Biomedical subjects

Zbigniew Lewandowski

Publications and source records attributed to Zbigniew Lewandowski.

15 recordsLinked to original sources

PubMed2006

Procedure for determining maximum sustainable power generated by microbial fuel cells.

Power generated by microbial fuel cells is computed as a product of current passing through an external resistor and voltage drop across this resistor. If the applied resistance is very low, then high instantaneous power generated by the cell is measured, which is not sustainable; the cell cannot deliver that much power for long periods of time. Since using small electrical resistors leads to erroneous assessment of the capabilities of microbial fuel cells, a question arises: what resistor should be used in such measurements? To address this question, we have defined the sustainable power as the steady state of power delivery by a microbial fuel cell under a given set of conditions and the maximum sustainable power as the highest sustainable power that a microbial fuel cell can deliver under a given set of conditions. Selecting the external resistance that is associated with the maximum sustainable power in a microbial fuel cell (MFC) is difficult because the operator has limited influence on the main factors that control power generation: the rate of charge transfer at the current-limiting electrode and the potential established across the fuel cell. The internal electrical resistance of microbial fuel cells varies, and it depends on the operational conditions of the fuel cell. We have designed an empirical procedure to predict the maximum sustainable power that can be generated by a microbial fuel cell operated under a given set of conditions. Following the procedure, we change the external resistors incrementally, in steps of 500 omega every 10, 60, or 180 s and measure the anode potential, the cathode potential, and the cell current. Power generated in the microbial fuel cell that we were using was limited by the anodic current. The anodic potential was used to determine the condition where the maximum sustainable power is obtained. The procedure is simple, microbial fuel cells can be characterized within an hour, and the results of the measurements can serve many purposes, such as: (1) estimating power generation in various MFCs, (2) comparing power generation in MFCs using different electroactive reactants, (3) quantifying the effects of the operational regime on the power generation in MFCs, and finally, (4) the purpose for which the procedure was designed, optimizing the performance of existing MFCs.

Bacteria↗

PubMed2005

Wireless sensors powered by microbial fuel cells.

Monitoring parameters characterizing water quality, such as temperature, pH, and concentrations of heavy metals in natural waters, is often followed by transmitting the data to remote receivers using telemetry systems. Such systems are commonly powered by batteries, which can be inconvenient at times because batteries have a limited lifetime and must be recharged or replaced periodically to ensure that sufficient energy is available to power the electronics. To avoid these inconveniences, a microbial fuel cell was designed to power electrochemical sensors and small telemetry systems to transmit the data acquired by the sensors to remote receivers. The microbial fuel cell was combined with low-power, high-efficiency electronic circuitry providing a stable power source for wireless data transmission. To generate enough power for the telemetry system, energy produced by the microbial fuel cell was stored in a capacitor and used in short bursts when needed. Since commercial electronic circuits require a minimum 3.3 V input and our cell was able to deliver a maximum of 2.1 V, a DC-DC converter was used to boost the potential. The DC-DC converter powered a transmitter, which gathered the data from the sensor and transmitted it wirelessly to a remote receiver. To demonstrate the utility of the system, temporal variations in temperature were measured, and the data were wirelessly transmitted to a remote receiver.

Bioelectric Energy Sources↗

PubMed2005

Microbial fuel cell using anaerobic respiration as an anodic reaction and biomineralized manganese as a cathodic reactant.

We have operated a microbial fuel cell in which glucose was oxidized by Klebsiella pneumoniae in the anodic compartment, and biomineralized manganese oxides, deposited by Leptothrix discophora, were electrochemically reduced in the cathodic compartment. In the anodic compartment, to facilitate the electron transfer from glucose to the graphite electrode, we added a redox mediator, 2-hydroxy-1,4-naphthoquinone. We did not add any redox mediator to the cathodic compartment because the biomineralized manganese oxides were deposited on the surface of a graphite electrode and were reduced directly by electrons from the electrode. We have demonstrated that biomineralized manganese oxides are superiorto oxygen when used as cathodic reactants in microbial fuel cells. The current density delivered by using biomineralized manganese oxides as the cathodic reactant was almost 2 orders of magnitude higher than that delivered using oxygen. Several fuel cells were operated for 500 h, reaching anodic potentials of -441.5 +/- 31 mVscE and cathodic potentials of +384.5 +/- 64 mVscE. When the electrodes were connected by a 50 Ohms resistor, the fuel cell delivered the peak power density of 126.7 +/- 31.5 mW/m2.

