Surface modification of titanium alloy implants

Innovative Design Methodology for Patient-Specific Short Femoral Stems

The biomechanical performance of hip prostheses is often suboptimal, which leads to problems such as strain shielding, bone resorption and implant loosening, affecting the long-term viability of these implants for articular repair. Different studies have highlighted the interest of short stems for preserving bone stock and minimizing shielding, hence providing an alternative to conventional hip prostheses with long stems. Such short stems are especially valuable for younger patients, as they may require additional surgical interventions and replacements in the future, for which the preservation of bone stock is fundamental. Arguably, enhanced results may be achieved by combining the benefits of short stems with the possibilities of personalization, which are now empowered by a wise combination of medical images, computer-aided design and engineering resources and automated manufacturing tools. In this study, an innovative design methodology for custom-made short femoral stems is presented. The design process is enhanced through a novel app employing elliptical adjustment for the quasi-automated CAD modeling of personalized short femoral stems. The proposed methodology is validated by completely developing two personalized short femoral stems, which are evaluated by combining in silico studies (finite element method (FEM) simulations), for quantifying their biomechanical performance, and rapid prototyping, for evaluating implantability.

Graphene nanocoating provides superb long-lasting corrosion protection to titanium alloy

OBJECTIVE

The presence of metallic species around failed implants raises concerns about the stability of titanium alloy (Ti-6Al-4V). Graphene nanocoating on titanium alloy (GN) has promising anti-corrosion properties, but its long-term protective potential and structural stability remains unknown. The objective was to determine GN's anti-corrosion potential and stability over time.

METHODS

GN and uncoated titanium alloy (Control) were challenged with a highly acidic fluorinated corrosive medium (pH 2.0) for up to 240 days. The samples were periodically tested using potentiodynamic polarization curves, electrochemical impedance spectroscopy and inductively coupled plasma-atomic emission spectroscopy (elemental release). The integrity of samples was determined using Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and scanning electron microscopy. Statistical analyses were performed with one-sample t-test, paired t-test and one-way ANOVA with Tukey post-hoc test with a pre-set significance level of 5%.

RESULTS

There was negligible corrosion and elemental loss on GN. After 240 days of corrosion challenge, the corrosion rate and roughness increased by two and twelve times for the Control whereas remained unchanged for GN. The nanocoating presented remarkably high structural integrity and coverage area (>98%) at all time points tested.

SIGNIFICANCE

Graphene nanocoating protects titanium alloy from corrosion and dissolution over a long period while maintaining high structural integrity. This coating has promising potential for persistent protection of titanium and potentially other metallic alloys against corrosion.

Reduced graphene oxide coating enhances osteogenic differentiation of human mesenchymal stem cells on Ti surfaces

BACKGROUND

Titanium (Ti) has been utilized as hard tissue replacement owing to its superior mechanical and bioinert property, however, lack in tissue compatibility and biofunctionality has limited its clinical use. Reduced graphene oxide (rGO) is one of the graphene derivatives that possess extraordinary biofunctionality and are known to induce osseointegration in vitro and in vivo. In this study, rGO was uniformly coated by meniscus-dragging deposition (MDD) technique to fabricate rGO-Ti substrate for orthopedic and dental implant application.

METHODS

The physicochemical characteristics of rGO-coated Ti (rGO-Ti) substrates were evaluated by atomic force microscopy, water contact angle, and Raman spectroscopy. Furthermore, human mesenchymal stem cells (hMSCs) were cultured on the rGO-Ti substrate, and then their cellular behaviors such as growth and osteogenic differentiation were determined by a cell counting kit-8 assay, alkaline phosphatase (ALP) activity assay, and alizarin red S staining.

RESULTS

rGO was coated uniformly on Ti substrates by MDD process, which allowed a decrease in the surface roughness and contact angle of Ti substrates. While rGO-Ti substrates significantly increased cell proliferation after 7 days of incubation, they significantly promoted ALP activity and matrix mineralization, which are early and late differentiation markers, respectively.

CONCLUSION

It is suggested that rGO-Ti substrates can be effectively utilized as dental and orthopedic bone substitutes since these graphene derivatives have potent effects on stimulating the osteogenic differentiation of hMSCs and showed superior bioactivity and osteogenic potential.

Corrosion Behavior of Titanium in Simulated Body Solutions with the Addition of Biomolecules

Titanium is one of the most used biomaterials for different applications. The aim of this study is to investigate the influence of adenine, thymine, and l-histidine as important biomolecules in the human body on the corrosion behavior of titanium in simulated body solutions. Open circuit measurements, potentiodynamic measurements, electrochemical impedance spectroscopy measurements, and quantum chemical calculations were employed during the investigation. All electrochemical methods used revealed that the investigated biomolecules provide better corrosion resistance to titanium in artificial body solutions. The increase in corrosion resistance is a result of the formation of a stable protective film on the metal surface. Also, quantum chemical calculations are in compliance with electrochemical test results and indicate that adenine, thymine, and l-histidine may act as corrosion inhibitors in the investigated solutions.

Selective modification of Ti6Al4V surfaces for biomedical applications

The surface of a medical implant is required to interact favourably with ions, biomolecules and cells in vivo, commonly resulting in the formation of the extracellular matrix. Medical grade Ti6Al4V alloy is widely used in orthopaedic and dental applications for bone replacement due to its advantageous mechanical properties and biocompatibility, which enhances the adhesion between native tissue and the implanted material. In this study, chemical and thermal modification of a medical-grade Ti6Al4V alloy were performed to enhance electrostatic interactions at the alloy surface with a synthetic peptide, suitable for conferring drug release capabilities and antimicrobial properties. The modified surfaces exhibited a range of topographies and chemical compositions depending primarily on the treatment temperature. The surface wetting behaviour was found to be pH-dependent, as were the adhesive properties, evidenced by chemical force titration atomic force microscopy.

