Damir Semenski

Effect of twin-screw extrusion parameters on mechanical hardness of direct-expanded extrudates

Mechanical properties of cereal (starch-based) extrudates are perceived by the final consumer as criteria of quality. We investigate one of the important characteristics of extrudates, mechanical hardness, which is one of the main texture parameters. Texture quality has an influence on taste sensory evaluation, and thus on the acceptability of the product. Characteristics that have great influence on acceptability are crispness, elasticity, hardness and softness.These attributes are narrowly related to, and affected by, the process parameters. A 2-level-4-factor factorial experimental design was used to investigate the influence of temperature of expansion, screw speed, feed moisture content and feed rate, and their interactions, on the mechanical hardness of extrudates. Feed moisture content, screw speed and temperature are found to influence, while feed rate does not have significant effect on extrudate hardness.Mechanical properties of specimens were measured by means of compression testing, based on the concept of nominal stress, using a universal testing machine and special grips that were constructed for this purpose.

Influence of surface layer on mechanical and corrosion properties of nickel-titanium orthodontic wires

OBJECTIVE To analyze the effect of various coating formulations on the mechanical and corrosion properties of nickel-titanium (NiTi) orthodontic wires. MATERIALS AND METHODS Uncoated, rhodium-coated, and nitrified NiTi wires were observed with a three-point-bend test, surface roughness (Ra) measurement, scanning electron microscopy, energy dispersive spectroscopy, and electrochemical testing (open circuit potential, electrochemical impedance spectroscopy, and cyclic polarization scan). Differences in the properties of tested wire types were analyzed with analysis of variance and Tukey post hoc test. RESULTS Uncoated and nitrified NiTi wires showed similar mechanical and anticorrosive properties, while rhodium-coated NiTi wires showed the highest Ra and significantly higher modulus of elasticity, yield strength, and delivery of forces during loading but not in unloading. Rhodium-coated NiTi wires also had the highest corrosion current density and corrosion potential, lowest impedance modulus, and two time constants on Bode plot, one related to the Rh/Au coating and the other to underlying NiTi. CONCLUSION Working properties of NiTi wires were unaffected by various coatings in unloading. Nitrification improved corrosion resistance. Rhodium coating reduced corrosion resistance and pronounced susceptibility to pitting corrosion in artificial saliva because of galvanic coupling between the noble coating and the base alloy.

Sevelamer Restores Bone Volume and Improves Bone Microarchitecture and Strength in Aged Ovariectomized Rats

Sevelamer hydrochloride, a noncalcium phosphate binder, has been shown to reduce coronary artery and aortic calcification, and to improve trabecular bone mineral density in hemodialysis patients with chronic kidney disease. Here, we examined whether sevelamer given orally for 12 wk with normal food could restore bone volume (BV) and strength in aged ovariectomized (OVX) rats starting at 4 wk after OVX. Dual-energy x-ray absorptiometry, microcomputerized tomography, and bone histomorphometry analyses showed that OVX animals receiving sevelamer had increased trabecular BV (51%), trabecular number (43%), trabecular thickness (9%), cortical thickness (16%), mineral apposition rate (103%), bone formation rate (25%), and enhanced cortical and trabecular bone mechanical strength as compared with OVX rats. Sevelamer decreased collagen C telopeptide, increased osteocalcin levels, and decreased phosphate and magnesium levels without affecting calcium levels in the blood. Although sevelamer was not absorbed systemically, it stimulated osteoblast differentiation in BM-derived mesenchymal stem cell cultures, as evaluated by alkaline phosphatase positive colony-forming units, and inhibited recombinant human soluble receptor activator of nuclear factor-kappaB ligand-induced osteoclast differentiation, as evaluated by tartrate-resistant acid phosphatase positive cells in bone mineral-hematopoietic stem cell cultures. Surface enhanced laser desorption/ionization time-of-flight mass spectrometry analysis revealed that 69 proteins were differently expressed after OVX, of which 30% (20 of 69) were reversed to sham activity after sevelamer intake. PTH, fibroblast growth factor-23, and cytokine profile in serum were not significantly changed. Together, these results suggest that sevelamer in food increases the BV and improves biomechanical properties of bone in OVX rats.

