[Show abstract][Hide abstract] ABSTRACT: The surface of aligned, electrospun poly-L-lactic acid (PLLA) fibers was chemically modified to determine if surface chemistry and hydrophilicity could improve neurite extension from chick dorsal root ganglia. Specifically, diethylenetriamine (DTA, for amine functionalization), 2-(2-aminoethoxy)ethanol (AEO, for alcohol functionalization), or GRGDS (cell adhesion peptide) were covalently attached to the surface of electrospun fibers. Water contact angle measurements revealed that surface modification of electrospun fibers significantly improved fiber hydrophilicity compared to unmodified fibers (p < 0.05). Scanning electron microscopy (SEM) of fibers revealed that surface modification changed fiber topography modestly, with DTA modified fibers displaying the roughest surface structure. Degradation of chemically modified fibers revealed no change in fiber diameter in any group over a period of seven days. Unexpectedly, neurites from chick DRG were longest on fibers without surface modification (1651 ± 488 μm) and fibers containing GRGDS (1560 ± 107 μm). Fibers modified with oxygen plasma (1240 ± 143 μm) or DTA (1118 ± 82 μm) produced shorter neurites than the GRGDS or unmodified fibers, but were not statistically shorter than unmodified and GRGDS modified fibers. Fibers modified with AEO (844 ± 151 μm) were significantly shorter than unmodified and GRGDS modified fibers (p<0.05). Based on these results, we conclude that fiber hydrophilic enhancement alone on electrospun PLLA fibers does not enhance neurite outgrowth. Further work must be conducted to better understand why neurite extension was not improved on more hydrophilic fibers, but the results presented here do not recommend hydrophilic surface modification for the purpose of improving neurite extension unless a bioactive ligand is used.
PLoS ONE 09/2015; 10(9):e0136780. DOI:10.1371/journal.pone.0136780 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Abstract 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 «low» 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. Graphical Abstract
Journal of Materials Science Materials in Medicine 08/2015; 26(8):1-11. DOI:10.1007/s10856-015-5553-9 · 2.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated the potential of solid-state NMR using magic angle spinning (MAS) with and without Dynamic Nuclear Polarization (DNP) and of EPR for the characterization of functionalized nanodiamonds (NDs). We showed that conventional 1H, 31P and 13C solid-state NMR spectra allow differentiating in a straightforward way NDs from commercial sources and custom-made NDs bearing aromatic or aliphatic phosphonate moieties at their surface. Besides, the short nuclear relaxation times prove the close proximity between the endogenous paramagnetic centers of NDs and the grafted organic moieties. EPR spectra confirmed the presence of these paramagnetic centers in functionalized NDs, which are centered on dangling bonds as well as a few N0 defects, corresponding to the substitution of carbon atoms by nitrogen ones. HYperfine Sublevel CORrElation spectroscopy indicates that the N0 paramagnetic centers are mostly located in the disordered shell of NDs. Preliminary DNP-enhanced NMR experiments at 9.4 T and 100 K under MAS have shown a lack of significant DNP enhancement which can be attributed to the short relaxation times of the unpaired electrons and the nuclei in NDs. When using exogenous polarizing agents, the endogenous unpaired electrons contribute to a leakage of polarization. Furthermore, low temperatures lead to a broadening of NMR signals. It therefore appears that conventional direct excitation remains the NMR method of choice for the characterization of functionalized NDs.
The Journal of Physical Chemistry C 05/2015; 119(22):150504162651003. DOI:10.1021/acs.jpcc.5b02171 · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Benzoxaboroles are a family of cyclic derivatives of boronic acids, whose reactivity makes them interesting candidates for the development of novel drugs. In this study, we describe the preparation of the first hybrid organic-inorganic materials involving benzoxaboroles, as a first step toward their use as new formulations for such drugs. The materials were prepared by intercalation of the simplest benzoxaborole (C7H6BO(OH), BBzx) or of its fluorinated analogue (C7H5FBO(OH), AN2690, a recently developed antifungal drug), both taken under their anionic form (benzoxaborolate), into a biodegradable inorganic matrix (a Mg-Al layered double hydroxide). Extensive characterization was carried out on the materials, notably by powder X-ray diffraction and multinuclear (11B, 27Al, 13C, 19F, 25Mg, and 1H) solid state NMR, in order to describe their structure, particularly in the vicinity of the organoboron species. Three crystalline phases involving benzoxaborolate anions in association with Ca2+ or Mg2+ cations were also prepared as part of this work (Mg(C7H6BO(OH)2)2·10H2O, Mg(C7H6BO(OH)2)2·7H2O and Ca3(C7H6BO(OH)2)5(C7H6BO2)·3H2O), in order to assist in the interpretation of the spectroscopic data. A DFT computational model of the interlayer space was proposed, which is consistent with the experimental observations. Several properties of the materials were then determined with a view of using them as part of novel formulations, namely the maximum loading capacity toward benzoxaborol(at)es, the optimal storage conditions, and the release kinetics in simulated physiological media. All in all, this study serves as a benchmark not only for the development of novel formulations for benzoxaborole drugs, but more generally for the preparation of a novel class of organic-inorganic materials involving benzoxaborol(at)es.
