Assem Hedayat

Morphological Characterization of the Polyflux 210H Hemodialysis Filter Pores

Background. Morphological characterization of hemodialysis membranes is necessary to improve pore design. Aim. To delineate membrane pore structure of a high flux filter, Polyflux 210H. Methods. We used a Joel JSM-6010LV scanning electron microscope (SEM) and a SU6600 Hitachi field emission scanning electron microscope (FESEM) to characterize the pore and fiber morphology. The maximal diameters of selected uremic toxins were calculated using the macromolecular modeling Crystallographic Object-Oriented Toolkit (COOT) software. Results. The mean pore densities on the outermost and innermost surfaces of the membrane were 36.81% and 5.45%, respectively. The membrane exhibited a tortuous structure with poor connection between the inner and outer pores. The apertures width in the inner surface ranged between 34 and 45 nm, which is 8.76–11.60 times larger than the estimated maximum diameter of β2-microglobulin (3.88 nm). Conclusion. The results suggest that the diameter size of inner pore apertures is not a limiting factor to middle molecules clearance, the extremely diminished density is. Increasing inner pore density and improving channel structure are strategies to improve clearance of middle molecules.

Wear and CO2 corrosion of steel couplings and tubing in heavy oil screw-pump wells

Abstract A prototype apparatus was used to investigate the effect of the conjoint action of CO2 corrosion and rotary sliding wear on steel couplings and tubing used in heavy oil screw-pump wells. The apparatus is versatile in design to simulate the oil-well conditions such as temperature, rotary speed, and the side forces exerted by the couplings on the tubing. Oil-well gases can also be passed through the system, and the apparatus can be converted to a three-electrode corrosion cell for conducting electrochemical studies. All tests were carried out in a produced heavy oil and formation water mixture. A comparison of the performance of various types of commercially available steel couplings and tubing grades through material loss measurements is presented. The couplings tested were made of plain carbon steel, and ‘hard metal’ coated steel. The steel tubing grades L-80, N-80, and P-110 as well as plain carbon steel were among the tubing materials tested. It was found that the martensitic tubin suffered the least thickness loss but caused the most damage to the couplings. Also, ‘hard metal’ coated couplings yielded the highest tubing thickness loss. The results are attributed to the microstructures of the various steels as well as their hardness values. The morphologies of the different materials surfaces were characterized using scanning electron microscopy (SEM) following testing.

Aqueous corrosion of plain carbon steel during sliding wear

Abstract The effects of the cojoint action of corrosion and sliding wear are found in many industrial applications; for example in the area of sucker rods and tubing in slant and directionally drilled oil wells. A prototype apparatus has been designed and built to simulate the cojoint action of corrosion and wear on sliding steel components. Sliding wear tests were conducted on AISI 1045 steel samples in a 10% NaCl aqueous solution. The samples were subjected to various loads to study the effect of contact pressure on the wear-corrosion process. A set of tests were also run under the same mechanical conditions but in the presence of potassium chromate to inhibit corrosion. The effect of the corrosion inhibitor was very pronounced in the case of samples representing sucker rods. The experimental results show a marked drop in the material loss rates of these samples. Optical and scanning electron microscopy was used to study the characteristics of wear scars on the samples after testing. An explanation for the role of corrosion in the sliding wear of the steel samples is presented.

Phase transformation in carbon-coated nitinol, with application to the design of a prosthesis for the reconstruction of the anterior cruciate ligament

Ultra-low temperature isotropic carbon was vapour-deposited on a near equiatomic Ti-Ni (Nitinol) alloy (49.9 at % Ti-50.1 at % Ni). The objective of the carbon coating was the induction of growth of collagenous tissue, as part of a preliminary design of a prosthesis for the reconstruction of the anterior cruciate ligament. Differential scanning calorimetry was used to study the phase transformation of carbon-coated Nitinol. X-ray diffraction and Auger electron spectroscopy were used in the study of the carbon/Nitinol interface. The results show that unannealed coatings do not inhibit the Nitinol phase transformation regardless of the thickness of the coatings. However, on heat treating the coated samples, a TiC layer forms at the carbon/Nitinol interface. The thickness of that layer increases with increasing the time of heat treatment. Surface constraint of the Nitinol by the TiC results in a marked drop in the austenitic start (As) and martensitic finish (Mf) temperatures of thin samples. The inhibition of both the premartensitic and martensitic transformations increases with the increase in thickness of the TiC interface.

The effect of surface constraint on the phase transformation of Nitinol

Ultra-low-temperature isotropic carbon was vapour deposited on a near equiatomic Ti-Ni (Nitinol) alloy (49.9 at% Ti-50.1 at% Ni) for components used in biomedical applications. The adhering carbon film, and carbide layer formed after annealing, introduced a surface constraint. Differential scanning calorimetry studies show a marked decrease in theAs andMf temperatures of such a surface-constrained alloy during phase transformation. TEM foils made of vertical and horizontal sections of carbon-coated Nitinol were examined using transmission electron microscopy. It is proposed that for surface-constrained samples, the martensite plates last to form were close to the surface, and these are first to disappear during reverse transformation. Moreover, for both coated and uncoated samples, the martensitic and reverse transformations can be described by equations of the formf(A) =exp[-α(Ms-T)] andf(A) =exp[-λ(Af-T)], respectively, wheref(A) is the fraction of austenitic phase present at the specific temperature (T), and α and γ are constants. Finally, the driving force for the martensitic and reverse transformations of both coated and uncoated samples was calculated.

