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PubMedDate not supplied

Esophagotomy closure in the dog. A comparison of a double-layer appositional and two single-layer appositional techniques.

Esophagotomies were performed on 36 dogs and closed with 3-0 polydioxanone in double-layer simple interrupted, single-layer simple interrupted, or single-layer simple continuous patterns. The operative time was shortest for single-layer simple continuous closure, followed by single-layer simple interrupted and double-layer simple interrupted, respectively. Three dogs with each suture pattern were euthanatized at hours 0 and 1, and days 4 and 28 after surgery. The esophagotomy incisions were subjected to bursting strength testing and examined microscopically. The bursting wall tension was higher for all three suture pattern groups at 28 days than at 0 and 1 hour. The double-layer closure had higher bursting wall tension than the single-layer closures at 0 hour and 4 days. Single-layer simple continuous closure had the lowest bursting wall tension for each time period. Single-layer simple interrupted closure had the highest bursting wall tension at 28 days. Microscopic examination revealed close approximation of tissue planes for the double-layer closure and mucosal eversion for the simple interrupted and simple continuous single-layer closures. Healing was superior histologically with the double-layer closure.

Animals↗

PubMed1986

Cat area 17. II. Response properties of infragranular layer neurons in the absence of supragranular layer activity.

Response properties of cells in the infragranular layers of cortical area 17 of the cat were examined in the absence of input from supragranular layers. Supragranular activity was silenced either reversibly by cooling the surface of cortex or permanently by making a cryogenic lesion of the supragranular layers. Visually driven responses of cells throughout the cortical column were recorded with a linear array of electrodes. Most infragranular layer cells continued to be visually responsive in the absence of supragranular layer input. These cells were similar to normal infragranular layer cells on measures of visual responsiveness, orientation selectivity, and direction selectivity. Special complex, but not standard complex, cells were absent in layer 5 when supragranular layers were destroyed. We found no evidence for a selective effect of removal of supragranular activity on the response properties of cells in layer 6. We propose that the intracolumnar projection from the supragranular layers drives the special complex cells of layer 5, but is not necessary for the visual driving of most other infragranular layer cells. This projection does not impose selectivity for stimulus orientation or direction on the remaining active cells of the infragranular layers.

Animals↗

PubMed2005

Single-layer versus multiple-layer closure of leg wounds after long saphenous vein harvest: a prospective randomized trial.

BACKGROUND: The long saphenous vein harvested by traditional techniques is an important conduit for coronary artery bypass grafting (CABG). The purpose of this study was to determine if a single-layer closure over a drain improved wound healing compared with the traditional two-layer closure after harvest. METHODS: Seventy-eight consecutive patients undergoing CABG were prospectively randomized to have their leg wound closed by either a single-layer technique with a suction drain or multiple layers. All wounds were assessed using the additional treatment, presence of serous discharge, erythema, purulent exudate, and separation of the deep tissues, isolation of bacteria, and the duration of inpatient stay (ASEPSIS) score postoperatively and 6 weeks later. RESULTS: Forty-four patients (5 females) had their wound closed by the single-layer technique and 34 (6 females) closed in multiple layers. The ASEPSIS scores were significantly lower (p = 0.001) in those patients closed with a single layer (mean, 4.4) than those with multiple layers (mean, 6.8). Patients whose legs were closed with the single-layer technique had less peripheral edema compared with the multiple-layer group (chi2, p < 0.001). Using univariate analysis there was no correlation between ASEPSIS scores and length of wound incision (p = 0.49), whereas increasing age was found to have a weak positive correlation (r =0.24; p = 0.04). CONCLUSIONS: Single-layer leg wound closure over a suction drain is superior to the traditional multiple-layer closure. A possible mechanism of better wound healing in the former technique might be through decreased tissue handling and a reduction in leg edema.

Aged↗

PubMed1998

Two steroidogenic pathways present in the chicken ovary: theca layer prefers delta 5 pathway and granulosa layer prefers delta 4 pathway.

