Structural allograft in two-stage revisions for failed septic hip arthroplasty

We report 11 patients having revision of total hip arthroplasty using massive structural allografts for failure due to sepsis and associated bone loss. All patients had a two-stage reconstruction and the mean follow-up was 47.8 months (24 to 72). Positive cultures were obtained at the first stage in nine of the 11 patients, with Staphylococcus epidermidis being the most common organism. The other two patients had draining sinuses with negative cultures. There was no recurrence of infection in any patient. The mean increase in the modified Harris hip score was 45 and all the grafts appeared to have united to host bone. Two patients required additional procedures, but only one was related to the allograft. Complications included an incomplete sciatic nerve palsy and one case of graft resorption. Our results support the use of massive allografts in failed septic hip arthroplasty in which there is associated bone loss.     

High Efficiency Poly(acrylonitrile) Electrospun Nanofiber Membranes for Airborne Nanomaterials Filtration

The potential of poly(acrylonitrile) electrospun membranes with tuneable pore size and fiber distributions were investigated for airborne fine‐particle filtration for the first time. The impact of solution concentration on final membrane properties are evaluated for the purpose of designing separation materials with higher separation efficiency. The properties of fibers and membranes are investigated systematically: the average pore distribution, as characterized by capillary flow porometry, and thermo‐mechanical properties of the mats are found to be dependent on fiber diameter and on specific electrospinning conditions. Filtration efficiency and pressure drop are calculated from measurement of penetration through the membranes using potassium chloride (KCl) aerosol particles ranging from 300 nm to 12 μm diameter. The PAN membranes exhibited separation efficiencies in the range of 73.8–99.78% and a typical quality factor 0.0224 (1 Pa^?1) for 12 wt% PAN with nanofibers having a diameter of 858 nm. Concerning air flow rate, the quality factor and filtration efficiency of the electrospun membranes at higher face velocity are much more stable than for commercial membranes. The results suggest that the structure of electrospun membranes is the best for air filtration in terms of filtration stability at high air flow rate.

     

Numerical analysis of coronary artery bypass grafts: An over view

Arterial bypass grafts tend to fail after some years due to the development of intimal thickening (restenosis). Non-uniform hemodynamics following a bypass operation contributes to restenosis and bypass failure can occur due to the focal development of anastomotic intimal hyperplasia. Additionally, surgical injury aggravated by compliance mismatch between the graft and artery has been suggested as an initiating factor for progress of wall thickening along the suture line Vascular grafts that are small in diameter tend to occlude rapidly. Computational fluid dynamics (CFD) methods have been effectively used to simulate the physical and geometrical parameters characterizing the hemodynamics of various arteries and bypass configurations. The effects of such changes on the pressure and flow characteristics as well as the wall shear stress during a cardiac cycle can be simulated. Recently, utilization of fluid and structure interactions have been used to determine fluid flow parameters and structure forces including stress and strains relationships under steady and transient conditions. In parallel to this, experimental diagnostics techniques such as Laser Doppler Anemometry, Particle Image Velocimetry, Doppler Guide wire and Magnetic Resonance Imaging have been used to provide essential information and to validate the numerical results. Moreover, clinical imaging techniques such as magnetic resonance or computed tomography have assisted considerably in gaining a detailed patient-specific picture of the blood flow and structure dynamics. This paper gives a review of recent numerical investigations of various configurations of coronary artery bypass grafts (CABG). In addition, the paper ends with a summary of the findings and the future directions.     

Friction and wear of copper/lead and aluminium/tin filled polyamide coatings

The friction and wear of steel pins coated with filled polyamides and loaded against a rotating cylinder of bearing steel were tested under dry, lubricated, and abrasive contaminated conditions. The filler materials were copper/lead and aluminium/tin powders. The test results show a significant reduction in friction with the Cu/Pb filled polyamides (8 wt.% Cu, 12 wt.% Pb, and 80 wt.% PA6). The Al/Sn filled polyamides (3 wt.% Al, 2 wt.% Sn, and 95 wt.% PA6) showed the best wear resistance, accompanied by an increase in the coefficient of friction.     

