Occupational Exposure to Respirable Dust, Respirable Crystalline Silica and Diesel Engine Exhaust Emissions in the London Tunnelling Environment.

Personal 8-h shift exposure to respirable dust, diesel engine exhaust emissions (DEEE) (as respirable elemental carbon), and respirable crystalline silica of workers involved in constructing an underground metro railway tunnel was assessed. Black carbon (BC) concentrations were also assessed using a MicroAeth AE51. During sprayed concrete lining (SCL) activities in the tunnel, the geometric mean (GM) respirable dust exposure level was 0.91mg m(-3), with the highest exposure measured on a back-up sprayer (3.20mg m(-3)). The GM respirable crystalline silica concentration for SCL workers was 0.03mg m(-3), with the highest measurement also for the back-up sprayer (0.24mg m(-3)). During tunnel boring machine (TBM) activities, the GM respirable dust concentration was 0.54mg m(-3). The GM respirable elemental carbon concentration for all the TBM operators was 18 µg m(-3); with the highest concentration measured on a segment lifter. The BC concentrations were higher in the SCL environment in comparison to the TBM environment (daily GM 18-54 µg m(-3) versus 3-6 µg m(-3)). This small-scale monitoring campaign provides additional personal data on exposures experienced by underground tunnel construction workers.

Bending characteristics of polymethylmethacrylate columns, connecting bars of carbon fiber, titanium, and stainless steel used in external skeletal fixation and an acrylic interface.

OBJECTIVE: To (1) mechanically evaluate polymethylmethacrylate (PMMA) columns of various sizes and compare them to connecting bar materials (carbon fiber composite, titanium, stainless steel) and (2) compare the properties of an intact PMMA column to those of an acrylic interface. STUDY DESIGN: Experimental mechanical study. SAMPLE POPULATION: Experiment 1: 6 groups of 6 specimens each; experiment 2: 2 groups of 12 specimens each. METHODS: All specimens were tested in 3-point bending. Stiffness, yield strength, and ultimate strength values were calculated for each specimen. RESULTS: PMMA 1 columns (23.25 mm) compared favorably to titanium or stainless-steel bars. PMMA 3 columns (30.15 mm) and carbon fiber bars had similar yield strength but PMMA 3 columns were less stiff than carbon fiber bars. PMMA 3 columns had lower bending modulus and a higher variability in their mechanical properties than PMMA 1 or PMMA 2 (25.64 mm) columns. Acrylic interface specimens were less strong but as stiff as intact specimens. CONCLUSION: An acrylic interface was easily created and had acceptable biomechanical characteristics. CLINICAL RELEVANCE: PMMA 2 and PMMA 3 columns are not recommended for clinical use at this time. Further tests are needed to analyze an acrylic patch in a more clinically relevant loading model.

The potential of Festuca rubra and Calamagrostis epigejos for the revegetation of fly ash deposits.

Two grass species, Festuca rubra (sown) and Calamagrostis epigejos (naturally recolonised), were studied at two fly ash deposit lagoons, weathered 5 (L1) and 13 years (L2). Both species were assessed in terms of their invasive ability, photosynthetic efficiency, trace elements accumulation, and damage symptoms, while the characteristics of the habitat were assessed in terms of trace element content, and the pH and EC of the ash. In the ash weathered for 5 and 13 years, B and Mn concentrations fell within the normal range for soils, while there was an As, Mo and Cu excess, and Se and Zn deficit. There was no difference in the photosynthetic efficiency (ns) of the C. epigejos populations at the different-aged ash lagoons, but differences were found between the populations of F. rubra (P<0.001). F. rubra displayed damage symptoms, in the form of leaf tip chlorosis and necrosis, and wilting seedlings--a result of B accumulation in toxic concentrations and a Cu and Mn deficit. After 13 years the sown F. rubra remained over 9.5% of the ash lagoon's area (L2), while over the same period the naturally recolonised C. epigejos had overgrown 87.5% of the area. The greater colonisation and survival potential of C. epigejos is a result of multiple tolerance to the conditions at ash deposits and of the competitive ability of this species to dominate the colonised habitat. Therefore, characteristics of naturally colonised species can be used for modelling future actions of biological restoration of fly ash deposits aimed at binding the ash with minimal investment (the short-term aim), and for providing conditions for revegetation, and shortening the successive phases in the revegetation of ash deposits after the closure of thermal plants (the long-term aim).

