Tribological behaviour of Ti or Ti alloy vs. zirconia in presence of artificial saliva

Abutment is the transmucosal component in a dental implant system and its eventual appearance has a major impact on aesthetics: use of zirconia abutments can be greatly advantageous in avoiding this problem. Both in the case of one and two-piece zirconia abutments, a critical issue is severe wear between the zirconia and titanium components. High friction at this interface can induce loosening of the abutment connection, production of titanium wear debris, and finally, peri-implant gingivitis, gingival discoloration, or marginal bone adsorption can occur. As in vivo wear measurements are highly complex and time-consuming, wear analysis is usually performed in simulators in the presence of artificial saliva. Different commercial products and recipes for artificial saliva are available and the effects of the different mixtures on the tribological behaviour is not widely explored. The specific purpose of this research was to compare two types of artificial saliva as a lubricant in titanium-zirconia contact by using the ball on disc test as a standard tribological test for materials characterisation. Moreover, a new methodology is suggested by using electrokinetic zeta potential titration and contact angle measurements to investigate the chemical stability at the titanium-lubricant interface. This investigation is of relevance both in the case of using zirconia abutments and artificial saliva against chronic dry mouth. Results suggest that an artificial saliva containing organic corrosion inhibitors is able to be firmly mechanically and chemically adsorb on the surface of the Ti c.p. or Ti6Al4V alloy and form a protective film with high wettability. This type of artificial saliva can significantly reduce the friction coefficient and wear of both the titanium and zirconia surfaces. The use of this type of artificial saliva in standard wear tests has to be carefully considered because the wear resistance of the materials can be overestimated while it can be useful in some specific clinical applications. When saliva is free from organic corrosion inhibitors, wear occurs with a galling mechanism. The occurrence of a super-hydrophilic saliva film that is not firmly adsorbed on the surface is not efficient in order to reduce wear. The results give both suggestions about the experimental conditions for lab testing and in vivo performance of components of dental implants when artificial saliva is used

Interactions Between the Physiological Environment and Titanium-Based Implant Materials: From Understanding to Control

Titanium and titanium alloys are widely used in different biomedical applications owing to their high biocompatibility, high corrosion resistance, good mechanical properties, and good osseointegration ability. Titanium and its alloys rapidly form a surface oxide layer in air and aqueous environments. This passive and thin (a few nanometers) surface oxide hinders active corrosion and ensures a low metal ion release, enhancing biocompatibility. Compared to that of other biomedical alloys, this surface oxide is exceptionally resistant to chemical attack by halides, primarily chlorides; the presence of fluorides can, in some cases, result in localized corrosion of titanium and its alloys. However, the combination of proteins, inflammatory conditions and bacteria, which for instance generate hydrogen peroxide, can result in a reduction of the corrosion resistance of titanium-based materials. Titanium and its alloying elements, such as aluminum and vanadium, can then be released as ions, which might trigger an immune system response and reduce biocompatibility. Several surface modifications have been proposed in order to improve the bone-bonding ability of titanium and its alloys, facilitate the healing process, and enhance the success of the implant with a decreased risk of micromotions. Moreover, antimicrobial ions/nanoparticles can be added to the surface to reduce the infection risk. Surface modification of titanium (e.g., with artificially grown, micrometer-thick, titanium oxide layers) can significantly increase the corrosion resistance under critical conditions (e.g., inflammatory response and infection); however, the surfaces are not completely inert and the effect of metal ion/nanoparticle release should be carefully taken into account. This chapter reviews and discusses the current strategies for modifying and controlling the surface of titanium-based implant materials, with particular focus on corrosion resistance, bone integration, inflammatory and infection control, and interactions with the physiological environment

Electron beam structuring of Ti6Al4V: New insights on the metal surface properties influencing the bacterial adhesion