Bioelectric Energy Sources↗

PubMed2004

Uranium immobilization by sulfate-reducing biofilms.

Hexavalent uranium [U(VI)] was immobilized using biofilms of the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans G20. The biofilms were grown in flat-plate continuous-flow reactors using lactate as the electron donor and sulfate as the electron acceptor. U(VI)was continuously fed into the reactor for 32 weeks at a concentration of 126 microM. During this time, the soluble U(VI) was removed (between 88 and 96% of feed) from solution and immobilized in the biofilms. The dynamics of U immobilization in the sulfate-reducing biofilms were quantified by estimating: (1) microbial activity in the SRB biofilm, defined as the hydrogen sulfide (H2S) production rate and estimated from the H2S concentration profiles measured using microelectrodes across the biofilms; (2) concentration of dissolved U in the solution; and (3) the mass of U precipitated in the biofilm. Results suggest that U was immobilized in the biofilms as a result of two processes: (1) enzymatically and (2) chemically, by reacting with microbially generated H2S. Visual inspection showed that the dissolved sulfide species reacted with U(VI) to produce a black precipitate. Synchrotron-based U L3-edge X-ray absorption near edge structure (XANES) spectroscopy analysis of U precipitated abiotically by sodium sulfide indicated that U(VI) had been reduced to U(IV). Selected-area electron diffraction pattern and crystallographic analysis of transmission electron microscope lattice-fringe images confirmed the structure of precipitated U as being that of uraninite.

Biofilms↗

PubMed2004

An optical microsensor to measure fluorescent light intensity in biofilms.

We have developed an optical microsensor to quantify fluorescent light intensity distribution in biofilms. The optical system consisted of a beam splitter, light couplers, filters and a spectrophotometer able to accept the fiberoptic cable to measure fluorescent light intensity. The emitted light, fluorescence from the biofilm, was collected at the tip of the optical microsensor and was transferred to a spectrophotometer via a fiberoptic cable. The total fluorescent light intensity was evaluated from the emission spectrum by numerical integration. The newly developed fiberoptic microsensor was tested using a Staphylococcus aureus strain producing yellow fluorescent protein (YFP) grown as biofilm. We used a 405-nm violet laser diode for excitation, and measured the emission intensity between 480 nm and 540 nm. The optical microsensor that quantifies fluorescent light intensity is a promising tool in biofilm research which often requires detection and quantification of fluorescent light intensity distribution generated by various fluorescent proteins.

Bacterial Proteins↗

PubMed2004

Three-dimensional biofilm structure quantification.

Quantitative parameters describing biofilm physical structure have been extracted from three-dimensional confocal laser scanning microscopy images and used to compare biofilm structures, monitor biofilm development, and quantify environmental factors affecting biofilm structure. Researchers have previously used biovolume, volume to surface ratio, roughness coefficient, and mean and maximum thicknesses to compare biofilm structures. The selection of these parameters is dependent on the availability of software to perform calculations. We believe it is necessary to develop more comprehensive parameters to describe heterogeneous biofilm morphology in three dimensions. This research presents parameters describing three-dimensional biofilm heterogeneity, size, and morphology of biomass calculated from confocal laser scanning microscopy images. This study extends previous work which extracted quantitative parameters regarding morphological features from two-dimensional biofilm images to three-dimensional biofilm images. We describe two types of parameters: (1) textural parameters showing microscale heterogeneity of biofilms and (2) volumetric parameters describing size and morphology of biomass. The three-dimensional features presented are average (ADD) and maximum diffusion distances (MDD), fractal dimension, average run lengths (in X, Y and Z directions), aspect ratio, textural entropy, energy and homogeneity. We discuss the meaning of each parameter and present the calculations in detail. The developed algorithms, including automatic thresholding, are implemented in software as MATLAB programs which will be available at site prior to publication of the paper.

