Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “layer”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources
PubMed1999

Immunoaffinity layering of enzymes. Stabilization and use in flow injection analysis of glucose and hydrogen peroxide.

A general procedure for the high yield immobilization of enzymes with the help of specific anti-enzyme antibodies is described. Polyclonal antibodies were raised against Aspergillus niger glucose oxidase and horseradish peroxidase in rabbits and the gamma globulin (IgG) fraction from the immune sera isolated by ammonium sulphate fractionation followed by ion-exchange chromatography. Immobilization of glucose oxidase and horseradish peroxidase was achieved by initially binding the enzymes to a Sepharose matrix coupled with IgG isolated from anti-(glucose oxidase) and anti-(horseradish peroxidase) sera, respectively. This was followed by alternate incubation with the IgG and the enzyme to assemble layers of enzyme and antibody on the support. The immunoaffinity-layered preparations obtained thus were highly active and, after six binding cycles, the amount of enzyme immobilized could be raised about 25 times over that bound initially. It was also possible to assemble layers of glucose oxidase using unfractionated antiserum in place of the IgG. The bioaffinity-layered preparations of glucose oxidase and horseradish peroxidase exhibited good enzyme activities and improved resistance to heat-induced inactivation. The sensitivity of a flow injection analysis system for measuring glucose and hydrogen peroxide could be remarkably improved using immunoaffinity-layered glucose oxidase and horseradish peroxidase. For the detection of glucose, a Clark-type oxygen electrode, constructed as a small flow-through cell integrated with a cartridge bearing immunoaffinity-layered glucose oxidase was employed. The hydrogen peroxide concentration was analysed spectrophotometrically using a flow-through cell and the layered horseradish peroxidase packed into a cartridge. The immunoaffinity-layered enzymes could be conveniently solubilized at acid pH and fresh enzyme loaded onto the support. Immunoaffinity-layered glucose oxidase was successfully used for the on-line monitoring of the glucose concentration during the cultivation of Streptomyces cerevisiae.

Animals↗
PubMed1986

Effect of enucleation on choline acetyltransferase activity in layers of goldfish optic tectum.

Choline acetyltransferase (ChAT) activity was determined in layers of optic tectum in control goldfish and in goldfish 4-20 days following unilateral enucleation. Significant changes in activity were found in the periventricular (PV) and superficial gray and white (SGW) layers. Within 4 days, ChAT activity in the PV layer on the lesioned side was about 75% of that on the control side. By 20 days, ChAT specific activity in the SGW layer on the lesioned side was about 150-160% of that on the control side. This increase in specific activity in the SGW layer was accounted for by the decrease in volume and in density of the layer after enucleation, so that the total amount of activity in the layer did not change significantly, indicating that the optic terminals contain little to no ChAT activity. ChAT activity in the optic tract was very low and did not decrease after enucleation. These data strongly indicate that the retinotectal pathway in goldfish is not cholinergic and, therefore, that the ChAT activity in the SGW layer is related to sources other than retinal ganglion cells. It is suggested that one such source might be neurons with somata in the PV layer.

Acetylcholinesterase↗
PubMed1992

Organization of layers II-III connections in human visual cortex revealed by in vitro injections of biocytin.

In the search for cortical mechanisms subserving psychological phenomena, a better understanding of human cortical circuitry is crucial. In this report we describe aspects of intrinsic connectivity of supragranular layers in human visual cortex, revealed by extracellular injections of the anterograde tracer biocytin in vitro. Human cortical slices were obtained from visual association cortex in the posterior-medial portion of the dorsal bank of the occipital lobe, removed during neurosurgical tumor ablations. Small iontophoretic injections of biocytin into layers II-III revealed intense Golgi-like staining of axonal projections emanating from the injection sites. Vertically descending axons are grouped in bundles 20 microns in diameter which are spaced 15 microns apart. Some of these axons enter the white matter and send long oblique and horizontal collaterals. The main horizontal spread of the axons could be observed in layers II-III and V. The bulk of projections extends to a distance of 1.5 mm in layers II-III and 1.1 mm in layer V. Few individual axons could be observed at greater distances. In contrast, layer IV is almost devoid of horizontal connections, forming a clear gap between supra- and infragranular layers. Axon collaterals in the infragranular layers project mostly in a descending oblique direction with long horizontal collaterals in lower layer VI.

