Comparison of the osteogenic potential of titanium- and modified zirconia-based bioceramics

Biological effects of gamma-ray sterilization on 3 mol% yttria-stabilized tetragonal zirconia polycrystal: An in vitro study

STATEMENT OF PROBLEM

Selecting the sterilization method is important because sterilization can alter the surface chemistry of implant materials, including zirconia, and influence their cellular biocompatibility. Studies on the biological effects of sterilization on implant materials are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the biocompatibility of gamma-ray irradiated 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) compared with unirradiated titanium, 3Y-TZP, and pure gold.

MATERIAL AND METHODS

Disk-shaped specimens each of commercially pure grade 4 titanium, 3Y-TZP, gamma-rayed 3Y-TZP, and pure gold were prepared and evaluated for osteogenic potential by using a clonal murine cell line of immature osteoblasts derived from mice (MC3T3-E1 cells). The surface topography (n=3), chemical analysis of the disks (n=3), and cell morphology cultured on these surfaces were examined using scanning electron microscopy, confocal laser scanning microscopy, and energy dispersive spectroscopy. Cellular biocompatibility was analyzed for 1 and 3 days after seeding. Cell adhesion and spreading were evaluated using confocal laser scanning microscopy (n=3). Cell proliferation was evaluated using methyl thiazolyl tetrazolium assay (n=3). Kruskal-Wallis and Bonferroni corrections were used to evaluate the statistical significance of the intergroup differences (α=.05).

RESULTS

Gamma-ray sterilization of 3Y-TZP showed significantly higher surface roughness compared with titanium and gold (P<.002). On day 1, the proliferation and adhesion of MC3T3-E1 cells cultured on gamma-rayed 3Y-TZP were significantly higher than those cultured on gold (P<.05); however, cell spreading was significantly lower than that of titanium on days 1 and 3 (P<.05). On day 3, cell proliferation of gamma-rayed 3Y-TZP was significantly lower than that of unirradiated 3Y-TZP (P<.05). Cell adhesion of gamma-rayed 3Y-TZP was slightly lower than that of zirconia and titanium but without significant difference (P>.05).

CONCLUSIONS

Gamma-rayed zirconia exhibited increased surface roughness compared with titanium and significantly decreased bioactivity compared with titanium and zirconia. The use of gamma-ray sterilization on zirconia is not promising regarding biocompatibility, and the effect of this sterilization method on implant materials warrants further investigation.

Bio-Piezoelectric Ceramic Composites for Electroactive Implants-Biological Performance

Barium titanate (BaTiO3) piezoelectric ceramic may be a potential alternative for promoting osseointegration due to its piezoelectric properties similar to bone electric potentials generated in loading function. In this sense, the aim of this in vitro study was to evaluate the cellular response of human osteoblasts and gingival fibroblasts as well as the impact on S. oralis when in contact with BaTiO3 functionalized zirconia implant surfaces with piezoelectric properties. Zirconia discs with BaTiO3 were produced and contact poling (piezo activation) was performed. Osteoblasts (hFOB 1.19), fibroblasts (HGF hTERT) and S. oralis were culture on discs. Cell viability and morphology, cell differentiation markers, bacterial adhesion and growth were evaluated. The present study suggests that zirconia composite surfaces with the addition of piezoelectric BaTiO3 are not cytotoxic to peri-implant cells. Also, they seem to promote a faster initial osteoblast differentiation. Moreover, these surfaces may inhibit the growth of S. oralis by acting as a bacteriostatic agent over time. Although the piezoelectric properties do not affect the cellular inflammatory profile, they appear to enable the initial adhesion of bacteria, however this is not significant over the entire testing period. Furthermore, the addition of non-poled BaTiO3 to zirconia may have a potential reduction effect on IL-6 mediated-inflammatory activity in fibroblasts.

