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Reproducing in vitro a model of the bone microenvironment is a current need. Preclinical in vitro screening, drug discovery, as well as pathophysiology studies may benefit from in vitro three-dimensional (3D) bone models, which permit high-throughput screening, low costs, and high reproducibility, overcoming the limitations of the conventional two-dimensional cell cultures. In order to obtain these models, 3D bioprinting offers new perspectives by allowing a combination of advanced techniques and inks. In this context, we propose the use of hydroxyapatite nanoparticles, assimilated to the mineral component of bone, as a route to tune the printability and the characteristics of the scaffold and to guide cell behavior. To this aim, both stoichiometric and Sr-substituted hydroxyapatite nanocrystals are used, so as to obtain different particle shapes and solubility. Our findings show that the nanoparticles have the desired shape and composition and that they can be embedded in the inks without loss of cell viability. Both Sr-containing and stoichiometric hydroxyapatite crystals permit enhancing the printing fidelity of the scaffolds in a particle-dependent fashion and control the swelling behavior and ion release of the scaffolds. Once Saos-2 cells are encapsulated in the scaffolds, high cell viability is detected until late time points, with a good cellular distribution throughout the material. We also show that even minor modifications in the hydroxyapatite particle characteristics result in a significantly different behavior of the scaffolds. This indicates that the use of calcium phosphate nanocrystals and structural ion-substitution is a promising approach to tune the behavior of 3D bioprinted constructs.

Orthopedic infections pose severe societal and economic burden and interfere with the capability of the implanted devices to integrate in the host bone, thus significantly increasing implants failure rate. To address infection and promote integration, here nanostructured antibacterial and bioactive thin films are proposed, obtained, for the first time, by Ionized Jet Deposition (IJD) of silver-substituted tricalcium phosphate (Ag-TCP) targets on titanium. Coatings morphology, composition and mechanical properties are characterized and proof-of-concept of biocompatibility is shown. Antimicrobial efficacy is investigated against four Gram positive and Gram negative bacterial strains and against C. albicans fungus, by investigating the modifications in planktonic bacterial growth in the absence and presence of silver. Then, for all bacterial strains, the capability of the film to inhibit bacterial adhesion is also tested. Results indicate that IJD permits a fine control over films composition and morphology and deposition of films with suitable mechanical properties. Biological studies show a good efficacy against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecalis and against fungus Candida albicans, with evidences of efficacy against planktonic growth and significant reduction of bacterial cell adhesion. No cytotoxic effects are evidenced for equine adipose tissue derived mesenchymal stem cells (ADMSCs), as no reductions are caused to cells viability and no interference is assessed in cells differentiation towards osteogenic lineage, in the presence of silver. Instead, thanks to nanostructuration and biomimetic composition, tricalcium phosphate (TCP) coatings favor cells viability, also when silver-substituted. These findings show that silver-substituted nanostructured coatings are promising for orthopedic implant applications., Graphical abstract Image 1, Highlights • Silver-substituted TCP films on titanium are prepared by Ionized Jet Deposition • Films are nanostructured, hard, with submicron thickness • Adipose mesenchymal stem cells differentiate into osteogenic lineage on the surface of films • Films show antimicrobial and anti-adhesive activity against several microorganisms • Films are promising for application in orthopedic titanium implants

Reconstruction of gradient organic/inorganic tissues is a challenging task in orthopaedics. Indeed, to mimic tissue characteristics and stimulate bone regeneration at the interface, it is necessary to reproduce both the mineral and organic components of the tissue ECM, as well as the micro/nano-fibrous morphology. To address this goal, we propose here novel biomimetic patches obtained by the combination of electrospinning and nanostructured bone apatite. In particular, we deposited apatite on the electrospun fibers by Ionized Jet Deposition, a plasma-assisted technique that allows conformal deposition and the preservation in the coating of the target's stoichiometry. The damage to the substrate and fibrous morphology is a polymer-dependent aspect, that can be avoided by properly selecting the substrate composition and deposition parameters. In fact, all the tested polymers (poly(l-lactide), poly(D,l-lactide-co-glycolide, poly(ε-caprolactone), collagen) were effectively coated, and the morphological and thermal characterization revealed that poly(ε-caprolactone) suffered the least damage. The coating of collagen fibers, on the other hand, destroyed the fiber morphology and it could only be performed when collagen is blended with a more resistant synthetic polymer in the nanofibers. Due to the biomimetic composition and multiscale morphology from micro to nano, the poly(ε-caprolactone)-collagen biomimetic patches coated with bone apatite supported MSCs adhesion, patch colonization and early differentiation, while allowing optimal viability. The biomimetic coating allowed better scaffold colonization, promoting cell spreading on the fibers.

