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Biomedical subjects

S L Barker

Publications and source records attributed to S L Barker.

At least 19 recordsLinked to original sources
PubMed2006

Correlation of clinical and ultrasonographic findings after Achilles tenotomy in idiopathic club foot.

Achilles tenotomy is a recognised step in the Ponseti technique for the correction of idiopathic congenital talipes equinovarus in most percutaneous cases. Its use has been limited in part by concern that the subsequent natural history of the tendon is unknown. In a study of 11 tendons in eight infants, eight tendons were shown to be clinically intact and ten had ultrasonographic evidence of continuity three weeks after tenotomy. At six weeks after tenotomy all tendons had both clinical and ultrasonographic evidence of continuity.

Achilles Tendon↗
PubMed2004

Management of congenital talipes equino varus in Scotland: a nationwide audit.

The Scottish Talipes Register is a record of all newly diagnosed cases of idiopathic congenital talipes equinovarus (CTEV) in Scotland over a four.year period. Two hundred and sixteen children were entered into the register, which recorded initial management and all subsequent interventions, both non-operative and operative. The data, therefore, represent a record of the different management regimens used within Scotland highlighting the variations in duration of conservative management and variations in surgical intervention following different methods of conservative management.

Casts, Surgical↗
PubMed2000

Control of flow direction in microfluidic devices with polyelectrolyte multilayers.

Electroosmotic flow (EOF) is commonly utilized in microfluidics. Because the direction of the EOF can be determined by the substrate surface charge, control of the surface chemical state offers the potential, in addition to voltage control, to direct the flow in microfluidic devices. We report the use of polyelectrolyte multilayers (PEMs) to alter the surface charge and control the direction of flow in polystyrene and acrylic microfluidic devices. Relatively complex flow patterns with simple arrangements of applied voltages are realized by derivatization of different arms of a single device with oppositely charged polyelectrolytes. In addition, flow in opposite directions in the same channel is possible. A positively derivatized plastic substrate with a negatively charged lid was used to achieve top-bottom opposite flows. Derivatization of the two sides of a plastic microchannel with oppositely charged polyelectrolytes was used to achieve side-by-side opposite flows. The flow is characterized using fluorescence imaging and particle velocimetry.

Journal Article↗
PubMed1999

Cellular applications of a sensitive and selective fiber-optic nitric oxide biosensor based on a dye-labeled heme domain of soluble guanylate cyclase.

Nitric oxide-selective sensors have been prepared with the heme domain of soluble guanylate cyclase (sGC), the only known receptor for signal transduction involving nitric oxide. Expressed in and purified from E. coli, the heme domain contains a stoichiometric amount of heme that has electronic and resonance Raman spectra almost identical to those of heterodimeric (native) sGC purified from bovine lung. The small size of the heme domain, its inability to bind oxygen, and its high affinity for nitric oxide make it well-suited for sensor applications. The heme domain has been labeled with a fluorescent reporter dye and changes in this dye's intensity are observed based on the sGC heme domain's characteristic binding of nitric oxide. The current sensors are prepared with 100-microns optical fiber but could also be prepared using submicrometer fiber tips. These sensors have fast, linear, and reversible responses to nitric oxide and are unaffected by numerous common interferents, such as oxygen, nitrite and nitrate. The sensor limit of detection is 1 microM nitric oxide. Glutathione has been shown to decrease the sensitivity of the sensor; however, the sensor response remains linear and can be calibrated on the basis of the glutathione concentration present in the biological environment of interest. The sensors have been used to measure extracellular nitric oxide production by BALB/c mouse macrophages. Minimal nitric oxide was produced by untreated cells, while high levels of nitric oxide were released from activated cells, e.g., 111 +/- 2 microM in a given cell culture.

Animals↗
PubMed1999

Ratiometric and fluorescence-lifetime-based biosensors incorporating cytochrome c' and the detection of extra- and intracellular macrophage nitric oxide.