Surface Topography of Titanium Affects Their Osteogenic Potential through DNA Methylation

It is widely accepted that sandblasted/large-grit/acid-etched (SLA) surfaces of titanium (Ti) have a higher osteogenic potential than machined ones. However, most studies focused on differential gene expression without elucidating the underlying mechanism for this difference. The aim of this study was to evaluate how the surface roughness of dental Ti implants affects their osteogenic potential. Mouse preosteoblast MC3T3-E1 cells were seeded on machined and SLA Ti discs. The cellular activities of the discs were analyzed using confocal laser scanning microscopy, proliferation assays, and real-time polymerase chain reaction (PCR). DNA methylation was evaluated using a methylation-specific PCR. The cell morphology was slightly different between the two types of surfaces. While cellular proliferation was slightly greater on the machined surfaces, the osteogenic response of the SLA surfaces was superior, and they showed increased alkaline phosphatase (Alp) activity and higher bone marker gene expression levels (Type I collagen, Alp, and osteocalcin). The degree of DNA methylation on the Alp gene was lower on the SLA surfaces than on the machined surfaces. DNA methyltransferase inhibitor stimulated the Alp gene expression on the machined surfaces, similar to the SLA surfaces. The superior osteogenic potential of the SLA surfaces can be attributed to a different epigenetic landscape, specifically, the DNA methylation of Alp genes. This finding offers novel insights into epigenetics to supplement genetics and raises the possibility of using epidrugs as potential therapeutic targets to enhance osteogenesis on implant surfaces.

Wettability and pre-osteoblastic behavior evaluations of a dense bovine hydroxyapatite ceramics

In this study, the wettability, cell viability, and roughness of an experimental dense bovine hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] ceramic block were evaluated so that, in the future, it could be used as a base material for dental implants. The results to commercial zirconia and a commercially pure titanium (Ti) alloy were compared. The surface roughness and contact angles were measured. An in vitro evaluation was conducted by means of tests in which pre-osteoblastic MC3T3-E1 cells were placed in indirect and direct contact with these materials. For cell viability, a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and crystal violet test were conducted. A qualitative analysis was conducted using variable pressure scanning electron microscopy (SEM). No statistically significant differences were observed in wettability and roughness tests among the groups. In both the MTT assay and crystal violet test, all groups demonstrated satisfactory results without cytotoxicity. SEM showed cell adhesion and cell proliferation results on the material surfaces after 24 h and 48 h. In conclusion, this dense Ca₁₀ (PO₄)₆(OH)₂ ceramic can be considered as a potential biocompatible material.

Laser Nd:YAG patterning enhance human osteoblast behavior on zirconia implants

Zirconia has been regarded as a promising material for dental implants, and Nd:YAG laser treatment has been proposed as a potential strategy to improve its bioactivity. The main aim of the present study was to evaluate the in vitro behavior of human fetal osteoblasts in contact with laser-textured zirconia implant surfaces assessing the effect of different texture patterns, spacing between laser passes and number of laser passes. Zirconia discs were produced and treated with Nd:YAG laser according to test group variables: texture (microgrooves and micropillar array), distance between surface features (25 μm, 30 μm and 35 μm), and laser passes [1, 2, 4, and 8]. Untextured sandblasted and acid-etched zirconia discs (SBAE) were used as controls. Human osteoblasts (hFOB 1.19) were cultured for 14 days on test and control samples. Morphology and cellular adhesion were observed using scanning electron microscopy (SEM). Cell viability and proliferation were evaluated at 1, 3, 7, and 14 days using a commercial resazurin-based method. Collagen type I was evaluated at 3 days using ELISA. Alkaline phosphatase (ALP) activity was evaluated at 7 days using a colorimetric enzymatic technique. Group comparisons were tested using ANOVA or Mann-Whitney test (Tukey's post hoc) using statistical software, and significance was set at p < 0.05. Cell viability and proliferation increased over time for all groups with statistically higher values for laser-textured groups when compared with control at 7 and 14 days in culture (p < 0.05). Collagen type I levels were higher for study groups (p < 0.05) when compared with control group. No statistically differences were detected for ALP activity levels between texture and control groups (p > 0.05). The results suggest that laser-machined zirconia implant surfaces may benefit biological osteoblast response. However, the type of texture, spacing at the range of 25-35 μm, and number of laser passes did not seem to be relevant variables.

