Sodium fusidate loaded apatitic calcium phosphates: Adsorption behavior, release kinetics, antibacterial efficacy, and cytotoxicity assessment.

The present work reports the adsorption, release, antibacterial properties, and in vitro cytotoxicity of sodium fusidate (SF) associated with a carbonated calcium phosphate bone cement. The adsorption study of SF on cement powder compared to stoichiometric hydroxyapatite and nanocrystalline carbonated apatite was investigated to understand the interaction between this antibiotic and the calcium phosphate phases involved in the cement formulation and setting reaction. The adsorption data revealed a fast kinetic process. However, the evolution of the amount of adsorbed SF was well described by a Freundlich-type isotherm characterized by a low adsorption capacity of the materials toward the SF molecule. The in vitro release results indicated a prolonged and controlled SF release for up to 34 days. The SF amounts eluted daily were at a therapeutic level (0.5-2 mg/L) and close to the antibiotic minimum inhibitory concentration (0.1-0.9 mg/L). Furthermore, the release data fitting and modeling suggested that the drug release occurred mainly by a diffusion mechanism. The antibacterial activity showed the effectiveness of SF released from the formulated cements against Staphylococcus aureus. Furthermore, the biological in vitro study demonstrated that the tested cements didn't show any cytotoxicity towards human peripheral blood mononuclear cells and did not significantly induce inflammation markers like IL-8.

Challenging applicability of ISO 10993-5 for calcium phosphate biomaterials evaluation: Towards more accurate in vitro cytotoxicity assessment.

Research on biomaterials typically starts with cytocompatibility evaluation, using the ISO 10993-5 standard as a reference that relies on extract tests to determine whether the material is safe (cell metabolic activity should exceed 70 %). However, the generalized approach within the standard may not accurately reflect the material's behavior in direct contact with cells, raising concerns about its effectiveness. Calcium phosphates (CaPs) are a group of materials that, despite being highly biocompatible and promoting bone formation, still exhibit inconsistencies in basic cytotoxicity evaluations. Hence, in order to test the cytocompatibility dependence on different experimental setups and material-cell interactions, we used amorphous calcium phosphate, α-tricalcium phosphate, hydroxyapatite, and octacalcium phosphate (0.1 mg/mL to 5 mg/mL) with core cell lines of bone microenvironment: mesenchymal stem cells, osteoblast-like and endothelial cells. All materials have been characterized for their physicochemical properties before and after cellular contact and once in vitro assays were finalized, groups identified as 'cytotoxic' were further analyzed using a modified Annexin V apoptosis assay to accurately determine cell death. The obtained results showed that indirect contact following ISO standards had no sensitivity of tested cells to the materials, but direct contact tests at physiological concentrations revealed decreased metabolic activity and viability. In summary, our findings offer valuable guidelines for handling biomaterials, especially in powder form, to better evaluate their biological properties and avoid false negatives commonly associated with the traditional standard approach.

Modeling Pkd1 gene-targeted strategies for correction of polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) causes renal cysts and leads to end-stage renal disease in midlife due mainly to PKD1 gene mutations. Virtually no studies have explored gene therapeutic strategies for long-term effective treatment of PKD. Toward this aim, the severely cystic Pkd1-null mouse model was targeted with a series of transgene transfers using genomic Pkd1 under its regulatory elements (Pkd1wt), a kidney-targeted Pkd1 gene (SBPkd1), or Pkd1Minigene. The introduced Pkd1wt gene constructs with ∼8-fold overexpression display similar endogenous cellular profiles and full complementation of Pkd1-/- phenotype and establish the referral Pkd1 genomic length for proper regulation. SBPkd1 transgene transfer expressing 0.6- or 7-fold Pkd1 endogenous levels is sufficient to correct glomerular and proximal tubular cysts and to markedly postpone cysts in other tubular segments as well, showing that the small SB elements appreciably overlap with Pkd1 promoter/5' UTR regulation. Renal-targeted Pkd1Minigene at high copy numbers conveys an expression level similar to that of the endogenous Pkd1 gene, with widespread and homogeneous weak Pkd1 cellular signal, partially rescuing all cystic tubular segments. These transgene transfers determine that Pkd1 intragenic sequences regulate not only expression levels but also spatiotemporal patterns. Importantly, our study demonstrates that Pkd1 re-expression from hybrid therapeutic constructs can ameliorate, with considerably extended lifespan, or eliminate PKD.

