Human T-Cell Responses to Metallic Ion-Doped Bioactive Glasses

Biomaterials are extensively used as replacements for damaged tissue with bioactive glasses standing out as bone substitutes for their intrinsic osteogenic properties. However, biomaterial implantation has the following risks: the development of implant-associated infections and adverse immune responses. Thus, incorporating metallic ions with known antimicrobial properties can prevent infection, but should also modulate the immune response. Therefore, we selected silver, copper and tellurium as doping for bioactive glasses and evaluated the immunophenotype and cytokine profile of human T-cells cultured on top of these discs. Results showed that silver significantly decreased cell viability, copper increased the T helper (Th)-1 cell percentage while decreasing that of Th17, while tellurium did not affect either cell viability or immune response, as evaluated via multiparametric flow cytometry. Multiplex cytokines assay showed that IL-5 levels were decreased in the copper-doped discs, compared with its undoped control, while IL-10 tended to be lower in the doped glass, compared with the control (plastic) while undoped condition showed lower expression of IL-13 and increased MCP-1 and MIP-1β secretion. Overall, we hypothesized that the Th1/Th17 shift, and specific cytokine expression indicated that T-cells might cross-activate other cell types, potentially macrophages and eosinophils, in response to the scaffolds.

Anticorrosion and Antimicrobial Tannic Acid-Functionalized Ti-Metallic Glass Ribbons for Dental Abutment

In this study, a recently reported Ti-based metallic glass (MG), without any toxic element, but with a significant amount of metalloid (Si-Ge-B, 18 atom %) and minor soft element (Sn, 2 atom %), was produced in ribbon form using conventional single-roller melt-spinning. The produced Ti60Zr20Si8Ge7B3Sn2 ribbons were investigated by differential scanning calorimetry and X-ray diffraction to confirm their amorphous structure, and their corrosion properties were further investigated by open-circuit potential and cyclic polarization tests. The ribbon's surface was functionalized by tannic acid, a natural plant-based polyphenol, to enhance its performance in terms of corrosion prevention and antimicrobial efficacy. These properties can potentially be exploited in the premucosal parts of dental implants (abutments). The Folin and Ciocalteu test was used for the quantification of tannic acid (TA) grafted on the ribbon surface and of its redox activity. Fluorescent microscopy and ζ-potential measurements were used to confirm the presence of TA on the surfaces of the ribbons. The cytocompatibility evaluation (indirect and direct) of TA-functionalized Ti60Zr20Si8Ge7B3Sn2 MG ribbons toward primary human gingival fibroblast demonstrated that no significant differences in cell viability were detected between the functionalized and as-produced (control) MG ribbons. Finally, the antibacterial investigation of TA-functionalized samples against Staphylococcus aureus demonstrated the specimens' antimicrobial properties, shown by scanning electron microscopy images after 24 h, presenting a few single colonies remaining on their surfaces. The thickness of bacterial aggregations (biofilm-like) that were formed on the surface of the as-produced samples reduced from 3.5 to 1.5 μm.

Nano-topography and functionalization with the synthetic peptoid GN2-Npm9 as a strategy for antibacterial and biocompatible titanium implants

In recent years, antimicrobial peptides (AMPs) have attracted great interest in scientific research, especially for biomedical applications such as drug delivery and orthopedic applications. Since they are readily degradable in the physiological environment, scientific research has recently been trying to make AMPs more stable. Peptoids are synthetic N-substituted glycine oligomers that mimic the structure of peptides. They have a structure that does not allow proteolytic degradation, which makes them more stable while maintaining microbial activity. This structure also brings many advantages to the molecule, such as greater diversity and specificity, making it more suitable for biological applications. For the first time, a synthesized peptoid (GN2-Npm9) was used to functionalize a nanometric chemically pre-treated (CT) titanium surface for bone-contact implant applications. A preliminary characterization of the functionalized surfaces was performed using the contact angle measurements and zeta potential titration curves. These preliminary analyses confirmed the presence of the peptoid and its adsorption on CT. The functionalized surface had a hydrophilic behaviour (contact angle = 30°) but the hydrophobic tryptophan-like residues were also exposed. An electrostatic interaction between the lysine residue of GN2-Npm9 and the surface allowed a chemisorption mechanism. The biological characterization of the CT_GN2-Nmp9 surfaces demonstrated the ability to prevent surface colonization and biofilm formation by the pathogens Escherichia coli and Staphylococcus epidermidis thus showing a broad-range activity. The cytocompatibility was confirmed by human mesenchymal stem cells. Finally, a bacteria-cells co-culture model was applied to demonstrate the selective bioactivity of the CT_GN2-Nmp9 surface that was able to preserve colonizing cells adhered to the device surface from bacterial infection.

Ce-doped MgO films on AZ31 alloy substrate for biomedical applications: preparation, characterization and testing

Magnesium ions, MgO nanoparticles and thin films, magnesium alloys and cerium compounds are materials intensively studied due to their corrosion protection, antibacterial and pharmacological properties. In this work, we have designed, prepared and investigated, novel thin films of MgO doped with cerium, deposited on Mg alloy (AZ31) for temporary implants, in order to enhance their life time. More precisely, we report on microstructure and corrosion behavior of MgO pure and doped with 0.1 at % Ce films, fabricated by sol-gel route coupled with spin-coating technique, on AZ31 alloy substrate. A modified sol-gel method that start from magnesium acetylacetonate, cerium nitrate and 2-methoxyethanol (as a stabilizer for the sol) was been used successfully for cerium doped MgO sol precursor preparation. The structure and morphology of the surface of the coatings, before and after immersion for 7-30 d in Hank's solution at 37 °C, were characterized by x-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscope, x-ray photoelectron spectroscopy and Fourier infrared transmittance spectrum (FT-IR). A comparison between the corrosion protection of undoped MgO and MgO doped with 0.1 at % Ce coatings on the AZ31 alloy substrate is performed by electrochemical tests and immersion tests using open circuit potential and electrochemical impedance spectroscopy in Hank's solution, at 37 °C. The electrochemical results showed that the protection of the AZ31 alloy substrate against corrosion was better with the doped with 0.1 at % Ce MgO film deposited than with pure MgO coting. The investigations of the films after immersion in Hank's solution, at 37 °C, for 7, 21 and 30 d indicated that the grown layer on the film is bone like apatite that suggests a good bioactivity of 0.1 at % Ce-doped MgO coating. Our work demonstrates that the performance corrosion protection of the biodegradable magnesium alloys used for orthopedic applications, in simulated physiological environments (Hank and Ringer) can be enhanced through coating with Ce3+doped MgO sol-gel thin film.

