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.

Development of Super-Paramagnetic Iron Oxide Nanoparticle-Coated Melt Electrowritten Scaffolds for Biomedical Applications

Polycaprolactone (PCL) is usually the material chosen for melt electrowriting (MEW) due to its biocompatibility, mechanical strength, and melt processability. This work first investigates the effect of different processing parameters to obtain optimum PCL-MEW scaffolds. Secondly, to increase PCL`s hydrophilicity and cell affinity, and to enable coating with superparamagnetic iron oxide nanoparticles (SPIONs) and silica-coated-SPIONs (Si-SPIONs), the scaffolds are modified with alkaline surface treatment. Finally, SPIONs and Si-SPIONs are successfully coated on MEW scaffolds. Results show that reproducible scaffolds are fabricated. Additionally, the alkaline treatment does not change the three-dimensional morphology of scaffolds while reducing fiber diameter. Furthermore, SEM images and ATR-FTIR results confirmed that SPIONs and Si-SPIONs-were coated on scaffolds. A cytocompatibility assay showed a non-toxic effect on MG-63 osteoblast-like cells in all scaffolds. Additionally, higher MC3T3-E1 pre-osteoblastic cell adhesion efficiency and proliferation are achieved for the alkaline-treated scaffolds and SPIONs/Si-SPIONs-coated scaffolds. All samples demonstrated the ability to generate heat, useful for hyperthermia-treatment, when subjected to an alternating magnetic field. Overall, the findings suggest that the strategy of coating PCL-MEW scaffolds with SPIONs/Si-SPIONs has the potential to improve scaffold performance for biomedical applications, especially for producing magnetically responsive MEW scaffolds.

3D bioprinting of multifunctional alginate dialdehyde (ADA)-gelatin (GEL) (ADA-GEL) hydrogels incorporating ferulic acid

The present work explores the 3D extrusion printing of ferulic acid (FA)-containing alginate dialdehyde (ADA)-gelatin (GEL) scaffolds with a wide spectrum of biophysical and pharmacological properties. The tailored addition of FA (≤0.2 %) increases the crosslinking between FA and GEL in the presence of calcium chloride (CaCl2) and microbial transglutaminase, as confirmed using trinitrobenzenesulfonic acid (TNBS) assay. In agreement with an increase in crosslinking density, a higher viscosity of ADA-GEL with FA incorporation was achieved, leading to better printability. Importantly, FA release, enzymatic degradation and swelling were progressively reduced with an increase in FA loading to ADA-GEL, over 28 days. Similar positive impact on antibacterial properties with S. epidermidis strains as well as antioxidant properties were recorded. Intriguingly, FA incorporated ADA-GEL supported murine pre-osteoblast proliferation with reduced osteosarcoma cell proliferation over 7 days in culture, implicating potential anticancer property. Most importantly, FA-incorporated and cell-encapsulated ADA-GEL can be extrusion printed to shape fidelity-compliant multilayer scaffolds, which also support pre-osteoblast cells over 7 days in culture. Taken together, the present study has confirmed the significant potential of 3D bioprinting of ADA-GEL-FA ink to obtain structurally stable scaffolds with a broad spectrum of biophysical and therapeutically significant properties, for bone tissue engineering applications.

UV-Cured Bio-Based Acrylated Soybean Oil Scaffold Reinforced with Bioactive Glasses

In this study, a bio-based acrylate resin derived from soybean oil was used in combination with a reactive diluent, isobornyl acrylate, to synthetize a composite scaffold reinforced with bioactive glass particles. The formulation contained acrylated epoxidized soybean oil (AESO), isobornyl acrylate (IBOA), a photo-initiator (Irgacure 819) and a bioactive glass particle. The resin showed high reactivity towards radical photopolymerisation, and the presence of the bioactive glass did not significantly affect the photocuring process. The 3D-printed samples showed different properties from the mould-polymerised samples. The glass transition temperature Tg showed an increase of 3D samples with increasing bioactive glass content, attributed to the layer-by-layer curing process that resulted in improved interaction between the bioactive glass and the polymer matrix. Scanning electron microscope analysis revealed an optimal distribution on bioactive glass within the samples. Compression tests indicated that the 3D-printed sample exhibited higher modulus compared to mould-synthetized samples, proving the enhanced mechanical behaviour of 3D-printed scaffolds. The cytocompatibility and biocompatibility of the samples were evaluated using human bone marrow mesenchymal stem cells (bMSCs). The metabolic activity and attachment of cells on the samples' surfaces were analysed, and the results demonstrated higher metabolic activity and increased cell attachment on the surfaces containing higher bioactive glass content. The viability of the cells was further confirmed through live/dead staining and reseeding experiments. Overall, this study presents a novel approach for fabricating bioactive glass reinforced scaffolds using 3D printing technology, offering potential applications in tissue engineering.

