Nanoporous hydroxyapatite/sodium titanate bilayer on titanium implants for improved osteointegration.

OBJECTIVE: The aim of this study was to improve the strength and quality of the titanium-hydroxyapatite interface in order to prevent long-term failure of the implanted devices originating from coating delamination and to test it in an in-vivo model. METHODS: Ti disks and dental commercial implants were etched in Kroll solution. Thermochemical treatments of the acid-etched titanium were combined with sol-gel hydroxyapatite (HA) coating processes to obtain a nanoporous hydroxyapatite/sodium titanate bilayer. The sodium titanate layer was created by incorporating sodium ions onto the Ti surface during a NaOH alkaline treatment and stabilized using a heat treatment. HA layer was added by dip-coating in a sol-gel solution. The bioactivity was assessed in vitro with murine MC3T3-E1 and human SaOs-2 cells. Functional and histopathological evaluations of the coated Ti implants were performed at 22, 34 and 60days of implantation in a dog lower mandible model. RESULTS: Nanoporous hydroxyapatite/sodium titanate bilayer on titanium implants was sensitive neither to crack propagation nor to layer delamination. The in vitro results on murine MC3T3-E1 and human SaOs-2 cells confirm the advantage of this coating regarding the capacity of cell growth and differentiation. Signs of progressive bone incorporation, such as cancellous bone formed in contact with the implant over the existing compact bone, were notable as early as day 22. Overall, osteoconduction and osteointegration mean scores were higher for test implants compared to the controls at 22 and 34 days. SIGNIFICANCE: Nanoporous hydroxyapatite/sodium titanate bilayer improves the in-vivo osteoconduction and osteointegration. It prevents the delamination during the screwing and it could increase HA-coated dental implant stability without adhesive failures. The combination of thermochemical treatments with dip coating is a low-cost strategy.

Growth of single-layer boron nitride dome-shaped nanostructures catalysed by iron clusters.

We report on the growth and formation of single-layer boron nitride dome-shaped nanostructures mediated by small iron clusters located on flakes of hexagonal boron nitride. The nanostructures were synthesized in situ at high temperature inside a transmission electron microscope while the e-beam was blanked. The formation process, typically originating at defective step-edges on the boron nitride support, was investigated using a combination of transmission electron microscopy, electron energy loss spectroscopy and computational modelling. Computational modelling showed that the domes exhibit a nanotube-like structure with flat circular caps and that their stability was comparable to that of a single boron nitride layer.

Development and applications of a DNA labeling method with magnetic nanoparticles to study the role of horizontal gene transfer events between bacteria in soil pollutant bioremediation processes.

Horizontal gene transfers are critical mechanisms of bacterial evolution and adaptation that are involved to a significant level in the degradation of toxic molecules such as xenobiotic pesticides. However, understanding how these mechanisms are regulated in situ and how they could be used by man to increase the degradation potential of soil microbes is compromised by conceptual and technical limitations. This includes the physical and chemical complexity and heterogeneity in such environments leading to an extreme bacterial taxonomical diversity and a strong redundancy of genes and functions. In addition, more than 99 % of soil bacteria fail to develop colonies in vitro, and even new DNA-based investigation methods (metagenomics) are not specific and sensitive enough to consider lysis recalcitrant bacteria and those belonging to the rare biosphere. The objective of the ANR funded project "Emergent" was to develop a new culture independent approach to monitor gene transfer among soil bacteria by labeling plasmid DNA with magnetic nanoparticles in order to specifically capture and isolate recombinant cells using magnetic microfluidic devices. We showed the feasibility of the approach by using electrotransformation to transform a suspension of Escherichia coli cells with biotin-functionalized plasmid DNA molecules linked to streptavidin-coated superparamagnetic nanoparticles. Our results have demonstrated that magnetically labeled cells could be specifically retained on micromagnets integrated in a microfluidic channel and that an efficient selective separation can be achieved with the microfluidic device. Altogether, the project offers a promising alternative to traditional culture-based approaches for deciphering the extent of horizontal gene transfer events mediated by electro or natural genetic transformation mechanisms in complex environments such as soil.