Exploring the Formation Kinetics of Octacalcium Phosphate from Alpha-Tricalcium Phosphate: Synthesis Scale-Up, Determination of Transient Phases, Their Morphology and Biocompatibility.

Even with decades of research studies behind octacalcium phosphate (OCP), determination of OCP phase formation has proved to be a cumbersome challenge. Even though obtaining a large quantity of OCP is important for potential clinical uses, it still remains a hindrance to obtain high yields of pure OCP. Taking that into consideration, the purpose of this study was to scale-up OCP synthesis for the first time and to use a multi-technique approach to follow the phase transformation pathway at multiple time points. In the present study, OCP has been synthesized from α-tricalcium phosphate (α-TCP), and subsequently scaled-up tenfold and hundredfold (100 mg → 10 g). The hydrolysis mechanism has been followed and described by using XRD and FTIR spectroscopy, as well as Raman and SEM. Gradual transformation into the OCP phase transpired through dicalcium phosphate dihydrate (brushite, DCPD, up to ~36%) as an intermediary phase. Furthermore, the obtained transitional phases and final OCP phases (across all scale-up levels) were tested with human bone marrow-derived mesenchymal stem cells (hBMSCs), in order to see how different phase mixtures affect the cell viability, and also to corroborate the safety of the scaled-up product. Twelve out of seventeen specimens showed satisfactory percentages of cell viability and confirmed the prospective use of scaled-up OCP in further in vitro studies. The present study, therefore, provides the first scale-up process of OCP synthesis, an in depth understanding of the formation pathway, and investigation of the parameters able to contribute in the OCP phase formation.

Tunable Behavior in Solution of Amorphous Calcium Ortho/Pyrophosphate Materials: An Acellular In Vitro Study.

Amorphous calcium phosphate-based materials are of major interest in the field of bone substitution. Very recently, the low-temperature synthesis of a new family of amorphous calcium phosphate containing both orthophosphate and pyrophosphate ions in controlled proportions has been reported. Despite their interest, especially due to the biochemical role and the hydrolysis of pyrophosphate occurring in vivo, the behavior of such materials when interacting with aqueous media has never been described. Consequently, we herein report the in vitro acellular evolution of three compositions of mixed calcium ortho- and pyrophosphate amorphous materials including a different orthophosphate proportion. As a first step to assess the physicochemical reactivity of these amorphous materials, they were tested in two different media at 37 °C, acidified water and simulated body fluid solution, from 1 h up to 15 days. The results demonstrated that they were quite stable and that they progressively released part of their constitutive ions, highlighting their potential for controlled delivery of bioactive ions (calcium, orthophosphate, and pyrophosphate ions). In addition to these properties, we showed that the material with the highest ortho/(ortho + pyro) phosphate ratio started to crystallize into nanocrystalline apatite analogous to bone mineral within 2 days or 2 weeks depending on the medium. For the other material compositions, no layer of apatite was detected at their surface with SBF testing despite the favorable supersaturation indexes, crystallization being probably inhibited by pyrophosphate ions released in the medium. This varying apatite-forming ability emphasizes the key role of the ortho/(ortho + pyro) phosphate ratio of these materials in their in vitro reactivity and bioactivity, which paves the way for the development of this promising family of amorphous calcium phosphate materials with tunable physicochemical and biological properties.

Injectable bone cement containing carboxymethyl cellulose microparticles as a silver delivery system able to reduce implant-associated infection risk.