Iron Oxide-Au Magneto-Plasmonic Heterostructures: Advances in Their Eco-Friendly Synthesis

In recent years, nanotechnologies have attracted considerable interest, especially in the biomedical field. Among the most investigated particles, magnetic based on iron oxides and Au nanoparticles gained huge interest for their magnetic and plasmonic properties, respectively. These nanoparticles are usually produced starting from processes and reagents that can be the cause of potential human health and environmental concerns. For this reason, there is a need to develop simple, green, low-cost, and non-toxic synthesis methods and reagents. This review aims at providing an overview of the most recently developed processes to produce iron oxide magnetic nanoparticles, Au nanoparticles, and their magneto-plasmonic heterostructures using eco-friendly approaches, focusing the attention on the microorganisms and plant-assisted syntheses and showing the first results of the development of magneto-plasmonic heterostructures.

In situ reduction of Ag on magnetic nanoparticles with gallic acid: effect of the synthesis parameters on morphology

Aim: Synthesis of Fe₃O₄-Ag composite nanoparticles (NPs) by a new in situ reduction of Ag NPs on the surface of Fe₃O₄ NPs using gallic acid as a reducing agent. Materials & methods: The influence of process parameters on NP morphology and functionalization was evaluated by means of field-emission scanning/scanning transmission electron microscopy and Fourier-transform IR spectroscopy. Results & conclusion: The synthesis conditions affected the morphology of the obtained NPs, evidence of the formation of polydispersed aggregates, nanoflower-like or nanodumbbell nanocomposites. In particular, well-defined nanodumbbells were obtained in aqueous media, with an NP/gallic acid ratio of 10:1, while the presence of a silica shell did not improve the morphology of Ag NPs nucleated on the Fe₃O₄ core.

Antioxidant Activity of Silica-Based Bioactive Glasses

Bioactive glasses are the materials of choice in the field of bone regeneration. Antioxidant properties of interest to limit inflammation and foreign body reactions have been conferred to bioactive glasses by the addition of appropriate ions (such as Ce or Sr). On the other hand, the antioxidant activity of bioactive glasses without specific ion/molecular doping has been occasionally cited in the literature but never investigated in depth. In the present study, three silica-based bioactive glasses have been developed and characterized for their surface properties (wettability, zeta potential, chemical composition, and reactivity) and radical scavenging activity in the presence/absence of cells. For the first time, the antioxidant activity of simple silica-based (SiO₂-CaO-Na₂O) bioactive glasses has been demonstrated.

Tellurium: A new active element for innovative multifunctional bioactive glasses

Bioactive glasses have been widely investigated for their ability to release ions with therapeutic effect. In this paper, a silica based bioactive glass was doped with a low amount of tellurium dioxide (1 and 5 mol%) to confer antibacterial and antioxidant properties. The obtained glasses were characterized in terms of morphology, composition, structure, characteristic temperatures and in vitro bioactivity. Moreover, comprehensive analyses were carried out to estimate the cytocompatibility, the antibacterial and antioxidant properties of Te-doped glasses. The performed characterizations demonstrated that the Te insertion did not interfere with the amorphous nature of the glass, the substitution of SiO₂ with TeO₂ led to a slight decrease in T_g and a TeO₂ amount higher than 1 mol% can induce a change in the primary crystal field. In vitro bioactivity test demonstrated the Te-doped glass ability to induce the precipitation of hydroxyapatite. Finally, the biological characterization showed a strong antibacterial and antioxidant effects of Te-containing glasses in comparison with the control glass, demonstrating that Te is a promising element to enhance the biological response of biomaterials.

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.

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.

