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PubMed1982

Resistance of the shell membrane and mineral layer to diffusion of oxygen and water in flexible-shelled eggs of the snapping turtle (Chelydra serpentina).

At oviposition, flexible eggshells of many turtles have an outer mineral layer and an inner membrane layer of approximately equal thickness. We measured conductances of both layers to H2O and O2 at various levels of eggshell hydration. Both the mineral layer of the eggshell and the shell membrane offer significant resistance to diffusion of water vapor and oxygen in eggshells of the snapping turtle, Chelydra serpentina. Conductance to water vapor increases in both the membrane and mineral layer with increasing hydration of the eggshell, but conductance to oxygen decreases under similar conditions. Removal of the mineral layer increases conductance to oxygen in moist and dry eggshells, but decreases conductance at intermediate levels of dehydration. Removal of the mineral layer consistently increases conductance to water vapor. The eggshell membrane accounts for 24-76% of overall resistance to diffusion of water vapor. These results suggest that bulk flow of H2O or physical changes in the shell may interact with diffusion to limit gas exchange through the turtle eggshell.

Animals↗
PubMed1988

Functional lamination in the ganglion cell layer of the macaque's retina.

Close to the fovea of the primate retina the ganglion cell layer is at its maximal thickness and several layers of cells deep. In whole-mount preparations in which the ganglion cells had been retrogradely labelled to reveal the dendritic trees we have studied the distribution of the different ganglion cell types across the depth of the ganglion cell layer. The ganglion cells which project to the parvocellular layers (P ganglion cells) are found more vitread than those which project to the magnocellular layers (M ganglion cells). The cells which project to the midbrain lie in the outer part of the ganglion cell layer among the M cells and adjacent to the inner plexiform layer. Within the P and M classes of ganglion cell the On-centre cells lie more vitread than the Off-centre cells. These results are discussed with relation to the proportions of different cell types sampled with intraocular recordings from ganglion cells and the possible significance for the development of different types of ganglion cell.

Animals↗
PubMedDate not supplied

Formation of 2-D paracrystals of F-actin on phospholipid layers mixed with quaternary ammonium surfactants.

Two-dimensional paracrystalline arrays of F-actin have been formed on positively charged lipid layers composed of phosphatidylcholine (PC) and quaternary ammonium surfactants. These quaternary ammonium surfactants were found to be better promoters of two-dimensional order than PC lipid layers mixed with stearylamine. In addition, the length of the hydrocarbon chain was found to influence the achievement of 2-D order. Lipid layers composed of dilauryl-PC and didodecyldimethylammonium bromide, which are saturated C12 lipids, promoted 2-D crystallization better than mixtures of dipalmitoyl-PC, a saturated C16 lipid, and dioctadecyldimethylammonium bromide, a saturated C18 lipid. Thus, the hydrocarbon chain length, which influences lipid layer fluidity, had a significant effect on paracrystal formation. We suggest that quaternary ammonium surfactants may have advantages in some cases for forming ordered arrays on lipid layers. In addition to investigating the effect of lipid layer composition on paracrystal formation, we found that the injection of G-actin rather than F-actin under a fluid lipid layer into a polymerizing solution produced better ordered paracrystals.

Actins↗
PubMedDate not supplied

Novel structural patterns in divalent cation-depleted surface layers of Aeromonas salmonicida.

The fish pathogen Aeromonas salmonicida possesses a regular surface layer (or A-layer) which is an important virulence determinant. The A-protein, a single bilobed protein organized in a p4 lattice of M4C4 arrangement with two morphological domains, comprises this layer. The role of divalent cations in the A-layer structure was studied to better understand A-protein subunit interactions affecting structural flexibility and function. Divalent cation bridges were found to be involved in the integrity of the A-layer. Two novel A-layer patterns were formed as the result of growth under calcium limitation or by chelation of divalent cations with EDTA or EGTA, thereby constituting the first reported case of formation of distinct regular arrays upon divalent cation depletion. Furthermore, under these conditions A-protein was sometimes released as tetrameric units, rather than in monomeric form. The formation of the two novel patterns is best explained by a sequence of structural rearrangements, following disruption of only one of the two A-layer morphological units, that is, those held together by divalent cation bridges. The free tetrameric units represent four A-protein subunits clustered around the unaffected four-fold axis.

Aeromonas↗
PubMed2005

Superficial and deep layer muscle fibre properties of the mouse masseter before and after weaning.

