Anti-Oxidant Multi-Functionalized Materials: Strontium-Substituted Monetite and Brushite as Delivery Systems for Curcumin.

Curcumin has numerous biological activities and pharmaceutical applications related to its ability to inhibit reactive oxygen species. Herein, strontium-substituted monetite (SrDCPA) and strontium-substituted brushite (SrDCPD) were synthesized and further functionalized with curcumin with the aim to develop materials that combine the anti-oxidant properties of the polyphenol, the beneficial role of strontium toward bone tissue, and the bioactivity of calcium phosphates. Adsorption from hydroalcoholic solution increases with time and curcumin concentration, up to about 5-6 wt%, without affecting the crystal structure, morphology, and mechanical response of the substrates. The multi-functionalized substrates exhibit a relevant radical scavenging activity and a sustained release in phosphate buffer. Cell viability, morphology, and expression of the most representative genes were tested for osteoclast seeded in direct contact with the materials and for osteoblast/osteoclast co-cultures. The materials at relatively low curcumin content (2-3 wt%) maintain inhibitory effects on osteoclasts and support the colonization and viability of osteoblasts. The expressions of Alkaline Phosphatase (ALPL), collagen type I alpha 1 chain (COL1A1), and osteocalcin (BGLAP) suggest that curcumin reduces the osteoblast differentiation state but yields encouraging osteoprotegerin/receptor activator for the NFkB factor ligand (OPG/RANKL) ratio.

Hydroxyapatite Decorated with Tungsten Oxide Nanoparticles: New Composite Materials against Bacterial Growth.

The availability of biomaterials able to counteract bacterial colonization is one of the main requirements of functional implants and medical devices. Herein, we functionalized hydroxyapatite (HA) with tungsten oxide (WO3) nanoparticles in the aim to obtain composite materials with improved biological performance. To this purpose, we used HA, as well as HA functionalized with polyacrilic acid (HAPAA) or poly(ethylenimine) (HAPEI), as supports and polyvinylpyrrolidone (PVP) as stabilizing agent for WO3 nanoparticles. The number of nanoparticles loaded on the substrates was determined through Molecular Plasma-Atomic Emission Spectroscopy and is quite small, so it cannot be detected through X-ray diffraction analysis. It increases from HAPAA, to HA, to HAPEI, in agreement with the different values of zeta potential of the different substrates. HRTEM and STEM images show the dimensions of the nanoparticles are very small, less than 1 nm. In physiological solution HA support displays a greater tungsten cumulative release than HAPEI, despite its smaller loaded amount. Indeed, WO3 nanoparticles-functionalized HA exhibits a remarkable antibacterial activity against the Gram-positive Staphylococcus aureus in absence of cytotoxicity, which could be usefully exploited in the biomedical field.

Antiosteoporotic Nanohydroxyapatite Zoledronate Scaffold Seeded with Bone Marrow Mesenchymal Stromal Cells for Bone Regeneration: A 3D In Vitro Model.

BACKGROUND: Bisphosphonates are widely employed drugs for the treatment of pathologies with high bone resorption, such as osteoporosis, and display a great affinity for calcium ions and apatitic substrates. Here, we aimed to investigate the potentiality of zoledronate functionalized hydroxyapatite nanocrystals (HAZOL) to promote bone regeneration by stimulating adhesion, viability, metabolic activity and osteogenic commitment of human bone marrow derived mesenchymal stromal cells (hMSCs). METHODS: we adopted an advanced three-dimensional (3D) in vitro fracture healing model to study porous scaffolds: hMSCs were seeded onto the scaffolds that, after three days, were cut in halves and unseeded scaffolds were placed between the two halves. Scaffold characterization by X-ray diffraction, transmission and scanning electron microscopy analyses and cell morphology, viability, osteogenic differentiation and extracellular matrix deposition were evaluated after 3, 7 and 10 days of culture. RESULTS: Electron microscopy showed a porous and interconnected structure and a uniform cell layer spread onto scaffolds. Scaffolds were able to support cell growth and cells progressively colonized the whole inserts in absence of cytotoxic effects. Osteogenic commitment and gene expression of hMSCs were enhanced with higher expressions of ALPL, COL1A1, BGLAP, RUNX2 and Osterix genes. CONCLUSION: Although some limitations affect the present study (e.g., the lack of longer experimental times, of mechanical stimulus or pathological microenvironment), the obtained results with the adopted experimental setup suggested that zoledronate functionalized scaffolds (GHAZOL) might sustain not only cell proliferation, but positively influence osteogenic differentiation and activity if employed in bone fracture healing.

