Biomimetic graphene for enhanced interaction with the external membrane of astrocytes.

Graphene and graphene substrates display huge potential as material interfaces for devices and biomedical tools targeting the modulation or recovery of brain functionality. However, to be considered reliable neural interfaces, graphene-derived substrates should properly interact with astrocytes, favoring their growth and avoiding adverse gliotic reactions. Indeed, astrocytes are the most abundant cells in the human brain and they have a crucial physiological role to maintain its homeostasis and modulate synaptic transmission. In this work, we describe a new strategy based on the chemical modification of graphene oxide (GO) with a synthetic phospholipid (PL) to improve interaction of GO with brain astroglial cells. The PL moieties were grafted on GO sheets through polymeric brushes obtained by atom-transfer radical-polymerization (ATRP) between acryloyl-modified PL and GO nanosheets modified with a bromide initiator. The adhesion of primary rat cortical astrocytes on GO-PL substrates increased by about three times with respect to that on glass substrates coated with standard adhesion agents (i.e. poly-d-lysine, PDL) as well as with respect to that on non-functionalized GO. Moreover, we show that astrocytes seeded on GO-PL did not display significant gliotic reactivity, indicating that the material interface did not cause a detrimental inflammatory reaction when interacting with astroglial cells. Our results indicate that the reported biomimetic approach could be applied to neural prosthesis to improve cell colonization and avoid glial scar formation in brain implants. Additionally, improved adhesion could be extremely relevant in devices targeting neural cell sensing/modulation of physiological activity.

Ionic substitutions in calcium phosphates synthesized at low temperature.

Ionic substitutions have been proposed as a tool to improve the biological performance of calcium phosphate based materials. This review provides an overview of the recent results achieved on ion-substituted calcium phosphates prepared at low temperature, i.e. by direct synthesis in aqueous medium or through hydrolysis of more soluble calcium phosphates. Particular attention is focused on several ions, including Si, Sr, Mg, Zn and Mn, which are attracting increasing interest for their possible biological role, and on the recent trends and developments in the applications of ion-substituted calcium phosphates in the biomedical field.

Interaction of Sr-doped hydroxyapatite nanocrystals with osteoclast and osteoblast-like cells.

This article reports the effect of strontium incorporation into hydroxyapatite nanocrystals on bone cells response. Hydroxyapatite nanocrystals were synthesized at strontium contents of 0, 1, 3, 7 atom %. Strontium incorporation for calcium is confirmed by the linear increase of the unit cell parameters of hydroxyapatite, in agreement with the different ionic radii of the two ions. Moreover, strontium substitution slightly affects hydroxyapatite structural order and the shape of the nanocrystals. Osteoblast-like MG63 cells cultured on the nanocrystals display good proliferation and increased values of the differentiation parameters. In particular, when cultured on samples with Sr concentration in the range 3-7 atom %, osteoblasts display increased values of ALP activity, collagen type I, and osteocalcin production. Moreover, the osteoclast number on all the Sr-doped samples is significantly smaller than on hydroxyapatite, and it decreases on increasing strontium content. The data indicate that strontium stimulates osteoblast activity and exerts its inhibitory effect on osteoclast proliferation even when incorporated into hydroxyapatite.

Nanocrystalline hydroxyapatite-polyaspartate composites.

The direct synthesis of hydroxyapatite-poly-L-aspartic acid (HA-PASP) nanocrystals has been carried out in presence of increasing amounts of PASP in solution up to 56 mmol/l. WAXS, TEM, TGA, IR and chemical analyses were used to characterize the structure, morphology and composition of the products. PASP is quantitatively incorporated into HA crystals, provoking a reduction of the coherent length of the crystalline domains. Furthermore, composite crystals display a greater length/width ratio with respect to the control HA crystals, and show a remarkable trend towards aggregation. The broadening of the X-ray diffraction reflections indicate a reduction of the coherent length along the long dimension 002 and the cross section 310 of the apatite crystals. The comparison between the morphological and structural data allows to suggest a specific interaction between PASP and HA structure.

A new method for the detection of low levels of free fibres of chrysotile in contaminated soils by X-ray powder diffraction.

A new method for the determination of free fibres of chrysotile in contaminated soils is described. The detection limit of 0.5 wt per thousand is reached by an enrichment process of the asbestos fraction of the sample using a standard laboratory elutriator for sedimentation analysis. The analysis of the enriched fraction is performed by X-ray powder diffraction using a conventional instrument. The procedure can be successfully applied to several soils of different nature throughout thermal treatment and removal of possible interferences due to some matrix components. This method is straightforward, routinized and has been especially developed to fulfil the request of public and private institutions for an appropriate quantitative determination of chrysotile free fibres in contaminated soils.

Determination of low levels of free fibres of chrysotile in contaminated soils by X-ray diffraction and FTIR spectroscopy.

