Effects of surface-treated cpTi and Ti6Al4V alloy on the initial attachment of human osteoblast cells

Effect of multi-purpose primer on bonding of acrylic resin to cast titanium and gold alloy after airborne-particle abrasion

PURPOSE

To clarify the effect of a multi-purpose primer combining several functional monomers on two prosthodontic materials (cast titanium and a gold alloy) after airborne-particle abrasion.

METHODS

Disk-shaped adherends were prepared from cast titanium (CP Titanium JIS2) and a gold alloy (Casting Gold M.C. Type IV). A silane-containing two-liquid primer (M&C primer (MC)) and two silane-free single-liquid primers (Alloy Primer (AP) and V-Primer (VP)) were used as surface-treatment agents. The shear bond strengths were determined before and after thermocycling to evaluate the adhesive durability, and the results were compared using a non-parametric statistical analysis. The effect of airborne-particle abrasion with alumina on the titanium surface was analyzed by X-ray photoelectron spectroscopy (XPS).

RESULTS

There was no significant difference in bond strength between the MC and AP before and after thermocycling, whereas VP showed significantly lower values. XPS revealed that the titanium acquired hydrophilic properties after the airborne-particle abrasion.

CONCLUSIONS

The novelty of this study is that it shows that the presence/absence of the silane had no effect on the bonding of cast titanium with an acrylic resin. The study also showed that the multi-purpose primer can be used without any problems with both cast titanium and gold alloy, in combination with airborne-particle abrasion with alumina.

The recognition of biomaterials: pattern recognition of medical polymers and their adsorbed biomolecules

All biomedical materials are recognized as foreign entities by the host immune system despite the substantial range of different materials that have been developed by material scientists and engineers. Hydrophobic biomaterials, hydrogels, biomaterials with low protein binding surfaces, and those that readily adsorb a protein layer all seem to incite similar host responses in vivo that may differ in magnitude, but ultimately result in encapsulation by fibrotic tissue. The recognition of medical materials by the host is explained by the very intricate pattern recognition system made up of integrins, toll-like receptors, scavenger receptors, and other surface proteins that enable leukocytes to perceive almost any foreign body. In this review, we describe the various pattern recognition receptors and processes that occur on biomedical material surfaces that permit detection of a range of materials within the host.

Nanometer-thin TiO₂ enhances skeletal muscle cell phenotype and behavior

Background

The independent role of the surface chemistry of titanium in determining its biological properties is yet to be determined. Although titanium implants are often in contact with muscle tissue, the interaction of muscle cells with titanium is largely unknown. This study tested the hypotheses that the surface chemistry of clinically established microroughened titanium surfaces could be controllably varied by coating with a minimally thin layer of TiO₂ (ideally pico-to-nanometer in thickness) without altering the existing topographical and roughness features, and that the change in superficial chemistry of titanium is effective in improving the biological properties of titanium.

Methods and results

Acid-etched microroughened titanium surfaces were coated with TiO₂ using slow-rate sputter deposition of molten TiO₂ nanoparticles. A TiO₂ coating of 300 pm to 6.3 nm increased the surface oxygen on the titanium substrates in a controllable manner, but did not alter the existing microscale architecture and roughness of the substrates. Cells derived from rat skeletal muscles showed increased attachment, spread, adhesion strength, proliferation, gene expression, and collagen production at the initial and early stage of culture on 6.3 nm thick TiO₂-coated microroughened titanium surfaces compared with uncoated titanium surfaces.

Conclusion

Using an exemplary slow-rate sputter deposition technique of molten TiO₂ nanoparticles, this study demonstrated that titanium substrates, even with microscale roughness, can be sufficiently chemically modified to enhance their biological properties without altering the existing microscale morphology. The controllable and exclusive chemical modification technique presented in this study may open a new avenue for surface modifications of titanium-based biomaterials for better cell and tissue affinity and reaction.

Effects of pico-to-nanometer-thin TiO2 coating on the biological properties of microroughened titanium

The independent, genuine role of surface chemistry in the biological properties of titanium is unknown. Although microtopography has been established as a standard surface feature in osseous titanium implants, unfavorable behavior and reactions of osteogenic cells are still observed on the surfaces. To further enhance the biological properties of microfeatured titanium surfaces, this study tested the hypotheses that (1) the surface chemistry of microroughened titanium surfaces can be controllably varied by coating with a very thin layer of TiO(2), without altering the existing topographical and roughness features; and (2) the change in the surface chemistry affects the biological properties of the titanium substrates. Using a slow-rate sputter deposition of molten TiO(2) nanoparticles, acid-etched microroughened titanium surfaces were coated with a TiO(2) layer of 300-pm to 6.3-nm thickness that increased the surface oxygen levels without altering the existing microtopography. The attachment, spreading behavior, and proliferation of osteoblasts, which are considered to be significantly impaired on microroughened surfaces compared with relatively smooth surfaces, were considerably increased on TiO(2)-coated microroughened surfaces. The rate of osteoblastic differentiation was represented by the increased levels of alkaline phosphatase activity and mineral deposition as well as by the upregulated expression of bone-related genes. These biological effects were exponentially correlated with the thickness of TiO(2) and surface oxygen percentage, implying that even a picometer-thin TiO(2) coating is effective in rapidly increasing the biological property of titanium followed by an additional mild increase or plateau induced by a nanometer-thick coating. These data suggest that a super-thin TiO(2) coating of pico-to-nanometer thickness enhances the biological properties of the proven microroughened titanium surfaces by controllably and exclusively modulating their surface chemistry while preserving the existing surface morphology. The improvements in proliferation and differentiation of osteoblasts attained by this chemical modification is of great significance, providing a new insight into how to develop new implant surfaces for better osseointegration, based on the established microtopographic surfaces.