Monetite vs. Brushite: Different Influences on Bone Cell Response Modulated by Strontium Functionalization.

Monetite and brushite are regarded with increasing interest for the preparation of biomaterials for applications in the musculoskeletal system. Herein, we investigated the influence of strontium substitution in the structures of these two phosphates on bone cell response. To achieve this aim, co-cultures of human primary osteoclasts and human osteoblast-like MG63 cells were tested on strontium-substituted monetite and strontium-substituted brushite, as well as on monetite and brushite, as controls. In both structures, strontium substitution for calcium amounted to about 6 at% and provoked enlargement of the cell parameters and morphologic variations. Cumulative release in physiological solution increased linearly over time and was greater from brushite (up to about 160 and 560 mg/L at 14 days for Sr and Ca, respectively) than from monetite (up to about 90 and 250 mg/L at 14 days for Sr and Ca, respectively). The increasing viability of osteoblast-like cells over time, with the different expression level of some typical bone markers, indicates a more pronounced trigger toward osteoblast differentiation and osteoclast inhibition by brushite materials. In particular, the inhibition of cathepsin K and tartrate-resistant acid phosphatase at the gene and morphological levels suggests strontium-substituted brushite can be applied in diseases characterized by excessive bone resorption.

Curcumin-Functionalized Gelatin Films: Antioxidant Materials with Modulated Physico-Chemical Properties.

In this paper we used curcumin as a functionalizing agent of gelatin films with the aim to get antioxidant materials with modulated physico-chemical properties. To this aim, we prepared gelatin films at different contents of curcumin up to about 1.2 wt%. The as-prepared films, as well as glutaraldehyde crosslinked films, were submitted to several tests: swelling, water solubility, differential scanning calorimetry, X-ray diffraction, mechanical tests and curcumin release. The radical scavenging activity of the as-prepared films is similar to that of free curcumin, indicating remarkable antioxidant properties. All the other tested properties vary as a function of curcumin content and/or the presence of the crosslinking agent. In particular, the films exhibit sustained curcumin release in different solvents. Thanks to its biocompatibility, biodegradability and lack of antigenicity, gelatin uses span from food processing to packaging and biomaterials. It follows that the modulated properties exhibited by the functionalized materials developed in this work can be usefully employed in different application fields.

Novel drug-loaded film forming patch based on gelatin and snail slime.

Gelatin-based films enriched with snail slime are proposed as novel biodegradable and naturally bioadhesive patches for cutaneous drug delivery. Films (thickness range 163-248 µm) were stretchable and they adhered firmly onto the wetted skin, especially those with high amount (70% V/V) of snail slime extract. Fluconazole was selected as model drug and added to films containing the highest amount of snail slime. The presence of Fluconazole (4.53 ± 0.07% w/w) did not modify significantly the mechanical properties, the swelling degree and the bioadhesive performances of the films. Structural investigations demonstrated that the crystalline form III of the drug changed to the amorphous one, forming an amorphous solid dispersion. Moreover, snail slime prevented the drug recrystallization over time. In vitro permeation studies showed that film exhibited a cumulative drug concentration (over 60% in 24 h) similar to that of the control solution containing 20% w/V of ethanol. Fluconazole-loaded gelatin films proved to be effective towards clinical isolates of Candida spp. indicating that the drug maintained its remarkable antifungal activity once formulated into gelatin and snail slime-based films. In conclusion, snail slime, thanks to its peculiar composition, has proved to be responsible of optimal skin adhesion, film flexibility and of the formation of a supersaturating drug delivery system able to increase skin permeation.

Strontium substituted hydroxyapatite with ß-lactam integrin agonists to enhance mesenchymal cells adhesion and to promote bone regeneration.