Chemistry of Materials 02/2015; 27(4):150205100647004. DOI:10.1021/cm504181w · 8.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Since 1991, in France, studies on the conditioning of iodine were carried out to assess the potential of several specific inorganic host matrices. The apatite family has been mainly studied because of its good chemical durability and its ability to confine iodine over geological time scales. A lead-bearing apatite, Pb10(VO4)4.8(PO4)1.2I2, and a calcium-bearing apatite, Ca10(PO4)6(OH)2-x(IO3)x, were selected on the basis of their incorporation rate (between 7 and 10 wt.%) and a satisfactory resistance to leaching (V0(50 °C, pure water) ∼ 10-2 g.m-2.d-1; Vr(50 °C, pure water) < 10-4 g.m-2.d-1). However, with such materials, the removal of open porosity requires non conventional sintering techniques like spark plasma sintering to decrease the surface exposed to water. This is why, in parallel, other matrices, like silver phosphate glasses, have also been investigated. To improve the chemical durability and thermal properties of these glasses, cross-linking reagents were added to their formulation.
[Show abstract][Hide abstract] ABSTRACT: In order to manage radioactive iodine-129 coming from nuclear spent fuel, robust host matrices with durable long term behaviour need to be developed. In this work, a new process of synthesis of an iodate-substituted hydroxyapatite by means of a cementation route is described. This material was obtained from a mixture of tetracalcium phosphate (TTCP), tricalcium phosphate (αTCP) and sodium iodate (NaIO3), taken in a molar ratio 1/2/0.5. The progress of the reaction leading to the setting and hardening of cement paste was monitored by combined measurements of electrical conductivity and heat flux release, together with XRD characterizations of materials at definite times of hydration. Sodium iodate acts as a set retarder, by leading to the precipitation of non-cohesive transient phases, which are then destabilized when the massive precipitation of hydroxyapatite occurs. These delays can however be limited by adding hydroxyapatite seeds to the cement paste, which means that it is possible to control the setting time in view of an industrial application. This novel cementitious system leads to a porous material composed of iodine-substituted hydroxyapatite needles covering residual TTCP and αTCP particles. Iodine has mainly entered the hydroxyapatite lattice under the form of iodate anions only. An iodine incorporation rate of 6.5 wt.% has been obtained by this cementitious system, which is a promising value in view of using these material for the conditioning of radioactive iodine.
[Show abstract][Hide abstract] ABSTRACT: Ultrasmall gold nanoparticles (Au UNPs) represent a unique class of nanomaterials making them very attractive for certain applications. Herein, we developed an organometallic approach to the synthesis of Au UNPs stabilized with the C18H37-NHC ligand by the solvent free thermolysis of [RMIM][Au(C6F5)2] (1) or [Au(C6F5)(RNHC)] (3) (with R = C18H37-), by controlling the reactivity of pentafluorophenyl ligands as deprotonating or reductive elimination agents; Au UNPs can be achieved by solvent free thermolysis. Pentafluorophenyl Au(I) complexes 1 and 3 are synthesized from the corresponding ionic and neutral precursors. The presence of long alkyl chain imidazolium or carbene species in the complexes makes them to behave as isotropic liquids at moderate temperatures. The use of multinuclear NMR allows the description of the mechanism of formation of the UNPs as well as the surface state of the UNPs.