It has been suggested that there is a shift in steroidogenic pathways of the theca layer from delta 5 to delta 4 during follicular maturation in the chicken ovary. However, the preferred steroid metabolic pathway in the theca and granulosa layers of small and preovulatory follicles has not been identified. Therefore, the goal of our study was to identify the preferred steroidogenic pathways used by these follicles. Previously, we found that small follicles that had not entered the follicular hierarchy did not use cholesterol but did use pregnenolone (P5) to produce testosterone and estradiol. For this reason, P5 was used as the substrate for steroid production in the present study. The theca layer of small follicles (2-4 mm in diameter), and the theca and granulosa layers of the fifth largest (F5), third largest (F3), and largest (F1) preovulatory follicles were isolated from the chicken ovary 22 hr before ovulation. The granulosa layer of small follicles was excluded from the study because it is steroidogenically incompetent. Tissues were incubated with [3H]-P5 for 1 hr at 37 degrees C. Production of steroid metabolites was determined on the basis of comparison with known steroid standards using two-dimensional thin layer chromatography (2D-TLC). Conversion of [3H]-P5 to [3H]-DHEA was greater than that of [3H]-P4 in the theca layer of small and preovulatory follicles. Even though the amount of [3H]-P4 was less than that of [3H]-DHEA, theca cells from F3 and F1 follicles did produce [3H]-P4. In contrast to the theca layer, conversion of [3H]-P4 was greater than that of [3H]-DHEA in the granulosa layer of preovulatory follicles. Conversion of [3H]-P5 to [3H]-DHEA by the granulosa layer gradually decreased as the follicle matured and approached ovulation. We conclude that both delta 5 and delta 4 pathways are functional in theca and granulosa cells. However, in contrast to earlier speculation, the theca layer preferentially metabolizes steroids via the delta 5 pathway regardless of the maturational stage of the follicle, whereas the granulosa layer of preovulatory follicles preferentially metabolizes steroids via the delta 4 pathway.

Animals↗

PubMed1999

Effects of feedback projections from area 18 layers 2/3 to area 17 layers 2/3 in the cat visual cortex.

In the absence of a direct geniculate input, area 17 cells in the cat are nevertheless able to respond to visual stimuli because of feedback connections from area 18. Anatomic studies have shown that, in the cat visual cortex, layer 5 of area 18 projects to layer 5 of area 17, and layers 2/3 of area 18 project to layers 2/3 of area 17. What is the specific role of these connections? Previous studies have examined the effect of area 18 layer 5 blockade on cells in area 17 layer 5. Here we examine whether the feedback connections from layers 2/3 of area 18 influence the orientation tuning and velocity tuning of cells in layers 2/3 of area 17. Experiments were carried out in anesthetized and paralyzed cats. We blocked reversibly a small region (300 microm radius) in layers 2/3 of area 18 by iontophoretic application of GABA and recorded simultaneously from cells in layers 2/3 of area 17 while stimulating with oriented sweeping bars. Area 17 cells showed either enhanced or suppressed visual responses to sweeping bars of various orientations and velocities during area 18 blockade. For most area 17 cells, orientation bandwidths remained unaltered, and we never observed visual responses during blockade that were absent completely in the preblockade condition. This suggests that area 18 layers 2/3 modulate visual responses in area 17 layers 2/3 without fundamentally altering their specificity.

Animals↗

PubMed2004

Rapid arrival and integration of ascending sensory information in layer 1 nonpyramidal neurons and tuft dendrites of layer 5 pyramidal neurons of the neocortex.

Ascending sensory inputs arriving in layer 1 of the neocortex carry crucial signals for detecting salient information; but how the inputs are processed in layer 1 is unknown. Using a whole-cell in vivo recording technique targeting nonpyramidal neurons in layer 1 and tuft dendrites of layer 5 pyramidal neurons in layers 1-2, we examined the processing of these ascending sensory inputs in the barrel cortex. Here, we show that local circuit and deeper-layer-projecting neurons in layer 1, as well as tuft dendrites and somata of layer 5 pyramidal neurons, respond to multiple whiskers (6-15) with robust EPSPs. Remarkably, the latency for primary whisker-evoked responses is as short as approximately 5-7 msec in layer 1 neurons and tuft dendrites of layer 5 pyramidal neurons. In addition, the latency for primary whisker-evoked responses in tuft dendrites of layer 5 pyramidal neurons is approximately 1 msec shorter than that in somata. These results indicate that ascending sensory inputs arrive in layers 1 and 4 concurrently, which provides a neural mechanism for rapid integration and coincident detection of salient sensory information.