Multi-functionalization of calcium phosphates to get delivery systems of therapeutic agents is gaining increasing relevance for the development of functional biomaterials aimed to solve problems related to disorders of the muscolo-skeletal system. In this regard, we functionalized Strontium substituted hydroxyapatite (SrHA) with some ß-lactam integrin agonists to develop materials with enhanced properties in promoting cell adhesion and activation of intracellular signaling as well as in counteracting abnormal bone resorption. For this purpose, we selected two monocyclic ß-lactams on the basis of their activities towards specific integrins on promoting cell adhesion and signalling. The amount of ß-lactams loaded on SrHA could be modulated on changing the polarity of the loading solution, from 3.5-24 wt% for compound 1 and from 3.2-8.4 wt% for compound 2. Studies on the release of the ß-lactams from the functionalized SrHA in aqueous medium showed an initial burst followed by a steady-release that ensures a small but constant amount of the compounds over time. The new composites were fully characterized. Co-culture of human primary mesenchymal stem cells (hMSC) and human primary osteoclast (OC) demonstrated that the presence of ß-lactams on SrHA favors hMSC adhesion and viability, as well as differentiation towards osteoblastic lineage. Moreover, the ß-lactams were found to enhance the inhibitory role of Strontium on osteoclast viability and differentiation.

Green synthesis of bioactive oligopeptides promoted by recyclable nanocrystalline hydroxyapatite.

Aim: The pharmaceutical industry is showing renewed interest in therapeutic peptides. Unfortunately, the chemical synthesis of peptides remains very expensive and problematic in terms of environmental sustainability. Hence, making peptides 'greener' has become a new front line for the expansion of peptide market. Results: We developed a mechanochemical solvent-free peptide bond-forming protocol using standard reagents and nanocrystalline hydroxyapatite as a bio-compatible, reusable inorganic base. The reaction was also conducted under ultra-mild, minimal solvent-grinding conditions, using common laboratory equipment. Conclusion: The efficacy of the described protocol was validated with the convenient preparation of endomorphin-1, H-Tyr-Pro-Trp-Phe-NH2, the endogenous ligand of the µ-opioid receptor, currently regarded as a lead for the discovery of painkillers devoid of harmful side effects.

Functional properties of chitosan films modified by snail mucus extract.

Snail mucus is an attractive natural substance, which is increasingly used in cosmetic creams and syrups thanks to its emollient, moisturizing, protective and reparative properties. The aim of the present study was to explore the physicochemical properties of chitosan-based films added with snail mucus extracted from Helix Aspersa Muller. To this aim, chitosan films at different content of snail mucus were fabricated by simple solvent casting technique. The results of X-ray diffraction analyses, tensile mechanical tests, Infrared spectroscopy and thermogravimetry demonstrated that snail mucus addition strongly modifies the properties of chitosan films. In particular, it acted like a plasticizer enhancing films extensibility up to ten times and strongly improving their water barrier and bioadhesion properties, with a trend depending on Snail mucus content. Furthermore, it provides the films with antibacterial properties and enhanced cytocompatibility, yielding materials with tailored properties for specific requirements.

Cylindrical Layered Bone Scaffolds with Anisotropic Mechanical Properties as Potential Drug Delivery Systems.

3D cylindrical layered scaffolds with anisotropic mechanical properties were prepared according to a new and simple method, which involves gelatin foaming, deposition of foamed strips, in situ crosslinking, strip rolling and lyophilization. Different genipin concentrations were tested in order to obtain strips with different crosslinking degrees and a tunable stability in biological environment. Before lyophilization, the strips were curled in a concentric structure to generate anisotropic spiral-cylindrical scaffolds. The scaffolds displayed significantly higher values of stress at break and of the Young modulus in compression along the longitudinal than the transverse direction. Further improvement of the mechanical properties was achieved by adding strontium-substituted hydroxyapatite (Sr-HA) to the scaffold composition and by increasing genipin concentration. Moreover, composition modulated also water uptake ability and degradation behavior. The scaffolds showed a sustained strontium release, suggesting possible applications for the local treatment of abnormally high bone resorption. This study demonstrates that assembly of layers of different composition can be used as a tool to obtain scaffolds with modulated properties, which can be loaded with drugs or biologically active molecules providing properties tailored upon the needs.

Strontium and Zinc Substitution in ß-Tricalcium Phosphate: An X-ray Diffraction, Solid State NMR and ATR-FTIR Study.