Characterization of Tannic Acid-Coated AZ31 Mg Alloy for Biomedical Application and Comparison with AZ91

Magnesium alloys are promising materials for bioresorbable implants that will improve patient life and reduce healthcare costs. However, their clinical use is prevented by the rapid degradation and corrosion of magnesium, which leads to a fast loss of mechanical strength and the formation of by-products that can trigger tissue inflammation. Here, a tannic acid coating is proposed to control the degradation of AZ31 and AZ91 alloys, starting from a previous study by the authors on AZ91. The coatings on the two materials were characterized both by the chemical (EDS, FTIR, XPS) and the morphological (SEM, confocal profilometry) point of view. Static degradation tests in PBS and electrochemical measurements in different solutions showed that the protective performances of the tannic acid coatings are strongly affected by the presence of cracks. The presence of fractures in the protective layer generates galvanic couples between the coating scales and the metal, worsening the corrosion resistance. Although degradation control was not achieved, useful insights on the degradation mechanisms of coated Mg surfaces were obtained, as well as key points for future studies: it resulted that the absence of cracks in protective coatings is of uttermost importance for novel biodegradable implants with proper degradation kinetics.

Deposition of Antioxidant and Cytocompatible Caffeic Acid-Based Thin Films onto Ti6Al4V Alloys through Hexamethylenediamine-Mediated Crosslinking

A promising approach for advanced bone implants is the deposition on titanium surfaces of organic thin films with improved therapeutic performances. Herein, we reported the efficient dip-coating deposition of caffeic acid (CA)-based films on both polished and chemically pre-treated Ti6Al4V alloys by exploiting hexamethylenediamine (HMDA) crosslinking ability. The formation of benzacridine systems, resulting from the interaction of CA with the amino groups of HMDA, as reported in previous studies, was suggested by the yellow/green color of the coatings. The coated surfaces were characterized by means of the Folin-Ciocalteu method, fluorescence microscopy, water contact angle measurements, X-ray photoelectron spectroscopy (XPS), zeta-potential measurements, and Fourier transform infrared spectroscopy, confirming the presence of a uniform coating on the titanium surfaces. The optimal mechanical adhesion of the coating, especially on the chemically pre-treated substrate, was also demonstrated by the tape adhesion test. Interestingly, both films exhibited marked antioxidant properties (2,2-diphenyl-1-picrylhydrazyl and ferric reducing antioxidant power assays) that persisted over time and were not lost even after prolonged storage of the material. The feature of the coatings in terms of the exposed groups (XPS and zeta potential titration evidence) was apparently dependent on the surface pre-treatment of the titanium substrate. Cytocompatibility, scavenger antioxidant activity, and antibacterial properties of the developed coatings were evaluated. The most promising results were obtained in the case of the chemically pre-treated CA/HMDA-based coated surface that showed good cytocompatibility and high reactive oxygen species' scavenging ability, preventing their intracellular accumulation under pro-inflammatory conditions; moreover, an anti-fouling effect preventing the formation of 3D biofilm-like bacterial aggregates was observed by scanning electron microscopy. These results open new perspectives for the development of innovative titanium surfaces with thin coatings from naturally occurring phenols for bone contact implants.

Influence of a Physiologically Formed Blood Clot on Pre-Osteoblastic Cells Grown on a BMP-7-Coated Nanoporous Titanium Surface

Titanium (Ti) nanotopography modulates the osteogenic response to exogenous bone morphogenetic protein 7 (BMP-7) in vitro, supporting enhanced alkaline phosphatase mRNA expression and activity, as well as higher osteopontin (OPN) mRNA and protein levels. As the biological effects of OPN protein are modulated by its proteolytic cleavage by serum proteases, this in vitro study evaluated the effects on osteogenic cells in the presence of a physiological blood clot previously formed on a BMP-7-coated nanostructured Ti surface obtained by chemical etching (Nano-Ti). Pre-osteoblastic MC3T3-E1 cells were cultured during 5 days on recombinant mouse (rm) BMP-7-coated Nano-Ti after it was implanted in adult female C57BI/6 mouse dorsal dermal tissue for 18 h. Nano-Ti without blood clot or with blood clot at time 0 were used as the controls. The presence of blood clots tended to inhibit the expression of key osteoblast markers, except for Opn, and rmBMP-7 functionalization resulted in a tendency towards relatively greater osteoblastic differentiation, which was corroborated by runt-related transcription factor 2 (RUNX2) amounts. Undetectable levels of OPN and phosphorylated suppressor of mothers against decapentaplegic (SMAD) 1/5/9 were noted in these groups, and the cleaved form of OPN was only detected in the blood clot immediately prior to cell plating. In conclusion, the strategy to mimic in vitro the initial interfacial in vivo events by forming a blood clot on a Ti nanoporous surface resulted in the inhibition of pre-osteoblastic differentiation, which was minimally reverted with an rmBMP-7 coating.

Conferring Antioxidant Activity to an Antibacterial and Bioactive Titanium Surface through the Grafting of a Natural Extract

The main unmet medical need of bone implants is multifunctional activity, including their ability to induce rapid and physiological osseointegration, counteract bacterial biofilm formation, and prevent in situ chronic inflammation at the same time. This research starts from an already developed c.p. titanium surface with proven bioactive (in vitro hydroxyl apatite precipitation) and antibacterial activities, due to a calcium titanate layer with nano- and micro-scale roughness and loaded with iodine ions. Here, antioxidant ability was added to prevent chronic inflammation by grafting polyphenols of a green tea extract onto the surface, without compromising the other functionalities of the surface. The surface was characterized before and after functionalization through XPS analysis, zeta potential titrations, ion release measurements, in vitro bioactivity tests, SEM and fluorescence microscopy, and Folin-Ciocalteu and biological tests. The presence of grafted polyphenols as a homogeneous layer was proven. The grafted polyphenols maintained their antioxidant ability and were anchored to the surface through the linking action of Ca²⁺ ions added to the functionalizing solution. Iodine ion release, cytocompatibility towards human mesenchymal stem cells (hMSC), and antibacterial activity were maintained even after functionalization. The antioxidant ability of the functionalized surface was effective in preserving hMSC viability in a chemically induced pro-inflammatory environment, thus showing a scavenger activity towards toxic active species responsible for inflammation.