Axons↗
PubMed1984

Fibroblast feeder layers inhibit differentiation of retinoic acid-treated embryonal carcinoma cells by increasing the probability of stem cell renewal.

The appearance of differentiated cells in embryonal carcinoma (EC) cultures can be inhibited by culturing the cells on fibroblast feeder layers. To determine whether or not feeder layers act by increasing the probability of stem cell renewal, growth and differentiation were monitored in cultures of F9 (subclone OTF9 -63) EC cells exposed to retinoic acid (RA) in either the presence or absence of feeder layers. By measuring the fraction of laminin-positive TROMA 1-positive or alkaline phosphatase-negative cells, it was determined that the frequency of differentiated cells in RA-treated F9 cultures was reduced by 70-80% when cells were cultured on fibroblast feeder layers instead of gelatin-coated dishes. Experiments in which EC cells were cultured in close proximity to a feeder layer demonstrated that cell-cell contact was required for maximal inhibition of differentiation. The probability of stem cell renewal was determined by measuring the number of colony-forming cells in RA-treated cultures as a function of time. Analysis of the data demonstrated that the probabilities of stem cell renewal were 0.5 and 0.25 during the first and second 48 h periods, respectively, following addition of RA for cells cultured without feeder layers. Cultures maintained on feeder layers exhibited a stem cell renewal probability of 0.72. Thus, feeder layers reduce the frequency of differentiated cells in RA-treated cultures by increasing the probability of stem cell renewal. Determining the mechanism by which feeder layers counteract the effect of a chemically defined differentiation inducer should help to uncover the processes that regulate the probability of stem cell renewal.

Animals↗
PubMed1996

Two-dimensional paracrystalline glycoprotein S-layers as a novel matrix for the immobilization of human IgG and their use as microparticles in immunoassays.

In the present study, cup-shaped 1-3 microns large cell wall fragments from Thermoanaerobacter thermohydrosulfuricus L111-69 covered with a hexagonal S-layer lattice composed of glycoprotein subunits were shown to act as a matrix for the immobilization of human IgG. After cross-linking the S-layer glycoprotein lattice with glutaraldehyde (S-layer microparticles), IgG was either bound to carbodiimide activated carboxyl groups from acidic amino acids from the protein moiety or to the carbohydrate chains activated with cyanogen bromide or oxidized with periodate. After determining the binding capacity of the S-layer lattice for human IgG, the orientation of the immobilized antibody molecules was investigated using anti-human IgG peroxidase conjugates with different specificity. Attachment of S-layer microparticles with covalently bound human IgG to microplates precoated with anti-human IgG of different specificity led to clear correlations between the amount of applied human IgG and the absorption values in the immunoassays. The steepest absorption curves were obtained when human IgG was bound to the carbohydrate chains exposed on the surface of the S-layer lattice. This confirmed that the location and the accessibility of the immobilized antibodies on S-layer microparticles is of major importance for the response in immunoassays. In addition to the high reproducibility of the amount of IgG which could be bound to the S-layer lattice and the high reproducibility of the absorption curves in the immunoassays, one major advantage of using cup-shaped S-layer microparticles can be seen in the considerable increase of the actual surface available for binding processes and immunological reactions.

Bacterial Outer Membrane Proteins↗
PubMed1993

Fracture toughness of posterior composite resins fabricated by incremental layering.