Theoretical Application of Irreversible (Nonequilibrium) Thermodynamic Principles to Enhance Solute Fluxes across Nanofabricated Hemodialysis Membranes

Objective. Nanotechnology has the potential to improve hemodialysis membrane technology. Thus, a major objective is to understand how to enhance toxic solute fluxes across these membranes. The aim of this concept building study is to review the application of irreversible thermodynamic (IT) to solute fluxes. Methods. We expanded the application of the Nernst-Planck equation to include the Kedem-Katchalsky equation, pH, membrane thickness, pore size, and electric potential as variables. Results. (1) Reducing the membranes thickness from 25 μm to 25 nm increased the flux of creatinine, β2-microglobulin, and tumor necrosis factor-α (TNF-α) by a thousand times but prevented completely albumin flux, (2) applying an electric potential of 50–400 mV across the membrane enhanced the flux of the respective molecules by 71.167 × 10−3, 38.7905 × 10−8, and 0.595 × 10−13 mol/s, and (3) changing the pH from 7.35 to 7.42 altered the fluxes minimally. Conclusions. The results supported an argument to investigate the application of IT to study forces of fluxes across membranes. Reducing the membranes thickness—together with the application of an electrical potential—qualities achievable by nanotechnology, can enhance the removal of uremic toxins by many folds. However, changing the pH at a specific membrane thickness does not affect the flux significantly.

STUDY OF UREMIC TOXIN FLUXES ACROSS NANOFABRICATED HEMODIALYSIS MEMBRANES USING IRREVERSIBLE THERMODYNAMICS

Introduction The flux of uremic toxin middle molecules through currently used hemodialysis membranes is suboptimal, mainly because of the membranes’ pore architecture. Aim Identifying the modifiable sieving parameters that can be improved by nanotechnology to enhance fluxes of uremic toxins across the walls of dialyzers’ capillaries. Methods We determined the maximal dimensions of endothelin, cystatin C, and interleukin – 6 using the macromolecular modeling software, COOT. We also applied the expanded Nernst-Plank equation to calculate the changes in the overall flux as a function of increased electro-migration and pH of the respective molecules. Results In a high flux hemodialyzer, the effective diffusivities of endothelin, cystatin C, and interleukin – 6 are 15.00 x 10-10 cm2/s, 7.7 x 10-10 cm2/s, and 5.4 x 10-10 cm2/s, respectively, through the capillaries’ walls. In a nanofabricated membrane, the effective diffusivities of endothelin, cystatin C, and interleukin – 6 are 13.87 x 10-7 cm2/s, 5.73 x 10-7 cm2/s, and 3.45 x 10-7 cm2/s, respectively, through a nanofabricated membrane. Theoretical modeling showed that a 96% reduction in the membranes thickness and the application of an electric potential of 10 mV across the membrane could enhance the flux of endothelin, cystatin C, and interleukin - 6 by a factor of 25. A ΔpH of 0.07 altered the fluxes minimally. Conclusions Nanofabricated hemodialysis membranes with a reduced thickness and an applied electric potential can enhance the effective diffusivity and electro-migration flux of the respective uremic toxins by 3 orders of magnitude as compared to those passing through the high flux hemodialyzer.

Synchrotron-radiation-based X-ray micro-computed tomography reveals dental bur debris under dental composite restorations

Dental burs are used extensively in dentistry to mechanically prepare tooth structures for restorations (fillings), yet little has been reported on the bur debris left behind in the teeth, and whether it poses potential health risks to patients. Here it is aimed to image dental bur debris under dental fillings, and allude to the potential health hazards that can be caused by this debris when left in direct contact with the biological surroundings, specifically when the debris is made of a non-biocompatible material. Non-destructive micro-computed tomography using the BioMedical Imaging & Therapy facility 05ID-2 beamline at the Canadian Light Source was pursued at 50 keV and at a pixel size of 4 µm to image dental bur fragments under a composite resin dental filling. The burs cutting edges that produced the fragment were also chemically analyzed. The technique revealed dental bur fragments of different sizes in different locations on the floor of the prepared surface of the teeth and under the filling, which places them in direct contact with the dentinal tubules and the dentinal fluid circulating within them. Dispersive X-ray spectroscopy elemental analysis of the dental bur edges revealed that the fragments are made of tungsten carbide-cobalt, which is bio-incompatible.

EndoCal 10 Obturation Voids in Root Canal and Isthmus of a Human Premolar: A Synchrotron micro-CT Imaging Study.

The objective of this research is to detect and characterize voids in an Endocal 10 obturated human premolar using synchrotron-radiation-based micro-computed tomography (SRμCT) and 3D visualization. Also, the aim is to investigate the extent of voids present in a fine structure such as an isthmus following obturation. We scanned an extracted human premolar that was obturated with EndoCal 10 using the Bio-Medical Imaging and Therapy (BMIT) 05ID-2 beamline at the Canadian Light Source. We applied the non-destructive monochromatic X-ray beam at 47 keV, and compiled 4.3 μm pixel size images utilizing a AA-40 (HAMAMATSU) beam monitor synchronized with a (HAMAMATSU C9300-124) charge-coupled camera. We used Fiji for reconstructing the images and Avizo 9.0 for 3D rendering. The results showed voids in different parts of the obturation as well as a partially obturated isthmus. Miicro-CT and 3D visualization show that voids exist in the pulp chamber, root canal, and isthmus following obturation with EndoCal 10 during endodontic therapy. We categorized the isthmus as a type V one. The study also highlights the reasons contributing to the difficulty of obturating the isthmus. The variation in isthmus’ diameter, its irregular branching, the presence of pulp tissue, as well as its angular orientation with respect to the root canals are some of the reasons that impede the flow of EndoCal 10 through it.