Afferent Pathways↗

PubMed2001

Layer-specific intracolumnar and transcolumnar functional connectivity of layer V pyramidal cells in rat barrel cortex.

Layer V pyramidal cells in rat barrel cortex are considered to play an important role in intracolumnar and transcolumnar signal processing. However, the precise circuitry mediating this processing is still incompletely understood. Here we obtained detailed maps of excitatory and inhibitory synaptic inputs onto the two major layer V pyramidal cell subtypes, intrinsically burst spiking (IB) and regular spiking (RS) cells, using a combination of caged glutamate photolysis, whole-cell patch-clamp recording, and three-dimensional reconstruction of biocytin-labeled cells. To excite presynaptic neurons with laminar specificity, the release of caged glutamate was calibrated and restricted to small areas of 50 x 50 microm in all cortical layers and in at least two neighboring barrel-related columns. IB cells received intracolumnar excitatory input from all layers, with the largest EPSP amplitudes originating from neurons in layers IV and VI. Prominent transcolumnar excitatory inputs were provided by presynaptic neurons also located in layers IV, V, and VI of neighboring columns. Inhibitory inputs were rare. In contrast, RS cells received distinct intracolumnar inhibitory inputs, especially from layers II/III and V. Intracolumnar excitatory inputs to RS cells were prominent from layers II-V, but relatively weak from layer VI. Conspicuous transcolumnar excitatory inputs could be evoked solely in layers IV and V. Our results show that layer V pyramidal cells are synaptically driven by presynaptic neurons located in every layer of the barrel cortex. RS cells seem to be preferentially involved in intracolumnar signal processing, whereas IB cells effectively integrate excitatory inputs across several columns.

Action Potentials↗

PubMed1998

Layer-specific NO dependence of long-term potentiation and biased NO release in layer V in the rat auditory cortex.

1. We investigated the role of nitric oxide (NO) in the induction of long-term potentiation (LTP) in slices prepared from the rat auditory cortex. 2. Tetanic stimulation of layer IV elicited LTP of field potentials in layer II-III (LTPII-III) and in layer V (LTPV). The magnitude of LTPII-III measured at 30 min after tetanic stimulation was 171 +/- 9% (n = 15, mean +/- s.e.m.) of the control measured before tetanic stimulation, while that of LTPV was 138 +/- 3% (n = 17). 3. NO synthase (NOS) inhibitors had no apparent effect on LTPII-III, but LTPV was significantly suppressed (P < 0.001). This suppression of LTPV was significantly antagonized by a NO donor (P < 0.001) or a cGMP analogue (P < 0.001). 4. Small non-pyramidal neurones in the auditory cortex were stained with an anti-neuronal NOS antibody. More neurones were stained with the antibody in the deeper cortical layers. 5. We measured neocortical NO release with electrochemical NO probes. Layer IV stimulation elicited significantly more NO release in layer V than in layer II-III (P < 0.001). The amplitude of the increase in NO concentration elicited by stimulation at 20 Hz for 5 s was 380 +/- 14 pM (n = 55) in layer V and 55 +/- 8 pM (n = 5) in layer II-III. 6. NO release in layer V was partially but significantly suppressed by non-NMDA (P < 0.002) or NMDA (P < 0.002) receptor antagonists. Simultaneous application of the antagonists of the two types blocked NO release almost completely. 7. These results clearly indicate the NO dependence of the induction of LTPV, and the greater NO release in the deeper layer of the rat auditory cortex.

Animals↗

PubMed1996

Dynamics in oxygen-induced changes in S-layer protein synthesis from Bacillus stearothermophilus PV72 and the S-layer-deficient variant T5 in continuous culture and studies of the cell wall composition.