[Influence of sterilization treatments on continuous carbon-fiber reinforced polyolefin composite].

OBJECTIVE: To evaluate the influence of sterilization treatment on continuous carbon-fiber reinforced polyolefin composite (CFRP) so as to provide experimental reference for selection of sterilization method for CFRP. METHODS: Seventy bars of CFRP were divided into 7 equal groups to undergo sterilization by autoclave, 2% glutaraldehyde soaking, 75% alcohol soaking, ethylene oxide sterilization, and Co-60 gamma ray irradiation of the dosages 11 kGy, 25 kGy, and 18 kGy respectively, and another 10 bars were used as blank controls. Then the bars underwent three-point bending test and longitudinal compression test so as to measure the biomechanical changes after sterilization treatment, including the maximum load, ultimate strength, and elastic modulus. RESULTS: Three-point bending test showed that the levels of maximum load of the all experimental groups were lower than that of the control group, however, only those of the 3 Co-60 irradiation groups were significantly lower than that of the control group and that Co-60 radiation lowered the level of maximum load dose-dependently; and that the levels of ultimate strength of all the all experimental groups were lower than that of the control group, however, only those of the 3 Co-60 groups were significantly lower than that of the control group and that the higher the dosage of Co-60 radiation the lower the level of ultimate strength, however, not dose-dependently. The elastic modulus of the Co-60 25 KGy group was significantly higher than that of the control group, and there was no significant difference in the level of ultimate strength among the other groups. Longitudinal compression test showed that the levels of maximum load and ultimate strength of the 3 Co-60 irradiation groups, autoclave group, and circular ethylene groups were significantly lower than that of the control group, and there was no significant difference in elastic modulus among different groups. CONCLUSION: During sterilized package of CFRP products produced in quantity autoclave sterilization and Co-60 gamma ray irradiation sterilization should be avoided. Ethylene oxide is proposed as the best sterilization method. If gamma ray irradiation is to be used further technology improvement is necessary.

An alternative parameter to characterize biogas materials: Available carbon-nitrogen ratio.

Available carbon-nitrogen ratio (AC/N) was proposed as an alternative parameter for evaluating the potential of biogas materials in this paper. In the calculation of AC/N ratio, only the carbon that could be effectively utilized in anaerobic digestion (AD) process is included. Compared with total C/N, AC/N is particularly more suitable for the characterization of biogas materials rich in recalcitrant components. Nine common biogas materials were selected and a series of semi-continuous tests for up to 110days were carried out to investigate the source of available carbon and the relationship between AC/N and the stability of AD process. The results showed that only the carbon existing in proteins, sugars, fat and hemicelluose should be considered as available carbon for anaerobic microbes. Besides, the optimal AC/N for semi-continuous AD process was preliminarily determined to be 11-15. Taken together, our results demonstrate that AC/N is more effective than total C/N in the evaluation of the potential performance of AD process.

MRI compatible electrodes for the induction of amygdala kindling in rats.

The rat electrical kindling model has been widely utilized in epilepsy research. This study aimed to identify the optimum "MRI compatible" bipolar stimulating and recording electrodes to enable serial MRI acquisition in this model. Two types of custom-made electrodes (gold and carbon) were compared with commercial platinum-iridium alloy electrodes for suitability based on size, effect on image quality and kindling induction. The custom-made gold electrodes, based on these parameters, were found to be most suitable. These electrodes enable the study of epileptogenesis utilizing MRI in this model of temporal lobe epilepsy (TLE).

Effect of surface modification of an engineered activated carbon on the sorption of 2,4-dichlorophenoxy acetic acid and benazolin from water.

The performance of a conventional (F400) and a surface modified activated carbon (F400AN) has been investigated for the sorption of benazolin and 2,4-dichlorophenoxy acetic acid (2,4-D) from water. It was observed that the modified carbon, F400AN, which was obtained by annealing the conventional sample had a higher BET surface area (960 m2 g(-1) compared to 790 m2 g(-1)) and it had a higher proportion of micropores. This was attributed to the loss of oxygen containing functional groups during the thermal treatment. Zeta potential and pH titration measurements also showed that acidic functionality had been lost on the F400AN sample. The adsorption data were analysed and were fitted well using the Langmuir isotherm. The modified carbon marginally out-performed the conventional activated carbon for sorption of these two herbicides. Thermodynamic parameters (DeltaG0, DeltaH0, and DeltaS0) were determined and their values indicated that the sorption process was spontaneous and endothermic for both herbicides. A pseudo-second-order kinetic model was employed for analysing the kinetic data. It was concluded that the herbicide sorption process was controlled by a film diffusion mechanism.