Osteoblast response to zirconia modified-ORMOSILs

In this study, an in vitro evaluation of the human osteoblasts response to Organically Modified Silicate (ORMOSIL) biomaterials was conducted. These materials were synthetized by sol-gel process being modified with zirconia (ZrO₂) and/or Ca²⁺. The materials were immersed into phosphate buffer solution (PBS) in order to test precipitation of mimetic apatite-like on their surfaces. ORMOSILs were characterized by SEM, FT-IR and X-RD analysis. The response of osteoblast to ORMOSILs was analyzed as a measure of cell adhesion, proliferation and differentiation. The results showed that the addition of Ca²⁺ ions modifies the surface morphology of ORMOSILs by forming precipitates of mimetic apatite-like with cauliflower and scales morphologies. On the other hand, biological results suggest that the incorporation of zirconia to ORMOSILs increases their ability to support cell adhesion and proliferation. However, the inclusion of both zirconia and Ca²⁺ in the ORMOSILs decreases their biological compatibility by showing less cell proliferation and lower osteonectin expression, a protein related to osteoblasts. The unfavorable effect of Ca²⁺ on cell proliferation and cell viability could be due to its ability to induce the formation of mimetic apatite-like with incompatible morphology. The analysis of other proteins related to bone formation on ORMOSIL-Zr and ORMOSIL-Zr-Ca surfaces demonstrated clear expression of osteopontin and osteocalcin in cells growth. In the case of ORMOSIL-Zr, the expression of osteonectin occurred at early stages while the expression of osteopontin and osteocalcin begun at later stages, indicating a switch from an early to a mature stage being stimulated by the biomaterial. Together, these results highlight the important role of zirconia and Ca²⁺ ions in the composition of materials regulating their biocompatibility when used as scaffolds in bone regeneration.

Novel laser textured surface designs for improved zirconia implants performance

The development of new surface designs to enhance the integration process between surgically placed implants and biological tissues remains a challenge for the scientific community. In this way and trying to overcome this issue, in this work, laser technology was explored to produce novel textures on the surface of green zirconia compacts produced by cold pressing technique. Two strategies regarding line design (8 and 16 lines design) and different laser parameters (laser power and number of laser passages) were explored to assess their influence on geometry and depth of created textures. The produced textures were evaluated with Scanning Electron Microscopy (SEM) and it was observed that well-defined textured surfaces with regular geometric features (cavities or pillars) were obtained by laser combining different strategies lines design and parameters. The potential of proposed textures was also evaluated regarding surface wettability, friction performance (static and dynamic coefficient of friction evolution) against bone, aging resistance and flexural strength. Results demonstrated that all the produced textures display a super hydrophilic or hydrophilic behavior. Regarding the friction behavior, it was experimentally observed a high initial static coefficient of friction (COF) for all produced textures. Concerning the aging resistance, all the textured surfaces revealed a low monoclinic content, less than 25% after 5 h of hydrothermal aging. The flexural strength results showed that the mechanical resistance of zirconia was not significantly compromised with the laser action. Based on the obtained results, it is possible to prove that the processing route used for manufacturing the new and different surface designs (cold pressing technique followed by laser texturing) showed to be particularly effective for the production of zirconia implants with customized surface designs according to the properties required in a specific application. These new surface designs besides to enhance the surface wettability and also to improve the fixation at the initial moment of the implantation, do not significantly compromise the resistance to aging and the mechanical performance of zirconia. Hence, a positive impact on the long-term performance of the zirconia implants may be expected with the proposed novel laser textured surface designs.

Development of novel zirconia implant's materials gradated design with improved bioactive surface

Zirconia implants are becoming a preference choice for different applications such as knee, dental, among others. In order to improve osseointegration, implant's surfaces are usually coated with bioactive materials like hydroxyapatite (HAp) and beta-tricalcium phosphate (β-TCP) that are very similar to the calcium phosphates found in bones. However, due to the implantation process, these coatings can be detached from the zirconia surface, leading to implant premature failure. In this work, a new component materials design aiming to avoid this coating detachment problem is proposed. It is based on the use of a bioactive zirconia-calcium phosphate composite outer layer onto the zirconia bulk, where the zirconia bulk provides mechanical strength and the outer layer provides biological performance. In order to assess the potential of this new materials design, two types of bioactive zirconia outer composite layers (zirconia reinforced by 10 vol% of HAp and by 10 vol% of β-TCP) were produced by press and sinter process and the gradated samples were fully characterized concerning materials, mechanical resistance, fatigue resistance, and biological performance, as measured by different approaches. Results showed that the novel component materials design and the manufacturing process proposed for producing the bioactive zirconia samples with outer composite layers on zirconia bulk substrates are a promising solution for implants, with improved biological performance without substantially compromising their overall mechanical and fatigue properties.