Background: In clinical practice, specific customization is needed to address foot pathology, which must be disease and patient-specific. To date, the traditional methods for manufacturing custom functional Foot Orthoses (FO) are based on plaster casting and manual manufacturing, hence orthotic therapy depends entirely on the skills and expertise of individual practitioners. This makes the procedures difficult to standardize and replicate, as well as expensive, time-consuming and material-wasting, as well as difficult to standardize and replicate. 3D printing offers new perspectives in the development of patient-specific orthoses, as it permits addressing all the limitations of currently available technologies, but has been so far scarcely explored for the podiatric field, so many aspects remain unmet, especially for what regards customization, which requires the definition of a protocol that entails all stages from patient scanning to manufacturing. Methods: A feasibility study was carried out involving interdisciplinary cooperation between industrial engineers and podiatrists. To that end: (i) For patient-specific data acquisition, 3D scanning of the foot is compared to traditional casting. (ii) a modelling GD workflow is first created to design a process permitting easy creations of customized shapes, enabling the end user (the podiatrist) to interactively customize the orthoses. Then, (iii) a comparison is made between different printing materials, in order to reproduce the same mechanical behavior shown by standard orthoses. To do this, the mechanical properties of standard materials (Polycarbonate sheets), cut and hand-shaped, are compared with four groups of 3D printed samples: poly(ethylene glycol) (PETG), poly(acrylonitrile-butadiene.styrene) (ABS), polycarbonate (PC) and poly(lactic acid) (PLA) obtained by Fused Filament Fabrication (FFF). Results: Differences found between the foot plaster model obtained with the plaster slipper cast in a neutral position and the model of the real foot obtained with 3D scanning in the same position can be ascribed to the non-stationarity of the patient during the acquisition process, and were limited by a locking system with which no substantial differences in the almost entire sole of the foot scan were observed. Conclusions: Using the designed GD workflow, podiatrists with limited CAD skills can easily design and interactively customize foot orthoses to adapt them to the patients’ clinical needs. 3D printing enables the complex shape of the orthoses to be reproduced easily and quickly. Compared to Polycarbonate sheets (gold standard), all the printed materials were less deformable and reached lower yield stress for comparable deformation. No modifications in any of the materials as a result of printing process were observed.

Phosphate treatments for conservation of stone have provided so far encouraging results in laboratory studies, as they exhibit good effectiveness, compatibility and durability to accelerated weathering tests. However, limited data are available about their long-term performance in real environment. Here, a systematic evaluation of phosphate consolidants after prolonged exposure in the field is reported for the first time. Naturally weathered marble specimens and a XVII century marble sculpture located in the Park of the Royal Palace in Versailles were treated by various formulations of the phosphate consolidant. Their conservation state was assessed before treatment by non-destructive methods (ultrasounds, color measurement, water absorption) and, in the case of the specimens, also by slightly destructive tests (SEM, FT-IR, MIP, IC). The conservation state of the specimens and the sculpture was further assessed right after treatment and then periodically monitored during exposure in the Versailles Park. Characterization after field exposure demonstrated that some formulations of the phosphate treatment are able to slow down marble deterioration, although it was not completely inhibited. Limited alterations in water absorption and aesthetic appearance confirmed the general compatibility of the phosphate treatment.

Chronic metabolic acidosis leads to bone-remodelling disorders based on excessive mineral matrix resorption and inhibition of bone formation, but also affects the homeostasis of citrate, which is an essential player in maintaining the acid&ndash, base balance and in driving the mineralisation process. This study aimed to investigate the impact of acidosis on the osteogenic properties of bone-forming cells and the effects of citrate supplementation in restoring the osteogenic features impaired by the acidic milieu. For this purpose, human mesenchymal stromal cells were cultured in an osteogenic medium and the extracellular matrix mineralisation was analysed at the micro- and nano-level, both in neutral and acidic conditions and after treatment with calcium citrate and potassium citrate. The acidic milieu significantly decreased the citrate release and hindered the organisation of the extracellular matrix, but the citrate supplementation increased collagen production and, particularly calcium citrate, promoted the mineralisation process. Moreover, the positive effect of citrate supplementation was observed also in the physiological microenvironment. This in vitro study proves that the mineral matrix organisation is influenced by citrate availability in the microenvironment surrounding bone-forming cells, thus providing a biological basis for using citrate-based supplements in the management of bone-remodelling disorders related to chronic low-grade acidosis.

In the framework of new materials for orthopedic applications, Magnesium Phosphate-based Cements (MPCs) are currently the focus of active research in biomedicine, given their promising features; in this field, the loading of MPCs with active molecules to be released in the proximity of newly forming bone could represent an innovative approach to enhance the in vivo performances of the biomaterial. In this work, we describe the preparation and characterization of MPCs containing citrate, an ion naturally present in bone which presents beneficial effects when released in the proximity of newly forming bone tissue. The cements were characterized in terms of handling properties, setting time, mechanical properties, crystallinity, and microstructure, so as to unravel the effect of citrate concentration on the features of the material. Upon incubation in aqueous media, we demonstrated that citrate could be successfully released from the cements, while contributing to the alkalinization of the surroundings. The cytotoxicity of the materials toward human fibroblasts was also tested, revealing the importance of a fine modulation of released citrate to guarantee the biocompatibility of the material.