To clarify changes in the properties of the masseter muscle superficial and deep layer muscle fibres, which initiate masticatory movement, myosin heavy chain isoforms were evaluated based on immunohistochemistry at the transcription level in male mice both before and after weaning. In the results, MHC-2b isoforms, the isoforms with the fastest contraction speed, were observed in the superficial layer after weaning. However, MHC-2a isoforms with slower contraction speeds were not apparent. By contrast, in the deep layer, MHC-2a isoforms were present, as were MHC-2b isoforms, however, there were fewer MHC-2b isoforms present than in the superficial layer. The most rapid movement in the mouse mandible was observed anteroposteriorly during mastication. As the superficial layer of the masseter muscle runs parallel to the direction of mandibular movement, the presence of MHC-2b isoforms in it is consistent. The presence of MHC-2a isoforms in the deep layer, lying at right angles to the direction of mastication movement, is consistent with the positional adjustment of the mandible contributed by the deep layer muscle fibres during masticatory movement. We therefore conclude that complicated masticatory movement is achieved by the presence of various muscle bundles within the masseter, each carrying out different roles.

Animals↗
PubMed2006

DNA/Poly(p-aminobenzensulfonic acid) composite bi-layer modified glassy carbon electrode for determination of dopamine and uric acid under coexistence of ascorbic acid.

A nano-composite of DNA/poly(p-aminobenzensulfonic acid) bi-layer modified glassy carbon electrode as a biosensor was fabricated by electro-deposition method. The DNA layer was electrochemically deposited on the top of electropolymerized layer of poly(p-aminobenzensulfonic acid) (Pp-ABSA). Scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical impedance spectrum were used for characterization. It demonstrated that the deposited Pp-ABSA formed a 2-D fractal patterned nano-structure on the electrode surface, and which was further covered by a uniform thin DNA layer. Cyclic voltammetry and electrochemical impedance spectrum were used to characterize the deposition, and demonstrated the conductivity of the Pp-ABSA layer. The biosensor was applied to the detection of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). In comparison with DNA and Pp-ABSA single layer modified electrodes, the composite bi-layer modification provided superior electrocatalytic actively towards the oxidation of DA, UA and AA, and separated the originally overlapped differential pulse voltammetric signals of UA, DA and AA oxidation at the bare electrode into three well-defined peaks at pH 7 solution. The peak separation between AA and DA, AA and UA was 176 mV and 312 mV, respectively. In the presence of 1.0 mM AA, the anodic peak current was a linear function of the concentration of DA in the range 0.19-13 microM. The detection limit was 88 nM DA (s/n=3). The anodic peak current of UA was also a linear function of concentration in the range 0.4-23 microM with a detection limit of 0.19 microM in the presence of 0.5 mM AA. The superior sensing ability was attributed to the composite nano-structure. An interaction mechanism was proposed.

Ascorbic Acid↗
PubMed2005

A three-layered nano-carbonated hydroxyapatite/collagen/PLGA composite membrane for guided tissue regeneration.

Functional graded materials (FGM) provided us one new concept for guided tissue regeneration (GTR) membrane design with graded component and graded structure where one face of the membrane is porous thereby allowing cell growth thereon and the opposite face of the membrane is smooth, thereby inhibiting cell adhesion in periodontal therapy. The goal of the present study was to develop a three-layered graded membrane, with one face of 8% nano-carbonated hydroxyapatite/collagen/poly(lactic-co-glycolic acid) (nCHAC/PLGA) porous membrane, the opposite face of pure PLGA non-porous membrane, the middle layer of 4% nCHAC/PLGA as the transition through layer-by-layer casting method. Then the three layers were combined well with each other with flexibility and enough high mechanical strength as membrane because the three layers all contained PLGA polymer that can be easily used for practical medical application. This high biocompatibility and osteoconductivity of this biodegraded composite membrane was enhanced by the nCHAC addition, for the same component and nano-level crystal size with natural bone tissue. The osteoblastic MC3T3-E1 cells were cultured on the three-layered composite membrane, the primary result shows the positive response compared with pure PLGA membrane.

Animals↗
PubMed2007

The construction of three-dimensional micro-fluidic scaffolds of biodegradable polymers by solvent vapor based bonding of micro-molded layers.