Stable synthesis of the hexagonally ordered (p6) S-layer protein from the wild-type strain of Bacillus stearothermophilus PV72 could be achieved in continuous culture on complex medium only under oxygen-limited conditions when glucose was used as the sole carbon source. Depending on the adaptation of the wild-type strain to low oxygen supply, the dynamics in oxygen-induced changes in S-layer protein synthesis was different when the rate of aeration was increased to a level that allowed dissimilation of amino acids. If oxygen supply was increased at the beginning of continuous culture, synthesis of the p6 S-layer protein from the wild-type strain (encoded by the sbsA gene) was immediately stopped and replaced by that of a new type of S-layer protein (encoded by the sbsB gene) which assembled into an oblique (p2) lattice. In cells adapted to a prolonged low oxygen supply, first, low-level p2 S-layer protein synthesis and second, synchronous synthesis of comparable amounts of both types of S-layer proteins could be induced by stepwise increasing the rate of aeration. The time course of changes in S-layer protein synthesis was followed up by immunogold labelling of whole cells. Synthesis of the p2 S-layer protein could also be induced in the p6-deficient variant T5. Hybridization data obtained by applying the radiolabelled N-terminal and C-terminal sbsA fragments and the N-terminal sbsB fragment to the genomic DNA of all the three organisms indicated that changes in S-layer protein synthesis were accompanied by chromosomal rearrangement. Chemical analysis of peptidoglycan-containing sacculi and extraction and recrystallization experiments revealed that at least for the wild-type strain, a cell wall polymer consisting of N-acetylglucosamine and glucose is responsible for binding of the p6 S-layer protein to the rigid cell wall layer.

Adaptation, Physiological↗

PubMed2001

Helicobacter pylori and two ultrastructurally distinct layers of gastric mucous cell mucins in the surface mucous gel layer.

BACKGROUND AND AIMS: Helicobacter pylori locate not only on the apical surface of surface mucous cells but also in the mucous gel layer covering the gastric mucosa. The present study was undertaken to observe the mucous gel layer itself and any H pylori in this layer at the electron microscopic level, and to determine whether H pylori proliferate in this layer. METHODS: We examined resected human stomachs (five cases, fixed in Carnoy's solution, paraffin embedded) under the light microscope, and gastric biopsy specimens (10 cases, fixed in glutaraldehyde with or without osmium, epoxy embedded) under the electron microscope. We performed histochemical staining for gastric mucins and immunostaining for H pylori, gastric gland mucous type mucins, and intestinal mucins. RESULTS: Under the electron microscope, surface mucous cell type mucins and gland mucous cell type mucins in the mucous gel layer covering gastric mucosa without intestinal metaplasia showed reticular and band like structures, respectively. H pylori were frequently found as small aggregates within the mucous gel layer of surface mucous cell type mucins, and H pylori within these aggregates were seen dividing. H pylori were frequently found in the mucous gel layer of the surface mucous cell type mucins along the border with the layer of gland mucous cell mucins. Occasionally, H pylori were trapped by frayed thin threads of the gland mucous cell type mucins. CONCLUSIONS: The two types of gastric mucins in the mucous gel layer differ in ultrastructure. H pylori preferentially colonise and form microcolonies within the mucous gel layer of surface mucous cell type mucins. Mucins from gland mucous cells may disturb the movement of H pylori within the mucous gel layer.

Adult↗

PubMed2002

Campylobacter surface-layers (S-layers) and immune evasion.

Many pathogenic bacteria have evolved mechanisms for evading host immune systems. One evasion mechanism is manifest by the surface layer (S-layer), a paracrystalline protein structure composed of S-layer proteins (SLPs). The S-layer, possessed by 2 Campylobacter species (C. fetus and C. rectus), is external to the bacterial outer membrane and can have multiple functions in immune avoidance. C. fetus is a pathogen of ungulates and immunocompromised humans, in whom it causes disseminated bloodstream disease. In C. fetus, the S-layer is required for dissemination and is involved in 2 mechanisms of evasion. First, the S-layer confers resistance to complement-mediated killing in non-immune serum by preventing the binding of complement factor C3b to the C. fetus cell surface. S-layer expressing C. fetus strains remain susceptible to complement-independent killing, utilizing opsonic antibodies directed against the S-layer. However, C. fetus has also evolved a mechanism for avoiding antibody-mediated killing by high-frequency antigenic variation of SLPs. Antigenic variation is accomplished by complex DNA inversion events involving a family of multiple SLP-encoding genes and a single SLP promoter. Inversion events result in the expression of antigenically variant S-layers, which require distinct antibody responses for killing. C. rectus is implicated in the pathogenesis of periodontal disease and also possesses an S-layer that appears to be involved in evading the human system. Although studied less extensively than its C. fetus counterpart, the C. rectus S-layer appears to confer resistance to complement-mediated killing and to cause the down-regulation of proinflammatory cytokines.

