Lauro Bucio

Thermal analysis study of human bone

We have studied the thermal stability of human bone tissue and also its bone-extracted type-I collagen. We have used differential thermal analysis (DSC), infrared spectroscopy (FTIR) and gas chromatography. For type-I Collagen, variations of an exothermic maximum peak were observed between 500 and 530°C depending on the extraction method. These variations are related to high thermal stability of extracted collagen as opposed to thermal stability found in bone tissue, which maximum exothermic peak was found at ≈350°C. Total combustion enthalpy ΔH values are similar: −8.4 ± 0.11 kJ/g for bone tissue, and between −7.9 to −8.9 kJ/g in extracted collagen (depending on the extracting method). These findings, along with the results obtained by infrared spectroscopy and chromatographic techniques, demonstrate that the loss of thermal stability in type I collagen is due to its interactions with carbonate hydroxyapatite nanocrystals. The interactions cause a change in the molecular properties of collagen during mineralization, (specifically in its cross-links and other chemical interactions) which have an effect on fiber elasticity and on strength of bone tissue as a whole. We discuss the decomposition/combustion process and also how calorimetric measurement affects specific interactions between mineral and organic phases.

Phase Composition of ProRoot Mineral Trioxide Aggregate by X-Ray Powder Diffraction

INTRODUCTION Composition and crystalline phases of the endodontic material mineral trioxide aggregate (MTA) is of fundamental importance for understanding its physical and chemical properties. This research was done to determine the composition of crystalline phases for ProRoot MTA. METHODS For phase identification, powder of ProRoot MTA was analyzed by x-ray diffraction (XRD), comparing the MTA peaks with the data contained in the Powder Diffraction File of the International Centre for Diffraction Data (ICDD). To help the task of identifying a phase, chemical analysis by energy-dispersive spectrometry (EDS) and particle-induced x-ray emission (PIXE) were applied. Quantitative phase analysis was performed by applying Rietveld refinement to the XRD data. RESULTS ProRoot MTA is composed of bismuth oxide (19.8%), tricalcium silicate (51.9%), dicalcium silicate (23.2%), calcium dialuminate (3.8%), and calcium sulfate dehydrated (1.3%). The trace elements detected were Fe, Ni, Cu, and Sr. CONCLUSIONS Rietveld refinement was able to analyze the composition of ProRoot MTA, which is based basically on a mixture of Portland cement (with smaller quantities of calcium dialuminate and calcium sulfate dehydrated) and bismuth oxide for radiopacity.

The crystal structure of InYGe2O7 germanate

Abstract A new indium yttrium germanate presenting the thortveitite structure with symmetry described by the space group C2/m (No. 12) has been prepared by high temperature solid state reaction as polycrystalline powder material. This crystallizes in the monoclinic system, with cell parameters a = 6.8286(1) Å, b = 8.8836(2) Å, c = 4.9045(1) Å, β= 101.8340(7)º, V = 291.195(9) Å3 and Z = 2. The structure was characterized by X-ray powder diffraction and Rietveld refinement of the diffraction pattern. The In3+ and Y+3 cations occupy the same octahedral site forming a hexagonal arrangement on the ab planes. In their turn, the hexagonal arrangements of InO6/YO6 octahedral layers are held together by sheets of isolated diorthogroups constituted by a double tetrahedra sharing a common vertex. In this compound, the Ge2O7 diorthogroup shows the C2h symmetry implying a Ge-O-Ge angle of 180º, being an important feature of the thortveitite structure, which has been controversial in some reported papers. A remarkable photo-luminescence effect (in comparison with glass) was observed when the sample was irradiated with α-particles beam during the RBS experiments employed to analyze the chemical stoichiometry.

Superstructure determination of the perovskite βLa0.33NbO3

New interesting results in the crystal structure of the perovskite βLa0.33NbO3 were revealed using selected area electron diffraction, powder X-ray diffraction techniques and Rietveld refinement method. Although the superstructure of βLa0.33NbO3 could not be seen by conventional X-ray powder diffraction technique, the electron diffraction patterns revealed weak spots resulting in a superstructure array for the atoms of βLa0.33NbO3. The crystal symmetry is compatible with an orthorhombic cell, space group Cmmm. From Rietveld refinement, the resulting lattice parameters are: a = 7.82(1) Å, b = 7.83(9) Å, c = 7.90(9) Å and goodness of fit R = 0.1107, Rwp = 0.15. The superstructure is built from distorted octahedra NbO6 along the [001] axis. Results suggest that this distortion may be produced by occupation of La atoms in (2a) and (4l) sites.

Rietveld refinement of Y2GeO5

Y2GeO5 (yttrium germanium pentaoxide) was synthesized by solid-state reaction at 1443 K. The arrangement, which has monoclinic symmetry, is isostructural with Dy2GeO5 and presents two independent sites for the Y atoms. Around these atoms there are distorted six-coordinated YO6 octahedra and seven-coordinated YO7 pentagonal bipyramids. The YO7 polyhedra are linked together, sharing their edges along a surface parallel to ab, forming a sheet. Each of these parallel sheets is interconnected by means of GeO4 tetrahedra, sharing an edge (or vertex) on one side and a vertex (or edge) on the other adjacent side. Parallel sheets of YO7 polyhedra are also interconnected by undulating chains of YO6 octahedra along the c axis. These octahedra are joined together, sharing a common edge, to form the chain and share edges with the YO7 polyhedra of the sheets.

Nano and micro reoriented domains and their relation with the crystal structure in the new ferroelectric boracite Zn3B7O13Br

A new zinc brome boracite Zn3B7O13Br has been grown by a chemical transport reaction in closed quartz ampoules at 920 K. The crystal structure was characterized by Rietveld refinement. Ferroelectric nano and micro reorientable domains were found in this material using polarizing optical microscopy (PLM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Chemical analysis was performed with x-ray energy dispersive spectroscopy (EDX). In the crystal, a new structure transition at 586 K from orthorhombic (Pca 21) to cubic cell () has been found. This transition was corroborated by differential scanning calorimetry (DSC).