Preliminary evaluation of hot extrusion miniaturization

Experiments were conducted to examine the feasibility of hot extruding metals on a miniature scale thus providing a quick and cheap method of studying extrusion in general. Aluminium was successfully extruded using a new miniature hot extrusion rig, producing aluminium wires (maximum diameter 2.6 mm) as opposed to rods. A preliminary comparison of extrusion pressures on the miniature rig and on a larger extrusion press was conducted. The effects of temperature, extrusion speed and extrusion ratio on the extrusion pressure were examined for both miniature and larger scale extrusions. Extrusion speed had little effect on extrusion pressure, because the range of speeds examined was too small (due to speed limitations on the larger extrusion press). Both extrusion sizes generally displayed similar dependencies on temperature and extrusion ratio. However, the extrusion pressures for miniature extrusions were found to be always lower than for the larger scale extrusions. This may have been due the evaluation of parameters in the expression used for strain rate in the comparison. Finite element analysis may prove useful in gaining a fuller understanding of the miniaturization process.     

Sorption of water vapor by B pattern starch

Water vapor sorption isotherms of cotton cellulose and B pattern starch preparations, potato starch, corn amylose, amylomaize, and retrograded potato starch, were determined at 5 and 25°C. The crystallinity fraction of these materials equilibrated with water vapor at various partial pressures was determined by x-ray diffraction. The thermodynamic functions of adsorption were calculated, and B.E.T. constants were determined.     

Effect of mechanical alloying time and carbon nanotube (CNT) content on the evolution of aluminum (Al)–CNT composite powders

One of the major obstacles to the effective use of carbon nanotubes as reinforcements in metal matrix composites is their agglomeration and poor distribution/dispersion within the metallic matrix. In the present work, we use mechanical alloying (MA) to mechanically mix CNT (2 and 5 wt.%) with Al powders. These powders would be used as precursors for subsequent consolidation to generate bulk CNT-Al composites. Hence controlling the initial powder characteristics prior to high temperature consolidation is important. Up to 48 h of milling was employed to investigate the effect of milling time on the particle size, morphology and CNT dispersions. The results show that particle size and morphology vary with milling time and CNT content. Also the addition of process control agents such as methanol can aid in controlling the powder characteristics.     

Effect of heat-treatment on the electrical and dielectric properties of a TiO2-containing lithia–calcia–silica glass and glass ceramics

The glass 65 SiO₂, 20 CaO, 15 Li₂O (mol%) containing 4 g TiO₂/100 g glass was prepared. Samples of this glass were heat treated at temperatures pre-determined by DTA to produce crystalline samples which were characterized by IR, XRD and SEM. The dielectric constant (?′), dielectric loss (?″) and conductivity σ_ac over a wide range of frequency and temperatures were measured. Optical absorption and values of the absorption edge were also determined for the transparent samples. Li–calcium silicate was found to crystallize at 964 °C as the main phase with lithium disilicate and quartz as minor phases. An enhancement in conductivity of about 1–3 orders of magnitude was obtained in the heat treated samples as compared to parent glass. Conduction takes place through an electronic mechanism in the low temperature region. In crystalline samples, the electronic conduction is extended to high temperature regions. Crystallized samples show high ?′ values, particularly at low frequencies. The values of (?′) reached 60–300 at 300 °C. The capacitance results indicated that these materials can be used in capacitors. Dielectric loss bands appeared in the range 0.32–5 MHz and the conduction relaxation times were calculated.     

Dielectric relaxation of monoesters based poly(styrene-co-maleic anhydride) copolymer

A series of alkyl-grafted copolymers based on styrene-maleic anhydride (SMA) copolymers were synthesized by esterification of SMA with several long chain normal aliphatic alcohols. The prepared copolymers were characterized by FT-IR and ¹H NMR and DSC. The dielectric behavior of these copolymers was investigated in the frequency 20–10⁵ Hz and temperature −40 to 180 °C ranges. Two relaxation processes were observed, α, and β-relaxation. The former is associated with the glass-rubber transition and is characterized by the Vogel–Fulcher–Tammann temperature dependence and the latter relaxation is related to the local motion of the ester side groups attached to the polymer backbone. The apparent activation energy for the β-relaxation was found to depend significantly on the alkyl chain length. The dielectric analysis of the β-relaxation process detected is discussed.