Zlatko Rakočević

Age-related deterioration in trabecular bone mechanical properties at material level: Nanoindentation study of the femoral neck in women by using AFM

Despite general belief that the mechanical properties of bone material contribute to whole bone strength, it is still obscure what the age effects are on mechanical behavior of the bone material, particularly in the case of the femoral neck trabeculae. In this study, atomic force microscopy was used for imaging and measuring the size of mineral grains, as well as nano-scale mechanical characterization (nanoindentation) of the bone mineralized matrix of trabeculae, with the aim to explore the age effects on bone elasticity and give new insight into age-related bone fragility. The bone samples in this study comprised trabecular bone specimens of the femoral neck region, collected from eight skeletal healthy women (five young adults: 27-38yrs., three elderly: 83-94yrs.) at autopsy. Bone trabeculae in the elderly displayed a higher modulus and nanohardness, signifying a decreased amount of energy that can be accommodated by the bone tissue during loading. Regression analysis revealed that nearly 65% of variability in the bone matrix elastic modulus can be statistically explained by the changes in size of the matrix mineral grains. This study revealed that the bone trabeculae of elderly women express less elastic behavior at the material level, which makes them more vulnerable to unusual impact loads originating from a fall. The observed age-related structural and mechanical alteration at the bone material level adds new evidence for understanding why hip fractures are more frequent in elderly women.

Nano-structural, compositional and micro-architectural signs of cortical bone fragility at the superolateral femoral neck in elderly hip fracture patients vs. healthy aged controls.

To unravel the origins of decreased bone strength in the superolateral femoral neck, we assessed bone structural features across multiple length scales at this cortical fracture initiating region in postmenopausal women with hip fracture and in aged-matched controls. Our combined methodological approach encompassed atomic force microscopy (AFM) characterization of cortical bone nano-structure, assessment of mineral content/distribution via quantitative backscattered electron imaging (qBEI), measurement of bone material properties by reference point indentation, as well as evaluation of cortical micro-architecture and osteocyte lacunar density. Our findings revealed a wide range of differences between the fracture group and the controls, suggesting a number of detrimental changes at various levels of cortical bone hierarchical organization that may render bone fragile. Namely, mineral crystals at external cortical bone surfaces of the fracture group were larger (65.22nm±41.21nm vs. 36.75nm±18.49nm, p<0.001), and a shift to a higher mineral content and more homogenous mineralization profile as revealed via qBEI were found in the bone matrix of the fracture group. Fracture cases showed nearly 35% higher cortical porosity and showed significantly reduced osteocyte lacunar density compared to controls (226±27 vs. 247±32#/mm(2), p=0.05). Along with increased crystal size, a shift towards higher mineralization and a tendency to increased cortical porosity and reduced osteocyte lacunar number delineate that cortical bone of the superolateral femoral neck bears distinct signs of fragility at various levels of its structural organization. These results contribute to the understanding of hierarchical bone structure changes in age-related fragility.

Ultrasonic spray pyrolysis of TiO2 nanoparticles

Abstract Synthesis of ultrafine spherical TiO 2 particles was achieved by using ultrasonic spray pyrolysis and nanoparticles of TiO 2 (≈2.5nm) as a precursor. The size distribution and morphology of TiO 2 particles obtained after ultrasonic spray pyrolysis were characterized by SEM and STM. Agreement between experimentally obtained results and theoretical calculation of particle size was found.

Sorption of zinc by novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid

Novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid were applied as adsorbents for the removal of Zn(2+) ions from aqueous solution. In batch tests, the influence of solution pH, contact time, initial metal ion concentration and temperature was examined. The sorption was found pH dependent, pH 5.5 being the optimum value. The adsorption process was well described by the pseudo-second order kinetic. The hydrogels were characterized by spectral (Fourier transform infrared-FTIR) and structural (SEM/EDX and atomic force microscopy-AFM) analyses. The surface topography changes were observed by atomic force microscopy, while the changes in surface composition were detected using phase imaging AFM. The negative values of free energy and enthalpy indicated that the adsorption is spontaneous and exothermic one. The best fitting isotherms were Langmuir and Redlich-Peterson and it was found that both linear and nonlinear methods were appropriate for obtaining the isotherm parameters. However, the increase of temperature leads to higher adsorption capacity, since swelling degree increased with temperature.

Nanostructure and mineral composition of trabecular bone in the lateral femoral neck: implications for bone fragility in elderly women.

Despite interest in investigating age-related hip fractures, the determinants of decreased bone strength in advanced age are not clear enough. Hitherto it has been obscure how the aging process affects the femoral neck nanostructure and composition, particularly in the lateral subregion of the femoral neck, which is considered as a fracture-initiating site. The femoral bone samples used in this study were obtained at autopsy in 10 women without skeletal disease (five younger: aged 20-40 years, and five elderly: aged 73-94 years). Atomic force microscopy (AFM) was applied to explore the mineral grain size in situ in young vs. old trabecular bone samples from the lateral femoral neck. The chemical compositions of the samples were determined using inductively coupled plasma optical emission spectroscopy and direct current argon arc plasma optical emission spectrometry. Our AFM study revealed differences in trabecular bone nanostructure between young and elderly women. The mineral grain size in the trabeculae of the old women was larger than that in the young (median: 95 vs. 59nm), with a particular bimodal distribution: 45% were small grains (similar to the young) and the rest were larger. Since chemical analyses showed that levels of calcium and phosphorus were unchanged with age, our study suggests that during aging the existing bone mineral is reorganized and forms larger aggregates. Given the mechanical disadvantage of large-grained structures (decreased material strength), the observed nanostructural differences contribute to our understanding of the increased fragility of the lateral femoral neck in aged females. Moreover, increasing data on mineral grains in natural bone is essential for advancing calcium-phosphate ceramics for bone tissue replacement.