Bone grafts and bone-based materials are widely used in orthopedic surgery. However, the selection of the bone type to be used is more focused on the biological properties of bone sources than physico-chemical ones. Moreover, although biogenic sources are increasingly used for deposition of biomimetic nanostructured coatings, the influence of specific precursors used on coating&rsquo, s morphology and composition has not yet been explored. Therefore, in order to fill this gap, we provided a detailed characterization of the properties of the mineral phase of the most used bone sources for allografts, xenografts and coating deposition protocols, not currently available. To this aim, several bone apatite precursors are compared in terms of composition and morphology. Significant differences are assessed for the magnesium content between female and male human donors, and in terms of Ca/P ratio, magnesium content and carbonate substitution between human bone and different animal bone sources. Prospectively, based on these data, bone from different sources can be used to obtain bone grafts having slightly different properties, depending on the clinical need. Likewise, the suitability of coating-based biomimetic films for specific clinical musculoskeletal application may depend on the type of apatite precursor used, being differently able to tune surface morphology and nanostructuration, as shown in the proof of concepts of thin film manufacturing here presented.

Hydroxyapatite (HAP) has a much lower dissolution rate and solubility than calcite, especially in an acidic environment, so it has been proposed for the protection of marble against acidic rain corrosion. Promising results were obtained, but further optimization is necessary as the treated layer is often incomplete, cracked and/or porous. In this paper, several parameters were investigated to obtain a coherent, uncracked layer, and to avoid the formation of metastable, soluble phases instead of HAP: the role of the pH of the starting solution; the effect of organic and inorganic additions, and in particular that of ethanol, as it is reported to adsorb on calcite, hence possibly favoring the growth of the HAP layer. Finally, a double application of the treatment was tested. Results were compared to those obtained with ammonium oxalate treatment, widely investigated for marble protection. Results indicate that adding small amounts of ethanol to the formulation remarkably increases the acid resistance of treated samples, and yields better coverage of the surface without crack formation. The effectiveness of the treatment is further enhanced when a second treatment is applied. The efficacy of ethanol-doped DAP mixtures was found to be remarkably higher than that of ammonium oxalate based treatments.

Biomimetic bone apatite coatings were realized for the first time by the novel Ionized Jet Deposition technique. Bone coatings were deposited on titanium alloy substrates by pulsed electron ablation of deproteinized bovine bone shafts in order to resemble bone apatite as closely as possible. The composition, morphology and mechanical properties of the coatings were characterized by GI-XRD, FT-IR, SEM-EDS, AFM, contact angle measurements, micro-scratch and screw-insertion tests. Different post-treatment annealing conditions (from 350 °C to 425 °C) were investigated. Bone apatite coatings exhibited a nanostructured surface morphology and a composition closely resembling that of the deposition target (i.e. natural bone apatite), also regarding the presence of magnesium and sodium ions. Crystallinity and composition of the coatings were strongly influenced by annealing temperature and duration; in particular, upon annealing at 400 °C and above, a crystallinity similar to that of bone was achieved. Finally, adhesion to the titanium substrate and hydrophilicity were significantly enhanced upon annealing, all characteristics being known to have a strong positive impact on promoting host cells attachment, proliferation and differentiation.

Simple Summary Three-dimensional bioprinting is a promising tool for the study of cancer development and progression in bone, as it permits modeling the complexity of the microenvironment and cell-to-cell interactions. To this aim, an ideal model should combine a proper structure design, biomaterials selection, and the cellular counterpart. In this review, 3D-bioprinted bone systems obtained by different bioinks, and strategies, are discussed, aimed at mimicking the bone cancer microenvironment. The main challenges and unmet needs to reach perfect biomimicry are highlighted. Abstract Bone cancer, both primary and metastatic, is characterized by a low survival rate. Currently, available models lack in mimicking the complexity of bone, of cancer, and of their microenvironment, leading to poor predictivity. Three-dimensional technologies can help address this need, by developing predictive models that can recapitulate the conditions for cancer development and progression. Among the existing tools to obtain suitable 3D models of bone cancer, 3D printing and bioprinting appear very promising, as they enable combining cells, biomolecules, and biomaterials into organized and complex structures that can reproduce the main characteristic of bone. The challenge is to recapitulate a bone-like microenvironment for analysis of stromal–cancer cell interactions and biological mechanics leading to tumor progression. In this review, existing approaches to obtain in vitro 3D-printed and -bioprinted bone models are discussed, with a focus on the role of biomaterials selection in determining the behavior of the models and its degree of customization. To obtain a reliable 3D bone model, the evaluation of different polymeric matrices and the inclusion of ceramic fillers is of paramount importance, as they help reproduce the behavior of both normal and cancer cells in the bone microenvironment. Open challenges and future perspectives are discussed to solve existing shortcomings and to pave the way for potential development strategies.