PMMA-Based Bone Cements and the Problem of Joint Arthroplasty Infections: Status and New Perspectives

Polymethyl methacrylate (PMMA)-based bone cement is a biomaterial that has been used over the last 50 years to stabilize hip and knee implants or as a bone filler. Although PMMA-based bone cement is widely used and allows a fast-primary fixation to the bone, it does not guarantee a mechanically and biologically stable interface with bone, and most of all it is prone to bacteria adhesion and infection development. In the 1970s, antibiotic-loaded bone cements were introduced to reduce the infection rate in arthroplasty; however, the efficiency of antibiotic-containing bone cement is still a debated issue. For these reasons, in recent years, the scientific community has investigated new approaches to impart antibacterial properties to PMMA bone cement. The aim of this review is to summarize the current status regarding antibiotic-loaded PMMA-based bone cements, fill the gap regarding the lack of data on antibacterial bone cement, and explore the progress of antibacterial bone cement formulations, focusing attention on the new perspectives. In particular, this review highlights the innovative study of composite bone cements containing inorganic antibacterial and bioactive phases, which are a fascinating alternative that can impart both osteointegration and antibacterial properties to PMMA-based bone cement.

Glass-ceramics for cancer treatment: So close, or yet so far?

After years of research on the ability of glass-ceramics in bone regeneration, this family of biomaterials has shown revolutionary potentials in a couple of emerging applications such as cancer treatment. Although glass-ceramics have not yet reached their actual potential in cancer therapy, the relevant research activity is significantly growing in this field. It has been projected that this idea and the advent of magnetic bioactive glass-ceramics and mesoporous bioactive glasses could result in major future developments in the field of cancer. Undoubtedly, this strategy needs further developments to better answer the critical questions essential for clinical usage. This review aims to address the existing research developments on glass-ceramics for cancer treatment, starting with the current status and moving to future advances. STATEMENT OF SIGNIFICANCE: Although glass-ceramics have not yet reached their potential in cancer therapy, research activity is significantly growing. It has been speculated that this idea and the advent of modern glass-ceramics could result in significant future advances. Undoubtedly, this strategy needs further investigations and many critical questions have to be answered before it can be successfully applied for cancer treatment. This paper reviews the current state-of-the-art, starting with current products and moving onto recent developments in this field. According to our knowledge, there is a lack of a systematic review on the importance and developments of magnetic bioactive glass-ceramics and mesoporous bioactive glasses for cancer treatment, and it is expected that this review will be of interest to those working in this area.

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.

PPARs are mediators of anti-cancer properties of superparamagnetic iron oxide nanoparticles (SPIONs) functionalized with conjugated linoleic acid

Breast cancer chemotherapy can cause side effects due to nonspecific drug delivery, low solubility and fast metabolism of drugs used in conventional therapy. Moreover, the therapeutic effect of the drugs is often reduced by the strengthening of chemoresistance, which occurs via a variety of mechanisms. Different strategies have been developed to reduce multidrug resistance (MDR)-associated gene expressions including the use of surfactants and polymers. In this study superparamagnetic iron oxide nanoparticles (SPIONs) functionalized with conjugated linoleic acid (CLA) reduced the number and viability of cells in comparison with both untreated cells or cells treated with SPIONs alone. This cytostatic effect correlated with the increase of peroxisome proliferator-activated receptors γ (PPARγ). The necrotic cell death induced, as a consequence, an inflammatory process, as evidenced by the decrease of the anti-inflammatory PPARα and increase of pro-inflammatory TNFα and IL-1β. PPARs were examined because CLA is one of their natural ligands. The antitumor effect observed was accompanied by a down-regulation of p-glycoprotein (P-gp), which was the first important discovered efflux transporter belonging to MDR, and of ALDH3A1, an enzyme able to metabolize some drugs, reducing their effects. The down-regulation of P-gp correlated with the increase of cytokines. The ALDH3A1 decrease correlated with the increase of PPARγ. Based on these results, PPARs are molecular mediators of anti-cancer effect of SPIONs functionalized with CLA, being changes in these nuclear receptors correlated with induction of cytotoxicity and inflammation, and decreased ability of cancer cells in blocking anti-cancer drug effect.