It is increasingly important to control cell growth into and within artificial scaffolds. Tissues such as skin, blood vessels, and cartilage have multi-layer structures with different cells in each layer. With the aid of micro-fabrication technology, a novel scaffolding method for biodegradable polymers such as polylactic acid (PLA), polyglycolic acid (PGA), and the copolymers poly(lactide-co-glycolide)(PLGA), was developed to construct three-dimensional multi-layer micro-fluidic tissue scaffolds. The method emphasizes micro-fluidic interconnections between layers within the scaffolds and maintenance of high-resolution geometries during the bonding process for the creation of multi-layered scaffolds. Micro-holes (10-100 microm), micro-channels, and micro-cavities were all created by micro-molding. Solvent-vapor based bonding of micro-molded layers preserved 20 microm sized structures. Sample scaffolds were constructed for purposes such as channel-directed cell growth and size-based cell sorting. Further extension of these techniques to create a micro-vascular network within or between layers is possible. Culturing of human coronary artery endothelial cells (HCAECs) on the sample scaffolds demonstrated the biocompatibility of the developed process and the strong influence of high-resolution micro-geometries on HCAEC growth.

Absorbable Implants↗
PubMed2006

Differential expression of neuregulins and their receptors in the olfactory bulb layers of the developing mouse.

Neuregulins (NRGs), and their cognate receptors (ErbBs), play essential roles in numerous aspects of neural development and adult synaptic plasticity. The goal of this study was to investigate the developmental expression profiles of these molecules during the olfactory bulb (OB) maturation. The OB is a highly organized structure with cell types and synaptic connections segregated into discrete anatomical layers. We employed a novel approach by combining single-layer microdissection at different development ages, with isoform-specific semi-quantitative RT-PCR and Western blotting to monitor layer-specific developmental profiles of these molecules and alternate splice variants. Layer and age specific regulation was observed for the ErbB4 splice variants JMa/JMb and NRG-1-beta1/beta2 forms. With the exception of the outermost (nerve) layer, ErbB4-JMb and NRG-1-beta1 are expressed throughout the OB and their expressions decrease in the adult age in most layers. In contrast both ErbB4-JMa and NRG-1-beta2 are highly expressed in the granule cell layer in the early postnatal OB. This early postnatal expression correlates with the dramatic change from radial glia to astrocytes and appearance of the bulk of granule cells occurring at this developmental stage.

Age Factors↗
PubMed2006

Protein adsorption and stability of poly(ethylene oxide)-modified surfaces having hydrophobic layer between substrate and polymer.

The materials covered with poly(ethylene oxide) (PEO) are of use in a wide variety of biomaterials due to blood compatibility of this polymer. The long-term sustainability of its blood compatibility strongly depends on the stability of the PEO layer against aqueous environment. An attempt was made in the present work to immobilize a PEO layer on the silicon surfaces using a silane coupling agent with the aim to improve the waterproof durability of the layer. Several kinds of PEO-modified substrates having a densely and closely packed hydrocarbon layer between substrate and PEO layer were prepared and the stability of the PEO layer against phosphate buffer saline (pH 7.4) was examined in terms of the density of hydrocarbon chains. Those substrates which have a dense hydrophobic chain layer showed a high waterproof durability and a good ability to suppress protein adsorption.

Adsorption↗
PubMed2005

The difficulty in the assessment of the compression behaviour of powder mixtures: Double layer tablets versus arithmetic additivity rule.

The weighted arithmetic mean from values of a feature derived from the individual components is often used to calculate the theoretically expected compression behaviour of powder mixtures if no interparticulate interactions between the components occur. Alternatively, simulated and experimental double layer tablets are presented. The suitability of the various methods to serve as a reference for the assessment of the compression behaviour of powder mixtures shall be compared. Narrow and similar sieve fractions of maltitol and metamizol were mixed in various ratios of true volumes. Constant total true volumes of the single substances, powder mixtures, and layered powders of the same composition were compressed on an eccentric tabletting machine to a constant maximum geometric mean punch force. In addition, the compression of double layer tablets was mathematically simulated from the dynamic relative density-force data of the pure materials. At a given momentary force, the relative density of a simulated double layered powder bed is given by the harmonic mean of the relative density values of the pure materials weighted by their true volume fractions. The results show that the total, the net, and the expansion work change indeed almost linearly with the true volume fraction of the components in the double layer tablets, with the consequence that the plasticity index (=net work/total workx100) proceeds non-linearly. The slope of the Heckel plot 'at pressure' and the apparent mean yield pressure obtained from these Heckel data are non-linearly related to the true volume fraction. If the weighted arithmetic mean is used to analyse the compression behaviour of the powder mixtures, results are obtained which are incompatible or even contradictory between interrelated features. On the other hand, the double layer model provides a consistent evaluation. A good agreement between the results of the experimental and the simulated double layer tablets is found.