An incremental buildup technique is advocated for placing posterior composite resin restorations. This technique is preferred because it assures complete polymerization of large restorations and also reduces the problem of polymerization shrinkage, which can adversely affect the seal at the gingival margin of class II and large class III restorations. Measurements of tensile bond strengths between layers have been published with conflicting results. This study measured the fracture toughness of layered posterior composite resin within the interfacial layer and in a direction perpendicular to the layering. A compact test-specimen geometry conforming to the ASTM standard E399-83 was used. Three groups were tested: Group A specimens were bulk-cured in one complete increment; group B specimens were incrementally cured in 1.2 +/- 0.2 mm layers perpendicular to the plane of fracture; and group C specimens were incrementally cured with the interface between layers parallel to and in the plane of fracture. The microfilled composite resin showed no significant difference in the mean fracture toughness from the bulk-cured control regardless of layering technique. The hybrid composite resin showed a significant decrease in fracture toughness for fractures occurring in the interfacial layer, and fractures perpendicular to layering showed no significant difference in fracture toughness compared with the bulk-cured control.

Acrylic Resins↗
PubMed1996

Toward selective elicitation of TH1-controlled vaccination responses: vaccine applications of bacterial surface layer proteins.

Bacterial surface layer proteins have been utilized as combined vaccine carrier/adjuvants and offer a number of advantages in these applications. The crystalline protein arrays contain functional groups in precisely defined orientations for coupling of haptens. Conventional applications of S-layer vaccines do not cause observable trauma or side effects. Depending on the nature of the S-layer preparations, antigenic conjugates will induce immune responses of a predominantly cellular or predominantly humoral nature. Immune responses to S-layer-hapten conjugates are also observed following oral/nasal application. In the present contribution, the status of investigations with S-layer conjugates in three main immunological projects is reviewed. In a project aimed at immunotherapy of cancer, conjugates of S-layer with small, tumor-associated oligosaccharides have been found to elicit hapten-specific DTH responses. An enlarged program of chemical synthesis has now been initiated to prepare a complete set of mucin-derived, tumor-associated oligosaccharides and their chemically modified analogues for elicitation of cell-mediated immune responses to certain tumors in humans. In another application, oligosaccharides derived from capsules of Streptococcus pneumoniae type 8 have been linked to S-layer proteins and have been found to elicit protective antibody responses in animals. Most recently, allergen S-layer conjugates have been prepared with the intention to suppress the TH2-directed, IgE-mediated allergic responses to Bet nu 1, the major allergen of birch pollen. In the former two applications, the S-layer vaccine technology appears to offer the versatility needed to direct vaccination responses toward predominant control by TH1 or TH2 lymphocytes to meet the different therapeutic or prophylactic requirements in each case. In the third application, work has progressed to a preliminary stage only.

Adjuvants, Immunologic↗
PubMed1992

Increased epsilon(gamma-glutamyl)lysine crosslinking associated with increased protein synthesis in the inner layers of healing rat skin wounds.

Three days after biopsy wounds were made in the dorsal skin of rats the animals were killed and explants of wounded and unwounded skin were incubated for 7 h with either [3H]glutamine or [3H]lysine. Both incubated and fresh control explants were then dissected into three layers which were homogenized, extracted, digested and then assayed for epsilon (gamma-glutamyl)lysine. The concentration of epsilon(gamma-glutamyl)lysine was greater in all three wounded layers than in the corresponding unwounded layers. The concentration in the wounded middle (dermal) layer and in the unwounded middle layer of younger rats was greater than in the unwounded outer (keratinized) layer, which has previously been shown to contain epsilon(gamma-glutamyl)lysine crosslinks. The incorporation of label from both [3H]glutamine and [3H]lysine into buffer-insoluble protein of the middle and inner (muscle) layers was much greater in the wounded explants than in the unwounded. Except for [3H]lysine in the inner layer there was also an increase in the fraction of incorporated label which was converted to epsilon(gamma-glutamyl)lysine. These results show that increased protein biosynthesis during repair in the wounded explants is associated with increased formation of epsilon(gamma-glutamyl)lysine. In addition, they indicate that the crosslink is involved in some process in the middle and inner layers which is distinct from its known function in keratinization of the epidermis.