Ratiometric and lifetime-based sensors have been designed for cellular detection of nitric oxide. These sensors incorporate cytochrome c', a hemoprotein known to bind nitric oxide selectively. The cytochrome c' is labeled with a fluorescent reporter dye, and changes in this dye's intensity or fluorescence lifetime are observed as the protein binds nitric oxide. The ratiometric sensors are composed of dye-labeled cytochrome c' attached to the optical fiber via colloidal gold, along with fluorescent microspheres as intensity standards. These ratiometric sensors exhibit linear response, have fast response times (< or = 0.25 s), and are completely reversible. The sensors are selective over numerous common interferents such as nitrite, nitrate, and oxygen species, and the limit of detection is 8 microM nitric oxide. The lifetime-based measurements are made using free, dye-labeled cytochrome c' in solution and have a limit of detection of 30 microM nitric oxide. The use of these two techniques has allowed measurement of intra- and extracellular macrophage nitric oxide. Employing the ratiometric fiber sensors gave a multicell culture average extracellular nitric oxide concentration of 210 +/- 90 microM for activated macrophages, while an average intracellular concentration of 160 +/- 10 microM was determined from the lifetime-based measurements of dye-labeled cytochrome c' in the macrophage cytosol. Microscopic adaptation of the lifetime-based methods described here would allow direct correlation of intracellular nitric oxide levels with specific cellular activities, such as phagocytosis.

Animals↗
PubMed1998

Development and cellular applications of fiber optic nitric oxide sensors based on a gold-adsorbed fluorophore.

A new design for optochemical sensors has been applied to the development of a nitric oxide selective fiber optic sensor. This sensor is composed of a fluorescein derivative dye attached to colloidal gold. The fluorescein dye rearranges as nitric oxide adsorbs onto the gold, inducing a decrease in the fluorescence intensity of the dye. This mechanism has allowed preparation of fiber optic dye-based nitric oxide sensors, which have been made ratio-metric by addition of reference dye microspheres. Previously developed fast, selective optical sensors for detection of aqueous nitric oxide involved a protein, such as cytochrome c'. The new fluorescein derivative chemical sensors have characteristics similar to those of the protein-based biosensors, including fast response times, excellent selectivity, and complete reversibility. In addition, the chemical sensors have advantages such as greater stability and commercially available components. These sensors were utilized to measure nitric oxide production by BALB/c mouse macrophages.

Adsorption↗
PubMed1998

Fiber-optic nitric oxide-selective biosensors and nanosensors.

Fiber-optic biosensors that are selective for nitric oxide and do not respond to most potential interferents have been prepared with cytochromes c'. Both micro- and nanosensors have been prepared, and their response is fast (< 1 s), reversible, and linear up to 1 mM nitric oxide. The detection limit is 20 microM, making the sensor useful for some biological samples, such as the macrophages studied here. While sensors have been prepared based on the fluorescence of the cytochromes c', optodes with greatly enhanced signal-to-noise ratios have been made by labeling the cytochrome c' with a fluorescent dye. Comparisons of cytochromes c' from three species of bacteria as well as of two matrixes were performed and the optimum sensor configuration is described.

Acrylic Resins↗
PubMed1998

Nitrite- and chloride-selective fluorescent nano-optodes and in vitro application to rat conceptuses.

Nitrite- and chloride-selective, ion correlation-based, nano-optodes have been prepared for application in vitro. These fluorescent, liquid polymer based sensors have theoretically predictable responses to anion activities and good selectivity. The nitrite sensor, prepared with a vitamin B12 derivative ionophore, would be useful for determination of oxidized nitric oxide. Chloride nano-optodes, as well as micro-optodes, prepared with an indium porphyrin ionophore, were utilized to determine chloride levels both on the surface and inside the visceral yolk sac of organogenesis-stage rat conceptuses.

Animals↗
PubMed1998

Predictive value of human footprints in a forensic context.

Previous work from the United States has shown close correlation between an individual's size and weight and predetermined measurements taken from his or her footprints. This study investigated the situation in a group of United Kingdom subjects, for which there is at present little data. Walking and standing footprints, fleshed foot measurements and stature were obtained from 105 adult volunteers from the staff and students of the United Medical and Dental Schools of Guy's and St Thomas' Hospitals, London. The footprints were measured using predetermined landmarks and the results analysed to investigate the significance of the parameters in a forensic context. Inter-observer and intra-observer errors were within acceptable limits. Regression equations were calculated for foot length from various parameters measured on a footprint. Topinard's finding that foot length represents between 14.9%-18.1% of stature in a given individual was confirmed. Footprint length showed a normal distribution in both sexes but male footprint length was greater than female footprint length for any given height. This study provides a quantitative method that could be used both with partial footprints and in the absence of dermatoglyphics to assist in the identification of an individual in a forensic context.

Adult↗
PubMed1998

Meniscal regeneration in the long-term after total meniscectomy?