Algorithms↗
PubMed2005

Development of an enteric-coated, layered multi-particulate formulation for ileal delivery of viable recombinant Lactococcus lactis.

Layering of recombinant hIL-10 producing Lactococcus lactis (L. lactis Thy12) on inert carriers is a promising technique for the preparation of a multi-particulate formulation of viable, hIL-10 producing L. lactis. To improve viability after layering and storage, L. lactis Thy12 was layered in different matrices (10% skim milk and/or 2.5, 5, 10% inulin). After layering, the highest viability was obtained in the 10% skim milk supplemented with 5% inulin matrix (8.7%). However, upon storage, 10% skim milk alone yielded the highest viability. Thereby, layered L. lactis Thy12 showed superior long term stability in comparison with freeze-dried L. lactis Thy12. The layering process was performed during 3h without encountering technical problems, with good layer consistence and constant viability. Enteric properties were obtained with a 30% Eudragit L30D-55 or 15% Eudragit FS30D coating and maintained during an initial six months storage period (-20 degrees C/20% RH). After in vitro simulation of the gastric stage, only 5% of the bacteria remained viable in Eudragit L30D-55 coated pellets, contrary to 85% in Eudragit FS30D coated pellets, indicating its superior protective capacity against gastric fluid. After eight months storage (-20 degrees C), 80% of the initial L. lactis Thy12 remained viable in the Eudragit FS30D coated pellets.

Chemistry, Pharmaceutical↗
PubMed2004

Development and evaluation of the tablets coated with the novel formulation termed thin-layer sugarless coated tablets.

The purpose of this study was to develop and evaluate the thin-layer sugarless coated tablets containing Vitamin C, Vitamin E, Vitamin B2, calcium pantothenate, and L-cysteine. As a result of the formulation study, three coating layers, 2% under coating (UC), 38% build-up coating (BC), and 5% syrup coating (SC) were necessary for sufficient impact toughness, elegant appearance, and improvement of appearance stability after storage at 25 degrees C/75% RH for 6 months under open conditions. We demonstrated that the thin-layer sugarless coated tablets are superior to the sugar-coated tablets in terms of small tablet size and stability of calcium pantothenate. It was due to the coating method, the continuous spray mist method, which can minimize the thicknesses of coating layers and the moisture content in the tablets. We also demonstrated that the thin-layer sugarless coated tablets are superior to the film-coated tablets in terms of masking ability of the unpleasant odor and the appearance, stability of the appearance, and low hygroscopicity. It was due to the dense, opaque, and stable coating layers mainly consist of erythritol. We revealed that thin-layer sugarless coated tablets have both advantages of film-coated tablets and sugar-coated tablets.

Dietary Supplements↗
PubMed2005

Development of three layered buccal compact containing metoprolol tartrate by statistical optimization technique.

The objective of this work to evaluate the effect of formulation variables on release properties and bioadhesive strength in development of three layered buccal compact containing highly water-soluble drug metoprolol tartrate (MT) by statistical optimization technique. Formulations were prepared based on rotatable central composite design with peripheral polymer ratio (carbopol 934P: HPMC 4KM) and core polymer ratio (HPMC 4KM: sodium alginate) as two independent formulation variables. The three layered buccal compact comprises a peripheral layer, core layer and backing layer. Four dependent (response) variables were considered: bioadhesion force, percentage MT release at 8 h, T50% (time taken to release 50% of drug) and release exponent (n). The release profile data was subjected to curve fitting analysis for describing the release mechanism of MT from three layered buccal compact. The main effects and interaction terms was quantitatively evaluated by quadratic model. The decrease in MT release was observed with an increase in both the formulation variables and as the carbopol: HPMC ratio increases the bioadhesive strength also increases. The desirability function was used to optimize the response variables, each having a different target and the observed responses were highly agreed with experimental values. The results demonstrate the feasibility of the model in the development of three layered buccal compact containing highly water-soluble drug MT.

Administration, Buccal↗
PubMed2004

A triple-layer model of the surface electrochemical properties of clay minerals.