In vitro adherence of Candida albicans to zirconia surfaces

OBJECTIVES

This study aimed to characterize surface properties such as roughness (Ra) and surface-free energy (SFE) of glazed and polished yttria-stabilized zirconia and to evaluate in vitro adherence of fungus Candida albicans and salivary bacteria, Staphylococcus epidermidis, mixed with C. albicans to these substrata. Additionally, the influence of salivary proteins (albumin, mucin and α-amylase) on yeast adhesion was studied.

MATERIAL AND METHODS

Ra and SFE of glazed and polished zirconia discs were measured. Specimens were wetted with saliva and salivary proteins prior to incubation with C. albicans and mixed suspension of C. albicans and S. epidermidis for 24 hr, respectively. Microbial adhesion was quantified by counting colony-forming units (CFU). Differences in physicochemical properties were proved by t test. "Linear mixed model" with the factors "type of surface" and "wetting media" was applied to analyse the effects on fungal adhesion (p < .05).

RESULTS

SFE and Ra of glazed specimens were significantly higher than corresponding values of polished ones. The wetting media significantly changed the fungal binding (p = .0016). Significantly higher quantities of adhering fungi were found after mucin incubation compared to saliva (p = .004). For the factor "surface" as well as the interaction between "surface" and "wetting media," no statistically significant differences have been found. In mixed suspension, the growth of Candida was completely prevented.

CONCLUSIONS

Glazed and polished zirconia differs in terms of physicochemical surface properties. These differences appear to be modulated by pellicle coating affecting the biomass of adhered Candida. Mucin seems to be good binding sites for adhesion of C. albicans.

Inhibiting Corrosion of Biomedical-Grade Ti-6Al-4V Alloys with Graphene Nanocoating

The identification of metal ions and particles in the vicinity of failed implants has raised the concern that biomedical titanium alloys undergo corrosion in healthy and infected tissues. Various surface modifications and coatings have been investigated to prevent the deterioration and biocorrosion of titanium alloys but so far with limited success. Graphene is a cytocompatible atom-thick film made of carbon atoms. It has a very high surface area and can be deposited onto metal objects with complex shapes. As the carbon lattice has a very small pore size, graphene has promising impermeability capacity. Here, we show that graphene coating can effectively protect Ti-6Al-4V from corrosion. Graphene nanocoatings were produced on Ti-6Al-4V grade 5 and 23 discs and subjected to corrosive challenge (0.5M NaCl supplemented with 2-ppm fluoride, pH of 2.0) up to 30 d. The linear polarization resistance curves and electrochemical impedance spectroscopy analysis showed that the graphene-coated samples presented higher corrosion resistance and electrochemical stability at all time points. Moreover, the corrosion rate of the graphene-coated samples was very low and stable (~0.001 mm/y), whereas that of the uncoated controls increased up to 16 and 5 times for grade 5 and 23 (~0.091 mm/y) at the end point, respectively. The surface oxidation, degradation (e.g., crevice defects), and leaching of Ti, Al, and V ions observed in the uncoated controls were prevented by the graphene nanocoating. The Raman mappings confirmed that the graphene nanocoating presented high structural stability and resistance to mechanical stresses and chemical degradation, keeping >99% of coverage after corrosion challenge. Our findings open the avenues for the use of graphene as anticorrosion coatings for metal biomedical alloys and implantable devices.

Corrosion performance of cold deformed austenitic stainless steels for biomedical applications

Austenitic stainless steels possess an excellent balance of strength and ductility along with the high ability to further raise their strength during cold deformation (CD). Corrosion resistance of austenitic stainless steels (SSs) is affected by cold deformation because passive films on the surface of steels are expected to be modified. A low level of CD enhances the surface diffusion, which results in the formation of a stable passive film leading to an increase in the corrosion resistance in neutral chloride solutions. The chromium content in the passive film on a deformed steel surface is usually richer, with a higher Cr/Fe ratio than that formed on annealed steels. A higher chromium content makes surface films more stable, which improves the corrosion resistance. However, severe CD results in the formation of strain-induced martensite phase and deformation twins, which decreases the localized corrosion resistance by increasing the number of active anodic sites on the surface. The corrosion resistance, especially the pitting resistance, in SSs is diminished with increasing volume fraction of the martensite. In this review, we highlighted the failure modes of corrosion of stainless steel implants, factors affecting corrosion, and effect of CD on mechanical properties and emphatically on the corrosion resistance of SSs for biomedical applications.

Microbially-Influenced Corrosion: Damage to Prostheses, Delight for Bacteria

In natural and man-made environments, microbial communities thrive as biofilms on living (e.g. tissue) and inanimate (e.g. plastic, metal, wood, mineral) surfaces. Biofilms are found in a wide range of aqueous habitats, including physiological fluids. Numerous types of microorganisms are able to colonize catheters, implants, prosthetics, and other medical devices manufactured from different metallic and non-metallic materials dwelling within a human body. The development of biofilm is facilitated by the production of extracellular polymeric substances (EPS).

Biofilms formed on surfaces of metallic materials may alter interfacial electrochemical processes, which can lead to increased corrosion of the colonized substratum. Deterioration of metallic materials in the presence of a biofilm is termed biocorrosion or microbially-influenced corrosion (MIC). In the field of biomaterials, “biocorrosion” is commonly used when describing the effect of host tissue on the corrosion of implant metals and alloys. Therefore, to avoid confusion, we will here use the term MIC as a reference to biofilm-influenced corrosion.