A cohort of 39 patients (28 male, 11 female) that had undergone total meniscectomy as adolescents (mean age 16 years) underwent FISP 3D Magnetic Resonance Imaging at a mean follow up of 30 years. The presence of meniscal tissue was assessed by two independent observers blinded to the operation details. The volume of any meniscal tissue present was calculated. A posterior horn remnant was seen in 57% of medial and 45% of lateral meniscectomy cases. The mean volume of an operated medial meniscal remnant was 0.29 mL compared with a mean volume of 1.15 mL for an intact medial meniscus. The mean volume of an operated lateral meniscal remnant was 0.30 mL compared with 1.07 mL for an intact lateral meniscus. We have shown that the incidence of incomplete excision of the posterior horn is more common after total medial meniscectomy, and that at a mean follow up of 30 years there is no convincing in vivo MRI evidence of long-term meniscal regeneration.

Adolescent↗
PubMed1997

Utilization of lipophilic ionic additives in liquid polymer film optodes for selective anion activity measurements.

Lipophilic anionic and cationic additives are investigated as components for use in liquid polymer film-based optodes. These ionic additives are known to strongly influence the selectivity behavior of anion-selective electrodes. They also make it possible to construct ion coextraction optodes that can measure anion activities. Theoretical, thermodynamic anion-optode equilibria formalisms were derived to help understand the influence these additives have on the overall optode response and on the selectivity behavior. Neutral and charged anion carrier film configurations are described and tested for two anion ionophores with known modes of action, ruthenium(II) octaethylporphyrin and a vitamin B12 derivative (cyanoaquacobyrinic acid heptakis(2-phenylethyl ester)). These film configurations were further tested using a less well-understood ionophore, indium(III) octaethylporphyrin. Notable is the indium(III) octaethylporphyrin optode, which has a dynamic range appropriate for physiological measurements of chloride at neutral pH values. Also of interest is the optode with the vitamin B12 derivative ionophore, which has a dynamic range appropriate for some physiological measurements of nitrite at neutral pH values.

Anions↗
PubMed1977

Effects of sodium ions on the electrical and pH gradients across the membrane of Streptococcus lactis cells.

Energized cells of Streptococcus lactis conserve and transduce energy at the plasma membrane in the form of an electrochemical gradient of hydrogen ions (deltap). An increase in energy-consuming processes, such as cation transport, would be expected to result in a change in the steady state deltap. We determined the electrical gradient (deltapsi) from the fluorescence of a membrane potential-sensitive cyanine dye, and the chemical H+ gradient (deltaph) from the distribution of a weak acid. In glycolyzing cells incubated at pH5 the addition of NaCl to 200 mM partially dissipated the deltap by decreasing deltapsi, while the delta pH was constant. The deltap was also determined independently from the accumulation levels of thiomethyl-beta-galactoside. The deltap values decreased in cells fermenting glucose at pH 5 or pH 7 when NaCl was added, while the deltapH values were unaffected; cells fermenting arginine at pH 7 showed similar effects. Thus, these nongrowing cells cannot fully compensate for the energy demand of cation transport.

Biological Transport, Active↗
PubMed1977

Effects of potassium ions on the electrical and pH gradients across the membrane of Streptococcus lactis cells.

Bacteria transduce and conserve energy at the plasma membrane in the form of an electrochemical gradient of hydrogen ions (deltap). Energized cells of Streptococcus lactis accumulate K+ ions presumably in exchange for H+. We reasoned that if the movement of H+ is limited, then an increase in H+ efflux, effected by potassium transport inward, should result in changes in the steady-state deltap. We determined the electrical gradient (deltapsi) from the fluorescence of a membrane potential-sensitive cyanine dye, and the chemical H+ gradient (deltapH) from the distribution of a weak acid. The deltap was also determined independently from the accumulation levels of the non-metabolizable sugar thiomethyl-beta-galactoside. KCl addition to cells fermenting glucose or arginine at pH 5 changed the deltap very little, but lowered the deltapsi, while increasing the deltapH. At pH 7, the deltapH only increased slightly; thus, the decrease in deltapsi, effected by addition of potassium ions, resulted in a lowered steady-state deltap. These effects were shown not to be due to swelling or shrinking of the cells. Thus, in these nongrowing cells, under conditions of energy utilization for the active transport of K+, the components of deltap can vary depending on the limitations on the net movement of protons.

Biological Transport, Active↗