Effect of microstructure on micromechanical performance of dry cortical bone tissues

The mechanical properties of bone depend on composition and structure. Previous studies have focused on macroscopic fracture behavior of bone. In the present study, we performed microindentation studies to understand the deformation properties and microcrack–microstructure interactions of dry cortical bone. Dry cortical bone tissues from lamb femurs were tested using Vickers indentation with loads of 0.245–9.8 N. We examined the effect of bone microstructure on deformation and crack propagation using scanning electron microscopy (SEM). The results showed the significant effect of cortical bone microstructure on indentation deformation and microcrack propagation. The indentation deformation of the dry cortical bone was basically plastic at any applied load with a pronounced viscoelastic recovery, in particular at lower loads. More microcracks up to a length of approximately 20 μm occurred when the applied load was increased. At loads of 4.9 N and higher, most microcracks were found to develop from the boundaries of haversian canals, osteocyte lacunae and canaliculi. Some microcracks propagated from the parallel direction of the longitudinal interstitial lamellae. At loads 0.45 N and lower, no visible microcracks were observed.     

Inhibition of lipoxygenase 1 by phosphatidylcholine micelles-bound curcumin

Curcumin (diferuloyl methane) from rhizomes of Curcuma longa L. binds to phosphatidylcholine (PC) micelles. The binding of curcumin with PC micelles was followed by fluorescence measurements. Curcumin emits at 490 nm with an excitation wavelength of 451 nm after binding to PC-mixed micelles stabilized with deoxycholate. Curcumin in aqueous solution does not inhibit dioxygenation of fatty acids by Lipoxygenase 1 (LOX1). But, when bound to PC micelles, it inhibits the oxidation of fatty acids. The present study has shown that 8.6 microM of curcumin bound to the PC micelles is required for 50% inhibition of linoleic acid peroxidation. Lineweaver-Burk plot analysis has indicated that curcumin is a competitive inhibitor of LOX1 with Ki of 1.7 microM for linoleic and 4.3 microM for arachidonic acids, respectively. Based on spectroscopic measurements, we conclude that the inhibition of LOX1 activity by curcumin can be due to binding to active center iron and curcumin after binding to the PC micelles acts as an inhibitor of LOX1.     

Anterior segment OCT-based diagnosis and management of retained Descemet''s membrane following penetrating keratoplasty

PURPOSE: To report a case of retained Descemet's membrane after penetrating keratoplasty for congenital hereditary endothelial dystrophy (CHED) documented by anterior segment optical coherence tomography and review of literature. METHODS: Case report and review of literature. RESULTS: A 14-year-old boy underwent penetrating keratoplasty for CHED. A retained host Descemet's membrane was detected with a supernumerary anterior chamber on the first postoperative day. The retained Descemet's membrane was documented using slit lamp adapted anterior segment optical coherence tomography (SLOCT). Surgical intervention for the Descemet's membrane removal was done in the third postoperative week. The complete removal of the membrane was confirmed on SLOCT. CONCLUSION: Inadvertent retention of the host Descemet's membrane is a rare but possible complication in penetrating keratoplasty for CHED. Proper anticipation, early detection and removal will help in preventing any undue risk of graft failure.     

Effect of Process Parameters and Heat Treatments on Properties of Cold Sprayed Copper Coatings

Cold gas dynamic spraying or cold spray is specifically suitable to obtain high-conductivity copper coatings for a variety of applications. Copper coatings at different coating parameters were deposited and subjected to various post treatments. The effect of process parameters and the treatment conditions on coating properties such as electrical conductivity, porosity, microhardness etc., was studied. The as-coated specimens exhibited low conductivities and conductivity was found to improve with heat treatment. Treatments were carried out in vacuum at different temperatures and for different durations and conductivities close to bulk annealed copper were achieved. Good correlation was observed between the conductivity, porosity and hardness of the as-coated and heat-treated specimens. Similar correlations were observed between conductivity-porosity and hardness-porosity of the coatings and the relative influence of cold work and porosity on coating properties was determined.     