The effect of superficial chemistry of titanium on osteoblastic function

The surface topography and chemistry of titanium are postulated to be two major factors that affect the osseointegration capacity of titanium implants. However, it is extremely difficult to control one factor without changing the other, which prevents the isolation of the genuine effect of one factor. This study aimed to determine whether surface chemistry of titanium alone affects osteoblastic function. Two different titanium surfaces were prepared by sputter depositioning of titanium (Ti; 99.99% purity) or titanium dioxide (TiO2; 99.99% purity) (50-nm thick for each) onto machined commercially pure titanium disks. Rat bone marrow-derived osteoblastic cells were cultured on each of the two surfaces. TiO2 surface showed 4.4 times higher elemental oxygen concentration and higher water wettability than Ti surface. Scanning electron microscopic and atomic force microscopic examination revealed no differences in surface topography and roughness values between the two surfaces. The cell proliferated more on TiO2 than on Ti by up to 60%. Although the expression of collagen I gene increased more rapidly on TiO2 at early culture stage of day 3, the late stage marker genes for osteoblastic differentiation, including osteopontin and osteocalcin, were not modulated between the two cultures. The alkaline phosphatase positive area and mineralized nodule area were approximately two times larger on TiO2 than on Ti. In conclusion, titanium materials having different superficial chemistry, that is, titanium or titanium dioxide, may exert different biological capacity of osteoblasts; titanium dioxide may induce superior osteoconduction, primarily because of the increased osteoblastic proliferation.

Corrosion degradation and prevention by surface modification of biometallic materials

Metals, in addition to ceramics and polymers, are important class of materials considered for replacement of non-functional parts in the body. Stainless steel 316, titanium and titanium alloys, Co-Cr, and nitinol shape memory alloys are the most frequently used metallic materials. These alloys are prone to corrosion in various extents. This review briefly discusses the important biomaterials, their properties, and the physiological environment to which these materials are exposed. Corrosion performance of currently used metallic materials has been assessed and threat to the biocompatibility from corrosion products/metal ions is discussed. The possible preventive measures to improve corrosion resistance by surface modification and to increase the bioactivity of the metallic surfaces have also been discussed. Importance of the formation of oxide layers on the metal surface, another aspect of corrosion process, has been correlated with the host response. The gap areas and future direction of research are also outlined in the paper.

Modulation of the human bone cell cycle by calcium ion-implantation of titanium

Ca ion implantation of Ti surfaces has previously been reported to enhances osseointegration in vivo. Although the mechanisms underlying the response of bone cells to these novel surfaces still remain unclear, it is possible that Ca ion-implanted Ti (Ca-Ti) may influence the growth of new bone by modulating the progression of the cell cycle. In the present study we have, therefore, examined the precise effects of Ca ion-implantation of Ti on the bone-like MG-63 cell line in vitro. The results of flow cytometry analysis showed that this surface markedly enhanced the proportion of cells which expressed Ki-67, a cell proliferation-associated nuclear antigen, compared with cells grown on the non-implanted Ti (control) surface. In addition, cultures grown on Ca-Ti and synchronized at the G1/S boundary by hydroxyurea more rapidly re-entered and progressed through the S and G2/M phases of the cell cycle than their counterparts on Ti. Ca ion-implantation also significantly increased the numbers of mitotic cells. These results thus show that alteration of the surface chemistry of Ti by high-energy implantation with Ca ion was able to substantially modulate the progression of the bone cell cycle, and suggest a possible means of enhancing the response of bone cells to implant materials.

Statistical demonstration of the relative effect of surface chemistry and roughness on human osteoblast short-term adhesion

The effects of material composition, surface chemistry or surface topography on cell attachment (short-term adhesion) have been largely studied on bone-derived cells. However, no statistical demonstration of these effects has been performed until now. With this objective, we quantified the attachment after 24 hours of human osteoblasts on pure titanium, titanium alloy and stainless steel substrates presenting 6 different surface morphologies and 2 different roughness amplitude obtained by sand-blasting, electro-erosion, acid etching, polishing and machine-tooling. The coating by a gold-palladium layer of these surfaces allowed determining the relative effect of the surface roughness and of the surface chemistry. By multiple analysis of variance, we demonstrated that neither material composition nor surface roughness amplitude influenced cell attachment except on sandblasted pure titanium substrates. On the contrary, a high significant influence of the process used to produce the surface was observed meaning that the main influent factor on cell attachment could be either the surface morphology or the surface chemistry induced by the process. As the coating of surfaces by a gold-palladium layer decreased significantly the attachment of cells on the majority of substrates, we concluded that attachment is rather influenced by surface chemistry than by surface topography.