[Show abstract][Hide abstract] ABSTRACT: Iodate-substituted hydroxyapatites are novel phases of potential interest for the immobilisation of radioactive iodine-129. However, the local environment of the iodine in these phases is still unclear. Here, a combined experimental-computational strategy has been used to investigate the mode of incorporation of iodates (IO3-) in Ca-hydroxyapatite and Sr-hydroxyapatite lattices. On one hand, I K- and L-3-edge XANES (X-ray Absorption Near Edge Structure) spectra are presented, showing that while the local structure around the iodate is similar in the two substituted hydroxyapatite lattices, it differs significantly from the one observed in a series of model compounds (NaIO3, KIO3, Ca(IO3)(2)center dot H2O). I K-edge EXAFS (Extended X-ray Absorption Fine Structure) spectra were then analysed, revealing the lack of order around the iodate, and also the absence of local clustering of the iodates along the hydroxyl columns of the apatite. Further insight into the local environment of iodates in apatites was then obtained by DFT (Density Functional Theory) computational modeling of iodate-substituted Ca-hydroxyapatite lattices.
[Show abstract][Hide abstract] ABSTRACT: Boronate ligands [R–B(OH)3–] have recently started to attract attention for the elaboration of coordination polymer networks. Here, three new crystalline structures involving butyl- and octylboronate ligands are described: Sr[Bu–B(OH)3]2, Ca[Oct–B(OH)3]2 and Sr[Oct–B(OH)3]2 (Bu = C4H9, Oct = C8H17). All were obtained as microcrystalline powders, and their structures were solved by synchrotron powder X-ray diffraction. IR and multinuclear (13C, 11B, 43Ca, 87Sr and 1H) solid-state NMR characterizations were performed on the materials. Computational models of the new Sr[Bu–B(OH)3]2 phase and the previously reported Sr[Ph–B(OH)3]2·H2O structure were then developed. The IR O–H stretching modes and NMR parameters were calculated for these models and are discussed in view of the experimental spectra. This work confirms the importance of computational studies on boronate phases to determine the nature of the H-bond network within the materials and to better understand their spectroscopic signatures.
Berichte der deutschen chemischen Gesellschaft 09/2014; 2015(7). DOI:10.1002/ejic.201402561 · 2.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: TiO2/conjugated polymers are promising materials in solar energy conversion where efficient photo-induced charge transfers are required. Here, a 'grafting-from' approach for the synthesis of TiO2 nanoparticles supported with conjugated polymer brushes is presented. Poly(3-hexylthiophene) (P3HT), a benchmark material for organic electronics, was selectively grown from TiO2 nanoparticles by Surface-Initiated Kumada Catalyst-Transfer Polycondensation (SI-KCTP). The grafting of the polymer onto the surface of the TiO2 nanoparticles by this method was demonstrated by 1H and 13C solid-state NMR, XPS (X-ray photoelectron spectrometry), thermogravimetric analysis (TGA), Transmission Electron Microscopy (TEM) and UV-Visible spectroscopy. Sedimentation tests in THF revealed improved dispersion stability for the TiO2@P3HT hybrid material. Films were produced by solvent casting and the quality of the dispersion of the modified TiO2 nanoparticles was evaluated by Atomic Force Microscopy (AFM). The dispersion of the P3HT-coated TiO2 NPs in the P3HT matrix was found to be homogeneous and the fibrillar structure of the P3HT matrix was maintained which is favourable for charge transport. Fluorescence quenching measurements on these hybrids materials in CHCl3 indicated improved photo-induced electron transfer efficiency. All in all, better physicochemical properties for P3HT/TiO2 hybrid material were reached via surface-initiated "grafted from" approach compared to the "grafting onto" approach.
[Show abstract][Hide abstract] ABSTRACT: A new method for the functionalization of detonation nanodiamonds (DNDs) is proposed, based on the surface modification with phosphonic dichloride derivatives. DNDs were first modified by phenylphosphonic dichloride and the grafting modes and hydrolytic stability were investigated using 1H, 13C and 31P solid state NMR spectroscopy, Fourier transform infrared spectroscopy, as well as elemental analysis. Then, in order to illustrate the possibilities offered by this method, DNDs functionalized by mesityl imidazolium groups were obtained by post-modification of DNDs modified by 12-bromododecylphosphonic dichloride. The oxidative thermal stability of the functionalized DNDs was investigated using thermogravimetric analysis.