Fluid-sorption phenomena in sterilized polyethylene acetabular prostheses.

The weight changes due to fluid-sorption were measured in 62 radiation-sterilized acetabular sockets and 10 unsterilized discs. The materials included two types of ultra-high molecular weight (UHMW) polyethylene (RCH 1000; Hi-Fax 1900) and a carbon-fibre-reinforced polyethylene (CFPE). The fluid absorption curve was consistently biphasic. In the first 30 d soak-period (Phase 1), the initial rate of fluid absorption averaged 153 micrograms/d for conventional UHMW polyethylene and 278 micrograms/d for carbon-fibre-reinforced polyethylene. In Phase 2, beyond 30 d and up to 400 d, fluid absorption reduced to linear rates of 27 micrograms/d for UHMW polyethylene and 43 micrograms/d for CFPE. The latter soak-weight-gain values corresponded to only 0.00016%/d and 0.00034%/d respectively. There was little difference in absorption rates between sterilized and unsterilized samples. However soak rates were generally higher in water compared to serum.

Ultrastructure at carbon fiber microelectrode implantation sites after acute voltammetric measurements in the striatum of anesthetized rats.

This work seeks to establish the feasibility of characterizing the ultrastructure of brain tissue disruption associated with the implantation of carbon fiber voltammetric microelectrodes. In vivo recording was performed by fast scan cyclic voltammetry in conjunction with carbon fiber microelectrodes (3.5 microm radius) in the striatum of rats anesthetized with chloral hydrate. After 4 h of in vivo recording, the microelectrodes were removed from the brain and the animals underwent intracardial perfusion. Brain tissue was collected and sectioned in the horizontal plane perpendicular to the axis of the microelectrodes. With microelectrodes of a conventional single barreled design, the tissue tracks were often too small to be followed by light microscopy to the point of deepest penetration, which would correspond to the implantation site of the carbon fiber itself. The enlarged tissue tracks formed by the implantation of double barreled electrodes, however, could be followed to their termination by light microscopy. Anatomical mapping was used to identify the fields laying 100 microm deeper than the deepest trace of such tracks. Electron microscopy of these fields revealed a spot of tissue damage presumed to be associated with the implantation site of the carbon fiber microelectrode. The spot of maximal tissue damage had a radius of 2.5 microm and was surrounded by an annular region with a width of 4 microm that contained a mix of healthy and damaged elements. Beyond this annular region, i.e. beyond 6.5 microm from the center of the spot of maximal damage, signs of microelectrode-associated damage were rare and consisted primarily of neurons with darkened cytoplasm.

A method for direct thalamic stimulation in fMRI studies using a glass-coated carbon fiber electrode.

Recent fMRI studies are of interest in exploring long-range interactions between different brain structures and the functional activation of specific brain regions by known neuroanatomical pathways. One of the experimental approaches requires the invasive implantation of an intracranial electrode to excite specific brain structures. In the present report, we describe a procedure for the production of a glass-coated carbon fiber electrode and the use of this electrode for direct activation of the brain in fMRI studies. The glass-coated carbon fiber microelectrode was implanted in the medial thalamus of anaesthetized rats and T2*-weighted gradient echo images in the sagittal plane obtained on a 4.7 T system (Biospec BMT 47/40) during electrical stimulation of the medial thalamus. The image quality obtained using this electrode was acceptable without reduction of the signal-to-noise ratio and image distortion. Cross-correlation analysis showed that the signal intensities of activated areas in the ipsilateral anterior cingulate cortex were significantly increased by about 4-5% during medial thalamus stimulation. The present study shows that glass-coated carbon fiber electrodes are suitable for fMRI studies and can be used to investigate functional thalamocingulate activation.

Can voltammetry measure nitrogen monoxide (NO) and/or nitrites?