Osteoblast response to thermally oxidized Ti6Al4V alloy

We have recently reported that thermal oxidation treatments of Ti6Al4V at 500 degrees and 700 degrees C for 1 h result in the formation of an outer "ceramic" layer of rutile that do not decrease the high in vitro corrosion resistance of the alloy. In the present work, surface roughness was measured and found marginally increased as a consequence of oxidation of the alloy at 700 degrees C, but not at 500 degrees C. We have evaluated the biocompatibility of the oxidized surfaces, by assessing cell adhesion, proliferation, and differentiation of primary cultures of human osteoblastic cells. Compared with polished alloy, both thermal treatments increased osteoblast adhesion measured as cell attachment, beta1 integrin and FAK-Y397 expression, as well as cytoskeletal reorganization. Compared with treatment at 500 degrees C, thermal oxidation at 700 degrees C enhanced cell adhesion. Treatment at 700 degrees C transiently impaired cell proliferation and viability, which were not altered in alloys oxidized at 500 degrees C. Several markers of osteoblastic differentiation such as procollagen I peptide, alkaline phosphatase, osteocalcin, and mineralized nodule formation were found either unaffected or differentially increased by alloys treated either at 500 degrees or 700 degrees C. In addition, thermal oxidation at 700 degrees C also increased osteoprotegerin secretion. Taken together, our results indicate that thermal oxidation treatments at 500 degrees or 700 degrees C for 1 h improve the in vitro biocompatibility of Ti6Al4V.

Human serum albumin adsorption on TiO2 from single protein solutions and from plasma

In the present work, the adsorption of human serum albumin (HSA) on commercially pure titanium with a titanium oxide layer formed in a H(2)O(2) solution (TiO(2) cp) and on TiO(2) sputtered on Si (TiO(2) sp) was analyzed. Adsorption isotherms, kinetic studies, and work of adhesion determinations were carried out. HSA exchangeability was also evaluated. Surface characterization was performed by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and wettability studies. The two TiO(2) surfaces have very distinct roughnesses, the TiO(2) sp having a mean R(a) value 14 times smaller than the one of TiO(2) cp. XPS analysis revealed consistent peaks representative of TiO(2) on sputtered samples as well as on Ti cp substrate after 48 h of H(2)O(2) immersion. Nitrogen was observed as soon as protein was present, while sulfur, present in disulfide bonds in HSA, was observed for concentrations of protein higher than 0.30 mg/mL. The work of adhesion was determined from contact angle measurements. As expected from the surface free energy values, the work of adhesion of HSA solution is higher for the TiO(2) cp substrate, the more hydrophilic one, and lower for the TiO(2) sp substrate, the more hydrophobic one. The work of adhesion between plasma and the substrates assumed even higher values for the TiO(2) cp surface, indicating a greater interaction between the surface and the complex protein solutions. Adsorption studies by radiolabeling of albumin ((125)I-HSA) suggest that rapid HSA adsorption takes place on both surfaces, reaching a maximum value after approximately 60 min of incubation. For the higher HSA concentrations in solution, a multilayer coverage was observed on both substrates. After the adsorption step from single HSA solutions, the exchangeability of adsorbed HSA molecules by HSA in solution was evaluated. The HSA molecules adsorbed on TiO(2) sp seem to be more easily exchanged by HSA itself than those adsorbed on TiO(2) cp after 24 h. In contrast, after 72 h, nearly all the adsorbed albumin molecules effectively exchange with other albumin molecules.

In vitro corrosion behaviour and osteoblast response of thermally oxidised Ti6Al4V alloy

In this work, the influence of thermal oxidation treatments of Ti6Al4V at 500 degrees C and 700 degrees C for 1 h on the in vitro corrosion behaviour and osteoblast response is studied. The potential of these treatments, aimed to improve the wear surface performance as biomaterial, relies in the formation of an outer "ceramic" layer of rutile. The corrosion behaviour was evaluated in simulated human fluids by electrochemical impedance spectroscopy and anodic polarisation tests. The effect of these thermal oxidation treatments on osteoblastic behaviour was studied in primary cultures of human osteoblastic cells. Results show that thermal oxidation treatments do not decrease the high in vitro corrosion resistance of the Ti6Al4V alloy. Osteoblast adhesion studies indicate that thermal oxidation treatments do not impair the material biocompatibility. Moreover, the thermal oxidation at 700 degrees C enhances the in vitro osteoblastic cell attachment compared to the thermal oxidation at 500 degrees C.