In the challenging quest for a solution to reduce the risk of implant-associated infections in bone substitution surgery, the use of silver ions is promising regarding its broad spectrum on planktonic, sessile as well as multiresistant bacteria. In view of controlling its delivery in situ at the desired dose, we investigated its encapsulation in carboxymethyl cellulose (CMC) microparticles by spray-drying and included the latter in the formulation of a self-setting calcium phosphate bone cement. We implemented an original step-by-step methodology starting from the in vitro study of the antibacterial properties and cytotoxicity of two silver salts of different solubility in aqueous medium and then in the cement to determine the range of silver loading able to confer anti-biofilm and non-cytotoxic properties to the biomaterial. A dose-dependent efficiency of silver was demonstrated on the main species involved in bone-implant infection (S. aureus and S. epidermidis). Loading silver in microspheres instead of loading it directly inside the cement permitted to avoid undesired silver-cement interactions during setting and led to a faster release of silver, i.e. to a higher dose released within the first days combining anti-biofilm activity and preserved cytocompatibility. In addition, a combined interest of the introduction of about 10% (w/w) silver-loaded CMC microspheres in the cement formulation was demonstrated leading to a fully injectable and highly porous (77%) cement, showing a compressive strength analogous to cancellous bone. This injectable silver-loaded biomimetic composite cement formulation constitutes a versatile bone substitute material with tunable drug delivery properties, able to fight against bone implant associated infection. STATEMENT OF SIGNIFICANCE: This study is based on two innovative scientific aspects regarding the literature: i) Choice of silver ions as antibacterial agent combined with their way of incorporation: Carboxymethylcellulose has never been tested into bone cement to control its drug loading and release properties. ii) Methodology to formulate an antibacterial and injectable bone cement: original and multidisciplinary step-by-step methodology to first define, through (micro)biological tests on two silver salts with different solubilities, the targeted range of silver dose to include in carboxymethylcellulose microspheres and, then optimization of silver-loaded microparticles processing to fulfill requirements (encapsulation efficiency and size). The obtained fully injectable composite controls the early delivery of active dose of silver (from 3 h and over 2 weeks) able to fight against bone implant-associated infections.

Antibacterial Electrodeposited Copper-Doped Calcium Phosphate Coatings for Dental Implants.

Dental implants provide a good solution for the replacement of tooth roots. However, the full restoration of tooth functions relies on the bone-healing period before positioning the abutment and the crown on the implant, with the associated risk of post-operative infection. This study aimed at developing a homogeneous and adherent thin calcium phosphate antibacterial coating on titanium dental implants by electrodeposition to favor both implant osseointegration and to limit peri-implantitis. By combining global (XRD, FTIR-ATR, elemental titration) and local (SEM, Raman spectroscopy on the coating surface and thickness) characterization techniques, we determined the effect of electrodeposition time on the characteristics and phases content of the coating and the associated mechanism of its formation. The 1-min-electrodeposited CaP coating (thickness: 2 ± 1 µm) was mainly composed of nano-needles of octacalcium phosphate. We demonstrated its mechanical stability after screwing and unscrewing the dental implant in an artificial jawbone. Then, we showed that we can reach a high copper incorporation rate (up to a 27% Cu/(Cu+Ca) molar ratio) in this CaP coating by using an ionic exchange post-treatment with copper nitrate solution at different concentrations. The biological properties (antibiofilm activity and cytotoxicity) were tested in vitro using a model of mixed bacteria biofilm mimicking peri-implantitis and the EN 10993-5 standard (direct contact), respectively. An efficient copper-doping dose was determined, providing an antibiofilm property to the coating without cytotoxic side effects. By combining the electrodeposition and copper ionic exchange processes, we can develop an antibiofilm calcium phosphate coating on dental implants with a tunable thickness and phases content.

A soft-chemistry approach to the synthesis of amorphous calcium ortho/pyrophosphate biomaterials of tunable composition.