It is important to realise that although most metals are prone to microbial colonization, i.e. to biofouling, this does not imply that they are susceptible to MIC. For example, a metal such as titanium, accumulates biofilm, however, it still demonstrates excellent resistance against MIC.

Corrosion is, by definition, an electrochemical process, therefore, electrochemical techniques are frequently employed to determine and measure the rate of abiotic, as well as biologically driven corrosion reactions. This communication addresses the use of electrochemical techniques for monitoring (i) biofilm formation on and (ii) MIC of implant metals and alloys.

The effect of manufacturing techniques on custom-made titanium cranioplasty plates: A pilot study

OBJECTIVE

This study investigated the effect of varying techniques on the surface characteristics of pressed titanium cranioplasty plates, commonly manufactured in laboratory practice. The aim was to highlight the variety of techniques currently used, assess these methods of manufacture and produce manufacturing recommendations.

METHODS

A questionnaire identified manufacturing methods commonly used by maxillofacial prosthetists. The plate surfaces were examined using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectrometry. The surface differences and titanium compositions were statistically analysed.

RESULTS

Bead blasting with aluminium oxide (Al₂O₃) showed a significant decrease (p < 0.001) in titanium surface composition, replaced by a large aluminium content. Trimming tool choice had a significant impact (p = 0.001) on surface contamination by smoothing wheel material deposition; however passivation and anodising techniques had no significant effect (p = 0.293 and p = 0.257, respectively) on the surface composition or roughness of titanium samples.

CONCLUSIONS

A large range of manufacturing techniques of titanium cranioplasty plates was confirmed and significant differences were found. Amongst other recommendations, bead blasting with Al₂O₃ is not recommended for commercially pure titanium implant surface finishing due to aluminium contamination. The recommendations outlined will minimise manufacturing time, reduce risk of complication (thus costs) and unify methods to enable a safe, reliable treatment.

Effect of Load Deflection on Corrosion Behavior of NiTi Wire

For dental orthodontic applications, NiTi wires are used under bending conditions in the oral environment for a long period. The purpose of this study was to investigate the effect of bending stress on the corrosion of NiTi wires using potentiodynamic and potentiostatic tests in artificial saliva. The results indicated that bending stress induces a higher corrosion rate of NiTi wires in passive regions. It is suggested that the passive oxide film of specimens would be damaged under bending conditions. Auger electron spectroscopic analysis showed a lower thickness of passive films on stressed NiTi wires compared with unstressed specimens in the passive region. By scanning electron microscopy, localized corrosion was observed on stressed Sentalloy specimens after a potentiodynamic test at pH 2. In conclusion, this study indicated that bending stress changed the corrosion properties and surface characteristics of NiTi wires in a simulated intra-oral environment.

Titanium-Based Hip Stems with Drug Delivery Functionality through Additive Manufacturing

Postoperative infections are a major concern in patients that receive implants. These infections generally occur in areas with poor blood flow and pathogens do not always respond to antibiotic treatment. With the latest developments in nanotechnology, the incorporation of antibiotics into prosthetic implants may soon become a standard procedure. The success will, however, depend on the ability to control the release of antibiotics at concentrations high enough to prevent the development of antibiotic-resistant strains. Through additive manufacturing, antibiotics can be incorporated into cementless femoral stems to produce prosthetic devices with antimicrobial properties. With the emerging increase in resistance to antibiotics, the incorporation of antimicrobial compounds other than antibiotics, preferably drugs with a broader spectrum of antimicrobial activity, will have to be explored. This review highlights the microorganisms associated with total hip arthroplasty (THA), discusses the advantages and disadvantages of the latest materials used in hip implants, compares different antimicrobial agents that could be incorporated, and addresses novel ideas for future research.

Surface characterization and corrosion behavior of calcium phosphate-base composite layer on titanium and its alloys via plasma electrolytic oxidation: A review paper

In recent years, calcium phosphate-base composites, such as hydroxyapatite (HA) and carbonate apatite (CA) have been considered desirable and biocompatible coating layers in clinical and biomedical applications such as implants because of the high resistance of the composites. This review focuses on the effects of voltage, time and electrolytes on a calcium phosphate-base composite layer in case of pure titanium and other biomedical grade titanium alloys via the plasma electrolytic oxidation (PEO) method. Remarkably, these parameters changed the structure, morphology, pH, thickness and crystallinity of the obtained coating for various engineering and biomedical applications. Hence, the structured layer caused improvement of the biocompatibility, corrosion resistance and assignment of extra benefits for Osseo integration. The fabricated layer with a thickness range of 10 to 20 μm was evaluated for physical, chemical, mechanical and tribological characteristics via XRD, FESEM, EDS, EIS and corrosion analysis respectively, to determine the effects of the applied parameters and various electrolytes on morphology and phase transition. Moreover, it was observed that during PEO, the concentration of calcium, phosphor and titanium shifts upward, which leads to an enhanced bioactivity by altering the thickness. The results confirm that the crystallinity, thickness and contents of composite layer can be changed by applying thermal treatments. The corrosion behavior was investigated via the potentiodynamic polarization test in a body-simulated environment. Here, the optimum corrosion resistance was obtained for the coating process condition at 500 V for 15 min in Ringer solution. This review has been summarized, aiming at the further development of PEO by producing more adequate titanium-base implants along with desired mechanical and biomedical features.