Due to poor mechanical properties and brittleness of bioactive glasses, the deposition of bioactive glass coatings on bioinert metallic implants for bone regeneration is a promising route to combine the high bioactivity of the glassy phase with the mechanical strength of metallic substrate. The Pulsed Electron Deposition (PED) technique has been recently demonstrated to be an effective method to fabricate highly-adherent and nanostructured bioactive thin films and coatings, with fine control over film composition. In this paper, we investigated the deposition by PED of 45S5 Bioglass ® and of a novel CaO-rich bioactive glass, also containing potassium oxide. Composition, microstructure, surface morphology, wettability and adhesion to the titanium substrate were assessed for both as-deposited and annealed coatings. All samples exhibited a nanostructured surface morphology and high hydrophilicity, both positive features for biological applications. In particular, annealed samples exhibited increased roughness and adhesion degree to the titanium substrate compared to the as-deposited ones. The results showed in this paper suggest that bioactive glass coatings deposited by PED are promising for being further investigated as bioactive coatings for bone implants.

Dissolution in pure and acid rain is among the main environmental degradation processes of marble. Coatings based on hydroxyapatite (HAP) have been proposed to prevent marble corrosion, providing encouraging results. In this paper, the resistance to dissolution was investigated on marble treated with different HAP-treatment formulations and compared to commercial ammonium oxalate. The ability of the coating to prevent corrosion was evaluated by performing wetting/drying cycles, by a custom-designed apparatus simulating rain. When ethanol is added to the solution used to form HAP, a significant reduction in calcium ions leached from marble is found, which is indicative of reduced corrosion.

In orthopedics and dentistry, novel approaches for fabricating biomimetic and mechanically robust bioactive coatings are highly desirable in order to truly improve the clinical results of coated implants compared to uncoated ones. In this paper, a biological-like apatite coating is deposited for the first time by plasma-assisted deposition of a natural apatite source. Specifically, we deposited bone apatite-like (BAL) thin films from bone apatite targets by pulsed electron deposition (PED). Morphology, composition, structure and mechanical properties of as-deposited and annealed BAL and stoichiometric hydroxyapatite (HA) films were investigated. While as-deposited BAL and HA films were poorly crystalline at room temperature, they crystallized to an extent very close to that of natural apatite when annealed at 400 °C. In addition, FTIR analysis pointed out that BAL films closely resembled the composition of the starting natural apatite target. Finally, nanoindentation tests indicated that BAL films with high mechanical properties could be deposited by PED.

One of the main critical aspects behind the failure or success of an implant resides in its ability to fast bond with the surrounding bone. To boost osseointegration, the ideal implant material should exhibit composition and structure similar to those of biological apatite. To this aim, the most common approach is to coat the implant surface with a coating of hydroxyapatite (HA), resembling the main component of mineralized tissues. However, bone apatite is a non-stoichiometric, multi-substituted poorly-crystalline apatite, containing significant amounts of foreign ions, with high biological relevance. Ion-substituted HAs can be deposited by so called “wet methods”, which are however poorly reproducible and hardly industrially feasible; at the same time bioactive coatings realized by plasma assisted method, interesting for industrial applications, are generally made of stoichiometric (i.e. un-substituted) HA. In this work, the literature concerning plasma-assisted deposition methods used to deposit ion-substituted HA was reviewed and the last advances in this field discussed. The ions taken into exam are those present in mineralized tissues and possibly having biological relevance. Notably, literature about this topic is scarce, especially relating to in vivo animal and clinical trials; further on, available studies evaluate the performance of substituted coatings from different points of view (mechanical properties, bone growth, coating dissolution, etc.) which hinders a proper evaluation of the real efficacy of ion-doped HA in promoting bone regeneration, compared to stoichiometric HA. Moreover, results obtained for plasma sprayed coatings (which is the only method currently employed for deposition at the industrial scale) were collected and compared to those of novel plasma-assisted techniques, that are expected to overcome its limitations. Data so far available on the topic were discussed to highlight advantages, limitations and possible perspectives of these procedures.

The response to thermal variations is the primary cause of marble deterioration in ancient and modern buildings. In this study, the thermal behavior of Carrara marble after consolidation by an innovative hydroxyapatite-based treatment was investigated in comparison with ammonium oxalate and ethyl silicate. Samples were subjected to heating-cooling cycles up to 80 °C. All the consolidating treatments were found to be fairly compatible, as in no case the residual strain after the thermal cycles was found to increase compared to the unweathered untreated marble. Anyway, the hydroxyapatite-treatment has the advantage of causing the highest increase in marble cohesion and the lowest residual strain, besides being more chromatically compatible and durable than the alternative commercial consolidants. Keywords: Hydroxyapatite, Calcium oxalate, Thermal expansion coefficient, Residual strain, Dilatometry

Nanostructured thin films of silver (Ag) are receiving attention in many production fields requiring adaptation to different substrate materials and fine control over surface texture, such as hi-tech industry and biomedicine. Here we report the deposition at room temperature of Ag thin films by pulsed electron ablation, the films thickness ranging from tens to hundreds of nanometers. Films micro- and nanostructure were investigated by means of AFM, STM and XRD, and chemical composition assessed by XPS. The data were elaborated and discussed in the context of depositions under non-local growth effects, and compared with pulsed electron ablation of different target materials. Our films resulted nanometrically smooth and homogeneous, with high degree of purity and characterized by a narrow distribution of grains of nanometric size at all the thicknesses considered. We suggest that a balance between the efficiency of the ablation process and the unique properties of Ag as a metal accounts for the overall reduction of the system size, and is at the origin of the observed nanostructuration. Our results are interesting in the perspective of metals ablation and provide an optimal platform for the study of functional surfaces with high surface-to-volume ratio.