Analysis of osteogenic potential on 3mol% yttria-stabilized tetragonal zirconia polycrystals and two different niobium oxide containing zirconia ceramics

PURPOSE

This study was performed to evaluate the osteogenic potential of 3mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) and niobium oxide containing Y-TZPs with specific ratios, new (Y,Nb)-TZPs, namely YN4533 and YN4533/Al20 discs.

MATERIALS AND METHODS

3Y-TZP, YN4533 and YN4533/Al20 discs (15 mm diameter and 1 mm thickness) were prepared and their average surface roughness (R_a) and surface topography were analyzed using 3-D confocal laser microscope (CLSM) and scanning electron microscope (SEM). Mouse pre-osteoblast MC3T3-E1 cells were seeded onto all zirconia discs and evaluated with regard to cell attachment and morphology by (CLSM), cell proliferation by PicoGreen assay, and cell differentiation by Reverse-Transcription PCR and Quantitative Real-Time PCR, and alkaline phosphatase (Alp) staining.

RESULTS

The cellular morphology of MC3T3-E1 pre-osteoblasts was more stretched on a smooth surface than on a rough surface, regardless of the material. Cellular proliferation was higher on smooth surfaces, but there were no significant differences between 3Y-TZP, YN4533, and YN4533/Al20. Osteoblast differentiation patterns on YN4533 and YN4533/Al20 were similar to or slightly higher than seen in 3Y-TZP. Although there were no significant differences in bone marker gene expression (alkaline phosphatase and osteocalcin), Alp staining indicated better osteoblast differentiation on YN4533 and YN4533/Al20 compared to 3Y-TZP.

CONCLUSION

Based on these results, niobium oxide containing Y-TZPs have comparable osteogenic potential to 3Y-TZP and are expected to be suitable alternative ceramics dental implant materials to titanium for aesthetically important areas.

Early cell response of osteogenic cells on differently modified implant surfaces: Sequences of cell proliferation, adherence and differentiation

OBJECTIVES

Osseointegration of dental implants is a crucial prerequisite for long-term survival. Therefore, surface modifications are needed to interact with the extracellular environment and to trigger osteogenic cell responses such as cell proliferation, adherence, and differentiation. The purpose of this study was to investigate different surface modifications in vitro over 2 weeks.

MATERIALS AND METHODS

Commercially available cells from a human osteogenic cell line (HHOB-c) were cultivated on the following surfaces: titanium with smooth surfaces (polished titanium (P), machined titanium (M), polyetheretherketone (Peek)), titanium with rough and hydrophilised surfaces (acid etched titanium (A), sandblasted acid etched titanium (SA and SA2), sandblasted acid etched hydrophilised (SAH), titanium plasma painted titanium (TPS)), titanium with calcium phosphate-containing surfaces (titanium plasma painted calcium phosphate modified titanium (TPS-CaP), sandblasted calcium phosphate modified titanium (S-CaP), sandblasted acid etched calcium phosphate modified titanium (SA-CaP)), and zirconium-oxide (yttrium amplified zirconium (Z), yttrium amplified Ca²⁺ delivering zirconium (Z-Ca)). Tissue culture polystyrene (TCPS) served as a control. Cell count was assessed after 24 h, 48 h, 72 h, 7 d, and 14 d; osteogenic cell adherence and differentiation were analysed by using cellular Quantitative Immuno-Cytochemistry (QIC) assay for alkaline phosphatase (AP), osteocalcin (OC), integrin alpha V (ITGAV), and talin (T).

RESULTS

All tested surfaces showed a positive influence on the differentiation and adherence of osteogenic cells, especially P, M, A, TCPS, and Peek. After 48 h, the surfaces M, SA and SAH had induced a positive influence on adherence, whereas SA2, SA, and SAH triggered proliferation after 14 d.

CONCLUSIONS

Rough and hydrophilised surface modifications, such as SAH, trigger osteogenic cell responses. These in vitro results highlight the potential use of SAH surface modifications of dental implants and indicate further clinical studies are warranted.