Surface Functionalization of Ti6Al4V-ELI Alloy with Antimicrobial Peptide Nisin

Implant-associated infections are a severe global concern, especially in the case of orthopedic implants intended for long-term or permanent use. The traditional treatment through systemic antibiotic administration is often inefficient due to biofilm formation, and concerns regarding the development of highly resistant bacteria. Therefore, there is an unfulfilled need for antibiotic-free alternatives that could simultaneously support bone regeneration and prevent bacterial infection. This study aimed to perform, optimize, and characterize the surface functionalization of Ti6Al4V-ELI discs by an FDA-approved antimicrobial peptide, nisin, known to hold a broad antibacterial spectrum. Accordingly, nisin bioactivity was also evaluated by in vitro release tests both in physiological and inflammatory pH conditions. Several methods, such as X-ray photoelectron spectroscopy (XPS), and Kelvin Probe atomic force microscopy confirmed the presence of a physisorbed nisin layer on the alloy surface. The functionalization performed at pH 6-7 was found to be especially effective due to the nisin configuration exposing its hydrophobic tail outwards, which is also responsible for its antimicrobial action. In addition, the first evidence of gradual nisin release both in physiological and inflammatory conditions was obtained: the static contact angle becomes half of the starting one after 7 days of soaking on the functionalized sample, while it becomes 0° on the control samples. Finally, the evaluation of the antibacterial performance toward the pathogen Staphylococcus aureus after 24 h of inoculation showed the ability of nisin adsorbed at pH 6 to prevent bacterial microfouling into biofilm-like aggregates in comparison with the uncoated specimens: viable bacterial colonies showed a reduction of about 40% with respect to the un-functionalized surface and the formation of (microcolonies (biofilm-like aggregates) is strongly affected.

UV-Cured Chitosan-Based Hydrogels Strengthened by Tannic Acid for the Removal of Copper Ions from Water

In this work, a new environmentally friendly material for the removal of heavy metal ions was developed to enhance the adsorption efficiency of photocurable chitosan-based hydrogels (CHg). The acknowledged affinity of tannic acid (TA) to metal ions was investigated to improve the properties of hydrogels obtained from natural and renewable sources (CHg-TA). The hydrogel preparation was performed via a simple two-step method consisting of the photocrosslinking of methacrylated chitosan and its subsequent swelling in the TA solution. The samples were characterized using ATR-FTIR, SEM, and Folin-Ciocalteu (F&C) assay. Moreover, the mechanical properties and the ζ potential of CHg and CHg-TA were tested. The copper ion was selected as a pollutant model. The adsorption capacity (Qe) of CHg and CHg-TA was assessed as a function of pH. Under acidic conditions, CHg-TA shows a higher Qe than CHg through the coordination of copper ions by TA. At an alkaline pH, the phenols convert into a quinone form, decreasing the Qe of CHg-TA, and the performance of CHg was found to be improved. A partial TA release can occur in the copper solution due to its high hydrophilicity and strong acidic pH conditions. Additionally, the reusability of hydrogels was assessed, and the high number of recycling cycles of CHg-TA was related to its high mechanical performance (compression tests). These findings suggest CHg-TA as a promising green candidate for heavy metal ion removal from acidic wastewater.

Effects of rmBMP-7 on Osteoblastic Cells Grown on a Nanostructured Titanium Surface

This study evaluates the effects of the availability of exogenous BMP-7 on osteoblastic cells’ differentiation on a nanotextured Ti surface obtained by chemical etching (Nano-Ti). The MC3T3-E1 and UMR-106 osteoblastic cell lines were cultured for 5 and 7 days, respectively, on a Nano-Ti surface and on a control surface (Control-Ti) in an osteogenic medium supplemented with either 40 or 200 ng/mL recombinant mouse (rm) BMP-7. The results showed that MC3T3-E1 cells exhibited distinct responsiveness when exposed to each of the two rmBMP-7 concentrations, irrespective of the surface. Even with 40 ng/mL rmBMP-7, important osteogenic effects were noticed for Control-Ti in terms of cell proliferation potential; Runx2, Osx, Alp, Bsp, Opn, and Smad1 mRNA expression; and in situ ALP activity. For Nano-Ti, the effects were limited to higher Alp, Bsp, and Opn mRNA expression and in situ ALP activity. On both surfaces, the osteogenic potential of UMR-106 cultures remained unaltered with 40 ng/mL rmBMP-7, but it was significantly reduced when the cultures were exposed to the 200 ng/mL concentration. The availability of rmBMP-7 to pre-osteoblastic cells at the concentrations used alters the expression profile of osteoblast markers, indicative of the acquisition of a more advanced stage of osteoblastic differentiation. This occurs less pronouncedly on the nanotextured Ti and without reflecting in higher mineralized matrix production by differentiated osteoblasts on both surfaces.

Functionalization with Polyphenols of a Nano-Textured Ti Surface through a High-Amino Acid Medium: A Chemical-Physical and Biological Characterization

The study aimed to identify an effective mechanism of adsorption of polyphenols on a nano-textured Ti surface and to evaluate the osteogenic differentiation on it. The source of polyphenols was a natural extract from red grape pomace. A chemical etching was used to form an oxide layer with a nanoscale texture on Ti; this layer is hydrophilic, but without hydroxyl groups with high acidic-basic chemical reactivity. The samples were characterized by electron and fluorescence microscopies, UV-Vis spectroscopy, contact angle measurements, zeta potential titration curves, and Folin-Ciocâlteu test. The presence of an adsorbed layer of polyphenols on the functionalized surface, maintaining redox ability, was confirmed by several tests. Consistent with the surface features, the adsorption was maximized by dissolving the extract in a high-amino acid medium, with respect to an inorganic solution, exploiting the high affinity of amino acids for polyphenols and for porous titanium surfaces. The osteogenic differentiation was assessed on an osteoblastic cell line by immunofluorescence, cell viability, expression of key osteoblast markers, and extracellular matrix mineralization. The surfaces functionalized with the extract diluted in the range 1 × 10^-5-1 mg/mL resulted in having a greater osteogenic activity for the highest concentration, with lower values of cell viability; higher expression of alkaline phosphatase, bone sialoprotein, and collagen; and lower levels of osteopontin. In conclusion, the functionalization of a nano-textured Ti surface with polyphenols can potentially favor the osteogenic activity of osseointegrated implants.