Gallic acid grafting modulates the oxidative potential of ferrimagnetic bioactive glass-ceramic SC-45

Magnetite-containing glass-ceramics are promising bio-materials for replacing bone tissue after tumour resection. Thanks to their ferrimagnetic properties, they generate heat when subjected to an alternated magnetic field. In virtue of this they can be employed for the hyperthermic treatment of cancer. Moreover, grafting anti-cancer drugs onto their surface produces specific anti-neoplastic activity in these biomaterials. Gallic acid (GA) exhibits antiproliferative activity which renders it a promising candidate for anticancer applications. In the present paper, the reactivity of ferrimagnetic glass-ceramic SC-45 grafted with GA (SC-45+GA) was studied in terms of ROS release, rupture of the C-H bond of the formate molecule and Fenton reactivity by EPR/spin trapping in acellular systems. The ability of these materials to cause lipid peroxidation was assessed by UV-vis/TBA assay employing linoleic acid as a model of membrane lipid. The results, compared to those obtained with SC-45, showed that GA grafting (i) significantly enhanced the Fenton reactivity and (ii) restored the former reactivity of SC-45 towards both the C-H bond and linoleic acid which had been completely suppressed by prolonged contact with water. Fe²⁺ centres at the surface are probably implicated. GA, acting as a pro-oxidant, reduces Fe³⁺ to Fe²⁺ by maintaining a supply of Fe²⁺ at the surface of SC-45+GA.

Cell Penetrating Peptide Adsorption on Magnetite and Silica Surfaces: A Computational Investigation

Magnetic nanoparticles (MNPs) represent one of the most promising materials as they can act as a versatile platform in the field of bionanotechnology for enhanced imaging, diagnosis, and treatment of various diseases. Silica is the most common compound for preparing coated iron oxide NPs since it improves colloidal stability and the binding affinity for various organic molecules. Biomolecules such as cell penetrating peptides (CPPs) might be employed to decorate MNPs, combining their promising physicochemical properties with a cell penetrating ability. In this work, a computational investigation on adsorption of Antennapedia homeodomain-derived penetrating peptide (pAntp) on silica and magnetite (MAG) surfaces is presented. By employing umbrella sampling molecular dynamics, we provided a quantitative estimation of the pAntp-surface adsorption free energy to highlight the influence of surface hydroxylation state on the adsorption mechanism. The interaction between peptide and surface has shown to be mainly driven by electrostatics. In case of MAG surface, also an important contribution of van der Waals (VdW) attraction was observed. Our data suggest that a competitive mechanism between MNPs and cell membrane might partially inhibit the CPP to carry out its membrane penetrating function.

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.

SBA-15 ordered mesoporous silica inside a bioactive glass-ceramic scaffold for local drug delivery

The paper reports the synthesis of an ordered silica mesostructure of the SBA-15 type inside a macroporous bioactive glass-ceramic scaffold of the type SiO(2)-CaO-K(2)O, to combine the bioactivity of the latter with the release properties of the former, in view of local drug delivery from implants designed for tissue engineering. The standard procedure for SBA-15 synthesis has been modified to minimize the damage to the scaffold caused by the acidic synthesis medium. The composite system has been characterized by means of Scanning Electron Microscopy (coupled with EDS analysis), Small Angle X-Ray Diffraction, Thermogravimetry analysis and Infrared Spectroscopy: the formation of a well ordered hexagonal mesostructure was confirmed. Ibuprofen has been chosen as model drug. The uploading properties have been investigated of the scaffold-mesoporous silica composite as compared with the scaffold as such, and a five-fold increase in the adsorbing properties toward ibuprofen was found, due to the presence of the ordered mesoporous silica. The ibuprofen release to a SBF solution in vitro is complete in 1 day. Retention of bioactivity from the glass-ceramic scaffold after the silica mesostructure incorporation has been observed.