The effect of rapid thermal annealing on structural and electrical properties of TiB2 thin films

Abstract This work reports on the effect of post-deposition rapid thermal annealing on the structural and electrical properties of deposited TiB2 thin films. The TiB2 thin films, thicknesses from 9 to 450 nm, were deposited by e-beam evaporation on high resistivity and thermally oxidized silicon wafers. The resistivity of as-deposited films varied from 1820 μΩ cm for the thinnest film to 267 μΩ cm for thicknesses greater than 100 nm. In the thickness range from 100 to 450 nm, the resistivity of TiB2 films has a constant value of 267 μΩ cm. A rapid thermal annealing (RTA) technique has been used to reduce the resistivity of deposited films. During vacuum annealing at 7 × 10−3 Pa, the film resistivity decreases from 267 μΩ cm at 200 °C to 16 μΩ cm at 1200 °C. Heating cycles during RTA were a sequence of 10 s. According to scanning tunneling microscopy analysis, the decrease in resistivity may be attributed to a grain growth through polycrystalline recrystallization, as well as to an increase in film density. The grain size and mean surface roughness of annealed films increase with annealing temperature. At the same time, the conductivity of the annealed samples increases linearly with grain size. The obtained results show that RTA technique has a great potential for low resistivity TiB2 formation.

Age-dependence of power spectral density and fractal dimension of bone mineralized matrix in atomic force microscope topography images: potential correlates of bone tissue age and bone fragility in female femoral neck trabeculae

There is an increasing interest in bone nano‐structure, the ultimate goal being to reveal the basis of age‐related bone fragility. In this study, power spectral density (PSD) data and fractal dimensions of the mineralized bone matrix were extracted from atomic force microscope topography images of the femoral neck trabeculae. The aim was to evaluate age‐dependent differences in the mineralized matrix of human bone and to consider whether these advanced nano‐descriptors might be linked to decreased bone remodeling observed by some authors and age‐related decline in bone mechanical competence. The investigated bone specimens belonged to a group of young adult women (n = 5, age: 20–40 years) and a group of elderly women (n = 5, age: 70–95 years) without bone diseases. PSD graphs showed the roughness density distribution in relation to spatial frequency. In all cases, there was a fairly linear decrease in magnitude of the power spectra with increasing spatial frequencies. The PSD slope was steeper in elderly individuals (−2.374 vs. −2.066), suggesting the dominance of larger surface morphological features. Fractal dimension of the mineralized bone matrix showed a significant negative trend with advanced age, declining from 2.467 in young individuals to 2.313 in the elderly (r = 0.65, P = 0.04). Higher fractal dimension in young women reflects domination of smaller mineral grains, which is compatible with the more freshly remodeled structure. In contrast, the surface patterns in elderly individuals were indicative of older tissue age. Lower roughness and reduced structural complexity (decreased fractal dimension) of the interfibrillar bone matrix in the elderly suggest a decline in bone toughness, which explains why aged bone is more brittle and prone to fractures.

Tailor made synthesis of Q-TiO2 powder by using quantum dots as building blocks

Abstract A simple synthetic procedure based on ultrasonic spray pyrolysis and usage of TiO 2 quantum dots as building blocks leads to the formation of submicronic TiO 2 spheres which preserved optical and catalytic properties of the constituting elements. The methodology is not limited to semiconductor quantum dots, but provides general procedures for the rational design of novel and potentially useful composite materials.

The influence of ion bombardment intensity during deposition on nickel films microstructure

Abstract Nickel films were deposited from a vapour phase (e-gun source) onto amorphous glass substrates at room temperature during a simultaneous bombardment with nitrogen ions at low pressure (4 × 10 −2 Pa). Under a constant partial pressure of nitrogen and negative substrate bias voltages the effect of bombardment intensity on the texture and morphology of Ni films (about 1 μm) has been investigated by XRD and STM methods. The films under investigation exhibit a variable degree of (200) preferred orientation by changing the ion to atom flux ratio ( IAR ) from 0.03 to 0.3. It was found that complete (200) texture was achieved for an IAR of about 0.1 and that further increase of IAR induces the decrease of preferred orientation. X-ray diffraction in combination with profiling by a 1 keV argon ion beam bombardment has been used for in. depth texture and grain size analysis. It has been shown that oriented growth, grain size and morphology correlate with changes of bombardment intensity during the deposition as well as with the substrate bias potential.

Mechanochemical treatment and structural properties of lead adsorption on kaolinite (Rudovci, Serbia)

In the present work, remediation of lead-containing solution using raw and modified kaolinite has been presented. The micro and nanostructure of samples has been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Laser diffraction and scattering (LDS), was analyzed by particle size analyzer based on laser diffraction and particle size distribution (PSD) was done. The degree of metal adsorption was evaluated analyzing the Pb(II) contaminated samples by inductively coupled plasma atomic emission spectrometry (micro- and nanostructure on immobilization efficiency correlCP AES). The results show the impact of immobilization efficiency and ation between micro- and nanostructure. The thermodynamic data (ΔH°, ΔS°, ΔG°) are calculated from the temperature-dependent sorption isotherms. The results suggest sorption process of Pb(II) on kaolinite as spontaneous and endothermic.