Polyphenols from Grape Pomace: Functionalization of Chitosan-Coated Hydroxyapatite for Modulated Swelling and Release of Polyphenols

Chitosan is known for its specific antibacterial mechanism and biodegradability, while polyphenols are known for their antioxidant and anti-inflammatory properties: coupling these properties on a surface for bone contact, such as hydroxyapatite, is of great interest. The system developed here allows the combination of hydroxyapatite, chitosan, and polyphenol properties in the same multifunctional biomaterial in order to modulate the host response after implantation. Crosslinked chitosan is used in this research to create a stable coating on hydroxyapatite, and then it is functionalized for a smart release of the polyphenols. The release is higher in inflammatory conditions and lower in physiological conditions. The properties of the coated and functionalized samples are characterized on the as-prepared samples and after the samples are immersed (for 24 h) in solutions, which simulate the inflammatory and physiological conditions. Characterization is performed in order to confirm the presence of polyphenols grafted within the chitosan coating, the stability of grafting as a function of pH, the morphology of the coating and distribution of polyphenols on the surface, and the redox reactivity and radical scavenging activity of the functionalized coating. All the results are in line with previous results, which show a successful coating with chitosan and functionalization with polyphenols. Moreover, the polyphenols have a different release kinetics that is faster in a simulated inflammatory environment compared to that in the physiological environment. Even after the release tests, a fraction of polyphenols are still bound on the surface, maintaining the antioxidant and radical scavenging activity for a longer time. An electrostatic bond occurs between the negative-charged polar groups of polyphenols (carboxyls and/or phenols) and the positive amide groups of the chitosan coating, and the substitution of the crosslinker by the polyphenols occurs during the functionalization process.

Iodine-Loaded Calcium Titanate for Bone Repair with Sustainable Antibacterial Activity Prepared by Solution and Heat Treatment

In the orthopedic and dental fields, simultaneously conferring titanium (Ti) and its alloy implants with antibacterial and bone-bonding capabilities is an outstanding challenge. In the present study, we developed a novel combined solution and heat treatment that controllably incorporates 0.7% to 10.5% of iodine into Ti and its alloys by ion exchange with calcium ions in a bioactive calcium titanate. The treated metals formed iodine-containing calcium-deficient calcium titanate with abundant Ti-OH groups on their surfaces. High-resolution XPS analysis revealed that the incorporated iodine ions were mainly positively charged. The surface treatment also induced a shift in the isoelectric point toward a higher pH, which indicated a prevalence of basic surface functionalities. The Ti loaded with 8.6% iodine slowly released 5.6 ppm of iodine over 90 days and exhibited strong antibacterial activity (reduction rate >99%) against methicillin-resistant Staphylococcus aureus (MRSA), S. aureus, Escherichia coli, and S. epidermidis. A long-term stability test of the antibacterial activity on MRSA showed that the treated Ti maintained a >99% reduction until 3 months, and then it gradually decreased after 6 months (to a 97.3% reduction). There was no cytotoxicity in MC3T3-E1 or L929 cells, whereas apatite formed on the treated metal in a simulated body fluid within 3 days. It is expected that the iodine-carrying Ti and its alloys will be particularly useful for orthopedic and dental implants since they reliably bond to bone and prevent infection owing to their apatite formation, cytocompatibility, and sustainable antibacterial activity.

Vitamin E: A Review of Its Application and Methods of Detection When Combined with Implant Biomaterials

Vitamin E is a common compound used for tocopherols and tocotrienols (α, β, γ, δ); it is the component of many natural products of both plant and animal origin. Thanks to its powerful antioxidant capacity, vitamin E has been very successful in hip and knee arthroplasty, used to confer resistance to oxidation to irradiated UHMWPE. The positive results of these studies have made vitamin E an important object of research in the biomedical field, highlighting other important properties, such as anti-bacterial, -inflammatory, and -cancer activities. In fact, there is an extensive literature dealing with vitamin E in different kinds of material processing, drug delivery, and development of surface coatings. Vitamin E is widely discussed in the literature, and it is possible to find many reviews that discuss the biological role of vitamin E and its applications in food packaging and cosmetics. However, to date, there is not a review that discusses the biomedical applications of vitamin E and that points to the methods used to detect it within a solid. This review specifically aims to compile research about new biomedical applications of vitamin E carried out in the last 20 years, with the intention of providing an overview of the methodologies used to combine it with implantable biomaterials, as well as to detect and characterize it within these materials.

Titanium and Protein Adsorption: An Overview of Mechanisms and Effects of Surface Features

Titanium and its alloys, specially Ti6Al4V, are among the most employed materials in orthopedic and dental implants. Cells response and osseointegration of implant devices are strongly dependent on the body-biomaterial interface zone. This interface is mainly defined by proteins: They adsorb immediately after implantation from blood and biological fluids, forming a layer on implant surfaces. Therefore, it is of utmost importance to understand which features of biomaterials surfaces influence formation of the protein layer and how to guide it. In this paper, relevant literature of the last 15 years about protein adsorption on titanium-based materials is reviewed. How the surface characteristics affect protein adsorption is investigated, aiming to provide an as comprehensive a picture as possible of adsorption mechanisms and type of chemical bonding with the surface, as well as of the characterization techniques effectively applied to model and real implant surfaces. Surface free energy, charge, microroughness, and hydroxylation degree have been found to be the main surface parameters to affect the amount of adsorbed proteins. On the other hand, the conformation of adsorbed proteins is mainly dictated by the protein structure, surface topography at the nano-scale, and exposed functional groups. Protein adsorption on titanium surfaces still needs further clarification, in particular concerning adsorption from complex protein solutions. In addition, characterization techniques to investigate and compare the different aspects of protein adsorption on different surfaces (in terms of roughness and chemistry) shall be developed.

