Results 1 - 10 of 5997
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[en] Mixtures of alginate and hydroxyapatite (HA) are promising materials for biomedical applications such as the fabrication of tissue scaffolds. In this paper, the flow behavior of alginate/HA mixtures was investigated and determined to be dependent on the concentration of both alginate and HA, and temperature. The relationships were mathematically established and verified with experimental results. As applied to the tissue scaffold fabrication, the flow rate of the biomaterial solution was predicted from the established flow behavior and verified by experiments. On this basis, the moving speed of the needle was determined and used in the tissue scaffold fabrication. The results obtained show that the knowledge of the flow behavior is essential to the fabrication of tissue scaffolds with an interconnected microstructure.
[en] In this research, hydroxyapatite (HA) nano-size powder was synthesized using wet chemical precipitation technique under atmospheric pressure where calcium hydroxide (Ca(OH)2) and ortho-phosphoric acid (H3PO4) were used as precursors. Distilled water was used as a diluting media for the reaction and sodium hydroxide (NaOH) was used to control the initial pH. The initial pH values, reaction temperature and calcined temperature play an important role in the morphology on HA as well as the phase formation and degree of crystallinity. Nano HA powder has been studied at different initial pH value which is between 9.00 to 11.00, reaction temperature from 80 to 100 degree Celsius and calcined temperature at 700 to 800 degree Celsius. The optimum initial pH value was found at pH 10.00, reaction temperature at 100 degree Celsius and calcined temperature was at 800 degree Celsius. The crystallographic properties were evaluated by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) and Field Emission Scanning Microscope (FESEM). The Design Expert version 9.0.2 with statistical and graphical analysis of the result, by using analysis of variance (ANOVA) was applied to optimize variable in the process of synthesis of HA. Based on analysis of variance (ANOVA) that has been perform, calcined temperature was to be influential variables on mass of HA with value of probability less than 0.05. (author)
[en] Structures of some bisphosphonates (clodronate, etidronate, pamidronate, alendronate, risedronate, zoledronate) were relaxed and analyzed by DFT method. By comparing their adsorption energies onto hydroxyapatite (001) surface with and without solvation effect and analyzing HOMOs (highest occupied molecular orbitals), LUMOs (lowest unoccupied molecular orbitals), and DOS (density of states) of bisphosphonates and hydroxyapatite (001) surface, it can be shown that the binding affinity of alkyl N-BPs (bisphosphonates containing nitrogen atom in an alkyl chain) is the highest among bisphosphonates, and the adsorption energy of bisphosphonates onto hydroxyapatite (001) surface is the main factor to determine the binding affinity of bisphosphoates with bone material.
[en] Confined fission track length analyses of apatites from the basement massifs of the western, central and eastern Pyrenees show a north-south regional trend in mean track length (MTL) and standard deviation (SD). High MTL (13.3-14.6 μm) and low SD (0.9-1.7 μm) in the north, and low MTL (11.9-13.9 μm) and high SD (1.3-3.2 μm) in the south are interpreted as recording rapid, Paleocene-Eocene uplift in the northern Pyrenees which, with related age data, pre-dates a protracted period of uplift/cooling in the southern Pyrenees. The difference in ''style'' of Tertiary uplift is attributed to the asymmetrical development of a Pyrenean wedge profoundly influenced by a strike-slip margin buttress inherited during the Cretaceous. (author)
[en] This work is dedicated both to investigation of the influence of different conditions on the molecular weight characteristics of poly- ε-caprolactone (PCL) and to the synthesis of composites based on PCL and hydroxyapatite (HA) by in situ and mechanical mixing methods. It was shown that in situ synthesis is accompanied by chemical interactions between PCL and HA that were confirmed by IR spectroscopy and thermal analysis. The morphology of in situ obtained composites has more homogeneous and regular distribution of HA particles in the polymeric matrix than composites synthesized by mechanical mixing of HA and PCL. (paper)
[en] Laser-Induced Breakdown Spectroscopy (LIBS) was applied to the analysis of bio-ceramic samples. The relationship between sample hardness and LIBS plasma properties was investigated, with comparison to conventional Vickers hardness measurements. The plasma excitation temperature Te was determined using the line-to-continuum ratio for the Si (I) 288.16 nm emission line; we have demonstrated a linear relationship between sample surface hardness and plasma temperature. Results indicate that hardness determination based on measurements of Te offers greater reproducibility than Vickers hardness measurements, under the conditions considered here. The validity of spectroscopic diagnostics based on LTE was confirmed.
[en] Fission Track Dating has undergone something of a renaissance in recent years. What began as a rather unreliable method of geochronology has now become a rigorous and dependable means of measuring not only geological time but also paleotemperatures. Developments such as the zeta calibration technique, rigorous satistical data analysis, investigation of confined track lengths and detailed studies of annealing behaviour have all contributed to advances in the technique
[en] It is possible to prepare dioxyapatites at high temperature (13500C) which contain two rare earths trivalent cations with the general formula Ca8Ln2(PO4)6O2, (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb). In these dioxyapatites, the trivalent ions substitute preferentially at the Ca(2) site; the consequence is an Ln-O interaction evidenced by infrared spectroscopy
[fr]Il est possible de preparer, a haute temperature (13500C), des dioxyapatites de formule generale Ca8Ln2(PO4)6O2 dans laquelle Ln est un ion trivalent de terre rare (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb). Dans ces apatites, les ions trivalents se substituent au cation Ca(2). Il en resulte une interaction Ln-O mise en evidence par spectroscopie d'absorption infrarouge