The choice of the appropriate material having suitable compositional and morphological surface characteristics, is a crucial step in the development of orthopedic implants. The purpose of this paper is to elucidate, on this regard, the influence of two important hits, i.e., biogenic apatite with bone-like composition and nanostructured morphology, providing the evidence of the efficacy of nanostructured biogenic apatite coatings in favoring adhesion, growth, proliferation, and in vitro osteogenic differentiation of human mesenchymal stromal cells (hMSCs) isolated from the bone marrow. The specific features of this coating in terms of topographical and biochemical cues, obtained by Ionized Jet Deposition, are perceived by hMSCs, as suggested by changes in different morphologic parameters as Aspect Ratio or Elongation index, suggesting the impact exerted by the nanostructure on early adhesion events, cytoskeleton organization, and cells fate. In addition, the nanostructured CaP coating sustained the metabolic activity of the cells and facilitated the osteogenic differentiation of MSC by supporting the osteogenesis-related gene expression. These findings support the use of a combined approach between technological advancement and instructive surfaces, both from the topographical and the biochemical point of view, in order to manufacture smart biomaterials able to respond to different needs of the orthopedic practice.

Rising damp is one of the main issues affecting masonry buildings. However, its consequences on the mechanical performance of masonry structures are not so largely explored. In this paper, the compressive and shear behaviour of masonry triplets, manufactured with solid fired-clay bricks and cement-based mortar, is investigated in dry and moist conditions. The results are interpreted on the basis of the features of the single materials, from both a mechanical and microstructural point of view.

The durability of a new phosphate consolidant for limestone, based on formation of hydroxyapatite (HAP), was investigated in comparison with ethyl silicate (ES). Untreated, HAP- and ES-treated samples were subjected to repeated wetting–drying, freezing–thawing and salt crystallization cycles. The weathering effects were monitored in terms of alterations in visual appearance, weight, dynamic elastic modulus, tensile strength and pore size distribution. HAP samples performed better than untreated samples and underwent less deterioration in original properties than ES samples. ES samples, subjected to salt crystallization cycles when the treated layer was still hydrophobic, experienced detachment of the consolidated layer.

For consolidation of weathered carbonate materials (such as marble, limestone and lime-based mortars) no fully satisfactory treatment currently exists. In this paper, an innovative phosphate treatment was investigated as a possible consolidant for limestone and compared with a commercial ethyl silicate (ES). The two treatments were evaluated in terms of effectiveness (i.e., ability to restore cohesion and mechanical properties, by measuring penetration depth, dynamic elastic modulus, tensile strength, resistance to abrasion) and compatibility (i.e., lack of any negative consequence on the original substrate, by assessing mechanical match, colour change, new phases composition, pore size distribution, water and water vapour transport properties, drying rate and thermal behaviour). The phosphate treatment proved to be very promising, being able to overcome some ES limitations.

Research is needed on novel consolidants to restore weathered marble, because the available products exhibit limitations. To test new consolidants, samples with features similar to naturally weathered marble (i.e., near-surface damage) are recommended. We developed a novel method that produces decayed samples with a gradient in properties that can be tuned to any desired level, in terms of depth from the surface and decrease in dynamic elastic modulus. The idea is to produce near-surface damage by putting a marble sample in contact with a plate at a certain temperature for a certain time, calculated by a mathematical model. The model was used to predict the heating conditions to produce a certain decrease in dynamic elastic modulus in the first 1 cm from the surface, comparable to naturally weathered marble. Good confirmation of the model predictions was found experimentally. The suitability of using thermally “weathered” samples for testing consolidants was demonstrated in the case of a hydroxyapatite-based treatment. The mathematical model can be tailored to other lithotypes or ceramics, using the relevant property data.

Plasma sprayed coatings composed of stoichiometric hydroxyapatite have been extensively used to improve integration of metallic implants in the host bone, as hydroxyapatite (HA) is normally regarded as similar to the mineralized phase of bone. However, these coatings exhibited several drawbacks that limited their success. On the one hand biological apatite is a carbonated-HA, containing significant amounts of foreign ions, having low crystallinity and a small crystals size. This means that it differs from stoichiometric HA in terms of composition, stoichiometry, crystallinity degree, crystal size/morphology and, as a direct consequence, solubility, and ions release in the peri-implant environment. On the other hand, thick plasma sprayed coatings can undergo cracking and delamination and are scarcely uniform. For these reasons, research is pushing into two directions: (i) Increasing the similarity of apatite coatings to real bone, and (ii) exploring deposition by alternative plasma assisted techniques, allowing to achieve thin films, and having superior adhesion and a better control over the coating composition. In this article, we review the latest advances in the field of plasma-assisted deposition of ion-substituted hydroxyapatite thin films, highlighting the state of the art, the limitations, potentialities, open challenges, and the future scenarios for their application.