Surface Functionalization of a Silica-Based Bioactive Glass with Compounds from Rosa canina Bud Extracts

Bud extracts are a new category of vegetal products, which are used in gemmotherapy. These products are liquid preparation sources of bioactive molecules (phytochemicals) and are used in medicine as health-promoting agents. Rosa canina is a medicinal plant belonging to the family Rosaceae. The R. canina bud extracts, in particular, possess anti-inflammatory and antioxidant activities due to the presence of flavonoids and other phenolic compounds. The combination of R. canina bud extracts with biomaterials can be promising for obtaining multifunctional materials carrying both inorganic and biological properties. In this work, a protocol of functionalization has been properly designed, for the first time in the literature, in order to graft various bud extracts of R. canina to a silica-based bioactive glass (CEL2). The Folin-Ciocalteu method was used to determine the redox capacity of total polyphenols in the extracts and on functionalized solid samples. X-ray photoelectron spectroscopy analysis and fluorescence microscopy were employed to investigate the presence of phenol substances on the material surface. Bioactivity (in terms of ability of inducing hydroxyapatite precipitation) has been investigated by soaking the samples, with or without functionalization, in simulated body fluid. The presence of the polyphenols from bud extracts not only preserved glass bioactivity but even enhanced it. In particular, the solution obtained from the byproducts of primary extraction in glycerol macerate showed the best performances. Moreover, the presence and antioxidant activity of bud extract compounds on the material surface after grafting demonstrate the possibility of combining the glass inorganic bioactivity with the biomolecule-specific properties, making possible a local action at the implant site. The promising results reported in this work pave the way for the realization of new multifunctional materials with a green approach.

Topographical and Biomechanical Guidance of Electrospun Fibers for Biomedical Applications

Electrospinning is gaining increasing interest in the biomedical field as an eco-friendly and economic technique for production of random and oriented polymeric fibers. The aim of this review was to give an overview of electrospinning potentialities in the production of fibers for biomedical applications with a focus on the possibility to combine biomechanical and topographical stimuli. In fact, selection of the polymer and the eventual surface modification of the fibers allow selection of the proper chemical/biological signal to be administered to the cells. Moreover, a proper design of fiber orientation, dimension, and topography can give the opportunity to drive cell growth also from a spatial standpoint. At this purpose, the review contains a first introduction on potentialities of electrospinning for the obtainment of random and oriented fibers both with synthetic and natural polymers. The biological phenomena which can be guided and promoted by fibers composition and topography are in depth investigated and discussed in the second section of the paper. Finally, the recent strategies developed in the scientific community for the realization of electrospun fibers and for their surface modification for biomedical application are presented and discussed in the last section.

The mechanical and chemical stability of the interfaces in bioactive materials: The substrate-bioactive surface layer and hydroxyapatite-bioactive surface layer interfaces

Bioactive materials should maintain their properties during implantation and for long time in contact with physiological fluids and tissues. In the present research, five different bioactive materials (a bioactive glass and four different chemically treated bioactive titanium surfaces) have been studied and compared in terms of mechanical stability of the surface bioactive layer-substrate interface, their long term bioactivity, the type of hydroxyapatite matured and the stability of the hydroxyapatite-surface bioactive layer interface. Numerous physical and chemical analyses (such as Raman spectroscopy, macro and micro scratch tests, soaking in SBF, Field Emission Scanning Electron Microscopy equipped with Energy Dispersive Spectroscopy (SEM-EDS), zeta potential measurements and Fourier Transformed Infra-Red spectroscopy (FTIR) with chemical imaging) were used. Scratch measurements evidenced differences among the metallic surfaces concerning the mechanical stability of the surface bioactive layer-substrate interface. All the surfaces, despite of different kinetics of bioactivity, are covered by a bone like carbonate-hydroxyapatite with B-type substitution after 28 days of soaking in SBF. However, the stability of the apatite layer is not the same for all the materials: dissolution occurs at pH around 4 (close to inflammation condition) in a more pronounced way for the surfaces with faster bioactivity together with detachment of the surface bioactive layer. A protocol of characterization is here suggested to predict the implant-bone interface stability.

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

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.

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.

Cytocompatible and Anti-bacterial Adhesion Nanotextured Titanium Oxide Layer on Titanium Surfaces for Dental and Orthopedic Implants

It is widely recognized that surface nanotextures applied on a biomaterial can affect wettability, protein absorption and cellular and/or bacterial adhesion; accordingly, they are nowadays of great interest to promote fast osseointegration and to maintain physiological healing around biomedical implants. In order to be suitable for clinical applications, surface nanotextures must be not only safe and effective, but also, they should be produced through industrial processes scalable to real devices with sustainable processes and costs: this is often a barrier to the market entry. Based on these premises, a chemical surface treatment designed for titanium and its alloys able to produce an oxide layer with a peculiar sponge like nanotexture coupled with high density of hydroxyl group is here presented. The modified Ti-based surfaces previously showed inorganic bioactivity intended as the ability to induce apatite precipitation in simulated body fluid. Physicochemical properties and morphology of the obtained layers have been characterized by means of FESEM, XPS, and Zeta-potential. Biological response to osteoblasts progenitors and bacteria has been tested. The here proposed nanotextured surfaces successfully supported osteoblasts progenitors' adhesion, proliferation and extracellular matrix deposition thus demonstrating good biocompatibility. Moreover, the nanotexture was able to significantly reduce bacteria surface colonization when the orthopedic and the periodontal pathogens Staphylococcus aureus and Aggregatibacter actinomycetemcomitans strains were applied for a short time. Finally, the applicability of the proposed surface treatment to real biomedical devices (a 3D acetabular cup, a dental screw and a micro-sphered laryngeal implant) has been here demonstrated.