[Show abstract][Hide abstract] ABSTRACT: Benzoxaboroles are organoboron molecules which are gaining growing interest in different fields, notably for the development of new drugs. However, extensive characterization of these molecules in the solid state is still lacking. Here, questions related to the structure and spectroscopic signatures of crystalline benzoxaborole phases are thus addressed, using a combined experimental-computational approach. Two simple benzoxaboroles were studied: 1,3-dihydro-1-hydroxy-2,1-benzoxaborole (denoted as BBzx) and 5-fluoro-1,3-dihydro-1-hydroxy-2,1-benzoxaborole (also referred to as AN2690, a newly developed antifungal drug). First, the crystal structures of AN2690 and BBzx at room temperature are discussed, emphasizing the intermolecular interactions which play an important role in their formation. Then, results of IR and multinuclear (1H, 11B, 13C and 19F) solid state NMR characterization are presented, together with density functional theory (DFT) calculations which were carried out to assist in the interpretation of the spectra. Finally, the influence of polymorphism and anisotropic thermal expansion properties of the crystal structures on the NMR parameters of BBzx and AN2690 is discussed.
[Show abstract][Hide abstract] ABSTRACT: In this contribution, the latest developments in solid state NMR are presented in the field of organic–inorganic (O/I) materials (or hybrid materials). Such materials involve mineral and organic (including polymeric and biological) components, and can exhibit complex O/I interfaces. Hybrids are currently a major topic of research in nanoscience, and solid state NMR is obviously a pertinent spectroscopic tool of investigation. Its versatility allows the detailed description of the structure and texture of such complex materials. The article is divided in two main parts: in the first one, recent NMR methodological/instrumental developments are presented in connection with hybrid materials. In the second part, an exhaustive overview of the major classes of O/I materials and their NMR characterization is presented.
Progress in Nuclear Magnetic Resonance Spectroscopy 02/2014; 77:1–48. DOI:10.1016/j.pnmrs.2013.10.001 · 7.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The reaction of gold nanoparticles with benzimididazol-2-ylidene ligands leads to the formation of well-defined bis-carbene gold(i) complexes, as shown by characterization techniques such as powder XRD and solid state NMR.
[Show abstract][Hide abstract] ABSTRACT: Mechanical resilience of bone tissue decreases with age. The ability to comprehensively probe and understand bone properties could help alleviate this problem. One important aspect of bone quality which has recently been made evident is the presence of dilatational bands formed by osteocalcin (OC) and osteopontin (OPN), which contribute to fracture toughness. However, experimental evidence of the structural role of these two proteins at the organic-mineral interface in bone is still needed. Solid state nuclear magnetic resonance (SSNMR) is emerging as a useful technique in probing molecular level aspects of bone. Here, we present the first SSNMR study of bone tissue from genetically modified mice lacking OC and/or OPN. Probing the mineral phase, the organic matrix and their interface revealed that despite the absence of OC and OPN, the organic matrix and mineral were well preserved, and the overall exposure of collagen to hydroxyapatite (HA) nanoparticles was hardly affected. However, the proximity to HA surface was slightly increased for a number bone components including less abundant amino acids like lysine, suggesting that this is how the tissue compensates for the lack of OC and OPN. Taken together, the NMR data supports the recently proposed model, in which the contribution of OC - OPN to fracture toughness is related to their presence at the extrafibrillar organic-mineral interfaces, where they reinforce the network of mineralized fibrils and form dilatational bands. In effort towards understanding further the structural role of individual amino acids of low abundance in bone, we then explored the possibility of specific 13C enrichment of mouse bone, and report the first SSNMR spectra of 97% 13C lysine-enriched tissues. Results show that such isotopic enrichment allows valuable molecular-level structural information to be extracted, and sheds light on post-translational modifications undergone by specific amino acids in vivo.
[Show abstract][Hide abstract] ABSTRACT: A novel, biocompatible, calcium-based coordination polymer was hydrothermally synthesized using as linker the bone antiresorptive bisphosphonate alendronate. Its structure was determined using single-crystal X-ray diffraction and characterized by chemical analysis, infrared spectroscopy (IR), X-ray powder diffraction (XRPD), solid state nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA). Its bioactivity was finally evaluated in vitro, revealing a very high stability towards simulated body fluid.