Animals↗
PubMed1996

Layer-specific sprouting of commissural fibres to the rat fascia dentata after unilateral entorhinal cortex lesion: a Phaseolus vulgaris leucoagglutinin tracing study.

After unilateral entorhinal cortex lesion commissural fibres to the inner molecular layer of the rat fascia dentata are said to sprout into the former termination zone of entorhinal afferents. This sprouting process has not yet been demonstrated at the level of individual fibres. In the present study, Phaseolus vulgaris leucoagglutinin tracing was used to analyse the commissural projection to the inner molecular layer in rats with longstanding entorhinal cortex lesions. In comparison with controls, the commissural fibre plexus in the inner molecular layer had expanded by 20-45 microns outwards on the side of the entorhinal lesion. Unexpectedly, only a small number of axons arising from the bulk of commissural fibres in the inner molecular layer left the main fibre plexus and entered the outer molecular layer. Thus, there was still a clearly recognizable border between the Phaseolus vulgaris leucoagglutinin-labelled commissural fibre plexus in the inner molecular layer and the unstained outer molecular layer. The few commissural axons invading the outer molecular layer rarely branched but formed multiple en passant boutons, and occasionally exhibited growth cones. The data indicate that only few commissural fibres appear to be able to sprout beyond the border of their appropriate layer suggesting that the characteristic laminar specificity of hippocampal afferents is largely retained following deafferentation.

Animals↗
PubMed2004

Electron holography of non-stained bacterial surface layer proteins.

We report transmission electron microscopy (TEM) investigations on bacterial surface layers (S-layers) which belong to the simplest biomembranes existing in nature. S-layers are regular 2D protein crystals composed of single protein or glycoprotein species. In their native form, S-layers are weak phase objects giving only poor contrast in conventional TEM. Therefore, they are usually examined negatively stained. However, staining with heavy metal compounds may cause the formation of structural artefacts. In this work, electron microscopy studies of non-stained S-layers of Bacillus sphaericus NCTC 9602 were performed. Compared to other proteins, these S-layers are found relatively stable against radiation damage. Electron holography was applied where information about phase and amplitude of the diffracted electron wave is simultaneously obtained. In spite of small phase shifts observed, the phase image reconstructed from the hologram of the non-stained S-layer is found to be sensitive to rather slight structure and thickness variations. The lateral resolution, obtained so far, is less than that of conventional electron microscopy of negatively stained S-layers. It corresponds to the main lattice planes of 12.4 nm observed in the reconstructed electron phase image. In addition, as a unique feature of electron holography the phase image provides thickness information. Thus, the existence of double layers of the protein crystals could be easily visualized by the height profile of the specimen.

Bacillus↗
PubMed2004

Hydroxyapatite coating on titanium substrate with titania buffer layer processed by sol-gel method.

Hydroxyapatite (HA) was coated onto a titanium (Ti) substrate with the insertion of a titania (TiO2) buffer layer by the sol-gel method. The HA layer was employed to enhance the bioactivity and osteoconductivity of the Ti substrate, and the TiO2 buffer layer was inserted to improve the bonding strength between the HA layer and Ti substrate, as well as to prevent the corrosion of the Ti substrate. The HA layer coated over the TiO2 showed a typical apatite phase at 400 degrees C and the phase intensity increased above 450 degrees C. The sol-gel derived HA and TiO2 films, with thicknesses of approximately 800 and 200 nm, respectively, adhered tightly to each other and to the Ti substrate. The bonding strength of the HA/TiO2 double layer coating on Ti was markedly improved when compared to that of the HA single coating on Ti. The highest strength of the double layer coating was 55 MPa after heat treatment at 500 degrees C. The improvement in bonding strength with the insertion of TiO2 was attributed to the resulting enhanced chemical affinity of TiO2 toward the HA layer, as well as toward the Ti substrate. Human osteoblast-like cells, cultured on the HA/TiO2 coating surface, proliferated in a similar manner to those on the TiO2 single coating and on the pure Ti surfaces. However, the alkaline phosphatase activity of the cells on the HA/TiO2 double layer was expressed to a higher degree than that on the TiO2 single coating and pure Ti surfaces. The corrosion resistance of Ti was improved by the presence of the TiO2 coating, as confirmed by a potentiodynamic polarization test.