We propose an electrical triple-layer model (TLM) to describe the electrochemical properties of clay minerals. This model includes a speciation model of the active crystallographic surface sites plus a classical description of the Stern and diffuse layers. In addition to the surface charges associated with the surface groups (aluminols, silanols, and Al--O--Si sites), the model takes into account the degree of isomorphic substitution rate inside the crystalline network. The model computes both the zeta potential and the low-frequency (few kHz) surface conductivity as these two properties are equally important to interpret electrokinetic properties of colloids and clay-rich porous materials. For surface conductivity, the model comprises two contributions; one is associated with the Stern layer (dynamic Stern layer) and the second is associated with the excess of counterions located in the diffuse Gouy-Chapman layer. The parameters of the TLM model are optimized using the Simplex algorithm. Comparison between the model and the experimental data shows good agreement for a reasonable choice of parameters close to the a priori values determined from quartz and gibbsite. Surface conductivity of smectite appears rather independent of salinity, while for kaolinite, surface conductivity increases with salinity. In both cases, the Stern layer contribution to surface conductivity dominates but the contribution associated with the diffuse layer cannot be neglected.

Journal Article↗
PubMed2004

Synthesis and characterization of tri(ethylene oxide)-attached poly(amidoamine) dendrimer layers on gold.

This paper describes the synthesis of a tri(ethylene oxide)-attached fourth-generation poly(amidoamine) dendrimer (EO3-dendrimer) and the characterization of its layers on gold. NMR analysis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed that about 61 amine groups of a G4 PAMAM dendrimer were covalently conjugated with tri(ethylene oxide) units, accounting for a 95% modification level. Layers of the EO3-dendrimer were formed on gold, and the resulting surface was characterized by infrared reflection absorption spectroscopy, ellipsometry, and contact angle goniometry. The EO3-dendrimer resulted in more hydrophilic and less compact layers with no substantial deformation of the molecule during layer formation by virtue of the EO3 units, compared to a PAMAM dendrimer. Interestingly, the specific binding of avidin to the biotinylated layers of the EO3-dendrimer approached a surface density of 5.2 +/- 0.2 ngmm-2, showing about 92% of full surface coverage. The layers of the EO3-dendrimer were found to be more resistant to nonspecific adsorption of proteins than PAMAM dendrimer layers when bovine serum albumin and serum proteins were tested.

Adsorption↗
PubMed2005

Effect of SiO2 coating layer morphology on TiH2 gas release characteristic.

In this study, a uniform and compact SiO2 film-coating layer was prepared on the surface of TiH2 particles by sol-gel method using inexpensive raw materials. The preparation process of SiO2-coated TiH2 particles and the effect of the coating layer morphology on the gas release characteristic were investigated in detail. When the pH value of TiH2 suspending solution is about 4.0 and the concentration of silicic acid is more than 0.5 mol/L, the coating layer shows a SiO2 particle-coating morphology. While a homogeneous and dense film-coating layer can be obtained when the solution pH value and concentration of silicic acid are about 4.0 and 0.5 mol/L. The results of gas release at 700 degrees C show that TiH2 particles coated with silicon dioxide layers can efficiently delay the starting time of gas release of TiH2 powders to 60-100 s. Comparing the particle-coating layer, the SiO2 film-coating layer has a better delaying effect on gas release of TiH2 particles.

Journal Article↗
PubMed2006

The effect of the layer structure on the activity of immobilized enzymes in ultrathin films.

The molecular engineering capability of the layer-by-layer (LbL) method for fabricating thin films has been exploited in order to immobilize glucose oxidase (GOD) in films with alternating layers of chitosan. Chitosan was proven a good scaffolding material, as GOD molecules preserved their catalytic activity towards glucose oxidation. Using electrochemical measurements, we showed that chitosan/GOD LbL films can be used to detect glucose with a limit of detection of 0.2 mmol l-1 and an activity of 40.5 microA mmol-1 L microg-1, which is highly sensitive when compared to other sensors in previous reports in the literature. The highest sensitivity of the LbL film was achieved when only the top layer contained GOD, thus indicating that GOD in inner layers did not contribute to glucose oxidation, probably because it hampers analyte diffusion and electron transport through the deposited layers. This may be explained by the dense packing of GOD molecules in the LbL films with chitosan, as inferred from estimates of the amount of GOD adsorbed per layer using a quartz crystal microbalance.

Aspergillus niger↗