Studies on Cell Compatibility, Antibacterial Behavior, and Zeta Potential of Ag-Containing Polydopamine-Coated Bioactive Glass-Ceramic

Dopamine is a small molecule that mimics the adhesive component (L-DOPA) of marine mussels with a catecholamine structure. Dopamine can spontaneously polymerize to form polydopamine (PDA) in a mild basic environment. PDA binds, in principle, to all types of surfaces and offers a platform for post-modification of surfaces. In this work, a novel Ag-containing polydopamine coating has been developed for the functionalization of bioactive glass-ceramics. In order to study the interactions between the surface of uncoated and coated samples and the environment, we have measured the surface zeta potential. Results confirmed that PDA can interact with the substrate through different chemical groups. A strongly negative surface zeta potential was measured, which is desirable for biocompatibility. The dual function of the material, namely the capability to exhibit bioactive behavior while being antibacterial and not harmful to mammalian cells, was assessed. The biocompatibility of the samples with MG-63 (osteoblast-like) cells was determined, as well as the antibacterial behavior against Gram-positive Staphylococcus carnosus and Gram-negative Escherichia coli bacteria. During cell biology tests, uncoated and PDA-coated samples showed biocompatibility, while cell viability on Ag-containing PDA-coated samples was reduced. On the other hand, antibacterial tests confirmed the strong antimicrobial properties of Ag-containing PDA-coated samples, although tailoring of the silver release will be necessary to modulate the dual effect of PDA and silver.

Green Tea Polyphenols Coupled with a Bioactive Titanium Alloy Surface: In Vitro Characterization of Osteoinductive Behavior through a KUSA A1 Cell Study

A chemically-treated titanium alloy (Ti6Al4V) surface, able to induce hydroxyapatite precipitation from body fluids (inorganic mineralization activity), was functionalized with a polyphenolic extract from green tea (tea polyphenols, TPH). Considering that green tea polyphenols have stimulating effects on bone forming cells (biological mineralization), the aim was to test their osteoinductive behavior due to co-operation of inorganic and biological mineralization on mesenchymal stem cells KUSA A1. The functionalized surfaces were characterized by using the Folin⁻Ciocalteu method and X-ray photoelectron spectroscopy to confirm the successful outcome of the functionalization process. Two cell cultures of mesenchymal stem cells, KUSA A1 were performed, with or without osteoinductive factors. The cells and surfaces were characterized for monitoring cell viability and hydroxyapatite production: Fourier Transform Infrared Spectroscopy and Raman spectroscopy analyses showed deposition of hydroxyapatite and collagen due to the cell activity, highlighting differentiation of KUSA A1 into osteoblasts. A higher production of extracellular matrix was highlighted on the functionalized samples by laser microscope and the fluorescence images showed higher viability of cells and greater presence of osteocalcin in these samples. These results highlight the ability of polyphenols to improve cell differentiation and to stimulate biological mineralization, showing that surface functionalization of metal implants could be a promising way to improve osteointegrability.

Zeta Potential Measurements on Solid Surfaces for in Vitro Biomaterials Testing: Surface Charge, Reactivity Upon Contact With Fluids and Protein Absorption

Surface properties of biomaterials (e.g., roughness, chemical composition, charge, wettability, and hydroxylation degree) are key features to understand and control the complex interface phenomena that happens upon contact with physiological fluids. Numerous physico-chemical techniques can be used in order to investigate in depth these crucial material features. Among them, zeta potential measurements are widely used for the characterization of colloidal suspensions, but actually poorly explored in the study of solid surfaces, even if they can give significant information about surface charge in function of pH and indirectly about surface functional groups and reactivity. The aim of the present research is application of zeta potential measurements of solid surfaces for the in vitro testing of biomaterials. In particular, bare and surface modified Ti6Al4V samples have been compared in order to evaluate their isoelectric points (IEPs), surface charge at physiological pH, in vitro bioactivity [in simulated body fluid (SBF)] and protein absorption. Zeta potential titration was demonstrated as a suitable technique for the surface characterization of surface treated Ti6Al4V substrates. Significant shift of the isoelectric point was recorded after a chemical surface treatment (because of the exposition of hydroxyl groups), SBF soaking (because of apatite precipitation IEP moves close to apatite one) and protein absorption (IEP moves close to protein ones). Moreover, the shape of the curve gives information about exposed functional groups (e.g., a plateau in the basic range appears due to the exposition of acidic OH groups and in the acidic range due to exposition of basic NH₂ groups).

Bore Disruption: An Unusual Mechanical Failure of Two Hip Hemiarthroplasties

We report a case of two hemiarthroplasties (HAs) that underwent an unexpected mechanical failure. Two patients affected by femoral fractures were treated with an HA. At 5 and 7 years after surgery, they showed a breakage of the HA at the head–stem junction. We analyzed macroscopically and microscopically (by a scanning electron microscopy) the surfaces of the broken prostheses. In both cases, a fracture was detected starting at the joining point between the femoral head and the slot that receives the taper cone of the stem (the so-called bore), with the typical macroscopic and microscopic pattern of a fatigue fracture. The fatigue fracture resulted from repeated cycles of torsional stresses throughout the years. In literature, we did not find any other report of such HA failure.

Silver-doped keratin nanofibers preserve a titanium surface from biofilm contamination and favor soft-tissue healing

Peri-implantitis is a severe condition affecting the success of transmucosal dental implants: tissue healing is severely limited by the inflammatory processes that come about to control homeostasis in the surrounding tissues. The main cause of peri-implantitis is bacterial biofilm infection; gingival fibroblasts play a pivotal role in regulating the inflammatory cascades. A new technology aimed at preventing bacterial colonization of titanium (Ti) implants, and enhancing the spread of gingival fibroblasts, is presented. Using electro-spinning, mirror-polished Ti disks were uniformly coated with keratin fibers obtained from discarded wool via sulfitolysis. The keratin-coated surfaces were then doped with silver (Ag) to introduce antibacterial properties, using different concentrations of silver nitrate as a precursor (0.01, 0.05 and 0.1 M). The resulting specimens were characterized in terms of morphology and chemical composition by FESEM, FTIR and XPS, revealing silver concentrations between 1.7 and 1.9%. Silver release into the medium was evaluated in the presence of cells (α-MEM) or bacteria (LB) by ICP; release was 0.2-1.4 mg l^-1 for α-MEM, and 10-40 mg l^-1 for LB. The antibacterial properties of the Ag-doped specimens were tested against a multidrug-resistant Staphylococcus aureus biofilm through morphology (FESEM) and metabolic assay (XTT); reduction in viability was significant (p < 0.05; >80% reduction within 72 h). Lastly, the cytocompatibility of the specimens was confirmed using human primary gingival fibroblasts, whose viability, spread and matrix deposition were found to be comparable to those of untreated Ti polished controls (p > 0.05). Thus, Ag surface enrichment was effective in reducing viability and maturation of S. aureus biofilm, without compromising human cell viability. Moreover, cell spread was found to be very sensitive to keratin fiber stimulation. The strategy thus appears to be very promising to introduce surface features in line with the main requirements for transmucosal dental implants.