Validation of a dendron concept to tune colloidal stability, MRI relaxivity and bioelimination of functional nanoparticles.

The functionalization of spherical superparamagnetic iron oxide nanoparticles (SPION) of 10 nm with a linear monophosphonate (L1) and also PEGylated mono-phosphonated dendrons of growing generation (D2-G1, -G2 and -G3) yielded dendritic nano-objects of 15 to 30 nm in size, stable in physiological media and showing both renal and hepatobiliary elimination. The grafting of the different molecules has been confirmed by IR spectroscopy and elemental analysis. The colloidal stability of functionalized NS10 has been evaluated in water and in different physiological media. All functionalized NS10 were stable over a long period of time and displayed a mean hydrodynamic diameter smaller than 50 nm whatever the molecule architecture or dendron generation. Only the NS10@L1 showed less stability in biological media at high ionic concentration. NMRD profiles and relaxivity measurements highlighted the influence of the molecule architecture on the water diffusion close to the magnetic core thus influencing the relaxation properties at low magnetic field. Coupling of a fluorescent dye on the functionalized NS10 allowed investigating their biodistribution and highlighting urinary and hepato-biliary eliminations.

Fluoride controlled release tablets for intrabuccal use.

We have developed a fluoride controlled release delivering system for intrabuccal use, permitting to reach high enough local concentrations for desirable therapeutic effect with minimal side effects. We have formulated tablets of 160-200mg intended to be fixed on a tooth. The tablets have a granular matrix composed of pure hydroxyapatite, Eudragit((R)) and/or ethylcellulose. NaF is added either by a mechanical mixing or an impregnation method. Profiles of continuous in vitro drug release in saline phosphate buffered solution were recorded by means of a fluoride selective electrode. Linear profiles are observed when ethylcellulose is used. The most reproducible results are obtained when the impregnation method is used. Eudragit((R)) increases the dissolution efficiencies while ethylcellulose decreases it.

Elaboration and evaluation of an intraoral controlled release delivering system.

In order to improve the administration of drugs for all pathology of the oral cavity, we have developed an intraoral controlled release delivering system, permitting to reach high enough local concentrations for desirable therapeutic effect with minimal side effects. We have formulated tablets of 200 mg intended to be fixed on a tooth. These tablets resist food and drink attacks. The tablets we elaborated have a granular matrix composed of hydroxyapatite, ethyl cellulose and Eudragit. Zinc sulfate is used as the first model of an active drug, it has a therapeutic effect on buccal mucous. Profiles of continuous in-vitro drug release in distilled water at 37 degrees C show that zinc sulfate release by the matrix structure for the different tablet formulations is regulated by the proportions of the different components.

[Sodium fluoride controlled release system for intra buccal use]. / Système intra buccal delibèration contrôlée de fluorurede sodium.

Hydroxyapatite which has the same elemental chemical composition as natural bone and teeth is one of the promising raw material for the design of drug controlled release system in intrabuccal use. It is stable and biocompatible and widely used in orthopedics and odontology. So, in order to improve the administration of drugs for intrabuccal use, we have developped a fluoride controlled release delivering system. We have formulated tablets of 160 to 200 mg to be fixed on the vestibular face of a molar or a premolar and permitting to reach high enough local concentrations for desirable therapeutic effect. The tablets have a granular matrix composed of hydroxyapatite and fillers, ethylcellulose and/or Eudragit. For all tablets, the pharmacotechnical values support the pharmacopoeia norms. On fragments of tissue maintained in culture, the sodium fluoride is released at constant rate. The release profiles observed are predictable. No disintegration of tablets have been observed during release studies and after. Histological analyses performed after release studies showed the biocompatibility qualities of the tablets.