Algorithms↗

PubMed2004

Dynamics of lead immobilization in sulfate reducing biofilms.

We have evaluated the effects of selected minerals present in subsoil environment on the efficiency of lead removal from contaminated groundwaters using biofilms composed of sulfate-reducing microorganisms, and examined the stability of metal deposits after the biofilms had been temporarily exposed to the air. To quantify the studied effects, lead was immobilized in biofilms of Desulfovibrio desulfuricans grown anaerobically in two flat-plate flow reactors, one filled with hematite and the other with quartz. While the biofilms in both reactors were heterogeneous and consisted of voids and channels, the biofilms grown on hematite were denser, thicker, and more porous than those grown on quartz. The average H2S concentrations, measured using microelectrodes, were higher in the biofilms grown on quartz than those measured in the biofilms grown on hematite. During 18 weeks of operation, iron was continuously released from the hematite. Lead was immobilized more efficiently in the biofilms grown on quartz than it was in the biofilms grown on hematite. Lead deposits were partially reoxidized, especially in biofilms grown on hematite, and the biofilms in both reactors responded to the presence of oxygen by lowering their density and increasing the H2S production rate.

Biofilms↗

PubMed2004

Quantifying biofilm structure: facts and fiction.

There is no doubt among biofilm researchers that biofilm structure is important to many biofilm processes, such as the transport of nutrients to deeper layers of the biofilm. However, biofilm structure is an elusive term understood only qualitatively, and as such it cannot be directly correlated with any measurable parameters characterizing biofilm performance. To correlate biofilm structure with the parameters characterizing biofilm performance, such as the rate of nutrient transport within the space occupied by the biofilms, biofilm structure must first be quantified and expressed numerically on an appropriate scale. The task of extracting numerical parameters quantifying biofilm structure relies on using biofilm imaging and image analysis. Although defining parameters characterizing biofilm structure is relatively straightforward, and multiple parameters have been described in the computer science literature, interpreting the results of such analyses is not trivial. Existing computer software developed by several research groups, including ours, for the sole purpose of analyzing biofilm images helps quantify parameters from biofilm images but does nothing to help interpret the results of such analyses. Although computing structural parameters from biofilm images permits correlating biofilm structure with other biofilm processes, the meaning of the results is not obvious. The first step to understanding the quantification of biofilm structure, developing image analysis, methods to quantify information from biofilm images, has been made by several research groups. The next step is to explain the meaning of these analyses. This presentation explains the meaning of several parameters commonly used to characterize biofilm structure. It also reviews the authors' research and experience in quantifying biofilm structure and their attempts to quantitatively relate biofilm structure to fundamental biofilm processes.

Anti-Bacterial Agents↗

PubMed2004

[Prediction of 29-years mortality rate from initial and emerging risk factors during follow-up in a Warsaw population].

Searching for clues through cohort studies requires introducing initial values of predictors likely to forecast future morbid events. This may put the end points on unequal footing, due to different timing of preceding exposures. A long follow-up mortality study of an urban population with repeated measurements in the midst of the observation enabled splitting predictors of death into time-related components making comparisons more alike with regards to time. A random sample of 1898 Warsaw adult population was interviewed in 1970 on a variety of demographic, social, behavioural and morbid circumstances as well as the use of health services. The 29-year-long search for death events was instituted with 751 (39.5%) deaths ascertained till the end of 1999 and 166 persons not traced (8.7%). In 1979 the inquiry was repeated in 1366 respondents alive and ready to take part, with the same set of questions asked. Beyond base-line values of traits in question, the estimates of change (possible predictors both times; appearance or vanishing of a trait; no trait whatsoever; no answer) were arranged as dummy variables tested for creating an excess risk against double absence of exposure. Cox multiple regression models were used for assessing relative odds of death. The base-line '70 predictions limited the risk of death for women mainly to non-structured evidence of disease whereas among men they included social circumstances, smoking & bronchitis, and possession of a personal doctor. With the '79 base-line recent hospital discharge was added to the prediction of remaining ('80-'99) mortality experience of both sexes, and disability appeared as a risk factor in men. Using time-related variables disclosed the mortality-boosting influence of twice-confirmed smoking in both sexes, as well as the excess death following the so far absent protracted illness among men and women. The appearance of the excess risk of death due to addition of hitherto neutral exposures was more frequent among men than women. The same pattern of the new exposures emerged for recent hospital discharge vs. no hospitalization. It seems that arranging exposure in the time-related fashion discloses a newly evolving excess risk of death which may pave the way towards death in more vulnerable fraction of a population in largely non-specific fashion.