The response of osteoblastic MC3T3-E1 cells to micro- and nano-textured, hydrophilic and bioactive titanium surfaces

The aim of the present work was to investigate the morphology and activity of the murine osteoblastic cell line MC3T3 on control smooth (Machined), commercially available rough (ZT) titanium discs, and on titanium samples obtained by modifying the ZT treatment protocol, and herein labelled as ZTF, ZTM and ZTFM. Cells were evaluated at SEM and immunofluorescence for morphology and cell-to-cell interactions and by MTT assay and real time PCR for cell growth and function. Microscopy showed that ZT modified protocols could differently affect cell shape and distribution. All the tested surfaces showed good biocompatibility by viability assay. However, cells on smoother surfaces appeared to express higher levels of transcript for Collagen 1a1, the main component of extracellular matrix, by real time PCR. Expression of the early differentiation marker Alkaline Phosphatase was higher on ZTF surfaces and ZTM enhanced the expression of later osteoblastic markers Osteoprotegerin and Osteocalcin. Noteworthy, the expression of Connexin 43, a component of cell-to-cell contacts and hemichannels, followed a similar pattern to differentiation marker genes and was higher in cells on ZTM surfaces, consistently with the microscopic observation of cell clusters. Taken together, this data showed that ZTF and ZTM treatment protocols appeared to improve the basal sand-blasting/acid-etching ZT procedure with ZTM surfaces promoting the most mature stage of differentiation.

Bone healing at bicortically installed implants with different surface configurations. An experimental study in rabbits

OBJECTIVE

To study the sequential healing at bicortically installed implants with surface modifications by the use of fluoroboric acid and/or H2 O2 .

MATERIAL AND METHODS

Twenty-eight albino New Zealand rabbits were used. Two recipient sites were prepared in the tibiae bilaterally, one in the metaphysis and the second in the diaphysis regions. Four implants with different surface characteristics were randomly installed with bicortical stabilization: (i) sandblasted and acid-etched; (ii) same surface as i, but with a substitution of the hydrofluoric acid with fluoroboric acid; (iii) same surface as i, additionally treated with H2 O2 ; and (iv) same surface modified as ii, additionally treated with H2 O2 . The animals were killed after 5, 8, 15, and 30 days. Ground sections were prepared for histological analyses.

RESULTS

No statistically significant differences in osseointegration were found among various surfaces at any of the healing periods. A higher degree of osseointegration was observed at the implants placed in the metaphysis compared to those placed in the diaphysis, especially during early healing. A higher degree of osseointegration was found at sites with proximity to compact (cortical) bone when compared to the middle portion of the implants, especially in the diaphysis region.

CONCLUSIONS

Surfaces modified with different acids or H2 O2 resulted in similar osseointegration compared to a standard sandblasted and acid-etched surface. The portion of the bicortically installed implants in close contact with the cortical compartment presented a higher percentage of osseointegration compared with the region in contact with the bone marrow compartment.

Tantalum-based thin film coatings for wear resistant arthroprostheses

Cobalt-chromium-molybdenum alloys with high carbon content (HC-CoCrMo) are widely used as materials for arthroprosthesis, in particular in metal-on-metal (MoM) hip joints. In spite of their good wear and corrosion resistance, production of metallic wear particles and metal ion release will occur on a large time-scale. An enhancement of the metal ion level in the patient's blood and urine is often reported in clinical data. Hypersensitivity, inflammatory response and cell necrosis can occur as consequence. So implants on young patients and women on childbearing age are not so widespread. The aim of this research is the realization of a thin film coating in order to improve the biocompatibility of Co-based alloys and to reduce debris production, ion release and citotoxicity. The innovative process consists of a thermal treatment in molten salts, in order to obtain a tantalum enriched thin film coating. Tantalum is chosen because it is considered a biocompatible metal with high corrosion resistance and low ion release. Three HC-CoCrMo alloys, produced by different manufacturing processes, are tested as substrates. The coating is a thin film of TaC or it can be composed by a multilayer of two tantalum carbides and metallic tantalum, depending on the temperature of the treatment and on the carbon content of the substrate. The thin films as well the substrates are characterized from the structural, chemical and morphological point of view. Moreover mechanical behaviour of treated and untreated materials is analyzed by means of nanohardness, scratch and ball-on-disc wear tests. The coating increases the mechanical and tribological properties of HC-CoCrMo.

Surface modification of Ti-6Al-4 V alloy for biomineralization and specific biological response: part II, alkaline phosphatase grafting

Titanium and its alloys are the most widespread materials for the realization of orthopaedic and dental implants due to their good mechanical properties and biocompatibility. Surface functionalization of biomaterials aimed to improve and quicken implant integration and tissue regeneration is an active research field. The opportunity to confer biological activity (ability to directly stimulate cells with proper biological signals) to the Ti6Al4 V alloy, previously modified to be bioactive from the inorganic point of view (apatite precipitation), was explored in this research work. The alkaline phosphatase (ALP) enzyme was grafted to metal surface via tresyl chloride activation, maintaining its activity. A synergistic effect between biological functionalization and inorganic bioactivity was observed.

Surface modification of Ti-6Al-4V alloy for biomineralization and specific biological response: Part I, inorganic modification

Titanium and its alloys represent the gold standard for orthopaedic and dental prosthetic devices, because of their good mechanical properties and biocompatibility. Recent research has been focused on surface treatments designed to promote their rapid osteointegration also in case of poor bone quality. A new surface treatment has been investigated in this research work, in order to improve tissue integration of titanium based implants. The surface treatment is able to induce a bioactive behaviour, without the introduction of a coating, and preserving mechanical properties of Ti6Al4V substrates (fatigue resistance). The application of the proposed technique results in a complex surface topography, characterized by the combination of a micro-roughness and a nanotexture, which can be coupled with the conventional macro-roughness induced by blasting. Modified metallic surfaces are rich in hydroxyls groups: this feature is extremely important for inorganic bioactivity (in vitro and in vivo apatite precipitation) and also for further functionalization procedures (grafting of biomolecules). Modified Ti6Al4V induced hydroxyapatite precipitation after 15 days soaking in simulated body fluid (SBF). The process was optimised in order to not induce cracks or damages on the surface. The surface oxide layer presents high scratch resistance.