Buffers↗
PubMed2006

Development of a self-sterilizing lancet coated with a titanium dioxide photocatalytic nano-layer for self-monitoring of blood glucose.

A photocatalyst was applied to a lancet for pricking the finger to obtain an antibacterial property. A photocatalytic and uniform nano-layer of titanium dioxide (TiO2) on the surface of the lancet (0.36 mm x 24.5 mm) was formed by sputtering and annealed for crystallization of the TiO2 layer. By elementary analysis of the TiO2 layer, titanium and oxygen were detected. Next, for the estimation of the antibacterial properties resulting from the photocatalytic effect, the lancet was packed into a capillary tube filled with a suspension of Escherichia coli K-12 (non-spore-forming bacterium), and was continuously rolled in a continuous UV-irradiation system under black-light irradiation. Distinct antibacterial effects after irradiation at 0.5 mW cm(-2) for 45 min were observed in the crystallized TiO2 layer on the lancet. Finally, lancing resistances obtained by pricking an artificial skin sheet were examined using control lancets, and lancets with an unannealed TiO2 layer or an annealed TiO2 layer. The results showed almost the same lancing resistances for the control (0.53+/-0 N, n=3) and the lancet with an annealed TiO2 layer (0.51+/-0.018 N), while the lancet with an unannealed TiO2 layer showed a high lancing resistance compared with the other lancets (0.62+/-0.05 N). In conclusion, the lancet coated with a crystallized, velvety nano-layer of TiO2 obtained by annealing had antibacterial properties and a similar lancing resistance compared with the bare lancet, and showed potential for application in monitoring blood glucose in diabetes.

Biosensing Techniques↗
PubMed2004

The apparent increase of the Young's modulus in thin cement layers.

OBJECTIVES: The bond of adhesive luting cements to the tooth tissues and restorative materials is expected to hinder their transverse contraction for the layer thickness applied in dental restorations. It was hypothesized that the hindering of the transverse deformation will influence the relation between stress and strain (the stiffness) in the direction perpendicular to the substrate surface. The aim of this study was to investigate the relation between cement layers with different ratio between bonded and free surface (C-factor) and the stiffness of these layers, i.e. an apparent increase of the Young's modulus of the dental luting cement. METHODS: A commercial luting cement RelyX ARC (3M, St Paul, MN, USA) was used in this study. The 'real" Young's modulus and the Poisson ratio were determined and these values were used in models with layers with different C-factors (0.5, 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0) in a three-dimensional Finite Element Analysis program (FEMAP, E.S.P., Maryland Height, MO, USA). The apparent Young's modulus was measured for layers with thicknesses of 0.5 mm (C = 6.0) and 6.0 mm (C = 0.5) and compared with the results of the Finite Element Analysis (FEA) analysis. RESULTS: The apparent Young's modulus in the 0.5 mm layer was 20% higher than the apparent Young's modulus in the 6.0 mm layer. This result was confirmed by the results of the F.E. analysis. For very thin layers the stiffness will be 25% higher than the Young's modulus. SIGNIFICANCE: The hindering of the transverse contraction has to be taken into account studying the mechanical properties of dental luting cements because it influences the behavior of these luting cements in thin layers.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2006

Identification and characterization of the genes encoding a unique surface (S-) layer of Tannerella forsythia.