ß-tricalcium phosphate (ß-TCP) is one of the most common bioceramics, widely applied in bone cements and implants. Herein we synthesized ß-TCP by solid state reaction in the presence of increasing amounts of two biologically active ions, namely strontium and zinc, in order to clarify the structural modifications induced by ionic substitution. The results of X-ray diffraction analysis indicate that zinc can substitute for calcium into a ß-TCP structure up to about 10 at% inducing a reduction of the cell parameters, whereas the substitution occurs up to about 80 at% in the case of strontium, which provokes a linear increase of the lattice constants, and a slight modification into a more symmetric structure. Rietveld refinements and solid-state 31P NMR spectra demonstrate that the octahedral Ca(5) is the site of ß-TCP preferred by the small zinc ion. ATR-FTIR results indicate that zinc substitution provokes a disorder of ß-TCP structure. At variance with the behavior of zinc, strontium completely avoids Ca(5) site even at high concentration, whereas it exhibits a clear preference for Ca(4) site. The infrared absorption bands of ß-TCP show a general shift towards lower wavenumbers on increasing strontium content. Particularly significant is the shift of the infrared symmetric stretching band at 943 cm-1 due to P(1), that is the phosphate more involved in Ca(4) coordination, which further supports the occupancy preference of strontium.

Effect of strontium substituted ß-TCP associated to mesenchymal stem cells from bone marrow and adipose tissue on spinal fusion in healthy and ovariectomized rat.

Despite alternatives to autogenous bone graft for spinal fusion have been investigated, it has been shown that osteoconductive materials alone do not give a rate of fusion comparable with autogenous bone. This study analyzed a strontium substituted ß-tricalcium phosphate (Sr-ßTCP) associated with syngeneic, unexpanded, and undifferentiated mesenchymal stem cells from bone marrow (BMSC) or adipose tissue (ADSC) as a new tissue engineering approach for spinal fusion procedures. A posterolateral fusion was performed in 15 ovariectomized (OVX) and 15 sham-operated (SHAM) Inbred rats. Both SHAM and OVX animals were divided into three groups: Sr-ßTCP, Sr-ßTCP + BMCSs, and Sr-ßTCP + ADSCs. Animals were euthanized 8 weeks after surgery and the spines evaluated by manual palpation, micro-CT, and histology. For both SHAM and OVX animals, the fusion tissue in the Sr-ßTCP + BMSCs group was more solid. This effect was significantly higher in OVX animals by comparing the Sr-ßTCP + BMCSs group with Sr-ßTCP + ADSCs. Radiographical score, based on micro-CT 2D image, highlighted that the Sr-ßTCP + BMCSs group presented a similar fusion to Sr-ßTCP and higher than Sr-ßTCP + ADSCs in both SHAM and OVX animals. Micro-CT 3D parameters did not show significant differences among groups. Histological score showed significantly higher fusion in Sr-ßTCP + BMSCs group than Sr-ßTCP and Sr-ßTCP + ADSCs, for both SHAM and OVX animals. In conclusion, our results suggest that addition of BMSCs to a Sr-ßTCP improve bone formation and fusion, both in osteoporotic and nonosteoporotic animal, whereas spinal fusion is not enhanced in rats treated with Sr-ßTCP + ADSCs. Thus, for conducting cells therapy in spinal surgery BMSCs still seems to be a better choice compared with ADSCs.

Role of Aspartic and Polyaspartic Acid on the Synthesis and Hydrolysis of Brushite.

Dicalcium phosphate dihydrate (DCPD) is one of the mineral phases indicated as possible precursors of biological apatites and it is widely employed in the preparation of calcium phosphate bone cements. Herein, we investigated the possibility to functionalize DCPD with aspartic acid (ASP) and poly-aspartic acid (PASP), as models of the acidic macromolecules of biomineralized tissues, and studied their influence on DCPD hydrolysis. To this aim, the synthesis of DCPD was performed in aqueous solution in the presence of increasing concentrations of PASP and ASP, whereas the hydrolysis reaction was carried out in physiological solution up to three days. The results indicate that it is possible to prepare DCPD functionalized with PASP up to a polyelectrolyte content of about 2.3 wt%. The increase of PASP content induces crystal aggregation, reduction of the yield of the reaction and of the thermal stability of the synthesized DCPD. Moreover, DCPD samples functionalized with PASP display a slower hydrolysis than pure DCPD. On the other hand, in the explored range of concentrations (up to 10 mM) ASP is not incorporated into DCPD and does not influence its crystallization nor its hydrolysis. At variance, when present in the hydrolysis solution, ASP, and even more PASP, delays the conversion into the more stable phases, octacalcium phosphate and/or hydroxyapatite. The greater influence of PASP on the synthesis and hydrolysis of DCPD can be ascribed to the cooperative action of the carboxylate groups and to its good fit with DCPD structure.