Reducing Fat Globules Particle-Size in Goat Milk : Ultrasound and High Hydrostatic Pressures Approach

Innovative and eco-friendly food technologies in practical usage today like Ultrasound (US) and High Hydrostatic Pressures (HHP) are feasible to adequately maintain various food properties while processed, such as texture, sensorial and organoleptic characteristics, and microbiological issues as well. Benchmarked attribute of the mentioned approach lies in the ability of US and HHP to control and withhold both temperature and treatment duration. While temperature could be controlled within room ambient, treatment time is mostly below 30 minutes. US and HHP treatment were performed as separate treatments in order to obtain better homogenization. Goat milk was exposed to ultrasonic propagation up to 100 W of nominal power and high pressures up to 600 MPa. Maximum treatment time was 9 minutes. Ultrasonic homogenization indicates enhanced homogeneity of fat globules while high pressure process parameters have a significant influence on the observed mean particle diameter (fat globules). Improved stability and quality of emulsions (goat milk) was obtained by both applied processes. Statistical analysis indicated the influence of process parameters on fat globule size distribution between 0.3 – 4 µm and variance lower than 0.6.

Contact caustics measurements expanded to anisotropic materials

Regions with high stress gradients represent critical zones of engineering structures, such as crack tip or vicinity of the contact zone. The optical method of caustics is one of the few experimental methods which provide applicable results in these locations. This method was originally developed for crack-tip measurements of stress intensity factors and J-integral for isotropic and then for anisotropic materials. Subsequently, it was extended to the contact problems, where the size and the shape of caustics are related to the amount and the inclination of loading force. Here, the application of the method of caustics is extended to the analysis of contact problems for mechanically anisotropic materials. This makes the caustics method widely applicable to the analysis of any high stress gradient locations in a structure.

Biomechanical Comparison of the Temporalis Muscle Fascia, the Fascia Lata, and the Dura Mater

Abstract The purpose of our research is to prove that elastic biomechanical characteristics of the temporalis muscle fascia are comparable to those of the fascia lata, which makes the temporalis muscle fascia adequate material for dural reconstruction in the region of the anterior cranial fossa. Fifteen fresh human cadavers, with age range from 33 to 83 years (median age: 64 years; mean age: 64.28 years), were included in the biomechanical study. Biomechanical stretching test with the comparison of elasticity among the tissues of the temporalis muscle fascia, the fascia lata, and the dura was performed. The samples were stretched up to the value of 6% of the total sample length and subsequently were further stretched to the maximum value of force. The value of extension at its elastic limit for the each sample was extrapolated from the force‐extension curve and was 6.3% of the total sample length for the fascia lata (stress value of 14.61 MPa), 7.4% for the dura (stress value of 6.91 MPa), and 8% for the temporalis muscle fascia (stress value of 2.09 MPa). The dura and temporalis muscle fascia shared the same biomechanical behavior pattern up to the value of their elastic limit, just opposite to that of the fascia lata, which proved to be the stiffest among the three investigated tissues. There was a statistically significant difference in the extension of the samples at the value of the elastic limit for the fascia lata in comparison to the temporalis muscle fascia and the dura (p = 0.002; Kruskal‐Wallis test). Beyond the value of elastic limit, the temporalis muscle fascia proved to be by far the most elastic tissue in comparison to the fascia lata and the dura. The value of extension at its maximum value of force for the each sample was extrapolated from the force‐extension curve and was 9.9% of the samples total length for the dura (stress value of 10.02 MPa), 11.2% for the fascia lata (stress value of 23.03 MPa), and 18.5% (stress value of 3.88 MPa) for the temporalis muscle fascia. There was a statistically significant difference in stress values at the maximum value of force between the dura and the temporalis muscle fascia (p = 0.001; Mann‐Whitney U test) and between the dura and the fascia lata (p < 0.001; Mann‐Whitney U test). Because of its elasticity and similarity in its mechanical behavior to the dura, the temporalis muscle fascia can be considered the most suitable tissue for dural reconstruction.