A newly emerged periodontopathic pathogen Tannerella forsythia (formerly Bacteroides forsythus), a Gram-negative, filament-shaped, strict anaerobic, non-pigmented oral bacterium, possesses a surface (S-) layer. In our previous studies, the S-layer has been isolated, and shown to mediate hemagglutination, adhesion/invasion of epithelial cell, and murine subcutaneous abscess formation. In the present study, biochemical and molecular genetic characterization of the S-layer are reported. Amino acid sequencing and mass spectrometry indicated that the S-layer is composed of two different proteins, termed 200 and 210 kDa proteins. It was also shown that these proteins are glycosylated. The genes encoding the core proteins of these glycoproteins, designated as tfsA and tfsB, have been identified in silico, cloned, and their sequences have been determined. The tfsA (3.5 kb) and tfsB (4.1 kb) genes are located in tandem, and encode for 135 and 152 kDa proteins, respectively. An apparent discrepancy in molecular weights, 135 vs. 200 kDa and 152 vs. 210 kDa, is accounted for carbohydrate residues attached to the core proteins. Amino acid sequence comparison exhibited a 24% similarity between the 200 and 210 kDa proteins. Further sequence analyses showed that TfsA and TfsB possess putative signal peptide sequences with cleavage sites at alanine residues, and transmembrane domains on the C-terminal region. Northern blot and RT-PCR analyses confirmed an operon structure of tfsAB, suggesting co-regulation of these genes in producing the S-layer. Putative promoter sequences and transcription termination sequences for this operon have also been identified. Comparison with database indicates that the S-layer of T. forsythia has a unique structure exhibiting no homology to other known S-layers of prokaryotic organisms. The present study shows that the T. forsythia S-layer is very unique, since it appears to be composed of two large glycoproteins, and it does not reveal any homology to other known S-layer proteins or glycoproteins of prokaryotic organisms.

Bacterial Proteins↗
PubMed2006

Effect of dispersion pH on the formation and stability of Pickering emulsions stabilized by layered double hydroxides particles.

Using positively charged plate-like layered double hydroxides (LDHs) particles as emulsifier, liquid paraffin-in-water emulsions stabilized solely by such particles are successfully prepared. The effects of the pH of LDHs aqueous dispersions on the formation and stability of the emulsions are investigated here. The properties of the LDHs dispersions at different pHs are described, including particle zeta potential, particle aggregation, particle contact angle, flow behavior of the dispersions and particle adsorption at a planar oil/water interface. The zeta potential decreases with increasing pH, leading to the aggregation of LDHs particles into large flocs. The structural strength of LDHs dispersions is enhanced by increasing pH and particle concentration. The three-phase contact angle of LDHs also increases with increasing pH, but the variation is very small. Visual observation and SEM images of the interfacial particle layers show that the adsorption behavior of LDHs particles at the planar oil/water interface is controlled by dispersion pH. We consider that the particle-particle (at the interface) and particle-interface electrostatic interactions are well controlled by adjusting the dispersion pH, leading to pH-tailored colloid adsorption. The formation of an adsorbed particle layer around the oil drops is crucial for the formation and stability of the emulsions. Emulsion stability improves with increasing pH and particle concentration because more particles are available to be adsorbed at the oil/water interface. The structural strength of LDHs dispersions and the gel-like structure of emulsions also influence the stability of the emulsions, but they are not necessary for the formation of emulsions. The emulsions cannot be demulsified by adjusting emulsion pH due to the irreversible adsorption of LDHs particles at the oil/water interface. TEM images of the emulsion drops show that a thick particle layer forms around the oil drops, confirming that Pickering emulsions are stabilized by the adsorbed particle layers. The thick adsorbed particle layer may be composed of a stable inner particle layer which is in direct contact with the oil phase and a relatively unstable outer particle layer surrounding the inner layer.

Journal Article↗
PubMed2004

Two-layered quasi-3D finite element model of the oesophagus.