The Impact of Confluence on Bone Marrow Mesenchymal Stem (BMMSC) Proliferation and Osteogenic Differentiation

Background: In the field of cellular therapy, the impact of confluence degreeonharvesting or differentiation of BMMSCs and the effect of cell-to-cell contact remain controversial. Therefore, the effect of confluence on properties of BMMSCs was studied and efficiency of confluence-associated osteogenic differentiation was identified. Materials andMethods: The impact of 20, 50, 70, 80 and 100% confluences on proliferation properties of BMMSCs, expression of ERK and p-ERK proteins and glucose consumption rate was studied. Efficiency of confluence-associated osteogenic differentiation was identified by determining calcium deposition, Alizarin Red staining, ALP activity and expression of osteopontin and osteocalcin genes. Results: There was a correlation between confluence % and BMMSCs density. Viability was declined at the lower and higher confluences. The highest CFU-F, Brd-U uptake and population doubling were obtained at 80% confluence. ERK band intensity in 100% confluent BMMSCs was lower compared to other confluences. Bands of p-ERK were highly detectable in 70% and 80% confluences. Glucose consumption rate of 70% and 80% confluences in the last days were higher than 20% and 100% confluences. Although higher osteogenic differentiation was estimated at 80% confluence using calcium deposition, Alizarin Red staining and ALP activity, it was also extended at 100% confluence Osteopontin gene was expressed among all confluences including 100% confluence, while osteocalcin gene was expressed highly in 70% confluent cells. Conclusion: We concluded that the optimum seeding density for maximal expansion and harvesting purposes is 80% confluence and for osteogenic differentiation up to 100% confluence is also acceptable.

Characterization of Human Gingival Fibroblasts on Zirconia Surfaces Containing Niobium Oxide

It was indicated that tetragonal zirconia polycrystal (TZP) containing yttria (Y₂O₃) and niobium oxide (Nb₂O₅) ((Y,Nb)-TZP) could be an adequate dental material to be used at esthetically important sites. The (Y,Nb)-TZP was also proved to possess its osteogenic potential comparable with those conventional dental implant material, titanium (Ti). The objective of the current study was to characterize cellular response of human gingival fibroblasts (HGFs) to smooth and rough surfaces of the (Y,Nb)-TZP disc, which were obtained by polishing and sandblasting, respectively. Various microscopic, biochemical, and molecular techniques were used to investigate the disc surfaces and cellular responses for the experimental (Y,Nb)-TZP and the comparing Ti groups. Sandblasted rough (Y,Nb)-TZP (Zir-R) discs had the highest surface roughness. HGFs cultured on polished (Y,Nb)-TZP (Zir) showed a rounded cell morphology and light spreading at 6 h after seeding and its proliferation rate significantly increased during seven days of culture compared to other surfaces. The mRNA expressions of type I collagen, integrin α2 and β1 were significantly stimulated for the Zir group at 24 h after seeding. The current findings, combined with the previous results, indicate that (Y,Nb)-TZP provides appropriate surface condition for osseointegration at the fixture level and for peri-implant mucosal sealing at the abutment level producing a suitable candidate for dental implantation with an expected favorable clinical outcome.

Osteogenic responses to zirconia with hydroxyapatite coating by aerosol deposition

Previously, we found that osteogenic responses to zirconia co-doped with niobium oxide (Nb2O5) or tantalum oxide (Ta2O5) are comparable with responses to titanium, which is widely used as a dental implant material. The present study aimed to evaluate the in vitro osteogenic potential of hydroxyapatite (HA)-coated zirconia by an aerosol deposition method for improved osseointegration. Surface analysis by scanning electron microscopy and x-ray diffraction proved that a thin as-deposited HA film on zirconia showed a shallow, regular, crater-like surface. Deposition of dense and uniform HA films was measured by SEM, and the contact angle test demonstrated improved wettability of the HA-coated surface. Confocal laser scanning microscopy indicated that MC3T3-E1 pre-osteoblast attachment did not differ notably between the titanium and zirconia surfaces; however, cells on the HA-coated zirconia exhibited a lower proliferation than those on the uncoated zirconia late in the culture. Nevertheless, ALP, alizarin red S staining, and bone marker gene expression analysis indicated good osteogenic responses on HA-coated zirconia. Our results suggest that HA-coating by aerosol deposition improves the quality of surface modification and is favorable to osteogenesis.