The development of amorphous phosphate-based materials is of major interest in the field of biomaterials science, and especially for bone substitution applications. In this context, we herein report the synthesis of gel-derived hydrated amorphous calcium/sodium ortho/pyrophosphate materials at ambient temperature and in water. For the first time, such materials have been obtained in a large range of tunable orthophosphate/pyrophosphate molar ratios. Multi-scale characterization was carried out thanks to various techniques, including advanced multinuclear solid state NMR. It allowed the quantification of each ionic/molecular species leading to a general formula for these materials: [(Ca2+y Na+z H+3+x-2y-z)(PO43-)1-x(P2O74-)x](H2O)u. Beyond this formula, the analyses suggest that these amorphous solids are formed by the aggregation of colloids and that surface water and sodium could play a role in the cohesion of the whole material. Although the full comprehension of mechanisms of formation and structure is still to be investigated in detail, the straightforward synthesis of these new amorphous materials opens up many perspectives in the field of materials for bone substitution and regeneration. STATEMENT OF SIGNIFICANCE: The metastability of amorphous phosphate-based materials with various chain length often improves their (bio)chemical reactivity. However, the control of the ratio of the different phosphate entities has not been yet described especially for small ions (pyrophosphate/orthophosphate) and using soft chemistry, whereas it opens the way for the tuning of enzyme- and/or pH-driven degradation and biological properties. Our study focuses on elaboration of amorphous gel-derived hydrated calcium/sodium ortho/pyrophosphate solids at 70 °C with a large range of orthophosphate/pyrophosphate ratios. Multi-scale characterization was carried out using various techniques such as advanced multinuclear SSNMR (31P, 23Na, 1H, 43Ca). Analyses suggest that these solids are formed by colloids aggregation and that the location of mobile water and sodium could play a role in the material cohesion.

Adsorption of Proteins on m-CPPD and Urate Crystals Inhibits Crystal-induced Cell Responses: Study on Albumin-crystal Interaction.

The biological effects and cellular activations triggered by monosodium urate (MSU) and calcium pyrophosphate dihydrate (monoclinic: m-CPPD) crystals might be modulated by protein coating on the crystal surface. This study is aimed at: (i) Identifying proteins adsorbed on m-CPPD crystals, and the underlying mechanisms of protein adsorption, and (ii) to understand how protein coating did modulate the inflammatory properties of m-CPPD crystals. The effects of protein coating were assessed in vitro using primary macrophages and THP1 monocytes. Physico-chemical studies on the adsorption of bovine serum albumin (BSA) upon m-CPPD crystals were performed. Adsorption of serum proteins, and BSA on MSU, as well as upon m-CPPD crystals, inhibited their capacity to induce interleukin-1-ß secretions, along with a decreased ATP secretion, and a disturbance of mitochondrial membrane depolarization, suggesting an alteration of NLRP3 inflammasome activation. Proteomic analysis identified numerous m-CPPD-associated proteins including hemoglobin, complement, albumin, apolipoproteins and coagulation factors. BSA adsorption on m-CPPD crystals followed a Langmuir-Freundlich isotherm, suggesting that it could modulate m-CPPD crystal-induced cell responses through crystal/cell-membrane interaction. BSA is adsorbed on m-CPPD crystals with weak interactions, confirmed by the preliminary AFM study, but strong interactions of BSA molecules with each other occurred favoring crystal agglomeration, which might contribute to a decrease in the inflammatory properties of m-CPPD crystals. These findings give new insights into the pathogenesis of crystal-related rheumatic diseases and subsequently may open the way for new therapeutic approaches.

Calcium phosphate coatings elaborated by the soaking process on titanium dental implants: Surface preparation, processing and physical-chemical characterization.

OBJECTIVE: Dental implant manufacturers are looking for new surfaces to improve osseointegration. It is accepted that calcium phosphate coatings favor bone healing. Among all the techniques, the soaking process seems attractive because of its ability in producing a bioactive coating at low temperature. The objective of this study is to improve the titanium implant surface roughness and chemistry by optimizing the surface preparation and the soaking process parameters to produce a bioactive and adherent calcium phosphate coating. METHODS: Titanium samples were sandblasted and acid etched. Coatings were realized by an alternate soaking process including a centrifugation step to create a phosphate solution thin film on the implant that reacts with the calcium of the second bath. We performed a characterization of the sample surface with complementary physical and physico-chemical techniques to assess the effect of surface preparation and coating process operating parameters on coating formation and characteristics. RESULTS: Surface preparation led to a roughness around 1.6µm, micro-porosities, high surface wettability and removed the embedded sandblasting particles. We showed that the centrifugation step is critical and determines the coating formation, coverage and thickness. A thin coating (∼2µm) composed of apatite analogous to bone mineral was deposited. The coating adhesion was demonstrated by screwing/unscrewing test in an artificial jawbone. SIGNIFICANCE: The titanium dental implant pre-treatment and coating developed in this study is expected to favor early implant osseointegration through coating dissolution in vivo and could be associated with biological active agents to confer additional functionality to the coating.

