Biphasic Calcium Phosphate and Activated Carbon Microparticles in a Plasma Clot for Bone Reconstruction and In Situ Drug Delivery: A Feasibility Study.

The development of bone-filling biomaterials capable of delivering in situ bone growth promoters or therapeutic agents is a key area of research. We previously developed a biomaterial constituting biphasic calcium phosphate (BCP) microparticles embedded in an autologous blood or plasma clot, which induced bone-like tissue formation in ectopic sites and mature bone formation in orthotopic sites, in small and large animals. More recently, we showed that activated carbon (AC) fiber cloth is a biocompatible material that can be used, due to its multiscale porosity, as therapeutic drug delivery system. The present work aimed first to assess the feasibility of preparing calibrated AC microparticles, and second to investigate the properties of a BCP/AC microparticle combination embedded in a plasma clot. We show here, for the first time, after subcutaneous (SC) implantation in mice, that the addition of AC microparticles to a BCP/plasma clot does not impair bone-like tissue formation and has a beneficial effect on the vascularization of the newly formed tissue. Our results also confirm, in this SC model, the ability of AC in particle form to adsorb and deliver large molecules at an implantation site. Altogether, these results demonstrate the feasibility of using this BCP/AC/plasma clot composite for bone reconstruction and drug delivery.

Long-Term Fate and Efficacy of a Biomimetic (Sr)-Apatite-Coated Carbon Patch Used for Bone Reconstruction.

Critical bone defect repair remains a major medical challenge. Developing biocompatible materials with bone-healing ability is a key field of research, and calcium-deficient apatites (CDA) are appealing bioactive candidates. We previously described a method to cover activated carbon cloths (ACC) with CDA or strontium-doped CDA coatings to generate bone patches. Our previous study in rats revealed that apposition of ACC or ACC/CDA patches on cortical bone defects accelerated bone repair in the short term. This study aimed to analyze in the medium term the reconstruction of cortical bone in the presence of ACC/CDA or ACC/10Sr-CDA patches corresponding to 6 at.% of strontium substitution. It also aimed to examine the behavior of these cloths in the medium and long term, in situ and at distance. Our results at day 26 confirm the particular efficacy of strontium-doped patches on bone reconstruction, leading to new thick bone with high bone quality as quantified by Raman microspectroscopy. At 6 months the biocompatibility and complete osteointegration of these carbon cloths and the absence of micrometric carbon debris, either out of the implantation site or within peripheral organs, was confirmed. These results demonstrate that these composite carbon patches are promising biomaterials to accelerate bone reconstruction.

In vivo effectiveness of carbonated calcium-deficient hydroxyapatite-coated activated carbon fiber cloth on bone regeneration.

We have previously shown that activated carbon fiber cloth (ACC) either uncoated or coated with carbonated calcium-deficient hydroxyapatite (CDA), namely ACC and ACC/CDA, were biocompatible in vitro with human osteoblasts. Here we hypothesized that ACC and ACC/CDA could be used as tissue patches in vivo to accelerate wounded bone healing. In a model of rat femoral defect, we have compared spontaneous cortical bone regeneration with regeneration in the presence of ACC and ACC/CDA patches. At Day 7, 14, and 21, bone formation was evaluated using microcomputed tomography, magnetic resonance imaging, and histological analysis. Our results demonstrate first that these ACC tissues are highly biocompatible in vivo, and second that ACC/CDA patches apposition results in the acceleration of bone reconstruction due to a guiding action of the ACC fibers and an osteogenic effect of the CDA phase. We guess that this approach may represent a valuable strategy to accelerate bone regeneration in human.

Activated Carbon Fiber Cloth/Biomimetic Apatite: A Dual Drug Delivery System.

A biomaterial that is both bioactive and capable of controlled drug release is highly attractive for bone regeneration. In previous works, we demonstrated the possibility of combining activated carbon fiber cloth (ACC) and biomimetic apatite (such as calcium-deficient hydroxyapatite (CDA)) to develop an efficient material for bone regeneration. The aim to use the adsorption properties of an activated carbon/biomimetic apatite composite to synthetize a biomaterial to be used as a controlled drug release system after implantation. The adsorption and desorption of tetracycline and aspirin were first investigated in the ACC and CDA components and then on ACC/CDA composite. The results showed that drug adsorption and release are dependent on the adsorbent material and the drug polarity/hydrophilicity, leading to two distinct modes of drug adsorption and release. Consequently, a double adsorption approach was successfully performed, leading to a multifunctional and innovative ACC-aspirin/CDA-tetracycline implantable biomaterial. In a second step, in vitro tests emphasized a better affinity of the drug (tetracycline or aspirin)-loaded ACC/CDA materials towards human primary osteoblast viability and proliferation. Then, in vivo experiments on a large cortical bone defect in rats was carried out to test biocompatibility and bone regeneration ability. Data clearly highlighted a significant acceleration of bone reconstruction in the presence of the ACC/CDA patch. The ability of the aspirin-loaded ACC/CDA material to release the drug in situ for improving bone healing was also underlined, as a proof of concept. This work highlights the possibility of bone patches with controlled (multi)drug release features being used for bone tissue repair.