Antigenic Variation↗

PubMed1999

Widespread projections from subgriseal neurons (layer VII) to layer I in adult rat cortex.

Theories of information processing and plasticity in mammalian cortex often rely on knowledge of intracortical networks studied in rodent cortex. Accordingly, the contribution of all cells involved in this circuitry is potentially significant, including connections from a subset of neurons that persist from the developmental subplate, called subgriseal neurons in the present study. Ascending corticocortical connections from subgriseal neurons were identified by using in vivo transport of fluorescent retrograde tracers from discrete applications confined to cortical layer I (approximately 1 mm2) or from injections placed into superficial cortical layers. Applications restricted to cortical layer I can be identified by a subsequent retrograde labeling pattern that includes neurons in layers II/III and V but not those in layer IV. In contrast, when retrograde tracer is deposited in layers II/III, layer IV cells are also labeled. By using this identification technique in juvenile and adult rats, widespread interareal projections to superficial layers, including unequivocal connections to cortical layer I, were found to originate from a tangential band of neurons directly below the conventionally identified gray matter (i.e., subgriseal) and from a smaller number of cells in the white matter (WM) proper. Subgriseal and WM neurons were labeled below application and injection sites in somatosensory, auditory, visual, motor, frontal, and adjacent areas at distances of more than 4 mm. However, the subgriseal-to-superficial pathway was not sensitive to nonfluorescent retrograde tracers including horseradish peroxidase. Because neurons in the deeper cortical layers can be strongly influenced through input to their apical dendritic extensions in cortical layer I, the widespread connections described in the present study indicate that the ascending subgriseal projections should be considered in models of mature cortical function.

Aging↗

PubMedDate not supplied

[Single-layer colonic anastomoses using polyglyconate (Maxon) vs. two-layer anastomoses using chromic catgut and silk. Experimental study].

BACKGROUND: The safety of an intestinal anastomosis is usually measured by its complication rate, especially the incidence of anastomotic leakage. A wide variety of methods have been described to reestablish intestinal continuity including single-layer continuous or two-layer interrupted anastomosis. OBJECTIVES: To evaluate if the single-layer continuous anastomosis using polygluconate is safer and reliable than two-layer interrupted anastomosis with chromic catgut and silk. MATERIAL AND METHODS: A prospective, experimental, randomized and comparative analysis was conducted in 20 dogs. They were divided in two groups; group 1 underwent two-layer interrupted anastomosis and group 2 underwent sigle-layer continuous technique. Anastomoses were timed. Both groups were under observation. Anastomotic leakage, and other complications were evaluated. The animals were sacrified and the anastomosis was taken out together with 10 cm of colon on both sides of the anastomosis. Breaking strength, histologic evaluation and hydroxyproline determination were performed. RESULTS: Ten two-layer anastomosis and ten single-layer anastomosis were performed. A median of 25 minutes (range: 20-30 minutes) was required to construct the anastomoses in group 1 versus 20 minutes (range: 12-25 minutes) in group 2. All animals survived and no leakage was observed. Wound infection ocurred in four dogs (20%). Median breaking strength was 230 mm Hg in group 1 and 210 mm Hg in group 2. Hydroxyproline concentration was 8.94 mg/g in group 1 (range: 5.33-16.71) and 9.94 mg/g in group 2 (range: 2.96-21.87). There was no difference among groups about the inflammatory response evaluated by pathology. There was no statistical significance in any variable evaluated. CONCLUIONS: This study demonstrates that a single-layer continuous is similar in terms of safety to the two-layer technique, but because of its facility to perform, the single-layer technique could be superior.