Inflammatory Potential of Four Different Phases of Calcium Pyrophosphate Relies on NF-κB Activation and MAPK Pathways.

Background: Calcium pyrophosphate (CPP) microcrystal deposition is associated with wide clinical phenotypes, including acute and chronic arthritis, that are interleukin 1ß (IL-1ß)-driven. Two CPP microcrystals, namely monoclinic and triclinic CPP dihydrates (m- and t-CPPD), have been identified in human tissues in different proportions according to clinical features. m-CPP tetrahydrate beta (m-CPPTß) and amorphous CPP (a-CPP) phases are considered as m- and t-CPPD crystal precursors in vitro. Objectives: We aimed to decipher the inflammatory properties of the three crystalline phases and one amorphous CPP phase and the intracellular pathways involved. Methods: The four synthesized CPP phases and monosodium urate crystals (MSU, as a control) were used in vitro to stimulate the human monocytic leukemia THP-1 cell line or bone marrow-derived macrophages (BMDM) isolated from WT or NLRP3 KO mice. The gene expression of pro- and anti-inflammatory cytokines was evaluated by quantitative PCR; IL-1ß, IL-6 and IL-8 production by ELISA; and mitogen-activated protein kinase (MAPK) activation by immunoblot analysis. NF-κB activation was determined in THP-1 cells containing a reporter plasmid. In vivo, the inflammatory potential of CPP phases was assessed with the murine air pouch model via cell analysis and production of IL-1ß and CXCL1 in the exudate. The role of NF-κB was determined by a pharmacological approach, both in vivo and in vitro. Results:In vitro, IL-1ß production induced by m- and t-CPPD and m-CPPTß crystals was NLRP3 inflammasome dependent. m-CPPD crystals were the most inflammatory by inducing a faster and higher production and gene expression of IL-1ß, IL-6, and IL-8 than t-CPPD, m-CPPTß and MSU crystals. The a-CPP phase did not show an inflammatory property. Accordingly, m-CPPD crystals led to stronger activation of NF-κB, p38, extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK) MAPKs. Inhibition of NF-κB completely abrogated IL-1ß and IL-8 synthesis and secretion induced by all CPP crystals. Also, inhibition of JNK and ERK1/2 MAPKs decreased both IL-1ß secretion and NF-κB activation induced by CPP crystals. In vivo, IL-1ß and CXCL1 production and neutrophil infiltration induced by m-CPPD crystals were greatly decreased by NF-κB inhibitor treatment. Conclusion: Our results suggest that the inflammatory potential of different CPP crystals relies on their ability to activate the MAPK-dependent NF-κB pathway. Studies are ongoing to investigate the underlying mechanisms.

Time-domain THz spectroscopy of the characteristics of hydroxyapatite provides a signature of heating in bone tissue.

Because of the importance of bone in the biomedical, forensic and archaeological contexts, new investigation techniques are constantly required to better characterize bone ultrastructure. In the present paper, we provide an extended investigation of the vibrational features of bone tissue in the 0.1-3 THz frequency range by time-domain THz spectroscopy. Their assignment is supported by a combination of X-ray diffraction and DFT-normal modes calculations. We investigate the effect of heating on bone tissue and synthetic calcium-phosphates compounds with close structure and composition to bone mineral, including stoichiometric and non-stoichiometric hydroxyapatite (HA), tricalcium phosphate, calcium pyrophosphate and tetracalcium phosphate. We thus demonstrate that the narrow vibrational mode at 2.1 THz in bone samples exposed to thermal treatment above 750 °C arises from a lattice mode of stoichiometric HA. This feature is also observed in the other synthetic compounds, although weaker or broader, but is completely smeared out in the non-stoichiometric HA, close to natural bone mineral composition, or in synthetic poorly crystalline HA powder. The THz spectral range therefore provides a clear signature of the crystalline state of the investigated bone tissue and could, therefore be used to monitor or identify structural transitions occurring in bone upon heating.