Multifunctionalization Modulates Hydroxyapatite Surface Interaction with Bisphosphonate: Antiosteoporotic and Antioxidative Stress Materials.

Multifunctionalized biomaterials with enhanced bone antiresorptive properties were obtained through adsorption of a bisphosphonate, risedronate, on hydroxyapatite (HA) nanocrystals functionalized with zinc ions and polyethylenimine (PEI). Zn incorporation into the HA structure amounts to about 8 atom %, whereas the PEI content of the bifunctionalized material ZnHAPEIBP is about 5.9 wt %. The mechanism of adsorption and release of the bisphosphonate on ZnHAPEI is compared with that on ZnHA: risedronate adsorption isotherm on ZnHA is a Langmuir type, whereas the isotherm of adsorption on ZnHAPEI is better fitted with a Freundlich model and involved a higher amount of adsorbed risedronate. In vitro cell tests were carried out with a coculture model of osteoblasts and osteoclasts using a model simulating oxidative stress and consequent cellular senescence and osteoporosis by the addition of H2O2. The conditions utilized in the coculture model strongly affect osteoblast behavior. The results show that the composite materials allow an increase in osteoblast viability and recover impairment, revealing a novel characteristic of risedronate that is able to counteract the negative effects of oxidative stress when associated with differently functionalized samples. Both PEI and the bisphosphonate reduce osteoclast viability. Moreover, PEI, and even more risedronate, exerts an inhibitory effect on osteoclast activity.

Modulation of Alendronate release from a calcium phosphate bone cement: An in vitro osteoblast-osteoclast co-culture study.

In this study, we loaded a biomimetic calcium phosphate bone cement (CPC) with relatively high amounts of a bisphosphonate through the use of Solid Lipid Microparticles (MPs) and investigated bone cells response to the composite cements. 10, 20 and 30% w/w of Alendronate (AL) were successfully introduced into microparticles of Cutina HR and Precirol, which were prepared by means of spray-congealing technique. Addition of AL-loaded MPs to the cement composition provoked a lengthening of the setting and of the hardening processes. However, setting times were still in a range useful for clinical applications, except for the cements at the highest Alendronate content. The composite cements displayed a sustained drug release over time. Cements with the best performances in terms of setting, hardening, mechanical properties and drug release were submitted to in vitro tests using a co-culture model of osteoblast and osteoclast. The results showed that the use of MPs to enrich the cement composition with Alendronate provides materials able to inhibit osteoclast viability and activity, while promoting osteoblast viability and earlier differentiation, indicating that the MPs-cements are good delivery systems for bisphosphonates.

Antiresorptive properties of strontium substituted and alendronate functionalized hydroxyapatite nanocrystals in an ovariectomized rat spinal arthrodesis model.

PURPOSE: The purpose of this study was to comparatively investigate the posterolateral fusion rate in ovariectomized (OVX) rats using two new bone graft materials: strontium (Sr) substituted hydroxyapatite (HA) nanocrystals and alendronate (AL) functionalized HA nanocrystals. SrHA was synthesized in presence of different Sr concentrations (SrHA5; SrHA10) and HA-AL nanocrystals at increasing bisphosphonate (BP) content (HA-AL7; HA-AL28). METHODS: A posterolateral spinal fusion model in twenty-five Sham operated and in twenty-five OVX female rats was used and materials were bilaterally implanted between transverse processes of lumbar vertebrae. Sham and OVX animals were divided in five groups depending on the material: HA, SrHA5, SrHA10, HA-AL7 and HA-AL28. The assessment of bone fusion was carried out by µCT, histology and histomorphometry. RESULTS: Some gaps between the transverse processes were observed by µCT in OVXHA group, while they were not present in all the other groups. These results were consistent with the histomorphometrical analyses showing that in OVX animals SrHA and HA-AL materials displayed significantly higher BV/TV and Tb.Th and significantly lower Tb.N and Tb.Sp in comparison with HA alone. CONCLUSIONS: Results of this study suggest that in spinal fusion the incorporation of bioactive ions or drugs as Sr and AL improves the biological performance of HA representing a promising strategy especially in osteoporosis patients with high risks of spinal fusion failure. Results also suggest the existence of a Sr and AL dose response effect and that HA containing the highest AL dose could be the candidate biomaterial for spinal fusion in osteoporotic subjects.