Soft tissue adhesion and infection prevention are currently challenging for dental transmucosal or percutaneous orthopedic implants. It has previously been shown that aligned micro-grooves obtained by Electron Beam (EB) can drive fibroblast alignment for improved soft tissue adhesion. In this work, evidence is presented that the same technique can also be effective for a reduction of the infection risk. Grooves 10-30 \u3bcm wide and around 0.2 \u3bcm deep were obtained on Ti6Al4V by EB. EB treatment changes the crystalline structure and microstructure in a surface layer that is thicker than the groove depth. Unexpectedly, a significant bacterial reduction was observed. The surfaces were characterized by field emission scanning electron microscopy, X-ray diffraction, confocal microscopy, contact profilometry, wettability and bacterial adhesion tests. The influence of surface topography, microstructure and crystallography on bacterial adhesion was systematically investigated: it was evidenced that the bacterial reduction after EB surface treatment is not correlated with the grooves, but with the microstructure induced by the EB treatment, with a significant bacterial reduction when the surface microstructure has a high density of grain boundaries. This correlation between microstructure and bacterial adhesion was reported for the first time for Ti alloys

Magnetic-Oriented Nickel Particles and Nickel-Coated Carbon Nanotubes: An Efficient Tool for Enhancing Thermal Conductivity of PDMS Composites

In this study, PDMS composites are thermally cured with nickel particles and nickel-coated carbon nanotubes as fillers. Both fillers are oriented with the aim to increase the thermal conductivity of the silicone polymer network, due to the formation of a continuous thermal path. Scanning electron microscopy (SEM) gives a picture of the polymer network's morphology, proving the effective alignment of the nickel particles. Rheology and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) studies confirm the full curing of the silicon network and no influence in the curing kinetics of the type and content of fillers and their orientation. Dynamic mechanical thermal analysis (DMTA) and tensile analysis show instead different thermo-mechanical behavior of the polymer network due to the presence of different fillers, different fillers percentage, and orientation. Finally, the thermal transmittance coefficient (k) is studied by means of hot disk analysis, revealing the increment of almost 200% due to magnetic filler orientation

Competitive surface colonization of antibacterial and bioactive materials doped with strontium and/or silver ions

Nowadays, there is a large amount of research aimed at improving the multifunctional behavior of the biomaterials for bone contact, including the concomitant ability to induce apatite formation (bioactivity), fast and effective osteoblasts colonization, and antibacterial activity. The aim of this study is to develop antibacterial and bioactive surfaces (Ti6Al4V alloy and a silica-based bioactive glass) by chemical doping with strontium and/or silver ions. The surfaces were characterized by Scanning Electron Microscopy equipped with Energy Dispersive X ray Spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and Transmission Electron Microscopy (TEM). To better focus on the cells–bacteria competition for the implant surface, in addition to the standard assays for the evaluation of the bacteria adhesion (ISO22196) and for single-cell cultures or biofilm formation, an innovative set of co-cultures of cells and bacteria is here proposed to simulate a competitive surface colonization. The results suggest that all the bioactive tested materials were cytocompatible toward the bone progenitor cells representative for the self-healing process, and that the doped ones were effective in reducing the surface colonization from a pathogenic drug-resistant strain of Staphylococcus aureus. The co-cultures experiments demonstrated that the doped surfaces were able to protect the adhered osteoblasts from the bacteria colonization as well as prevent the infection prior to the surface colonization by the osteoblasts

Bioactive materials: In vitro investigation of different mechanisms of hydroxyapatite precipitation