Development of a new family of monolithic calcium (pyro)phosphate glasses by soft chemistry.

UNLABELLED: The development of bioactive phosphate-based glasses is essential in biomaterials science, and especially for bone substitution applications. In this context, the preparation of amorphous calcium-phosphorus hydroxide/oxide monoliths at low temperature is a key challenge for being able to develop novel hybrid materials for these applications. We herein report for the first time the synthesis and physical chemical characterisation of a novel family of pyrophosphate-based glasses (with the formula: {[(Ca(2+))1-x(H(+)/K(+))2x]2[(P2O7(4-))1-y(PO4(3-))4y/3]} n(H2O)), which were prepared by soft chemistry using low temperatures (T<70°C) and water as a solvent. The effect of the initial Ca/Pyrophosphate ratio on the structure and morphology of these pyrophosphate glasses was investigated in detail. Depending on this ratio, a glass (mixed calcium pyro- and orthophosphate) or a glass-ceramic (Ca10K4(P2O7)6·9H2O crystals embedded in the amorphous phase) was obtained. The proportion of the crystalline phase increased with an increase in the Ca/Pyrophosphate ratio in the batch solution. As expected for a glass, the formation of the glassy material was demonstrated not to be thermodynamically but rather kinetically driven, and the washing step was found to be crucial to prevent crystallisation. The stability of the amorphous phase was discussed considering the structural degrees of freedom of pyrophosphate entities, ionic strength of the initial solution and the inhibitory effect of orthophosphate ions. Overall, this new strategy of preparation of monolithic calcium-(pyro)phosphate based glasses using soft chemistry in water is highly promising in view of preparing new functional organic-inorganic hybrids for bone substitution applications. STATEMENT OF SIGNIFICANCE: Phosphate-based glasses have gradually emerged as a potential alternative to silicate bioactive glasses in order to induce different biological mechanisms of degradation. The synthesis of such monolithic glasses at low temperature is a key step to allow new inorganic glass compositions to be reached and hybrid materials to be prepared. Although sol-gel and coacervate methods (respectively orthophosphate and metaphosphate precursors) have already been described to prepare such glasses, the use of toxic solvents and/or the final temperature treatment associated to these processes could limit the use of these materials for biomedical applications and/or the further development of hybrids. It is shown here that pyrophosphate precursors are an alternative strategy to obtain monolithic calcium (pyro)phosphate glasses under soft conditions (water solvent, 70°C).

close: Closure of patent foramen ovale, oral anticoagulants or antiplatelet therapy to prevent stroke recurrence: Study design.

RATIONALE: Currently available data do not provide definitive evidence on the comparative benefits of closure of patent foramen ovale, oral anticoagulants and antiplatelet therapy in patients with patent foramen ovale-associated cryptogenic stroke AIM: To assess whether transcatheter patent foramen ovale closure plus antiplatelet therapy is superior to antiplatelet therapy alone and whether oral anticoagulant therapy is superior to antiplatelet therapy, for secondary stroke prevention in patients aged 16 to 60 years with a large patent foramen ovale or a patent foramen ovale associated with an atrial septal aneurysm, and an otherwise unexplained ischaemic stroke or retinal ischaemia. SAMPLE SIZE: Six hundred and sixty-four patients were included in the study. METHODS AND DESIGN: CLOSE is an academic-driven, multicentre, randomized, open-label, three-group, superiority trial with blinded adjudication of outcome events. The trial has been registered with Clinical Trials Register (Clinicaltrials.gov, NCT00562289). Patient recruitment started in December 2007. Patient follow-up will continue until December 2016. Expected mean follow-up = 5.6 years. STUDY OUTCOMES: The primary efficacy outcome is the occurrence of fatal or nonfatal stroke. Safety outcomes include fatal, life-threatening or major procedure- or device-related complications and fatal, life-threatening or major haemorrhagic complications. DISCUSSION: CLOSE is the first specifically designed trial to assess the superiority of patent foramen ovale closure over antiplatelet therapy alone and the superiority of oral anticoagulants over antiplatelet therapy to prevent stroke recurrence in patients with patent foramen ovale-associated cryptogenic stroke.