(9R)-9-Hydroxystearate-Functionalized Anticancer Ceramics Promote Loading of Silver Nanoparticles.

Functionalization of calcium phosphates for biomedical applications has been proposed as a strategy to enrich the good osteoinductive properties of these materials with specific therapeutic characteristics. Herein, we prepared and characterized hydroxyapatite nanocrystals functionalized with an anticancer agent, (9R)-9-hydroxystearate (HSA), and loaded with an antimicrobial agent, namely silver nanoparticles (AgNPs). Nanocrystals at two different contents of HSA, about 4 and 9 wt %, were prepared via direct synthesis in aqueous solution. Loading with the antibacterial agent was achieved through interaction with different volumes of AgNPs suspensions. The amount of loaded nanoparticles increases with the volume of the AgNPs suspension and with the hydroxystearate content of the nanocrystals, up to about 3.3 wt %. The structural, morphological, and hydrophobic properties of the composite materials depend on hydroxystearate content, whereas they are not affected by AgNPs loading. At variance, the values of zeta potential slightly increase with the content of AgNPs, which exhibit a sustained release in cell culture medium.

Strontium-Substituted Hydroxyapatite-Gelatin Biomimetic Scaffolds Modulate Bone Cell Response.

Strontium has a beneficial role on bone remodeling and is proposed for the treatment of pathologies associated to excessive bone resorption, such as osteoporosis. Herein, the possibility to utilize a biomimetic scaffold as strontium delivery system is explored. Porous 3D gelatin scaffolds containing about 30% of strontium substituted hydroxyapatite (SrHA) or pure hydroxyapatite (HA) are prepared by freeze-drying. The scaffolds display a very high open porosity, with an interconnectivity of 100%. Reinforcement with further amount of gelatin provokes a modest decrease of the average pore size, without reducing interconnectivity. Moreover, reinforced scaffolds display reduced water uptake ability and increased values of mechanical parameters when compared to as-prepared scaffolds. Strontium displays a sustained release in phosphate buffered saline: the quantities released after 14 d from as-prepared and reinforced scaffolds are just 14 and 18% of the initial content, respectively. Coculture of osteoblasts and osteoclasts shows that SrHA-containing scaffolds promote osteoblast viability and activity when compared to HA-containing scaffolds. On the other hand, osteoclastogenesis and osteoclast differentiation are significantly inhibited on SrHA-containing scaffolds, suggesting that these systems could be usefully applied for local delivery of strontium in loci characterized by excessive bone resorption.

Gradient coatings of strontium hydroxyapatite/zinc ß-tricalcium phosphate as a tool to modulate osteoblast/osteoclast response.

The chemistry, structure and morphology of the implant surface have a great influence on the integration of an implant material with bone tissue. In this work, we applied Combinatorial Matrix-Assisted Pulsed Laser Evaporation (C-MAPLE) to deposit gradient thin films with variable compositions of Sr-substituted hydroxyapatite (SrHA) and Zn-substituted ß-tricalcium phosphate (ZnTCP) on Titanium substrates. Five samples with different SrHA/ZnTCP composition ratios were fabricated by a single step laser procedure. SrHA was synthesized in aqueous medium, whereas ZnTCP was obtained by reaction at high temperature. Both powders were separately suspended in deionized water, frozen at liquid nitrogen temperature and used as targets for C-MAPLE experiments, which proceed via simultaneous laser vaporization of two distinct material targets. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy analyses confirmed that the coatings contain the same crystalline phases as the as-prepared powder samples, with a homogeneous distribution of the two phosphates along deposited thin films. Human osteoclast precursor 2T-110 and human osteoblast-like cells MG63 were co-cultured on the coatings. The results indicate that osteoblast viability and production of osteocalcin were promoted by the presence of ZnTCP. On the other hand, SrHA inhibited osteoclastogenesis and osteoclast differentiation, as demonstrated by the observed increase of the osteoprotegerin/RANKL ratio and decrease of the number of TRAP-positive multinucleated cells when increasing SrHA amount in the coatings. The results indicate that the possibility to tailor the composition of the coatings provides materials able to modulate bone growth and bone resorption.