In situ electrochemical study of the interaction of cells with thermally treated titanium

Micromotion and fretting wear between bone and Ti-based alloys in stem and dental implants breaks the passive film and exposes the metal to the action of the complex surrounding medium, generating substantial amounts of debris and continuous Ti ion release. In this work, oxidation treatments at low temperatures (277 °C, 5 h) have been used to promote the formation of wear-corrosion resistant titanium oxide on the Ti surface. The objective of this paper has been the study of the influence of live cells on the protectiveness of the oxide formed at these low temperatures. The interaction of cells with the modified surface has been studied by scanning electron microscopy, electrochemical impedance spectroscopy, polarization curves, and x-ray photoelectron spectroscopy (XPS). The chemical composition of the thermally treated Ti surface is mainly TiO2 as anatase-rich titanium dioxide with a low concentration of hydroxyl groups and a low mean nanoroughness that could promote good cell adhesion. The electrochemical results indicate that the cells alter the overall resistance of the thermally treated Ti surfaces by decreasing the oxide resistance with time. At the same time, the anodic current increases, which is associated with cathodic control, and is probably due to the difficulty of access of oxygen to the Ti substrate. XPS reveals the presence of proteins on the surface of the treated specimens in contact with the cells and a decrease in the Ti signal associated with the extracellular matrix on the surface and the reduction of the oxide thickness.

Effect of different sterilization modes on the surface morphology, ion release, and bone reaction of retrieved micro-implants

OBJECTIVE

To compare as-received and sterilized micro-implants in order to assess the prospects of reusing them.

MATERIALS AND METHODS

Forty micro-implants from a single manufacturing lot were used in the study. Thirty were retrieved from patients after successful service in their mouth and with no signs of failure. The retrieved micro-implants were divided into three groups, according to method of sterilization: autoclave, gamma radiation, or ultraviolet radiation. All groups were subjected to scanning electron microscope analysis for surface morphology assessment. The specimens were immersed in a standard simulated body-fluid solution kept at 37°C in an incubator; the solution was then withdrawn at 24 hours and 30 days to evaluate aluminum and vanadium ion release by atomic absorption spectrophotometer in parts per billion. The micro-implants were then surgically implanted into the tibia of rabbits for a 1-month healing period, and the bone-implant blocks were processed for routine histologic examination.

RESULTS

This study revealed that sterilized micro-implants had altered surface topography, different ion release values, and different histologic cell reactions than the as-received micro-implants.

CONCLUSIONS

Within the limitations of this study, it can be concluded that retrieved self-drilling micro-implants have tip sharpness variations that require correction before insertion by bone drilling. The autoclave-sterilized micro-implants showed better histologic results than micro-implants sterilized by gamma or ultraviolet rays.

Oral biofilm formation on the titanium and zirconia substrates

OBJECTIVE

The aim of this randomized crossover investigation was to assess the biofilm formation on two titanium and one zirconia substrates in relation to the topography and surface roughness of the materials.

METHODS

Twenty-four discs specimens for each evaluated material (Machined pure titanium, Cast pure titanium, or Zirconia) were evaluated after oral cavity exposure in six healthy subjects. The study was conducted in 3 phases according to the material evaluated. Each subject was asked to use a removable splint containing 4 disks of the same tested substrate, 2 located in the anterior, and 2 in the posterior region. Participants were asked to use the intraoral splint during 24 h. The total biofilm covering on the discs was evaluated by 1% of neutral red staining. EMV and surface roughness was carried out to correlate with the biofilm found between different substrates.

RESULTS

Data showed higher mean roughness values for zirconia (Zc) when compared with titanium specimens (MPT and CPT; P < 0.001). MPT and CPT presented no differences between them (P > 0.05). The mean percentage (%) of covering biofilm on substrates was 84.14 for MPT, 86.22 for CPT and 90.90 for Zc.

CONCLUSION

There were no significant differences in the total area of formed biofilm among the tested groups. No correlation was found between surface roughness and the total amount of formed biofilm in the groups.

Influence of the microstructure and topography on the barrier properties of oxide scales generated on blasted Ti6Al4V surfaces

The long-term interfacial bond between an implant and bone may be improved by creating a rough surface on the implant in order to increase the surface area available for bone/implant apposition. A natural consequence of surface roughening is an increase in metal ion release, which is itself a surface dominated process. Based on this fact, the aim of this work is to study the influence of the microstructure and topography on the barrier properties of oxide scales thermally generated at 700 °C for 1h on Ti6Al4V surfaces after blasting with Al(2)O(3) particles (coarse) or SiO(2) and ZrO(2) particles (fine). The microstructural and topographical characterization of the thermally treated blasted surfaces has been studied by means of scanning electron microscopy coupled with energy dispersive X-ray analysis, contact profilometry and X-ray diffraction. The barrier properties and corrosion behaviour of the oxide layers have been studied by means of electrochemical impedance spectroscopy (EIS) in Hank's solution. Thermal treatment at 700 °C for 1h promotes the formation of oxide scales with different morphologies and crystalline structures depending on the degree of deformation of the blasted surface. The oxide scale grown on the finely blasted sample has a pine needle-like morphology which is mainly formed of anatase TiO(2). In contrast, the oxide scale grown on the coarsely blasted sample has a globular morphology formed mainly of rutile TiO(2). The differences in morphology, i.e. fine or coarse, of the oxide scales influence the corrosion response of the blasted thermally treated samples in Hank's solution. The EIS results permit evaluation of the different oxide scales from the capacitance and resistance values obtained in the high-frequency region and show a good correlation between the morphology and barrier properties. Oxidation treatment at 700 °C for 1h of Ti6Al4V samples coarsely blasted with Al(2)O(3) improves the corrosion behaviour due to an increase in the thickness of a compact, ordered and more structurally stable oxide scale. This is due to the globular morphology of the rutile (TiO(2)) structure maintaining an average surface roughness suitable for optimal osseo-integration with long-term interfacial bonding between the implant and bone.