Crystal structure of monoclinic calcium pyrophosphate dihydrate (m-CPPD) involved in inflammatory reactions and osteoarthritis.

Pure monoclinic calcium pyrophosphate dihydrate (m-CPPD) has been synthesized and characterized by synchrotron powder X-ray diffraction and neutron diffraction. Rietveld refinement of complementary diffraction data has, for the first time, allowed the crystal structure of m-CPPD to be solved. The monoclinic system P2(1)/n was confirmed and unit-cell parameters determined: a = 12.60842 (4), b = 9.24278 (4), c = 6.74885 (2) Å and ß = 104.9916 (3)°. Neutron diffraction data especially have allowed the precise determination of the position of H atoms in the structure. The relationship between the m-CPPD crystal structure and that of the triclinic calcium pyrophosphate dihydrate (t-CPPD) phase as well as other pyrophosphate phases involving other divalent cations are discussed by considering the inflammatory potential of these phases and/or their involvement in different diseases. These original structural data represent a key step in the understanding of the mechanisms of crystal formation involved in different types of arthritis and to improve early detection of calcium pyrophosphate (CPP) phases in vivo.

From crystalline to amorphous calcium pyrophosphates: A solid state Nuclear Magnetic Resonance perspective.

Hydrated calcium pyrophosphates (CPP, Ca2P2O7·nH2O) are a fundamental family of materials among osteoarticular pathologic calcifications. In this contribution, a comprehensive multinuclear NMR (Nuclear Magnetic Resonance) study of four crystalline and two amorphous phases of this family is presented. (1)H, (31)P and (43)Ca MAS (Magic Angle Spinning) NMR spectra were recorded, leading to informative fingerprints characterizing each compound. In particular, different (1)H and (43)Ca solid state NMR signatures were observed for the amorphous phases, depending on the synthetic procedure used. The NMR parameters of the crystalline phases were determined using the GIPAW (Gauge Including Projected Augmented Wave) DFT approach, based on first-principles calculations. In some cases, relaxed structures were found to improve the agreement between experimental and calculated values, demonstrating the importance of proton positions and pyrophosphate local geometry in this particular NMR crystallography approach. Such calculations serve as a basis for the future ab initio modeling of the amorphous CPP phases. STATEMENT OF SIGNIFICANCE: The general concept of NMR crystallography is applied to the detailed study of calcium pyrophosphates (CPP), whether hydrated or not, and whether crystalline or amorphous. CPP are a fundamental family of materials among osteoarticular pathologic calcifications. Their prevalence increases with age, impacting on 17.5% of the population after the age of 80. They are frequently involved or associated with acute articular arthritis such as pseudogout. Current treatments are mainly directed at relieving the symptoms of joint inflammation but not at inhibiting CPP formation nor at dissolving these crystals. The combination of advanced NMR techniques, modeling and DFT based calculation of NMR parameters allows new original insights in the detailed structural description of this important class of biomaterials.

Injectability, microstructure and release properties of sodium fusidate-loaded apatitic cement as a local drug-delivery system.