Alkaline phosphatase grafting on bioactive glasses and glass ceramics

Bone integration of orthopaedic or dental implants and regeneration of damaged bone at the surgical site are still unresolved problems in prosthetic surgery. For this reason, biomimetic surfaces (i.e. both inorganic and biological bioactive surfaces) represent a challenge for bone implantation. In this research work a hydrolase enzyme (alkaline phosphatase) was covalently grafted to inorganic bioactive glass and glass ceramic surfaces, in order to impart biological bioactivity. The functionalized samples were analysed by means of X-ray photoelectron spectroscopy in order to verify enzyme presence on the surface. Enzyme activity was measured by means of UV-visual spectroscopy after reaction with the natural substrate. Scanning electron microscopy-energy-dispersive spectroscopy observations allowed monitoring of the morphological and chemical modification of the materials during the different steps of functionalization. In vitro inorganic bioactivity was investigated by soaking samples in simulated body fluid. Enzymatic activity of the samples was tested and compared before and after soaking. Enzymatic activity of the solution was monitored at different experimental times. This study demonstrates that alkaline phosphatase could be successfully grafted onto different bioactive surfaces while maintaining its activity. Presence of the enzyme in vitro enhances the inorganic bioactivity of the materials tested.

The influence of crystallised Fe3O4 on the magnetic properties of coprecipitation-derived ferrimagnetic glass-ceramics

Ferrimagnetic glass-ceramics are potential candidates for magnetic induction hyperthermia, which is one form of inducing deep-regional hyperthermia, by using a magnetic field. The aim of this work was to analyse the influence of the amount of crystallised magnetite on the magnetic properties of glass-ceramic samples. Thus, two different ferrimagnetic glass-ceramics with the composition of the system Na(2)O-CaO-SiO(2)-P(2)O(5)-FeO-Fe(2)O(3) were prepared by melting at 1500 degrees C for 30 min of the coprecipitation-derived starting products. The X-ray diffraction patterns show the presence of nanometric magnetite crystals in a glassy matrix after cooling from melting temperature. The estimated amount of crystallised magnetite varies between 20 and 45 wt.%, as a function of the chemical composition. The morphology of the crystals was studied by scanning electron micrography and transmission electron micrography. Glass transition temperature and thermal stability were investigated by differential thermal analysis. Magnetic hysteresis cycles were analysed using a vibrating sample magnetometer with a maximum applied field of 17 kOe, at room temperature, in quasi-static conditions. Calorimetric measurements were carried out using a magnetic induction furnace. The power losses estimated from calorimetric measurements under a magnetic field of 40 kA/m and 440 kHz are 65 W/g for the glass-ceramic with lower iron oxides content and 25 W/g for the glass-ceramic with higher iron oxide content.

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.

New chemical treatment for bioactive titanium alloy with high corrosion resistance

It was recently claimed that titanium metal and its alloys can bond to the living bone, without being coated by apatite (VPS coatings), but by being chemically and heat-treated. The bioactivity of treated titanium is of interest because of the opportunity to obtain orthopaedic or dental implants presenting, at the same time, high toughness, strength and fatigue resistance as well as bone-bonding ability. The bioactive behaviour of the treated implants is due to the presence of a modified surface, which, during soaking in body fluid, promotes the precipitation of apatite. The apatite formed is strongly bonded to the substrate and promotes living bone bonding. In this work were characterised samples of Ti-6Al-7Nb alloy with surfaces presenting a different chemical and mechanical state. The aim of the research was twofold. The first objective was to characterise chemically and heat-treated samples with different surface topography, in order to define the best conditions for osteogenic integration. The second aim was to assess the corrosion behaviour of the bioactive implants, because they expose a microporous and quite thin modified surface layer. No-treated and passivated samples, with a surface state closed to that nowadays used on implants, were used as reference. The surface structure, morphology, electrochemical behaviour and bioactivity of the different samples were assessed by means of XRD, SEM-EDS, anodic polarizations, open circuit measurements and in-vitro tests. Results evidence that it is possible to modify the surface of the Ti-6Al-7Nb alloy in order to obtain the formation of a bioactive layer and that the substrate roughness influences the characteristics of the surface layer formed. It was also evidenced that the as treated surfaces present inadequate corrosion behaviour, so a new two-step chemical treatment has been developed in order to obtain a bioactive material with good corrosion resistance.

Fluoroapatite glass-ceramic coatings on alumina: structural, mechanical and biological characterisation

The aim of this work was to realise bioactive coatings on full density alpha-alumina substrates. An SiO2-CaO-based glass (SC) and an SiO2-Al2O3-P2O5-K2O-CaO-F--based glass-ceramic (SAF) were used for this purpose. Specifically, SAF is a fluoroapatite containing glass-ceramic and previous studies have shown that it is a highly bioactive biomaterial. Furthermore, these fluoroapatite crystals possess a needle-shaped morphology which mimics that of hydroxylapatite found in human hard tissues, particularly in teeth. SAF is a very viscous glass-ceramic and for this reason an intermediate, less viscous, SC layer was interposed in direct contact with alumina aiming to obtain a good coating adhesion. Moreover, this intermediate layer strongly lowers the Al3+ diffusion and thus minimises both compositional changes in the SAF outer layer and the risk of detrimental modifications of the nature of the crystalline phases. A complete characterisation of the coated samples was performed by means of X-ray diffraction, optical and scanning microscopy. Coating adhesion on alumina was tested by comparative shear tests while biocompatibility was investigated on alumina. bulk SAF and on the realised coatings. For this purpose, cytotoxicity, adhesion and proliferation of human osteoblast-like cells were cultured onto the three materials. Results showed that the interposition of the SC layer was successful in allowing a good softening and spreading of the SAF outer layer and in avoiding the crystallisation of undesired crystalline phases maintaining the good bioactive properties of the bulk one. In vitro results on the coatings showed osteoblast-like cell behaviour similar to bulk fluoroapatite glass-ceramic and better respect to alumina substrates, being a promising index of bone material integration and of its in vivo possible applications.