The effect of adding ethanol and isopropanol to aqueous solutions of diammonium hydrogen phosphate, used to create a passivating layer of calcium phosphates over marble, was investigated. Thanks to its weakening effect on the hydration sphere of ions in solution, ethanol allowed complete coverage of marble surface by a crack-free and pore-free layer of octacalcium phosphate. Even better results were obtained using isopropanol, because it has lower adsorption affinity to calcite than ethanol. Treatments involving alcohols provided good acid protection and also restored cohesion among calcite grains in weathered marble.

In this study, we investigated by FIB-SEM the microstructure of protective coatings formed by two inorganic treatments (namely, ammonium oxalate and ammonium phosphate solutions), with the aim of identifying the factors limiting the protective efficacy of the coatings and outlining possible improvement strategies. In the case of the oxalate treatment, the resulting layer of whewellite was found to contain vertical channels, which can allow water to reach the marble surface and trigger dissolution. Possible prevention of the formation of these channels by addition of a calcium source to the oxalate solution was attempted, but even micromolar additions led to rapid precipitation in the solution. In the case of the phosphate treatment, the resulting hydroxyapatite and octacalcium phosphate coating was found to be cracked and porous. To prevent cracks and pores, diminishing the ammonium phosphate concentration and adding ethanol to the solution were found to be effective strategies, as cracks were prevented and pores were reduced almost to zero. The resulting protective efficacy of the coating was found to be significantly improved, although still not perfect.

Neutron radiography was used to determine the penetration depth and the homogeneity of distribution of an innovative inorganic consolidant, based on formation of hydroxyapatite. The consolidant was applied to a porous limestone by three alternative methods (brushing, poultice, partial immersion). Neutron radiography was complemented by XRD, FT-IR and SEM/EDS, which provide information also on mineralogical composition and morphology of the new phases. Neutron radiography proved to be a powerful tool to determine the presence of hydrogen-rich hydroxyapatite and to evaluate the homogeneity of its distribution in the substrate. Nonetheless, combination with other techniques is necessary to reliably assess its penetration depth.

No fully satisfactory consolidant for sugaring marble currently exists, hence the use of ammonium phosphate to form hydroxyapatite (HAP) inside marble micro-cracks has recently been proposed. This study was aimed at: (i) investigating different treatment formulations (application of a 3 M aqueous solution of diammonium hydrogen phosphate (DAP), with/without addition of 1 mM or 3 mM CaCl2, with/without subsequent limewater poultice application) and characterizing the new Ca–P phases; (ii) systematically testing mechanical effectiveness and compatibility with the substrate of the most promising formulations, in comparison with ethyl silicate and ammonium oxalate; (iii) performing a pilot application of the most promising formulation to a real marble artwork affected by sugaring. The results of the study indicate that application of a 3 M DAP solution, followed by limewater poultice application, produces remarkable consolidation of weathered marble, with only slight alterations in pore size distribution and color change, thus providing much better results than both ethyl silicate and ammonium oxalate. Notably, while the above-described treatment conditions caused formation of tricalcium phosphate and octacalcium phosphate in artificially weathered samples, the same conditions caused formation of HAP in the historic artwork, presumably because some gypsum residues were present and calcite grains had high surface roughness. Keywords: Hydroxyapatite, TEOS, Calcium oxalate, Calcium phosphates, Grain disaggregation, Carrara marble

Given the high energy consumption connected to old buildings and their large environmental impact, there is a strong need for effective solutions for the building envelope retrofitting. Among these solutions, external thermal insulation composite systems (ETICS) have found large application in recent decades. In this paper a new kind of large-size thermal insulation composite boards, prefabricated using porcelain stoneware slab finishing, was developed. Different thermal insulating materials and adhesives, with and without glass fibre mesh, were tested by both current methodologies and purposely designed tests, in order to assess their physical–mechanical properties and durability performance, finally selecting the most suitable materials for the composite board. The strong points of this composite board are mainly: (i) its short placing time and improved execution quality, due to prefabrication; (ii) its high aesthetical value; (iii) its high durability, as the finishing layer is mostly insensible to weathering. The results highlight the good performances of the prefabricated composite board developed in this study (generally higher than current ETICS). The testing procedure followed in this study is also meant to give a contribution to the establishment of methodologies for the selection and durability assessment of materials for the building envelope retrofitting.

Ethyl silicate (TEOS) is nowadays the most widely used consolidant for stone, due to its efficacy on silicate stones and also on limestones containing small amounts of quartz. However, because of the very long time required for TEOS curing reactions to be completed, the final mechanical improvement caused by the treatment is reached only after several months and, during this period, the treated stone is temporarily hydrophobic. This latter aspect is one of the most relevant drawbacks of TEOS, as it makes it impossible to perform water-based interventions after consolidation. Therefore, in this study the possible acceleration of TEOS curing reactions by prolonged contact with water, some time after consolidant application, was investigated. A commercial TEOS-based product was applied on Globigerina limestone, a porous stone from Malta containing also small amounts of quartz. After that preliminary tests indicated that prolonged contact with water is actually effective in both removing hydrophobicity and improving mechanical strength, a new consolidation cycle, based on TEOS application followed by application of a water-impregnated poultice was tested. The results of the study indicate that water application by poultice, after curing for 7 days, allows to remove the hydrophobicity and achieve higher mechanical properties than those obtained after curing for 4 weeks in laboratory conditions. Moreover, such mechanical properties are around 90 % of those achieved after curing for as much as 7 months, which points out that the proposed method is a very promising technique for accelerating TEOS curing reactions.