Adult↗

PubMed2003

Pretransplant and early posttransplant predictors of chronic allograft nephropathy in cadaveric kidney allograft--a single-center analysis of 1112 cases.

This retrospective series reviews risk factors for chronic allograft nephropathy (CAN) based on the 10-year experience of a single institution. One thousand one hundred and twelve primary cadaveric renal transplant recipients whose graft survived for more than 6 months were followed for a mean of 4.6 years. The data were analyzed using the multivariate Cox proportional hazards model. CAN was defined as an irreversible rise of serum creatinine (SCr) by 30% in the absence of other causes and occurred in 42% of the patients. The risk of CAN was significantly increased in patients who experienced late rejections. Recipients of organs from donors that were older than 50 years and from such who died secondary to cerebrovascular accident were at increased risk of incurring CAN. Early markers of progression to CAN found at 6 months after transplantation included SCr levels of greater than 1.8 mg/ml, proteinuria, hypoalbuminemia, and hypertension. In conclusion, immune and non-immune factors affect progression to CAN in renal allograft recipients.

Adult↗

PubMed2003

Compromised host defense on Pseudomonas aeruginosa biofilms: characterization of neutrophil and biofilm interactions.

Pseudomonas aeruginosa is an opportunistic pathogen that forms biofilms on tissues and other surfaces. We characterized the interaction of purified human neutrophils with P. aeruginosa, growing in biofilms, with regard to morphology, oxygen consumption, phagocytosis, and degranulation. Scanning electron and confocal laser microscopy indicated that the neutrophils retained a round, unpolarized, unstimulated morphology when exposed to P. aeruginosa PAO1 biofilms. However, transmission electron microscopy demonstrated that neutrophils, although rounded on their dorsal side, were phagocytically active with moderate membrane rearrangement on their bacteria-adjacent surfaces. The settled neutrophils lacked pseudopodia, were impaired in motility, and were enveloped by a cloud of planktonic bacteria released from the biofilms. The oxygen consumption of the biofilm/neutrophil system increased 6- and 8-fold over that of the biofilm alone or unstimulated neutrophils in suspension, respectively. H(2)O(2) accumulation was transient, reaching a maximal measured value of 1 micro M. Following contact, stimulated degranulation was 20-40% (myeloperoxidase, beta-glucuronidase) and 40-80% (lactoferrin) of maximal when compared with formylmethionylleucylphenylalanine plus cytochalasin B stimulation. In summary, after neutrophils settle on P. aeruginosa biofilms, they become phagocytically engorged, partially degranulated, immobilized, and rounded. The settling also causes an increase in oxygen consumption of the system, apparently resulting from a combination of a bacterial respiration and escape response and the neutrophil respiratory burst but with little increase in the soluble concentration of H(2)O(2). Thus, host defense becomes compromised as biofilm bacteria escape while neutrophils remain immobilized with a diminished oxidative potential.

Biofilms↗

PubMed2003

[The influence of lamivudine therapy on the course of chronic hepatitis B in renal allograft recipients].

The aim of this study was to evaluate efficacy and safety of lamivudine therapy in renal allograft recipients with chronic hepatitis B infection. Twenty-four patients with chronic hepatitis B after renal transplantation were observed. We obtained HBV replication blockage in 95% of patients, in half of them also ALT normalisation was observed. Delayed HBV replication blockage was observed in patients with prolonged duration of haemodialysotherapy or HBV infection and HCV coinfection, although listed parameters did not influence overall treatment efficacy. After lamivudine discontinuation HBV replication relapsed, in part of patients with ALT activity elevation. We did not observed any serious adverse reactions under lamivudine therapy.