Selection of the implant and coating materials for optimized performance by means of nanoindentation

Mechanical compatibility between a coating and a substrate is important for the longevity of implant materials. While previous studies have utilized the entire coating for analysis of mechanical compatibility of the surface, this study focuses on the nanoindentation of a uniformly thermally sprayed splat. Hydroxyapatite was thermally sprayed to create a homogeneous deposit density, as confirmed by microRaman spectroscopy, of amorphous calcium phosphate. Substrates were commercially pure Ti, Ti-6Al-4V, Co-Cr alloy and stainless steel. Nanoindentation revealed that splats deposited on the different metals have similar hardness and elastic modulus values of 4.2 ± 0.2 GPa and 80 ± 3 GPa, respectively. The mechanical properties were affected by the substrate type more than residual stresses, which were found to be low. It is recommended that amorphous calcium phosphate is annealed to relieve the quenching stress or that appropriate temperature histories are chosen to relax the stress created in cooling the coating assembly.

Adhesion of Candida albicans to various dental implant surfaces and the influence of salivary pellicle proteins

Dental implants may be considered a potential reservoir for (re)infection with oral Candida albicans. Our aim was to evaluate initial fungal adhesion to three differentially textured titanium and one zirconia implant surface, and to correlate these findings to differences in specific surface characteristics (surface roughness (R(a)) and surface free energy (SFE)). Additionally, we investigated the influence of salivary protein films and two pellicle proteins (mucin and albumin). Implant surfaces were characterized by perthometer (R(a)) and goniometer (SFE) measurements. Implant specimens were rinsed with human whole saliva, mucin, albumin, or phosphate buffered saline and incubated in C. albicans suspension for 2.5h. Adherent fungi were quantified by means of a bioluminometric assay. The lowest amount of fungal cells was found on sand-blasted titanium, whereas zirconia implants did not show any reduced potential to adhere C. albicans. The influence of the implant SFE on fungal biofilm formation appears to be more important than the influence of R(a). The protein mucin enhanced C. albicans accumulation. In contrast, albumin is unlikely to be involved in the adhesion process of C. albicans.

Electrochemical behaviour of titanium in ammine and stannous fluoride and chlorhexidine 0.2 percent mouthwashes

Titanium (Ti) is widely used in dentistry. Fluorides at acid pH could destabilize Ti oxide and make it susceptible to corrosion. The behaviour of IV grade machined Ti disks in 5 electrolytic solutions: Fusayama artificial saliva (Fas), ammine fluoride-stannous fluoride (Am-SnF2), 0.2 percent Chlorexidine (CHX) 0.20 percent, Fas with 20 percent Am-SnF2, and Fas with 20 percent CHX, was evaluated. Open circuit potential Ecorr was determined by immersing Ti disks for 24 hours in an electrochemical cell containing the solutions, potential changes were measured until a stable value was obtained. Examination by Scanning Electronic Microscope and Energy Dispersive X-ray Analysis were then performed. One way ANOVA analysis showed a significant difference of Ecorr values regarding the 5 solutions (p less than 0.001). The highest values were observed for Fas (-37.6 mV), intermediate for Am-SnF2 (-81mV) and lowest for CHX (-87.6mV). SEM analysis of disks after polarization curve in CHX showed a marked localized corrosion, while the other solutions showed no considerable corrosive action on Ti surface. When considering corrosive potential range in oral cavity, Ti had an excellent behaviour on both antiseptics evaluated. The results obtained in this study will enable us to recommend the use of Am-SnF2 mouthwash for patients with dental implants.

Dental implant systems

Among various dental materials and their successful applications, a dental implant is a good example of the integrated system of science and technology involved in multiple disciplines including surface chemistry and physics, biomechanics, from macro-scale to nano-scale manufacturing technologies and surface engineering. As many other dental materials and devices, there are crucial requirements taken upon on dental implants systems, since surface of dental implants is directly in contact with vital hard/soft tissue and is subjected to chemical as well as mechanical bio-environments. Such requirements should, at least, include biological compatibility, mechanical compatibility, and morphological compatibility to surrounding vital tissues. In this review, based on carefully selected about 500 published articles, these requirements plus MRI compatibility are firstly reviewed, followed by surface texturing methods in details. Normally dental implants are placed to lost tooth/teeth location(s) in adult patients whose skeleton and bony growth have already completed. However, there are some controversial issues for placing dental implants in growing patients. This point has been, in most of dental articles, overlooked. This review, therefore, throws a deliberate sight on this point. Concluding this review, we are proposing a novel implant system that integrates materials science and up-dated surface technology to improve dental implant systems exhibiting bio- and mechano-functionalities.

In vitro cellular response and in vivo primary osteointegration of electrochemically modified titanium

Anodic spark deposition (ASD) is an attractive technique for improving the implant-bone interface that can be applied to titanium and titanium alloys. This technique produces a surface with microporous morphology and an oxide layer enriched with calcium and phosphorus. The aim of the present study was to investigate the biological response in vitro using primary human osteoblasts as a cellular model and the osteogenic primary response in vivo within a short experimental time frame (2 and 4 weeks) in an animal model (rabbit). Responses were assessed by comparing the new electrochemical biomimetic treatments to an acid-etching treatment as control. The in vitro biological response was characterized by cell morphology, adhesion, proliferation activity and cell metabolic activity. A complete assessment of osteogenic activity in vivo was achieved by estimating static and dynamic histomorphometric parameters at several time points within the considered time frame. The in vitro study showed enhanced osteoblast adhesion and higher metabolic activity for the ASD-treated surfaces during the first days after seeding compared to the control titanium. For the ASD surfaces, the histomorphometry indicated a higher mineral apposition rate within 2 weeks and a more extended bone activation within the first week after surgery, leading to more extensive bone-implant contact after 2 weeks. In conclusion, the ASD surface treatments enhanced the biological response in vitro, promoting an early osteoblast adhesion, and the osteointegrative properties in vivo, accelerating the primary osteogenic response.