Pulsed electrodeposition of Ag+ doped prosthetic Fluorohydroxyapatite coatings on stainless steel substrates.

In order to reinforce the antibacterial character of fluorohydroxyapatite (FHA) prosthetic layers on 316L stainless steel (316L SS), Ag+ ions (an antibacterial agent) are included in the electrodeposition medium to be incorporated in the FHA layers created by pulsed protocol. The doped coatings (Ag-FHA) with different concentrations of silver ions (5, 10, 20, 40 and 100 ppm) were characterized electrochemically (polarization curves and electrochemical impedance spectroscopy) in simulated body fluid (SBF) solution and microbiologically against two pathogenic bacteria (Staphylococcus aureus and Escherichia coli). XPS, EDX and Raman spectroscopies were used to complement these evaluations. Whatever the concentration of incorporated Ag+ ions, the FHA morphology, structure and composition are not affected. The XPS and EDX results confirm the Ag+ presence within the apatite crystals, mostly concentrated at the extreme surface of the coatings. They also show the lowering of the stoichiometry of the coatings, confirmed by Raman analyses. The corrosion studies indicate that the prosthetic coatings act as a barrier against corrosion of the 316L SS alloy. Moreover, the results of the microbiological tests show that a content of 40 ppm of silver, introduced into the prosthetic coatings, inhibits the bacterial growth. Lower concentrations showing only a partial inhibition. In conclusion, using a pulsed current mode in the electrodeposition processes generates Ag-FHA/316L SS systems suitable for biomedical applications.

Synthesis and application of hydride silica composites for rapid and facile removal of aqueous mercury.

The adsorption of ionic mercury(II) from aqueous solution on functionalized hydride silicon materials was investigated. The adsorbents were prepared by modification of mesoporous silica C-120 with triethoxysilane or by converting alkoxysilane into siloxanes by reaction with acetic acid. Mercury adsorption isotherms at 208C are reported, and maximum mercury loadings were determined by Langmuir fitting. Adsorbents exhibited efficient and rapid removal of ionic mercury from aqueous solution, with a maximum mercury loading of approximately 0.22 and 0.43 mmol of Hg g1 of silica C-120 and polyhedraloligomeric silsesquioxane (POSS) xerogel, respectively. Adsorption efficiency remained almost constant from pH 2.7 to 7. These inexpensive adsorbents exhibiting rapid assembly, low pH sensitivity, and high reactivity and capacity, are potential candidates as effective materials for mercury decontamination in natural waters and industrial effluents.

Filling of carbon nanotubes with selenium by vapor phase process.

A vapor phase method was developed to fill different kinds of nanotubes (including multiwall and singlewall nanotubes), which inner diameters range from 200 down to 1.5 nm. Experiments were performed with selenium in a sealed reactor in order to control the selenium partial pressure. This process allows a full control of the nanotube filling (partial or complete), i.e., either a selective diameter filling or a full filling rate. The weight gain of all the samples was plotted for different reaction temperature as a function of selenium pressure. Experimental isotherms are characteristic of capillary condensation of selenium, which occurs at first in the smallest nanotube inner diameters. X-ray diffraction data show that selenium confined in nanotubes with diameters larger than 3 nm keeps its trigonal structure.

Patching and tearing single-wall carbon-nanotube ropes into multiwall carbon nanotubes.

Bundles of single-wall carbon nanotubes (SWCNTs) coalesce forming multiwall carbon nanotubes (MWCNTs), containing from two to six nested tubes, under thermal treatment at high temperatures [(2200-2400) degrees C]. This structural transformation is confirmed by extensive molecular dynamics (MD) simulations. The simulations suggest a "patching-and-tearing" mechanism for the single-wall-to-multiwall transformation underlying the "concerted" coalescence of the tubes that begins with their polymerization. Tubes of different sizes and chiralities are considered.

High yield of pure multiwalled carbon nanotubes from the catalytic decomposition of acetylene on in-situ formed cobalt nanoparticles.

For the first time, multiwalled carbon nanotubes (MWNTs) could be formed selectively in a high yield, free of any disordered carbon by-product, from the catalytic decomposition of acetylene at 600 degrees C on a CoxMg(1-x)O solid solution. Starting from 1 g of catalytic substrate, 4 g of pure MWNTs were obtained after its dissolution in boiling concentrated HCl, without any additional purification in strongly oxidizing medium, as is required for other methods of nanotube production. In situ reduction of CoO by dihydrogen liberated from acetylene decomposition allows highly divided metal particles to be continuously produced as synthesis proceeds. This is undoubtedly the reason for the good performance of the catalyst and for the ability to produce nanotubes in a narrow diameter range, namely from 10 to 15 nm. With the use of acetylene instead of methane, the synthesis proceeds at low temperature, which prevents the growth of carbon shells, in which the metal particles are generally embedded, decreasing their activity. Because of the very low specific surface area of the catalyst support, the amount of disordered carbon by-product formed is negligible.