The introduction of an antibiotic, sodium fusidate (SF), into the liquid phase of calcium carbonate-calcium phosphate (CaCO3-CaP) bone cement was evaluated, considering the effect of the liquid to powder ratio (L/P) on the composition and microstructure of the set cement and the injectability of the paste. In all cases, we obtained set cements composed mainly of biomimetic carbonated apatite analogous to bone mineral. With this study, we evi-denced a synergistic effect of the L/P ratio and SF presence on the injectability (i.e., the filter-pressing pheno-menon was suppressed) and the setting time of the SF-loaded cement paste compared to reference cement (without SF). In addition, the in vitro study of SF release, according to the European Pharmacopoeia recommendations, showed that, regardless of the L/P ratio, the cement allowed a sustained release of the antibiotic over 1month in sodium chloride isotonic solution at 37°C and pH7.4; this release is discussed considering the microstructure characteristics of SF-loaded cements (i.e., porosity, pore-size distribution) before and after the release test. Finally, modelling antibiotic release kinetics with several models indicated that the SF release was controlled by a diffusion mechanism.

Biomimetic apatite-based composite materials obtained by spark plasma sintering (SPS): physicochemical and mechanical characterizations.

Nanocrystalline calcium phosphate apatites are biomimetic compounds analogous to bone mineral and are at the origin of the bioactivity of most biomaterials used as bone substitutes. Their unique surface reactivity originates from the presence of a hydrated layer containing labile ions (mostly divalent ones). So the setup of 3D biocompatible apatite-based bioceramics exhibiting a high reactivity requests the development of «low¼ temperature consolidation processes such as spark plasma sintering (SPS), in order to preserve the characteristics of the hydrated nanocrystals. However, mechanical performances may still need to be improved for such nanocrystalline apatite bioceramics, especially in view of load-bearing applications. The reinforcement by association with biopolymers represents an appealing approach, while preserving the advantageous biological properties of biomimetic apatites. Herein, we report the preparation of composites based on biomimetic apatite associated with various quantities of microcrystalline cellulose (MCC, 1-20 wt%), a natural fibrous polymer. The SPS-consolidated composites were analyzed from both physicochemical (X-ray diffraction, Fourier transform infrared, solid state NMR) and mechanical (Brazilian test) viewpoints. The preservation of the physicochemical characteristics of apatite and cellulose in the final material was observed. Mechanical properties of the composite materials were found to be directly related to the polymer/apatite ratios and a maximum crushing strength was reached for 10 wt% of MCC.

Comparison of Physical-chemical and Mechanical Properties of Chlorapatite and Hydroxyapatite Plasma Sprayed Coatings.

Chlorapatite can be considered a potential biomaterial for orthopaedic applications. Its use as plasma-sprayed coating could be of interest considering its thermal properties and particularly its ability to melt without decomposition unlike hydroxyapatite. Chlorapatite (ClA) was synthesized by a high-temperature ion exchange reaction starting from commercial stoichiometric hydroxyapatites (HA). The ClA powder showed similar characteristics as the original industrial HA powder, and was obtained in the monoclinic form. The HA and ClA powders were plasma-sprayed using a low-energy plasma spraying system with identical processing parameters. The coatings were characterized by physical-chemical methods, i.e. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, including distribution mapping of the main phases detected such as amorphous calcium phosphate (ACP), oxyapatite (OA), and HA or ClA. The unexpected formation of oxyapatite in ClA coatings was assigned to a side reaction with contaminating oxygenated species (O2, H2O). ClA coatings exhibited characteristics different from HA, showing a lower content of oxyapatite and amorphous phase. Although their adhesion strength was found to be lower than that of HA coatings, their application could be an interesting alternative, offering, in particular, a larger range of spraying conditions without formation of massive impurities.

Hierarchical analysis and multi-scale modelling of rat cortical and trabecular bone.

The aim of this study was to explore the hierarchical arrangement of structural properties in cortical and trabecular bone and to determine a mathematical model that accurately predicts the tissue's mechanical properties as a function of these indices. By using a variety of analytical techniques, we were able to characterize the structural and compositional properties of cortical and trabecular bones, as well as to determine the suitable mathematical model to predict the tissue's mechanical properties using a continuum micromechanics approach. Our hierarchical analysis demonstrated that the differences between cortical and trabecular bone reside mainly at the micro- and ultrastructural levels. By gaining a better appreciation of the similarities and differences between the two bone types, we would be able to provide a better assessment and understanding of their individual roles, as well as their contribution to bone health overall.