Increased Biocompatibility and Bioactivity after Energetic PVD Surface Treatments

Ion implantation, a common technology in semiconductor processing, has been applied to biomaterials since the 1960s. Using energetic ion bombardment, a general term which includes conventional ion implantation plasma immersion ion implantation (PIII) and ion beam assisted thin film deposition, functionalization of surfaces is possible. By varying and adjusting the process parameters, several surface properties can be attuned simultaneously. Extensive research details improvements in the biocompatibility, mainly by reducing corrosion rates and increasing wear resistance after surface modification. Recently, enhanced bioactivity strongly correlated with the surface topography and less with the surface chemistry has been reported, with an increased roughness on the nanometer scale induced by self-organisation processes during ion bombardment leading to faster cellular adhesion processes.

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.

Effect of passivation and surface modification on the dissolution behavior and nano-surface characteristics of Ti-6Al-4V in Hank/EDTA solution

The aim of the present study was to investigate the effects of passivation treatment (34% nitric acid passivation, 400 ( composite function)C heated in air, and aged in 100 ( composite function)C de-ionized water) and surface modification (2 hr and 8 hr vacuum-brazed treatments) on the ion dissolution and nano-surface characteristics of Ti-6Al-4V exposed in Hank's solution with 8.0 mM ethylene diamine tetra-acetic acid (EDTA) at 37 ( composite function)C. The results indicated that the original nano-surface characteristics and microstructure would influence the ion dissolution but not change the capability of the Ca and P adsorption upon immersion. Of the three passivated treatments, 400 ( composite function)C thermal treatment for both 2 hr brazed Ti-6Al-4V (B2) and 8 hr brazed Ti-6Al-4V (B8) exhibits a substantial reduction in the constituent release compared to the acid passivated and water aged treatment, because the thicker thickness and rutile structure of surface oxide could provide the better dissolution resistance for 400 ( composite function)C-treated specimens. Moreover, the reduced Ti(2)Cu and increased alpha -titanium structure in B8 specimen could also improve ion dissolution resistance in comparison with B2 specimen. After soaking in Hank/EDTA solution, the adsorbed non-elemental Ca and P for all groups of specimens were observed by XPS analysis, and the AES depth-profile analysis indicate that the oxide films of all groups of specimens thicken with the longer immersion periods. The increasing oxide thickness may be the factor in the improved dissolution resistance at the longer immersion periods. The relation between lower dissolution rate and thicker oxide films were observed for all groups of specimens. The results suggest that the dissolution kinetics was governed by the metal ion transport through the oxide film in this study.

Concentration-dependent effects of titanium and aluminium ions released from thermally oxidized Ti6Al4V alloy on human osteoblasts

Thermal oxidation treatments of Ti6Al4V, at 500 and 700 degrees C, for 1 h result in the formation of an outer "ceramic" layer of rutile, which enhances osteoblast response. In the present study, we have measured in vitro Ti and Al ion release from Ti64 alloy in the as-received state and after thermal oxidation treatments at 500 or 700 degrees C, to culture medium under standard cell-culture conditions. Concentrations of both Ti and Al released from both thermal oxidation treatments were lower than from polished alloy. Al was released from the treated or untreated surfaces in substantially lower extent than Ti. Titanium and aluminium ions affected primary human osteoblast proliferation, metabolic activity, and differentiation in a dose-dependent manner. Treatments with individual Ti or Al metal ions in similar concentration ranges than released from the surfaces did not alter osteoblast response, which also remained unaffected after treatments with combinations of Ti plus Al applied in the proportional relations than detected in ion-release experiments. We then selected higher concentrations of Ti that impaired osteoblast proliferation and differentiation, while the proportional lower concentrations of Al did not alter osteoblast behavior. In spite of its inert character, it was found that Al significantly enhanced the deleterious effect of Ti on osteoblast differentiation. Therefore, thermal oxidation treatments of Ti6Al4V alloy may improve the biocompatibility of the alloy by reducing both Ti and Al release, and thus attenuating ion-mediated interference with osteoblast differentiation.

Decreased bacterial adhesion to surface-treated titanium

Osteointegrative dental implants are widely used in implantology for their well-known excellent performance once implanted in the host. Remarkable bacterial colonization along the transgingival region may result in a progressive loss of adhesion at gum-implant interface and an increase of the bone area exposed to pathogens. This phenomenon may negatively effect the osteointegration process and cause, in the most severe cases, implant failure. The presence of bacteria at implant site affect the growth of new bone tissue and consequently, the achievement of a mechanically stable bone-implant interface, key parameters for a suitable implant osteointegration. In the present work, a novel surface treatment has been developed and optimized in order to convert the amorphous titanium oxide in a crystalline layer enriched in anatase capable of providing not only antibacterial properties but also of stimulating the precipitation of apatite when placed in simulated body fluid. The collected data have shown that the tested treatment results in a crystalline anatase-type titanium oxide layer able to provide a remarkable decrease in bacterial attachment without negatively effecting cell metabolic activity. In conclusion, the surface modification treatment analyzed in the present study might be an elegant way to reduce the risk of bacterial adhesion and increase the lifetime of the transgingival component in the osteointegrated dental implant.