Recently, voltammetry with carbon fibre electrodes (CFE) has been implemented for real time measurement of nitrogen monoxide (NO) indicating that it is oxidised at the potential value of nitrites, approximately +700 mV. In contrast, here we show that modified CFE can monitor NO at oxidation potentials different than that of nitrites, i.e. +550 mV. Indeed, at +550 mV a significant increase of amperometric current levels was obtained when NO but not nitrites, were added to a phosphate buffer saline solution (PBS). Differential pulse voltammetry (DPV) supports these findings as two oxidation peaks were obtained when examining air preserved NO; peak 1 at +550 mV and peak 2 at +700 mV, respectively. In contrast, only peak 2 was monitored when nitrites or a solution of NO oxidised in air was added to PBS. Biological support to these in vitro data comes from the observation that the relaxation of an adrenaline-contracted aortic ring produced via addition of NO is concomitant with peak 1 at +550 mV. The relaxation is almost completed before the appearance of peak 2 at +700 mV. Furthermore, in vivo experiments performed in the striatum of rats show that the amperometric signal monitored at +550 mV is responsive to glutamatergic stimulation or inhibition of NO synthase.

A rapid method for the quantification of C, N and O in biomedical samples by proton-induced gamma-ray emission analysis applied to human placental samples.

A new fast, accurate and simple quantification method for C, N and O in biomedical samples by external-beam proton-induced gamma-ray emission analysis is presented. Concentration values for C, N and O in commercial standards of NBS bovine liver 1577a, IAEA animal muscle H-4 and IAEA horse kidney H-8 were determined using the new method. The concentrations of C, N, O, Na, Mg and P were determined from placental samples of 13 alcoholic mothers and from 16 abstinent controls. The values obtained for C, N, O, Mg and P were the first values ever obtained for human placentas.

Structural failure of pyrolytic carbon heart valves.

Pyrolite carbon has been used for the manufacture of mechanical heart valve prostheses for the past 25 years. In general, pyrolytic carbon mechanical heart valves have provided adequate physiological function and satisfactory structural performance. Although rare in occurrence, incidents of valve failure due to fracture of one or more components have been reported. These reports of failure are reviewed and a few representative examples are examined in detail in order to determine the characteristic failure mechanism. Understanding the underlying factors responsible for causing these failures provides a solid basis for improved design and manufacture of future mechanical heart valve prostheses.

Structural integrity assessment of heart valve prostheses: a damage tolerance analysis of the CarboMedics Prosthetic Heart Valve.

The design of mechanical heart valve prostheses must satisfy three basic requirements: biocompatibility, efficiency and durability. Over the past 25 years of clinical use, pyrolytic carbon has proven to be biocompatible and thromboresistant, and is therefore the material of choice for mechanical heart valve prostheses. However, in recent years the material has been questioned in this application because it is brittle and susceptible to subcritical crack growth. This has raised concerns regarding the structural reliability of prostheses constructed from this material. This paper describes the application of the damage tolerance methodology to assess the structural integrity of heart valve prostheses made of pyrolytic carbon. In particular, an analysis of the CarboMedics Prosthetic Heart Valve (CPHV) is presented. A new measure of fatigue lifetime, the fatigue safe-life index, is introduced. Additionally, the degradation of structural integrity from cavitation erosion is examined. It is shown that structural integrity, especially for brittle materials, is not just a function of design, but involves the entire manufacturing process. The damage tolerance method can be applied to assess and ensure the structural integrity of pyrolytic carbon prosthetic heart valve components.

An initial investigation into the wear and damage within the pivots of three types of bileaflet mechanical heart valves.

Two 29 mm St. Jude Medical valves, two 29 mm CarboMedics valves and two 29 mm Sorin Bicarbon valves were tested in a real time fatigue test rig. The test rig was run at 72 beats/min with a stroke volume of 70 ml for approximately one million cycles. Optical microscopy was used to investigate the valve surfaces. Possible deterioration of the surface finish was observed on the stops of the hinge recesses in the St. Jude Medical and CarboMedics valves. In the Sorin valves areas of the pyrolytic carbon coating was worn away adjacent to and on the valve stops.

Mechanical cardiac valve prostheses: wear characteristics and magnitudes in three bileaflet valves.