When consolidants are applied to porous stones, redistribution may occur inside the pore system after the treatment application, which influences their final penetration depth and performance. In this paper, the kinetics of redistribution were investigated for a 2-step hydroxyapatite-based consolidant, applied by brushing and immersion. The results of the study indicate that both the application method and the drying phase are crucial in determining the final penetration depth, the amount of hydroxyapatite that forms and the redistribution kinetics. In all cases, the limewater poultice applied during the second step of the treatment proved to be effective in removing soluble compounds.

Given the lack of satisfying treatments for consolidating marble affected by thermally induced grain detachment (the so-called "sugaring"), the use of aqueous solutions of diammonium hydrogen phosphate (DAP) has recently been proposed. The idea is to form a new binding mineral (hydroxyapatite, HAP) as the reaction product between the DAP solution and the calcitic substrate. In this study, we investigated the effects of adding small quantities of ethanol (EtOH) to the DAP solution, with the aim of favoring HAP formation. The results of the study indicate that, when a 0.1 M DAP and 0.1 mM CaCl2 solution in 10 vol% EtOH is used, complete coverage of marble surface with a crack-free coating with reduced porosity is achieved (whereas no coating is formed without EtOH addition). This is thought to be a consequence of the weakening of hydration shells of phosphate ions in the DAP solution, thanks to the presence of ethanol molecules. When used to restore mechanical properties of weathered marble, the treatment with 10 vol% EtOH was found to significantly improve the dynamic elastic modulus after a single application and to completely restore it after a second application.

Self-cleaning finishing treatments based on the use of TiO 2 nanoparticles have been recently proposed for the protection of materials in cultural heritage, with the aim of increasing the durability of these materials in polluted environments. The results on stone seem encouraging, but the experimental tests on different porous materials, such as bricks and renders used in historical buildings, are still extremely limited. In the present paper, the application of water dispersion of titania nanoparticles to the repair renders of the former Del Corso hotel (XVIII cent., Bologna, Italy) was evaluated. The building and its environment were first analysed for assessing the appropriateness of such finishing, then samples of painted renders identical to those provided for in the intervention work were manufactured and treated with the dispersion, both by brushing on the dry paint and by brushing on the wet paint (the latter procedure in order to enhance the particles retention by exploiting the mechanism of fresco paintings). The outcome of the different treatments was investigated mainly to evaluate its compatibility with the substrate and its durability, which could be of interest also for the application of photocatalytic finishing to renders in new constructions.

Mechanical behaviour of old masonry may differ from the theoretical one to a great extent, hence it needs to be properly evaluated for quantifying the safety and serviceability of real structures, in view of their rehabilitation and/or seismic reliability assessment. Among the factors affecting such behaviour, the presence of moisture, mainly from rising damp, plays a key role in the deterioration state of old masonry structures, owing to salt crystallisation, frost damage, etc. Besides, water presence in the material pores may also directly influence their mechanical properties (compressive and tensile strength, elastic modulus), due to the interactions with the pore surface, enhancement of crack propagation velocity and other mechanisms. Although the effect of water saturation has been investigated for clay-bearing rocks, ceramics and concrete, its consequences on the mechanical behaviour of brick masonry still requires in-depth elucidation. For this reason, in the present paper the compressive strength and Young’s modulus of fired-clay bricks, cement-based and lime-based mortars as well as masonry triplets are investigated, in dry and wet conditions. The results are interpreted in the light of the microstructural features of the materials, i.e., total voids amount and pores size distribution.

The efficacy of stone consolidating treatments is significantly affected by the application procedure, including the technique used and the amount of product applied. Indeed, in the common on-site practice, consolidants are not applied until ‘apparent refusal’ (i.e. a drastic slowing down of the liquid absorption by the substrate), as usually recommended in commercial products’ technical data sheets and performed in laboratory tests, but a lower number of applications is performed for practical and economic reasons. Nevertheless, the influence of the application procedure on the absorption mechanism and distribution of the consolidant has not been fully elucidated yet, especially for solvent-based products, for which a competition between capillary uptake and solvent evaporation might arise. In this study, the influence of the treatment conditions on the consolidant efficacy was investigated with the aim of determining whether increasing the number of applications results in a deeper penetration depth and remarkably higher mechanical properties or in a higher saturation of the surface layer. For the experimental tests, an organic solvent-based ethyl silicate (or tetra-ethyl-ortho-silicate, TEOS) was selected, as it is the most commonly-used product in stone consolidation. Brushing was selected as the application method, because it is widely used in current practice and because it involves a discontinuous fluid supply to the stone, possibly causing an over-accumulation of product near the surface. Two different treatments were compared: brushing application by 5 strokes (T1) and 10 strokes (T2). The effect of the two treatments, applied on a porous limestone, was evaluated in terms of increase in mechanical properties (tensile strength, resistance to abrasion), alteration in microstructural features (determined by mercury intrusion porosimetry) and penetration depth (assessed by visual inspection of fractured samples, water sorptivity test and dynamic X-ray radiography). The results of the study indicate that increasing the number of TEOS applications from 5 to 10 brush strokes leads to a higher (but less than proportional) increase in mechanical properties (+33 % for T1, +47 % for T2) and a higher penetration depth (7–8 mm for T1, 12–13 mm for T2), while no accumulation of the additional product near the surface and no hard crust formation were found.