Adult↗

PubMed2002

[Birth weight, health status and physical development of young men after 20 years].

The aim of the study was to assess the health status and physical development of young men with low birth weight (LBW) compared to normal birth weight (NBW). The study was based on the birth cohort of children born in Warsaw at six obstetric wards in 1970-74. The data from the medical records of military conscription units, concerning 682 persons with LBW and 408 persons with NBW, were taken for comparison. Mean height and weight of LBW persons were lower then for those with NBW, with similar weight-for-height proportions. The prevalence of hearing loss was higher among LBW then NBW individuals despite similar rates of ear disorders assessed at the mid-point of the follow-up. Also, neurological disorders were more prevalent among LBW then NBW individuals at the time of conscription, which could not be fully ascribed to the possible birth injuries.

Adolescent↗

PubMedDate not supplied

Internal and external mass transfer in biofilms grown at various flow velocities.

It appears that biofilms arrange their internal structure according to the flow velocity at which they are grown, which affects the internal mass transfer rate and microbial activity. In biofilms grown at various flow velocities we determined the vertical profiles of the local relative effective diffusivity (termed D(l)) at several locations within each biofilm. From these profiles we calculated the surface-averaged relative effective diffusivity (termed D(sa)) at various distances from the bottom and plotted it against these distances. The D(sa) decreased linearly toward the bottom, forming well-defined profiles that were different for each biofilm. The gradients of these profiles were multiplied by the diffusivity of oxygen, zeta = D(w) dD(sa)/dz, and plotted versus the flow velocity at which each biofilm was grown. The gradients were low at flow velocities below 10 cm/s, reached a maximum at a flow velocity of 10 cm/s, and decreased again at flow velocities exceeding 10 cm/s. The existence of a maximum indicates a possibility that two opposing forces were affecting the slope of the profiles. To explain these observations we hypothesized that biofilms, depending on the flow velocity at which they are grown, arrange their internal architecture to control (1) the nutrient transport rate and (2) the mechanical pliability needed to resist the shear stress of the water flowing past them. It appears that biofilms attempt to satisfy the second goal first, to increase their mechanical strength, and that they do so at the expense of the nutrient transfer rate to deeper layers. This strength increase is associated with an increase in biofilm density, which slows down the internal mass transport rate. Biofilms grown at low flow velocities exhibit low density and high effective diffusivity but cannot resist higher shear stress, whereas biofilms grown at higher flow velocities are denser and can resist higher shear stress but have a lower effective diffusivity.

Biofilms↗

PubMedDate not supplied

Multiple substrate growth kinetics of Leptothrix discophora SP-6.

The growth parameters of Leptothrix discophora SP-6 were quantified on the basis of the steady-state concentrations and utilization rates of pyruvate, dissolved oxygen, and concentration of microorganisms in a chemostat operated at 25 degrees C, pH 7.2, and an agitation rate of 350 rpm. The results showed that the microbial growth was limited by both pyruvate and dissolved oxygen. A combined growth kinetics model using Monod growth kinetics for pyruvate and Tessier growth kinetics for oxygen showed the best correlation with the experimental data when analyzed using an interactive multiple substrate model. The growth kinetics parameters and the respective confidence limits, estimated using the Monte Carlo simulation, were mu(max) = 0.576 +/- 0.021 h(-1), K(sMp) = 38.81 +/- 4.24 mg L(-1), K(sTo) = 0.39 +/- 0.04 mg L(-1), Y(X/p) = 0.150 (mg microorganism mg(-1) pyruvate), Y(X/o) = 1.24 (mg microorganism mg(-1) oxygen), the maintenance factors for pyruvate and oxygen were m(p) = 0.129 (mg pyruvate consumed mg(-1) microorganism h(-1)) and m(o) = 0.076 (mg oxygen consumed mg(-1) microorganism h(-1)), respectively.

Bioreactors↗