zirconia surface after non-thermal plasma (NTP) treatment, specimens were treated with plasma for 60, 300, and 600 s, after which P. gingivalis was inoculated onto the surface and incubated for 48 h. To assess osteoblast activity after NTP treatment, osteoblasts (MC3T3-E1) were dispensed onto the specimens contaminated with P. gingivalis immediately after NTP for 60 and 120 s, followed by incubation for 48, 72, and 96 h. P. gingivalis was cultured after 60 s of NTP treatment of zirconia. The NTP and control groups showed no significant difference (p = 0.91), but adhesion was significantly increased following NTP treatment for 300 s or longer (300, 600 s groups) (p < 0.05). After NTP treatment of P. gingivalis-contaminated zirconia, osteoblast activity significantly increased at 72 and 96 h (I60 and I120 s group) in the groups treated with plasma (p < 0.017). Application of NTP to dental zirconia implants for 60 s not only inhibits the proliferation of P. gingivalis, which causes peri-implantitis but also increases osseointegration on zirconia surfaces contaminated with P. gingivalis.

Surface modification of zirconia ceramics through cold plasma treatment and the graft polymerization of biomolecules

Although zirconia ceramics were highly versatile as dental implants, their long-term presence in the human body may slow down healing and impede cell growth in the past. To enhance the cytocompatibility of zirconia ceramics, surface activation modification was used to immobilize biopolymers such that a biomimetic environment was created. Hexamethyldisilazane thin films were deposited onto the surface of inorganic zirconia through cold plasma treatment under various power and deposition time settings to form an organosilane interface layer. Next, oxygen plasma treatment was performed to activate the free radicals on the surface. Subsequently, ultraviolet light was employed to graft and polymerize acrylic acid for generating carboxyl groups on the surface. This was followed by a condensation reaction with biopolymers (chitosan, chitosan/poly-γ-glutamic acid, and gelatin). Under a 20-min deposition time at 40W and 150 mTorr, the thin films had a maximum graft density of 2.1mg/cm2. MG-63cells (human osteosarcoma cells) were employed to evaluate cell compatibility. Chitosan and chitosan/poly-γ-glutamic acid promoted the compatibility of MG-63cells (a human osteosarcoma cell line) with zirconia ceramics, whereas gelatin reduced this compatibility. The findings confirm that cold plasma treatment and graft polymerization can promote the immobilization of biomolecules and improve the biocompatibility of zirconia ceramics. This approach can be applied to the modification of zirconia ceramic implants.

Investigation on microstructure, mechanical properties and tribological behavior of AlZnMgCu1.5-T6/zirconia surface nanocomposites developed by FSP

This research aimed to find the suitable condition for the fabrication of AlZnMgCu1.5-T6/ZrO2 nanocomposites to improve the mechanical properties and wear resistance of the produced surface nanocomposites. The effects of rotational speed and the number of passes were investigated to obtain the desired properties. For this purpose, rotational speeds of 1000 rpm, 1200 rpm, and 1400 rpm were used along with a constant traverse speed of 40 mm/min, and the number of processing passes was considered to be one and two passes. Optical microscopy and electron microscopy equipped with an EDS system were used to study the microstructural evolution, such as grain refinement and distribution of nanoparticles in these nanocomposites. To evaluate the mechanical and wear properties of the nanocomposites, tension, hardness, and wear tests were performed according to related standards. In the next step, the fracture surfaces were examined by XRD to investigate the formation of possible phases. Finally, fracture and wear surfaces were investigated to determine dominant mechanisms. In addition to the absence of defects, an extreme grain refinement due to the severe plastic deformation of the grains and the presence of ceramic nanoparticles were confirmed by microscopic observations. According to the results, due to the extreme grain refinement and the presence of ZrO2 hard ceramic nanoparticles, the average and maximum hardness values increased up to 33% and 48%, respectively, compared to those of the aluminum alloy matrix. Also, the wear rate was reduced up to 65%. It was concluded that according to the findings, the most suitable condition for achieving the optimal mechanical and wear properties is 1400 rpm-two passes.