A new analytical method for the determination of low levels (0.01-1 wt%) of free fibres of chrysotile in contaminated clayey, sandy and sandy-organic soils is described. The detection limit of 0.01 wt% is reached with an enrichment of free fibres of chrysotile in the sample using a standard laboratory elutriator for sedimentation analysis. The chrysotile quantitative determination is performed both by X-ray powder diffraction, using the internal standard and reference intensity ratio methods, and by Fourier-transform infrared absorption spectroscopy. The procedure can be successfully applied to different soils after removal, by a thermal treatment, of the matrix components which can interfere. This straightforward method fulfils the request of public institutions and private companies for an appropriate quantitative determination of chrysotile-free fibres in contaminated soils.

Electrocatalytic activity of cobalt phthalocyanine stabilized by different matrixes.

The behavior of cobalt phthalocyanine complexes incorporated inside an hydrotalcite-like clay (HT) or a sonogel-carbon composite has been investigated in order to develop chemically modified electrodes suitable for use as amperometric detectors. The electrocatalytic oxidation process of cysteine at this new electrode has been studied by cyclic voltammetry. For comparison, the oxidation of cysteine catalyzed by the cobalt phthalocyanine complex as a redox mediator, either dissolved in solution or entrapped inside the HT structure, has been followed by polarography. The sonogel-carbon composite electrode is stable and its response is repeatable. Cysteine oxidation is actually induced by the electrogenerated Co(III) complex, and the relevant anodic peak current varies linearly with cysteine concentration within the range 9.0x10(-4) to 1.0x10(-2) mol L(-1).

Bacterial poly(3-hydroxybutyrate): an optical microscopy and microfocus X-ray diffraction study.

Two-dimensional spatially resolved microfocus X-ray diffraction has been used to investigate spherulites of pure bacterial poly(3-hydroxybutyrate) (PHB) and of a blend of natural and synthetic atactic PHB (a-PHB) crystallized at a relatively high temperature (Tc = 140 degrees C). Both samples investigated contained practically two-dimensional spherulites, characterized by wide extinction bands (band spacing > 80 microns). The X-ray diffraction patterns confirmed that the unit cell alpha-axis is oriented along the spherulite radius in PHB and that the same is true for the a-PHB containing blend. Comparison of the matrix of diffraction patterns with the polarized optical micrograph of the scanned sample area indicated a very clear correlation between pattern changes and banding, yielding a straightforward picture of the structural variations within the spherulite.

Relationship between Solid State NMR Parameters and X-ray Structural Data in Tricadmium Phosphates.

31P and (113)Cd MAS NMR spectra of solid beta'-tricadmium phosphate (beta'-TCdP) show a number of highly resolved resonances that agree well with the number of independent crystallographic sites indicated by the results of X-ray diffraction studies. A correlation of the (31)P chemical shifts with the crystallographic sites for the six different PO(4)(3)(-) groups in the unit cell of beta'-TCdP has been obtained by a method based on the computation of bond strength at oxygen atoms in phosphate moieties. The assignment of the (113)Cd resonances has been carried out on the basis of the relationship between the asymmetry of the chemical shift tensor (evaluated by analysis of the spinning side bands intensities in the MAS spectrum) and a geometric parameter related to the distortion from the bipyramidal trigonal coordination at each cadmium center. Samples of tricadmium phosphate with different degrees of magnesium substitution for cadmium were investigated by (31)P MAS NMR, (113)Cd MAS NMR, and X-ray diffraction. The results of these investigations showed that the magnesiums distribute randomly in the cadmium sites, inducing a marked decrease in the order of the structure.

Thermal conversion of octacalcium phosphate into hydroxyapatite.

The thermal conversion of octacalcium phosphate into hydroxyapatite has been investigated by a crystallographic, thermogravimetric, and calorimetric study. The conversion of octacalcium phosphate takes place through the remotion of three of its five water molecules and yields a poor crystalline apatitic phase. The three water molecules are lost in two steps. The first one, which is reversible, corresponds to the remotion of one water molecule and induces a slight contraction of the unit cell of OCP. The successive remotion of two water molecules, which provokes the structural conversion of OCP into apatite, is in irreversible process. The mechanism of the water loss of OCP is explained in terms of its crystal structure.

Structural and chemical characterization of inorganic deposits in calcified human mitral valve.

X-ray diffraction, i.r. absorption, and chemical analyses have been carried out on the mineral deposits of calcified human mitral valves and glutaraldehyde-preserved porcine aortic grafts. The mineral deposits isolated from highly calcified mitral valves and porcine aortic grafts are constituted of type B-carbonate apatite. Magnesium substituted beta-tricalcium phosphate is present, together with an apatitic phase similar to dahllite, in the ashes of poorly calcified mitral valves. The contraction of the unit cell of beta-tricalcium phosphate due to magnesium incorporation is compared with the variation of the lattice constants of synthetic beta-tricalcium phosphate at different degree of magnesium substitution for calcium. The results reveal the important role of magnesium on the calcification of human valves. In fact, the apatitic phase deposited at the beginning of the calcification process, when there is a high magnesium content, converts completely into beta-tricalcium phosphate by heat treatment at 1,000 degrees C. On the other hand, when the calcification becomes massive, magnesium content appears highly reduced, and the deposited apatitic phase is characterized by a high thermal stability.