Optical, electrical and thermoelectric power studies of Al-Sb thin film bilayer structure

The III-V semiconductors are of great importance due to their applications in various electro-optic devices. The Al-Sb thin film was deposited on glass substrate by thermal evaporation method at a pressure of 10^-5 torr. The samples were annealed for 3 h at different constant temperatures in a vacuum chamber at a pressure of 10^-5 torr. The electrical resistance vs temperature studies show phase transformation from metallic to semiconducting. The observed positive thermoelectric power indicates that Al-Sb thin films arep-type in nature. The Rutherford back scattering analysis and optical band gap measurements also indicate that the inter-diffusion concentration varies with temperature.     

Multi-scale modeling of thermo-oxidation effects on the flexural behavior of cross-ply bismaleimide composites

Mechanics of Time-Dependent Materials - Mechanical properties of high-temperature polymer matrix composites deteriorate during their service. Oxidation plays a significant role in determining the...     

2D and 3D mapping of microindentations in hydrated and dehydrated cortical bones using confocal laser scanning microscopy

We report on responses of hydrated and dehydrated cortical bone tissues to mechanical loading applied by a Vickers indenter. The Vickers indentations were imaged in two- and three-dimensions (2D and 3D) using confocal laser scanning microscopy (CLSM) to understand mechanical behavior of bone tissues. Serial optical sections of indentation patterns of dry and wet bones were collected using CLSM. The indention surface structures were mapped using topographical CLSM imaging. The observation of CLSM shows the fundamental indentation responses for both the hydrated and dehydrated bone tissues were plastic deformation. No visible fracture was observed in the Vickers indentation patterns in the wet bone tissue, while non-propagating lamellar microcracks occurred in the dry bone tissue. This indicates that drying resulted in increased brittleness of the bone tissue. The Vickers hardness values of dry bone tissue were significantly higher than those of wet bone tissue at any applied loads (analysis of variation, ANOVA, p < 0.05). The resolution limits of confocal microscopy were also discussed for bone tissue scanning.     

A simple stochastic model for yielding in specimens with limited number of dislocations

A simple statistical model is developed based on a random distribution and orientation of dislocations in order to explain recent experimental observations of the strength of small specimens containing a limited number of dislocations. Two different types of randomness are introduced, namely, randomness in the spatial location of the dislocations and randomness in the stress needed to activate them. For convenience, the randomness in the activation stress is modeled by assigning a random Schmid factor to the dislocations. In contrast to previous stochastic models, the current model predicts the yield strength not only in the presence of dislocations but also in their absence. Furthermore, the model predicts the scatter in the yield strength in addition to the mean. The model is found to quantitatively explain the yield strength and scatter in micro-compression/tension tests of Mo-alloy fibers using dislocation densities and arrangements measured by transmission electron microscopy. The results of Brenner’s classic tensile tests on metallic whiskers are qualitatively reconciled. The model adds credence to the notion that “smaller is stronger” from a purely statistical point of view.     

Optical Diagnostics Study of Gas Particle Transport Phenomena in Cold Gas Dynamic Spraying and Comparison with Model Predictions

Cold gas dynamic spraying (CGDS), a relatively new thermal spraying technique has drawn a lot of attention due to its inherent capability to deposit a wide range of materials at relatively low-operating temperatures. A De Laval nozzle, used to accelerate the powder particles, is the key component of the coating equipment. Knowledge concerning the nozzle design and effect of process parameters is essential to understand the coating process and to enable selection of appropriate parameters for enhanced coating properties. The present work employs a one-dimensional isentropic gas flow model in conjunction with a particle acceleration model to calculate particle velocities. A laser illumination-based optical diagnostic system is used for validation studies to determine the particle velocity at the nozzle exit for a wide range of process and feedstock parameters such as stagnation temperature, stagnation pressure, powder feed rate, particle size and density. The relative influence of process and feedstock parameters on particle velocity is presented in this work.