Microstructural and in vitro characterization of SiO2-Na2O-CaO-MgO glass-ceramic bioactive scaffolds for bone substitutes

In the present research work, the preparation and characterization of bioactive glass-ceramic scaffolds for bone substitutes are described. The scaffolds were prepared by starch consolidation of bioactive glass powders belonging to the SiO2-Na2O-CaO-MgO system using three different organic starches (corn, potatoes and rice) as reported in a previous screening process. The scaffolds, characterized by scanning electron microscopy, showed a porous structure with highly interconnected pores. The pores sizes assessed by mercury intrusion porosimetry put in evidence the presence of pores of 50-100 microm. The structure of the scaffolds was investigated by X-ray diffraction and revealed the glass-ceramic nature of the obtained material. The mechanical properties of the scaffolds were evaluated by means of compressive tests on cubic samples and the obtained results demonstrated their good mechanical strength. The in vitro bioactivity of the scaffolds was tested by soaking them in a simulated body fluid (SBF) and by subsequently characterizing the soaked surfaces by SEM, EDS and X-ray diffraction. Good in vitro bioactivity was found for the starting glass and for the obtained scaffolds. Moreover, the scaffold bioresorption, tested by measuring the samples weight loss in SBF at different periods of time, showed a partial resorption of the scaffolds. Cell culture testing of the three different scaffolds indicated no differences in cell number and in alkaline phosphatase activity; the morphology of the osteoblasts showed good spreading, comparable to bulk material which was used as the control.

Surface characterization of silver-doped bioactive glass

A bioactive glass belonging to the system SiO(2)-CaO-Na(2)O was doped with silver ions by ion exchange in molten salts as well as in aqueous solution. The ion exchange in the solution was done to check if it is possible to prepare an antimicrobial material using a low silver content. The doped glass was characterized by means of X-ray diffraction, SEM observation, EDS analysis, bioactivity test (soaking in a simulated body fluid), leaching test (GFAAS analyses) and cytotoxicity test. It is demonstrated that these surface silver-doped glasses maintain, or even improve, the bioactivity of the starting glass. The measured quantity of released silver into simulated body fluid compares those reported in literature for the antibacterial activity and the non-cytotoxic effect of silver. Cytotoxicity tests were carried out to understand the effect of the doped surfaces on osteogenic cell adhesion and proliferation.

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 coating on alumina: surface behavior with biological fluids

The results of a surface analysis performed on a fluoroapatite-based glass ceramic (SAF) also coating a full-density alpha-alumina substrate (SAF-alumina coating) are presented. These two materials have also been evaluated after soaking in simulated body fluid to understand their ability to induce hydroxyapatite growth on them. Aiming to understand the fluoroapatite glass-ceramic interaction with some plasma proteins, in the second part of this study, fibronectin, albumin, immunoglobulin G, IgA, and complement factor C3c SAF binding have been evaluated; surface activity on complement activation has also been quantified. SAF-alumina coating provides good sites for the nucleation and growth of an apatite layer, equivalent to the mineral component of bone and binds preferentially plasma fibronectin, which is well known to enhance cell adhesion and spreading. Moreover, SAF-alumina coating reduces alumina complement activation directly or via reduced IgA binding. Alumina was shown to bind the same C3 fragments as Zymosan, used as complement activating control, and to induce increased levels of serum soluble iC3b and Bb. A mechanical resistant material with enhanced bioactivity, bone integration, and reduced inflammatory potential respect to alumina has been obtained.

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.

In vitro characterisation of zirconia coated by bioactive glass

An in vitro evaluation of a biomedical device, which combines the mechanical properties of zirconia substrates with the bioactivity of two different glass layers (AP40 and RKKP), was performed. In this work, data on different kinds of analysis were reported both on as-sintered zirconia samples and on RKKP- and AP40-coated zirconia substrates. Structure, composition and morphology of the apatite layer growth on the coated samples after 30 days of soaking in an acellular simulated body fluid, serum protein adsorption, fibroblasts and human osteoblast-like cells adhesion, growth, morphology and biochemical aspects were studied. Results of soaking test in SBF, revealed the growth of an apatite layer on the surface of the glass-coated samples. Proteins adsorbed to the materials were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and results evidenced that the two glass-coated materials bound a higher amount of total protein than did the zirconia substrate. Fibroblasts and osteoblast-like cells cultured on RKKP- and AP40-coated zirconia showed a higher proliferation rate, leading to confluent cultures with higher cell density and a generally better expression of osteoblast alkaline phosphatase activity in comparison with zirconia substrate. In conclusion, our results indicate that the surface chemical characteristics of the two glass coatings AP40 and RKKP, with no great differences between them, substantially enhance zirconia integration with bone cells at least in vitro. This effect may be of significance in the stability of glass-coated zirconia orthopaedic and dental implants.