Three different bileaflet mechanical heart valves were evaluated for wear and durability characterization. The designs of the three mechanical heart valves encompass both geometrical and material interface differences. The St. Jude Medical mechanical heart valve is partially characterized by a flat-on-flat leaflet-to-orifice closing stop interface with the orifice constructed of a graphite substrate with pyrolytic carbon coating. The CarboMedicsTM mechanical heart valve is partially characterized by a flat-on-cylindrical leaflet-to-orifice closing stop interface and the orifice is constructed of solid pyrolytic carbon. The Sorin Biomedica BicarbonTM mechanical heart valve is characterized by a flat-on-flat leaflet-to-orifice closing stop interface with the leaflets constructed of pyrolytic carbon and the orifice constructed of a titanium alloy. In vitro mechanical wear analysis was performed in accordance with current FDA and ISO guidelines for accelerated life and durability testing. Comparisons revealed that the St. Jude Medical mechanical heart valve had the lowest magnitude of wear, but both the St. Jude Medical and CarboMedics mechanical heart valves proved to be very wear resistant. The Sorin Biomedica Bicarbon mechanical heart valve showed an extremely high wear rate and magnitude. The overall mechanism for material removal and wear must be fully determined to assess the long term efficacy of the mechanical heart valve.

Wear assessment in bileaflet heart valves.

Sorin Biomedica has accumulated 20 years of experience in designing and manufacturing heart valves as well as in the development of turbostratic carbons, both as bulk coating (pyrolytic carbon, PyC) and as a thin film (Carbofilm). In designing a bileaflet valve, where hinges represent the most critical elements since wear occurs mainly at these points, we took into account: a) theoretical considerations on the geometry (flat-to-flat vs. curved-to-flat) of the coupling elements undergoing impact wear; b) kinematic coupling (sliding, rotation, rolling) between the moving parts in relation to friction wear; c) experimental wear rates of different material couples (PyC/PyC, metal/PyC) assessed by paying attention to test artifacts due to particle contamination; and d) wear mechanisms involving brittle fracture mechanics for bulk PyC and ductile fracture mode for metals. On the basis of the above evaluations a Carbofilm coated titanium alloy housing and PyC leaflets were developed for the Sorin Bicarbon valve. A flat-to-flat coupling between hinge stops and mating pivot surfaces for reducing the impact wear and a rolling action aimed at minimizing the friction wear were designed for the hinge. The Bicarbon long term durability has been assessed by accelerated wear tests conducted in comparison with clinically accepted bileaflet prostheses (CarboMedics and St. Jude Medical). The main results for the Bicarbon valve were, wear rates slightly lower or comparable to those found in the reference valves and wear morphology free from microfractures, while deep cracks associated with higher stress concentrations were detected on the PyC components of the reference valves. No mechanical failure or loss of functionality occurred up to 2,100 million cycles (equivalent of 52.5 years).

Fatigue and fracture of pyrolytic carbon: a damage- tolerant approach to structural integrity and life prediction in "ceramic" heart valve prostheses.

BACKGROUND AND AIMS OF THE STUDY: The fracture and fatigue properties of Si-alloyed LTI pyrolytic carbon and pyrolytic carbon-coated graphite are described as a framework for establishing damage-tolerant analyses for maintaining structural integrity and for predicting the lifetimes of mechanical heart valve prostheses fabricated from these materials. METHODS: The analyses are based on fracture-mechanics concepts and provide conservative (worst-case) estimates of the time, or number of loading cycles, before the valve will fail, or more precisely for pre-existing defects in valve components to grow subcritically to critical size under elevated physiologic loading and environmental conditions. RESULTS: For structural life in excess of patient life-times, a minimum required detectable defect size is computed which must be detected by quality-control procedures prior to the device entering service; this defect size is typically of the order of tens of microns for such "ceramic" valves, compared to sizes in the hundreds of microns for corresponding metal valves. CONCLUSIONS: It is concluded that in light of the brittle nature of pyrolytic carbon and the unacceptable cost of mechanical valve failures, the use of such analyses should be regarded as essential in order to provide maximum assurance of patient safety.

Effect of repetitive impact on the mechanical strength of pyrolytic carbon.

Impact loading is experienced by mechanical heart valve components when the leaflet comes into contact with the housing orifice as the valve opens and closes during the cardiac cycle. Since the human heart beats approximately 40 million times per year, a large number of impact loading cycles are imposed on the carbon valve components. Contact loading can produce high mechanical stress at the contact area, leading to potential material damage and fracture. This paper describes a procedure for characterizing the effect of repetitive impact on the mechanical strength of pyrolytic carbon. The results shed light on the basic understanding of the damage formation and its strength degradation effect. In particular, fatigue crack growth was identified as the primary mechanism which causes the observed strength degradation. Design procedures based on fracture mechanics and contact mechanics are used in mechanical heart valve design to prevent structural failure associated with impact fatigue.