The magnetic relaxation spectra of different types of single crystalline magnetite are investigated in the temperature range 4 IC < 27 < 450 K and compared with corresponding spectra obtained on stoichiometric (Fe,O,) and vacancy-doped polycrystals (Fes-dO,). Three basic relaxation mechanisms are revealed within the following temperature ranges 4 K < TI < 35 K, 40 K < < T~I < 130 I< and 200K< !7'111< 450 lC, which may be associated t o either electronic ( T I , T I I ) or ionic ( TIII) hopping processes. I n crystals with systematically reduced stoichiometry characteristic modifications in the structure of these spectra are observed from which additional information for a theoretical understanding may be obtained.
The aim of this study was the preparation and characterization of different biomorphic implants based on calcined cattle bones coated with hydroxyapatite (Hap) based nanocomposites in different ratios. For comparison, molded nanocomposites were also produced as biomorphic implants. The obtained nanocomposite/implants were characterized using Xray diffraction, light microscopy and scanning electron microscopy, Brunauer-Emmett-Teller surface area and apparent porosity. The release of Ca and P in simulated body fluid was monitored by X-ray fluorescence. The adsorption capacity and extended-release dosage of implants were investigated with ibuprofen, an anti-inflammatory drug, by UV-VIS spectroscopy. The highest adsorption efficiency and stability were obtained for sintered (S) (Hap-) and 20% gelatin (G) nanocomposite (Hap-20G-S) and bone parts coated with Hap-S and Hap-20G-S nanocomposite, respectively. The best results (high adsorption efficiency and slow release-low desorption capacity) were obtained for molded Hap-20G-S composite, without bone. In summary, the cattle bones with hydroxyapatite coatings show great promise in production of inexpensive and patient-specific bone implants.
During the biomedical and biotechnological applications of hydroxyapatite based magnetic biomaterials the response to various magnetic fields (i.e. change in flow behavior) plays a pivotal role in manipulating these materials. Numerous studies discuss the synthesis, characterization and possible applications of magnetic hydroxyapatite, however the number of reports related to the magnetic response is limited. In this study we investigated the response of aqueous suspensions of magnetite/hydroxyapatite composites with gelatin as an additive to homogeneous and inhomogeneous magnetic fields. Under homogeneous field the change in rheological properties was determined, and correlated with the composition of the composites. The effect of magnetite and gelatin content on the zero field viscosity and magnetic susceptibility were also evaluated. The response to inhomogeneous field was characterized by measuring the magnetic body force acting on droplets of the aqueous suspensions. We found that the formulation of the composites and the presence of additive largely affect the magnetic response.
The mesoporous silica particles were prepared by the sol-gel method in one-step synthesis, in acidic conditions, from tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES), varying the mole ratio of the silica precursors. Nitric acid was used as catalyst at room temperature and hexadecyltrimethyl ammonium bromide (CTAB) as structure directing agent. Optical properties, porosity and microstructure of the materials in function of the MTES/TEOS ratio were evaluated using infrared spectroscopy, nitrogen adsorption and small angle X-ray scattering. All materials showed the ordered pore structure and the high specific surfaces, making them suitable as the drug delivery systems. Drug loading and release tests using ketoprofen were performed to assess their performance for drug delivery applications. The amount of the methylated precursor used in the synthesis had little effect on the drug loading capacity, but had a strong influence on the initial rate of the drug release.
The aim of this study was the synthesis of composites containing hydroxyapatite (Hap) or silicon substituted hydroxyapatite (HapSi), carboxyl functionalized carbon nanotubes (fMWCNT) and gelatin (G) in different ratios. Ibuprofen (IBU) was chosen as a model drug for the formulation of extended-release dosage forms. The obtained composites were characterized using X-ray diffraction, laser diffraction particle size analyzer, Brunauer-Emmett-Teller surface area measurements, transmission electron microscopy and Fourier transformed infrared spectroscopy. IBU adsorption and desorption was monitored by UV-VIS spectroscopy. The obtained results revealed that composites containing three components exhibit higher adsorption efficiency (Hap-fMWCNT-20G-82.7% and HapSi-fMWCNT-20G-84.6%) and extended-release of IBU, due to the chemical bonds between the carboxyl groups of IBU and the functional groups on the composite surface. The adsorption capacity of Hap composites is important for dental or orthopedic implants, the anti-inflammatory substances being adsorbed on their surface; but the adsorption capacity also enhances new bone formation (osteosynthesis) around the implants. These composites are thus attractive materials to be used in bone tissue engineering and drug delivery systems.
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