Analysis of oesophageal mechanoreceptor-dependent responses requires knowledge about the distribution of stresses and strains in the layers of the organ. A two-layered and a one-layered quasi-3D finite element model of the rat oesophagus were used for simulation. An exponential pseudo-strain energy density function was used as the constitutive equation in each model. Stress and strain distributions at the distension pressures 0.25 and 1.0 kPa were studied. The stress and strain distributions depended on the wall geometry. In the one-layered model, the stress ranged from -0.24 to 0.38 kPa at a pressure of 0.25 kPa and from -0.67 to 2.57 kPa at a pressure of 1.0 kPa. The stress in the two-layered model at the pressure of 0.25 and 1.0 kPa varied from -0.52 to 0.64 kPa and from -1.38 to 3.84 kPa. In the two-layered model, the stress was discontinuous at the interface between the muscle layer and the mucosa-submucosa layer. The maximum stress jump was 1.67 kPa at the pressure of 1.0 kPa. The present study provides a numerical simulation tool for characterising the mechanical behaviour of a multi-layered, complex geometry organ.

Animals↗
PubMed2006

In vivo laser confocal microscopy of Bowman's layer of the cornea.

PURPOSE: To investigate in vivo microstructures of Bowman's layer in normal human subjects using a cornea-specific in vivo laser scanning confocal microscope (Heidelberg Retina Tomograph 2 Rostock Cornea Module, HRT2-RCM). DESIGN: Single-center, prospective, observational case series. PARTICIPANTS: Nineteen normal volunteers (10 male, 9 female; mean age, 46.2+/-21.7 years [range, 18-77]). METHODS: The central and peripheral cornea, specifically the epithelium, Bowman's layer, and its subjacent stroma, were examined using the HRT2-RCM. MAIN OUTCOME MEASURES: Selected images of the corneal layers were evaluated qualitatively for the shape and degree of light reflection of the microstructures. RESULTS: In all subjects, normal epithelial (superficial, wing, basal) cells, subbasal nerve plexus, Bowman's layer, and its subjacent stoma were observed clearly. However, in all subjects, polymorphic structures composed of fibrillar materials with less reflectivity than corneal nerves were observed beneath Bowman's layer. After application of pressure by a Tomo-cap, we observed numerous ridges that protruded into the epithelial basal and wing cell layers. Superficial stromal striae were also observed. These ridges and striae corresponded exactly to the orientation of the fibrous structures located beneath the epithelial cells. CONCLUSION: We report for the first time, the presence of polymorphic structures composed of fibrillar materials (K-structures) beneath Bowman's layer in normal human subjects, detected by HRT2-RCM. We surmise that these microstructures may correspond to the modified and condensed anterior stromal collagen fibers/lamellae that merge into Bowman's layer and that these fibrillar materials may be responsible for the formation of the anterior corneal mosaic. Further investigation of these microstructures in diseased eyes may provide insights into their pathophysiologic role in Bowman's layer.

Adolescent↗
PubMed2006

A KLM-circuit model of a multi-layer transducer for acoustic bladder volume measurements.

In a preceding study a new technique to non-invasively measure the bladder volume on the basis of non-linear wave propagation was validated. It was shown that the harmonic level generated at the posterior bladder wall increases for larger bladder volumes. A dedicated transducer is needed to further verify and implement this approach. This transducer must be capable of both transmission of high-pressure waves at fundamental frequency and reception of up to the third harmonic. For this purpose, a multi-layer transducer was constructed using a single element PZT transducer for transmission and a PVDF top-layer for reception. To determine feasibility of the multi-layer concept for bladder volume measurements, and to ensure optimal performance, an equivalent mathematical model on the basis of KLM-circuit modeling was generated. This model was obtained in two subsequent steps. Firstly, the PZT transducer was modeled without PVDF-layer attached by means of matching the model with the measured electrical input impedance. It was validated using pulse-echo measurements. Secondly, the model was extended with the PVDF-layer. The total model was validated by considering the PVDF-layer as a hydrophone on the PZT transducer surface and comparing the measured and simulated PVDF responses on a wave transmitted by the PZT transducer. The obtained results indicated that a valid model for the multi-layer transducer was constructed. The model showed feasibility of the multi-layer concept for bladder volume measurements. It also allowed for further optimization with respect to electrical matching and transmit waveform. Additionally, the model demonstrated the effect of mechanical loading of the PVDF-layer on the PZT transducer.

Animals↗