A novel inorganic consolidant has recently been proposed for the treatment of carbonate stones used in architectural and cultural heritage. The consolidant is an aqueous solution of diammonium hydrogen phosphate (DAP), which penetrates inside the stone and reacts with calcite to form hydroxyapatite (HAP). This HAP-based treatment seems very promising in several respects. It is effective in enhancing mechanical properties, only slightly alters stone transport properties, causes limited color change, and involves the use of non-toxic water solvent. However, several different treatment conditions and application methods have been investigated so far in the literature and the most suitable procedure for application in situ has not been identified yet. Therefore, in this paper a systematic investigation of the effects of different application methods of the DAP solution (brushing, poultice and immersion) was carried out. After DAP application, a further step consisting in a limewater-saturated poultice, aimed at overcoming possible issues connected to the presence of unreacted DAP in the treated stone, was performed and an “application cycle” was finally proposed. The treatments were tested on artificially weathered samples of Globigerina limestone (“Franka” type), a highly porous stone typically used in historical architecture in Malta and severely affected by decay processes. Even if Globigerina limestone is usually subject to salt-induced damage in the field, in this study artificial weathering was performed by heating to induce a controlled and uniformly distributed decay in the samples, as the presence of soluble salts would have interfered with the mechanisms of penetration and distribution of the DAP solution in the substrate, which was the main research objective. The outcome of the different treatments was evaluated in terms of consolidant penetration depth, mechanical properties, microstructure, contact angle, water sorptivity and color change, with respect to the untreated samples. The newly formed phases were characterized by SEM/EDS, FT-IR and ion chromatography. Based on the results of the study, brushing seems to be the most suitable method for DAP application, as it induces significant mechanical improvement but still limited microstructural, physical and chromatic alterations. Moreover, the benefits deriving from a higher consolidant absorption, as achieved by poultice and immersion applications (which are however much more laborious on site) are not so great in terms of HAP distribution in the substrate and consolidating performances.

In this paper an experimental study conducted on fired-clay brick masonry triplets built with cement- and hydraulic lime-based mortars and subjected to artificial weathering cycles is presented. A cycle is constituted by (1) a wetting phase by capillary rise of either a saline solution or deionized water and (2) a drying phase in oven. The aim of the accelerate weathering cycles is to simulate on-site conditions of masonry structures subjected to rising damp and salts attack due to daily and seasonal microclimatic changes. For comparison purposes, triplets subjected to drying cycles only were also considered. At the end of the weathering process, the triplets were shear tested in order to quantitative assess the separate and combined effect of water and salts within the pores on the mechanical behaviour. Shear parameters were interpreted on the basis of the microstructural characteristics of the constituent materials. Particular attention was given to the pore size distribution, salt amount, and distribution within the specimens after the conditioning procedure, finding significant correlations. Results show that the triplets shear behaviour is influenced by the damp/salts presence to a different extent depending on the materials involved.

Fired clay elements are widely diffused in architectural heritage, for both structural and ornamental purposes, and are susceptible to severe decay forms, hence their conservation is a very urgent task, requiring appropriate consolidants to restore their cohesion and mechanical strength. As fired clay bricks and terracotta artefacts contain silicate fractions, allowing ethyl silicate (ES) to chemically bond to the substrate, ES is supposed to be suitable for their consolidation and indeed it is used in some conservation works on this kind of material. However, its behaviour and performance on fired clay elements has not been systematically evaluated in the scientific literature, mostly when durability is concerned. This aspect is particularly relevant as diverging data can be found in the literature about the impact of ES on substrate durability, to such an extent that it was found to either increase or hamper materials resistance to decay, depending on the specific case in exam. In this study, the behaviour towards salts crystallisation of fired clay bricks treated by ethyl silicate was investigated, specifically focussing on the role of the application procedure, an aspect which is usually left to the conservatorists’ skilfulness but which is however of paramount importance for the treatment outcome. In particular, ES was applied by five and ten brush strokes, to assess how the different amount of product absorbed and its different distribution inside the porous substrate influence the final resistance of bricks to salt weathering. As a matter of fact, salt crystallization is commonly considered one of the most frequent and severe decay mechanism affecting bricks on site. Despite both treatments providing significant increases in mechanical properties and a limited modification in samples microstructure, durability was found to be dependent on the treatment conditions. Particular attention should be devoted to the amount of product applied, as higher product absorption, despite generally leading to better efficacy, could cause higher microstructural modifications, possibly hampering materials durability.