Abstract Bioactive materials, able to induce hydroxyapatite precipitation in contact with body fluids, are of great interest for their bone bonding capacity. . The aim of this paper is to compare bioactive materials with different surface features to verify the mechanisms of action and the relationship with kinetics and type of precipitated hydroxyapatite over time. Four different surface treatments for Ti/Ti6Al4V alloy and a bioactive glass were selected and a different mechanism of bioactivity is supposed for each of them. Apart from the conventional techniques (FESEM, XPS and EDX), less common characterizations (zeta potential measurements on solid surfaces and FTIR chemical imaging) were applied. The results suggest that the OH groups on the surface have several effects: the total number of the OH groups mainly affects hydrophilicity of surfaces, while the isoelectric points, surface charge and ions attraction mainly depend on OH acidic/basic strength. Kinetics of hydroxyapatite precipitation is faster when it involves a mechanism of ion exchange while it is slower when it is due to electrostatic effects . The electrostatic effect cooperates with ion exchange and it speeds up kinetics of hydroxyapatite precipitation. Different bioactive surfaces are able to differently induce precipitation of type A and B of hydroxyapatite, as well as different degrees of crystallinity and carbonation. Statement of significance The bone is made of a ceramic phase (a specific type of hydroxyapatite), a network of collagen fibers and the biological tissue. A strong bond of an orthopedic or dental implant with the bone is achieved by bioactive materials where precipitation and growth of hydroxyapatite occurs on the implant surface starting from the ions in the physiological fluids. Several bioactive materials are already known and used, but their mechanism of action is not completely known and the type of precipitated hydroxyapatite not fully investigated. In this work, bioactive titanium and bioglass surfaces are compared through conventional and innovative methodologies. Different mechanisms of bioactivity are identified, with different kinetics and the materials are able to induce precipitation of different types of hydroxyapatite, with different degree of crystallinity and carbonation

Surface modification of silicate, borosilicate and phosphate bioactive glasses to improve/control protein adsorption: PART I

Bioactive glasses (BGs) are promising for bone tissue regeneration. BG composition can be tailored, according to the application of interest, and/or functionalized with organic molecules/biomolecules to improve their performances. However, despite the wide knowledge concerning BGs, their interaction with proteins, fundamental for controlling the fate of the implant, has not been deeply investigated yet. Controlling or predicting protein adsorption requires a full understanding of the materials surface physico-chemical properties. In this work, four different BGs (S53P4, B25, SCNB, PhGlass) were surface-modified by four different treatments: 72 h-soaking in TRIS, 72 h soaking in simulated body fluid, APTES grafting and quaternized APTES grafting. The surfaces were then characterized both untreated and after each treatment by contact angle, zeta potential analysis, X-ray photoelectron spectroscopy, Fourier Transform InfraRed–Attenuated Total Reflectance spectroscopy and Scanning Electron Microscopy and Energy Dispersive Spectroscopy. Inductively Coupled Plasma – Optical Emission Spectrometry was then performed to investigate the ion leaching. The aim of this study (Part I) is the physico-chemical characterization of BGs as a function of the implemented treatments, aiming to better understand how the superficial properties are successively affecting protein adsorption. Protein adsorption on untreated and treated BGs will be discussed in a following manuscript (Part II)

Advanced characterization of albumin adsorption on a chemically treated surface for osseointegration: An innovative experimental approach

Surface chemistry, charge, wettability, and roughness affect the adsorbed protein layer, influencing biocompatibility and functionality of implants. Material engineering seeks innovative, sensitive, and reliable characterization techniques for study the adsorbed proteins. These techniques must be suitable to be directly used on the surfaces of clinical interest. In this paper, the characterization of surfaces with topography and chemistry developed for osseointegration is performed by innovative surface analysis techniques to investigate the properties of adsorbed bovine serum albumin. Ti6Al4V alloy chemically treated with an oxidative process to obtain peculiar surface features (roughness and surface hydroxylation) was tested and compared with mirror-polished titanium. Albumin forms a continuous layer on both Ti surfaces when adsorbed from near physiological concentrations, as proved by Kelvin force probe microscopy. It was observed that the hydroxylation degree plays a pivotal role in determining the conformation of proteins after adsorption, where it strongly drives protein unfolding, as confirmed by Surface Enhanced Raman scattering, and in influencing the mechanism and chemical stability of protein-surface interactions, which was highlighted by zeta potential titration curves