Surface properties and cell response of low metal ion release Ti-6Al-7Nb alloy after multi-step chemical and thermal treatments

Ti-6Al-7Nb samples treated by innovative multi-step chemical and thermal processes were characterized in order to evaluate their surface properties and cell interaction. The main object was to asses if the treatments were effective in order to obtain a surface presenting at the same time bone-like apatite induction ability, low metal ion release, good cell response and high protein binding. The morphology, crystallographic structure, porosity and wettability of the treated materials were investigated, as well as their interaction with simulated body fluid during soaking for different times. Cytotoxicity, protein adsorption tests and in vitro fibroblast and osteoblast-like cell cultures were also performed.

Characterization of surface modified Ti-6Al-7Nb alloy

In the last years different types of surface modifications were developed with the aim of improving the osteointegration ability of titanium alloys. The chemical composition, crystallographic structure and morphology of a surface layer can be modified in order to obtain a better interaction between the implant, the cells and the organic fluids. The final goal is to obtain a more efficient bone growth also in critical clinical cases. In the present paper were reported several data about the characterization of the Ti-6Al-7Nb alloy treated by two innovative surface treatments. They consist of blasting, followed by a two step chemical etching and heat treatment performed in air or in vacuum. TEM, XRD and SEM investigations were performed in order to assess the structure and morphology of the modified surfaces. The surface chemical composition was investigated by XPS ad AES analyses. The ability to interact with physiological fluids was tested by immersion of the treated materials in an acellular simulated body fluid (SBF). Metal ion concentration analyses of the fluid and SEM observations of the samples were performed after different times of soaking. The mechanical characterization involved scratch and fatigue tests. The surface of treated samples shows chemical, structural and morphological modifications. The passivation pre-treatment has influence on the surface modification. The treated samples evidenced a quite low metal ion release and interact with SBF solution, showing a moderate bioactivity. A relevant decrease in fatigue strength was observed on modified samples.

Comparison of metal release from various metallic biomaterials in vitro

To investigate the metal release of each base and alloying elements in vitro, SUS316L stainless steel, Co-Cr-Mo casting alloy, commercially pure Ti grade 2, and Ti-6Al-4V, V-free Ti-6Al-7Nb and Ti-15Zr-4Nb-4Ta alloys were immersed in various solutions, namely, alpha-medium, PBS(-), calf serum, 0.9% NaCl, artificial saliva, 1.2 mass% L-cysteine, 1 mass% lactic acid and 0.01 mass% HCl for 7d. The difference in the quantity of Co released from the Co-Cr-Mo casting alloy was relatively small in all the solutions. The quantities of Ti released into alpha-medium, PBS(-), calf serum, 0.9% NaCl and artificial saliva were much lower than those released into 1.2% L-cysteine, 1% lactic acid and 0.01% HCl. The quantity of Fe released from SUS316L stainless steel decreased linearly with increasing pH. On the other hand, the quantity of Ti released from Ti materials increased with decreasing pH, and it markedly attenuated at pHs of approximately 4 and higher. The quantity of Ni released from stainless steel gradually decreased with increasing pH. The quantities of Al released from the Ti-6Al-4V and Ti-6Al-7Nb alloys gradually decreased with increasing pH. A small V release was observed in calf serum, PBS(-), artificial saliva, 1% lactic acid, 1.2% l-cysteine and 0.01% HCl. The quantity of Ti released from the Ti-15Zr-4Nb-4Ta alloy was smaller than those released from the Ti-6Al-4V and Ti-6Al-7Nb alloys in all the solutions. In particular, it was approximately 30% or smaller in 1% lactic acid, 1.2% L-cysteine and 0.01% HCl. The quantity of (Zr + Nb + Ta) released was also considerably lower than that of (Al + Nb) or (Al + V) released. Therefore, the Ti-15Zr-4Nb-4Ta alloy with its low metal release in vitro is considered advantageous for long-term implants.

Einfluss einer TiO2-Beschichtung auf Biokompatibilität, Korrosionsund Auslaugverhalten verschiedener Implantatlegierungen / Corrosion behaviour, metal release and biocompatibility of implant materials coated by TiO2-sol gel chemistry

Alloys based on titanium or cobalt have been used as implant materials for decades with good success. Because of their natural oxide layer these alloys reveal good corrosion behaviour. In contact with physiological solution metal release takes place, which can cause inflammation. Coatings can improve the corrosion behaviour. In this study Ti6Al4V and Co28Cr6Mo alloys, which are frequently used as implant materials, were tested. Polished discs of these alloys and polished discs, which were coated with TiO2-layers by sol-gel chemistry, were compared regarding their corrosion behaviour and metal ion releasing. The releasing of Al, V, Ti, Co, Cr and Mo was quantified by ICP-MS analysis. The TiO2-coating reduced the release of all ions except of the Al-ion. Both alloys showed a deviating kinetic of ion releasing. In addition, cell response (cell vitality, cell proliferation, endothelial marker CD31 and actin allocation) of osteoblasts and endothelial cells were investigated.

Attachment and proliferation of neonatal rat calvarial osteoblasts on Ti6Al4V: effect of surface chemistries of the alloy

This study examined the cell attachment and proliferation of neonatal rat calvarial osteoblasts on Ti6Al4V alloy as affected by the surface modifications. The modifications could alter simultaneously the surface chemistries of the alloy (elemental difference of Ti, Al, V, Cu and Ni about 300-600mum thick examined by EDS) as well as the XPS nano-surface characteristics of oxides on the metal surface (chemistries of oxides, amphoteric OH group adsorbed on oxides, and oxide thickness). Three materials including two from modifications and a control were examined. It is argued that a slight change of the nano-surface characteristics of oxides as a result of the modifications neither alters the in vitro capability of Ca and P ion adsorption nor affects the metal ion dissolution behavior of the alloy. This implies that any influence on the cytocompatibility of the materials should only be correlated to the effect of surface chemistries of the alloy and the associated metal ion dissolution behavior of the alloy. The experimental results suggest that the cell response of neonatal rat calvarial osteoblasts on the Ti6Al4V alloy should neither be affected by the variation of surface chemistries of the alloy in a range studied.