Grain growth and phase transformations induced by shock waves on alpha-GeO2 powder

An impact experiment on a mixture of water and microcrystalline alpha-GeO2 powder was performed with a single-stage gas gun. The recovered sample contained micrometer-scale crystals of different sizes and morphologies that correspond to 88% of alpha-GeO2, 6.0% of monoclinic phase (P21/c, space group No. 14), 4.9% of orthorhombic phase (Pnnm, space group No. 58) and 1.1% of rutile-type phase.

Crystal chemistry study of the solid solutions in the system La2BaZnO5-Eu2BaZnO5

Abstract In this work, a complete crystallochemical characterization of two solid solutions, which were founded in the binary end members system La2BaZnO5—Eu2BaZnO5, is reported. Both compounds belong to the family of mixed oxides with formula Ln2BaMO5 which presents interesting magnetic, electric and optical properties. Several works have been reported about this family of compounds with the same stoichiometry but with different structures depending on the M2+ coordination and rare earth content. Two solid solutions were obtained and characterized. Cell parameters, density measurements and solubility limits were determined for both solid solutions. Structure refinements of Eu2BaZnO5, La2BaZnO5 and the two solid solution series were carried out by the Rietveld method. Both structures and their relationship were discussed.

Thermal Properties of Mineralized and Non Mineralized Type I Collagen in Bone

Facultad de Ciencias Marinas, UABC, Km 103 carret. Tijuana Ensenada. C.P. 453. Ensenada,Baja California, Mexico.ABSTRACTThe research about the structural stability of bone, as a composite material, compromisesa complete understanding of the interaction between the mineral and organic phases. The thermalstability of human bone and type I collagen extracted from human bone by different methods wasstudied in order to understand the interactions between the mineral and organic phases when. isaffected by a degradation/combustion process. The experimental techniques employed werecalorimetry and infrared spectroscopy (FTIR) techniques. The extracted type I collagens result tohave a bigger thermal stability with a Tmax at 500 and 530 Celsius degrees compared with thecollagen present in bone with Tmax at 350 Celsius degrees. The enthalpy value for the completedegradation/combustion process were similar for all the samples, being 8.4 +- 0. 11 kJ/g for recentbones diminishing with the antiquity, while for extracted collagens were 8.9 +- 0.07 and 7.9 +-1.01 kJ/g. These findings demonstrate that the stability loss of type I collagen is due to itsinteractions with the mineral phase, namely carbonate hydroxyapatite. This cause a change in themolecular properties of the collagen during mineralization, specifically in its cross-links andother chemical interactions, which have a global effect over the fibers elasticity, but gainingtensile strength in bone as a whole tissue. We are applying this characterization to analyze thediagenetic process of bones with archaeological interest in order to identify how theenvironmental factors affect the molecular structure of type I collagen. In bone samples thatproceed from an specific region with the same environmental conditions, the enthalpy value perunit mass was found to diminish exponentially with respect to the bone antiquity.INTRODUCTIONBone is one of the biological structures that has been analyzed in different areas, asmedicine, biology, archaeology, science materials, etc. by means of different techniques. It iscompose of a mineral and an organic phase, which arehydroxyapatite and collagen respectively.This biomaterial properties are of main importance for developing new materials that mimics itsstructure and for other applications in which it plays a specific and transcending role. Tounderstand its structural characteristics, as the collagen-hydroxyapatite relationship, the collagenthermal stability, the collagen degradation process, we have, in a recent work, address theseproblems by the use of different calorimetric, gas chromatography and FTIR techniques (6).These findings demonstrate that the stability loss of type I collagen is due to its interactions with

Interconnected porosity analysis by 3D X-ray microtomography and mechanical behavior of biomimetic organic-inorganic composite materials

Hydroxyapatite-based materials have been used for dental and biomedical applications. They are commonly studied due to their favorable response presented when used for replacement of bone tissue. Those materials should be porous enough to allow cell penetration, internal tissue growth, vascular incursion and nutrient supply. Furthermore, their morphology should be designed to guide the growth of new bone tissue in anatomically applicable ways. In this work, the mechanical performance and 3D X-ray microtomography (X-ray μCT) study of a biomimetic, organic-inorganic composite material, based on hydroxyapatite, with physicochemical, structural, morphological and mechanical properties very similar to those of natural bone tissue is reported. Ceramic pieces in different shapes and several porous sizes were produced using a Modified Gel Casting Method. Pieces with a controlled and 3D hierarchical interconnected porous structure were molded by adding polymethylmethacrylate microspheres. Subsequently, they were subject to a thermal treatment to remove polymers and to promote a sinterization of the ceramic particles, obtaining a HAp scaffold with controlled porosity. Then, two different organic phases were used to generate an organic-inorganic composite material, so gelatin and collagen, which was extracted from bovine tail, were used. The biomimetic organic-inorganic composite material was characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Diffraction, Fourier Transform Infrared Spectroscopy and 3D X-ray microtomography techniques. Mechanical properties were characterized in compression tests, obtaining a dramatic and synergic increment in the mechanical properties due to the chemical and physical interactions between the two phases and to the open-cell cellular behavior of the final composite material; the maximum compressive strength obtained corresponds to about 3 times higher than that reported for natural cancellous bone. The pore size distribution obtained could be capable to allow cell penetration, internal tissue in-growth, vascular incursion and nutrient supply and this material has tremendous potential for use as a replacement of bone tissue or in the manufacture and molding of prosthesis with desired shapes.