Properties and suspension stability of dendronized iron oxide nanoparticles for MRI applications.

Functionalized iron oxide nanoparticles have attracted an increasing interest in the last 10 years as contrast agents for MRI. One challenge is to obtain homogeneous and stable aqueous suspensions of iron oxide nanoparticles without aggregates. Iron oxide nanoparticles with sizes around 10 nm were synthesized by two methods: the particle size distribution in water suspension of iron oxide nanoparticles synthesized by the co-precipitation method was improved by a process involving two steps of ligand exchange and phase transfer and was compared with that of iron oxide nanoparticles synthesized by thermal decomposition and functionalized by the same dendritic molecule. The saturation magnetization of dendronized nanoparticles synthesized by thermal decomposition was lower than that of nanoparticles synthesized by co-precipitation. The r(2) relaxivity values were shown to decrease with the agglomeration state in suspension and high r(2) values and r(2) /r(1) ratios were obtained with nanoparticles synthesized by co-precipitation by comparison with those of commercial products. Dendronized iron oxide nanoparticles thus have potential properties as contrast agent.

Size-dependent properties of magnetic iron oxide nanocrystals.

The fine control of iron oxide nanocrystal sizes within the nanometre scale (diameters range from 2.5 to 14 nm) allows us to investigate accurately the size-dependence of their structural and magnetic properties. A study of the growth conditions of these nanocrystals obtained by thermal decomposition of an iron oleate precursor in high-boiling point solvents has been carried out. Both the type of solvent used and the ligand/precursor ratio have been systematically varied, and were found to be the key parameters to control the growth process. The lattice parameters of all the nanocrystals deduced from X-ray diffraction measurements are consistent with a structure of the type Fe3-xO4, i.e. intermediate between magnetite and maghemite, which evolves toward the maghemite structure for the smallest sizes (x=1/3). The evolution of the magnetic behavior with nanoparticle sizes emphasizes clearly the influence of the surface, especially on the saturation magnetization Ms and the magneto-crystalline anisotropy K. Dipolar interactions and thermal dependence have been also taken into account in the study on the nanoscale size-effect of magnetic properties.

Water soluble dendronized iron oxide nanoparticles.

The grafting of pegylated dendrons on 9(2) nm and 39(5) nm iron oxide nanoparticles in water, through a phosphonate group as coupling agent has been successfully achieved and its mechanism investigated, with a view to produce biocompatible magnetic nano-objects for biomedical applications. Grafting has been demonstrated to occur by interaction of negatively charged phosphonate groups with positively charged groups and hydroxyl at the iron oxide surface. The isoelectric point of the suspension of dendronized iron oxide nanoparticles is shifted towards lower pH as the amount of dendron increases. It reaches 4.7 for the higher grafting rate and for both particle size. Thus, the grafting of molecules using a phosphonate group allows stabilizing electrostatically the suspensions at physiological pH, a prerequisite for biomedical applications. Moreover the grafting step has been shown to preserve the magnetic properties of iron oxide nanoparticles due to super-super exchange interactions through the phosphonate group.

[Development and evaluation of an active substance controlled-release device for use in the oral cavity]. / Elaboration et évaluation d'un dispositif à libération contrôlée de substance active au niveau de la cavité buccale.

In order to improve drug administration for diseases of the oral cavity, we have developed an intraoral controlled release delivery system enabling local concentrations high enough for desirable therapeutic effect with minimal side effects. We have formulated 200 mg tablets to be fixed on a tooth. These tablets resist attacks by food and beverages. The tablets have a granular matrix composed of hydroxyapatite, ethyl cellulose and Eudragit. Zinc sulfate, which has a therapeutic effect on the buccal mucosa was used as the first model of an active drug. Profiles of continuous in vitro drug release in distilled water at 37 degrees C show that zinc sulfate release by the matrix structure for the different tablet formulations is regulated by the proportions of the different components.