Effect of chemical etching and aging in boiling water on the corrosion resistance of Nitinol wires with black oxide resulting from manufacturing process

The effect of chemical etching in a HF/HNO(3) acid solution and aging in boiling water on the corrosion resistance of Nitinol wires with black oxide has been evaluated with the use of potentiodynamic, modified potentiostatic ASTM F746, and scratch tests. Scanning-electron microscopy, elemental XPS, and Auger analysis were employed to characterize surface alterations induced by surface treatment and corrosion testing. The effect of aging in boiling water on the temperatures of martensitic transformations and shape recovery was evaluated by means of measuring the wire electroresistance. After corrosion tests, as-received wires revealed uniformly cracked surfaces reminiscent of the stress-corrosion-cracking phenomenon. These wires exhibited negative breakdown potentials in potentiostatic tests and variable breakdown potentials in potentiodynamic tests (- 100 mV to + 400 mV versus SCE). Wires with treated surfaces did not reveal cracking or other traces of corrosion attacks in potentiodynamic tests up to + 900-1400-mV potentials and no pitting after stimulation at + 800 mV in potentiostatic tests. They exhibited corrosion behavior satisfactory for medical applications. Significant improvement of corrosion parameters was observed on the reverse scans in potentiodynamic tests after exposure of treated wires to potentials > 1000 mV. In scratch tests, the prepared surfaces repassivated only at low potentials, comparable to that of stainless steel. Tremendous improvement of the corrosion behavior of treated Nitinol wires is associated with the removal of defect surface material and the growth of stable TiO(2) oxide. The role of precipitates in the corrosion resistance of Nitinol-scratch repassivation capacity in particular-is emphasized in the discussion.

Detachment of titanium and fluorohydroxyapatite particles in unloaded endosseous implants

The shape, surface composition and morphology of orthopaedic and endosseous dental titanium implants are key factors to achieve post-surgical and long-term mechanical stability and enhance implant osteointegration. In this study a comparison was made between 12 titanium screws, plasma-spray-coated with titanium powders (TPS), and 12 screws with an additional coating of fluorohydroxyapatite (FHA-Ti). Screws were implanted in the femoral and tibial diaphyses of two mongrel sheep and removed with peri-implant tissues 12 weeks after surgery. The vibrational spectroscopic, ultrastructural and morphological analyses showed good osteointegration for both types of implants in host cortical bone. The portion of the FHA-Ti implants in contact with the medullary canal showed a wider area of newly formed peri-implant bone than that of the TPS implants. Morphological and EDAX analyses demonstrated the presence of small titanium debris in the bone medullary spaces near the TPS surface, presumably due to the friction between the host bone and the implant during insertion. Few traces of titanium were detected around FHA-Ti implants, even if smaller FHA debris were present. The present findings suggest that the FHA coating may act as a barrier against the detachment of titanium debris stored in the medullary spaces near the implant surface.

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.

Large-scale gene expression analysis of osteoblasts cultured on three different Ti-6Al-4V surface treatments

To improve implant biocompatibility, we developed a simple cost-effective thermal surface treatment allowing an increase in the oxide layer thickness of a titanium (Ti) alloy used in orthopaedic implants. The goal of this study was to test in vitro the reaction of osteoblasts to the developed surface treatment and to compare it to the osteoblast reaction to two other surface treatments currently used in the practice of implant surgery. Quantification of osteoblast gene expression on a large scale was used in this study. The kinetics of gene expression over 120 h was followed for 58 genes to quantify the effect of the developed surface treatment. Twenty eight genes were further selected to compare the effects of surface treatments on osteoblasts. Based on the genes studied, we could propose a general pathway for the cell reaction according to the surface treatments used: (1) metal ion release changes the time course of gene expression in the FAK pathway; (2) once the accumulation of metal ions released from the Ti surface exceeds a threshold value, cell growth is diminished and apoptosis may be activated; (3) PTK up-regulation is also induced by metal ion release; (4) the expression of Bcl-2 family and Bax may suggest that metal ions induce apoptosis. The developed treatment seems to increase the Ti-6Al-4V biocompatibility as highlighted by the lower impact of this treatment by the different pathways studied, on the lower inflammatory reaction that could be induced, as well as by the lower induced osteoblast apoptosis compared to the two other surface treatments.

Ultra high-resolution fMRI in monkeys with implanted RF coils

Spatiotemporally resolved functional MRI (fMRI) in animals can reveal how wide-spread neural networks are organized and accompanying electrophysiological recordings can show how small neural assemblies contribute to this organization. Here we present a novel technique that yields high-resolution structural and functional images of the monkey brain with small, tissue-compatible, intraosteally implantable radiofrequency coils. Voxel sizes as small as 0.0113 microl with high signal-to-noise and contrast-to-noise ratios were obtained, revealing both structural and functional cortical architecture in great detail. Up to a certain point, contrast sensitivity increased with decreasing voxel size, probably because of the decreased partial volume effects. Spatial specificity was demonstrated by the lamina-specific activation in experiments comparing responses to moving and flickering stimuli. The implications of this technique for combined fMRI/electrophysiology experiments and its limitations in terms of spatial coverage are discussed.