Anastomosis, Surgical↗

PubMed1998

Signals from the superficial layers of the superior colliculus enable the development of the auditory space map in the deeper layers.

We have examined whether the superficial layers of the superior colliculus (SC) provide the source of visual signals that guide the development of the auditory space map in the deeper layers. Anatomical tracing experiments with fluorescent microspheres revealed that a retinotopic map is present in the newborn ferret SC. Aspiration of the caudal region of the superficial layers of the right SC on postnatal day 0 did not cause a reorganization of this projection. Consequently, recordings made when the animals were mature showed that visual units in the remaining superficial layers in rostral SC had receptive fields that spanned a restricted region of anterior space. Auditory units recorded beneath the remaining superficial layers were tuned to corresponding anterior locations. Both the superficial layer visual map and the deeper layer auditory map were normal in the left, unoperated SC. The majority of auditory units recorded throughout the deeper layers ventral to the superficial layer lesion were also tuned to single sound directions. In this region of the SC, however, we observed much greater scatter in the distribution of preferred sound directions and a significant increase in the proportion of units with spatially ambiguous responses. The auditory representation was degraded, although many of these units were also visually responsive. Equivalent lesions of the superficial layers made in adult ferrets did not alter the topographic order in the auditory representation, suggesting that visual activity in these layers may be involved in aligning the different sensory maps in the developing SC.

Age Factors↗

PubMed2003

Randomized clinical trial of three-layer paste and four-layer bandages for venous leg ulcers.

BACKGROUND: Both four-layer and three-layer paste bandages are widely used in the treatment of venous leg ulcers. The aim of this study was to compare the efficacy of these two bandaging regimens. METHODS: The study was a prospective, randomized, open comparison of a consecutive cohort of 133 patients with venous ulcers. Participants were stratified by ulcer size into one of three groups and were randomized within each group to receive either three-layer paste or four-layer bandages. All patients were followed for 1 year. The time taken to complete ulcer healing was the primary endpoint. The time taken to apply the bandages, comfort, tolerability and cost were also assessed. Analysis was performed on the basis of intention to treat. RESULTS: Ulcers healed completely in 51 (80 per cent) of 64 patients treated with three-layer paste bandages compared with 45 (65 per cent) of 69 patients treated with the four-layer regimen (P = 0.031). This difference developed only after 20 weeks of treatment. The median times to complete healing were 12 weeks for three-layer and 16 weeks for four-layer treatment (P = 0.040). Results of venous function tests, including half-refilling times, were similar in the two groups. CONCLUSION: Three-layer paste bandages were significantly more effective at healing venous ulcers than the four-layer regimen in this study.

Aged↗

PubMed1993

GABAergic innervation of the rat fascia dentata: a novel type of interneuron in the granule cell layer with extensive axonal arborization in the molecular layer.

By using the combined Golgi/electron microscopy (EM) technique and postembedding immunocytochemistry for gamma-aminobutyric acid (GABA), we describe a novel type of local circuit neuron in the rat fascia dentata that gives rise to an axon profusely ramifying in the dentate molecular layer. The relatively small ovoid cell body (long axis 12-15 microns) is located directly underneath the granular layer. From both poles of the cell body dendritic processes emerge that enter the molecular layer and hilar region, respectively. The apical dendrites traverse the granular layer, invade the molecular layer, and branch in the same way as granule cell dendrites. Some branches reach the hippocampal fissure. Thus, the apical dendrites of these neurons may receive a similar input pattern as the granule cells. The dendrites are smooth, occasionally bearing varicosities. A few spines are regularly observed. The axon originates from the apical dendrite and traverses the molecular layer horizontally for up to 500 microns. It gives off numerous collaterals that are distributed throughout the entire width of the molecular layer and only rarely enter the granule cell layer. Electron microscopy of the cell body of gold-toned neurons revealed the well-known fine-structural characteristics of nonpyramidal neurons, i.e., an indented nucleus with nuclear inclusions and large aggregations of endoplasmic reticulum. Apical as well as basal dendrites are densely covered with presynaptic boutons, mainly forming asymmetric synapses. The axon terminals of these cells form symmetric synapses with dendritic shafts and, to a lesser extent, with spines. These symmetric synapses, together with the results of our GABA postembedding immunocytochemical study, suggest that this cell is a GABAergic inhibitory neuron that almost exclusively innervates the dentate molecular layer. Together with data from the literature on dentate axoaxonic cells (which innervate the axon initial segments of the granule cells) and GABAergic basket cells (which innervate the granule cell somata and proximal dendrites in the granular layer), the present results indicate that there is a lamination of the GABAergic innervation of the fascia dentata corresponding to the well-known segregated termination of entorhinal and commissural afferents to this region.

Animals↗

PubMed2000

Layer Buildup on Two-Layered Porous Substrate by Dip-Coating: Modeling and Effect of Additives on Growth Rate.

A model was developed to describe layer buildup on a two-layered substrate during dip-coating. In this model, the growth rate can be used to estimate the permeability of the cast layer. Layers of submicron alumina were dip-coated onto the asymmetric porous substrate to evaluate the model. The layer buildup and properties were studied with different slip additives. Slips were deflocculated with nitric acid or sodium poly(methacrylic acid) (Na-PMAA) to achieve electrostatic or electrosteric stabilization. Properties of the slips with electrostatic stabilization were varied with poly(vinyl alcohol) (PVA) concentration. Properties of the slips with electrosteric stabilization were varied with Na-PMAA concentration. PVA addition decreased the growth rate of the layer by reducing capillary pressure and increasing the viscosity of the filtrate. Electrostatic stabilization of the slip with PVA addition also led to almost complete deflocculation and a rather high density of layers. Na-PMAA addition led to fast growth of the layer. Na-PMAA addition increased the capillary pressure and had a minor effect on the viscosity of the liquid phase. Na-PMAA addition led to an incomplete dispersion of particles and therefore a high porosity of layers. Permeability values of coated layers obtained from the model were compared with permeability values predicted by the Kozeny-Carman equation. In the case of complete deflocculation of the slip, the permeability values estimated with the model correlated reasonably well with the predicted values. Incomplete deflocculation led to higher permeability values than predicted by the Kozeny-Carman equation. Copyright 2000 Academic Press.

Journal Article↗

PubMed2005

In situ neutron reflectometry investigation of gold-chemisorbed PEO layers of varying chain density: relationship of layer structure to protein resistance.

In work reported previously [L.D. Unsworth, H. Sheardown, J.L. Brash, Langmuir 21 (2005) 1036] we investigated protein interactions with polyethylene oxide (PEO) layers formed by chemisorption of thiol-PEO on gold. It was shown that, as a function of surface chain density, protein adsorption passed through a minimum. In follow-on work reported here, neutron reflectometry (NR) was used to investigate the formation and properties (volume fraction and chain density) of such PEO layers in situ, i.e., in contact with water. Chain density was varied by varying solubility conditions (far from and near the cloud point) and chemisorption time. Neutron experiments were carried out using neutrons of de Broglie wavelength 2.37 A. Contrast matching techniques were used to improve sensitivity. Layers formed under high solubility conditions were found to have PEO volume fraction, layer thickness and chain density of 0.33, 28 A, and 0.56 chains/nm2, respectively, after 0.5 h chemisorption; and 0.31, 28.5 A, and 0.59 chains/nm2, respectively, after 11 h, suggesting that the layer is fully formed within 0.5 h. Both chain density and PEO volume fraction in the chemisorbed layers were significantly greater when the layers were formed under low solubility conditions. The PEO layers shown in our previous work to have maximum protein resistance were found to have a PEO volume fraction of approximately 40%. Moreover the limiting volume fraction in the PEO films formed under low solubility conditions was approximately 57%, a value similar to the solubility limit of PEO in aqueous solution, suggesting that local regions in the layers may be phase separated under these conditions. This may result in increased hydrophobicity and may explain why protein adsorption was found to increase on the layers of higher chain density.

Adsorption↗