1,721,054 research outputs found
Functional heterogeneity of periglomerular cells in the rat olfactory bulb
No full textThe periglomerular cells of the rat olfactory bulb, a virtually unknown population of interneurons, have been studied applying the whole-cell patch-clamp technique to thin slices. A prominent result, obtained under current-clamp conditions, is that these cells appear to be functionally heterogeneous, and show distinct excitability profiles. Voltage-clamp analysis allows the identification of the ionic basis of these differences and suggests a division into at least two classes, based on the characteristics of the K+ conductances. The first group displays two K+ conductances (delayed rectifier, gKV, and fast transient, gA) of similar amplitude, and under current-clamp conditions shows the usual outward rectifying behaviour at depolarized potentials. The second group has a large gA, and a small or absent gKV. Consequently, following sustained depolarizations under current-clamp conditions leading to inactivation of gA, these neurons do not show any sign of outward rectification and behave as ohmic elements, as normally observed only at hyperpolarized potentials. The transition ion zinc (10-300 microM) affects gA but not gKV The inactivation process (steady-state curve and rate constant) is strongly altered by Zn2+, the activation process less so; open-channel conductance is not affected. The Zn2+ effect is unlikely to be due to surface charge screening or to a mechanism involving channel block. In view of the substantial presence of zinc ions in the olfactory nerve terminals, its actions on the A-current could be of some relevance for physiological function
Thermo-Mechanical Properties of Injection Molded Components Manufactured by Engineered Biodegradable Blends
No full textEngineering of ductile, tough and thermal resistant PLA-based materials requires blending of PLA with other constituents by reactive twin-screw co-rotating extrusion to achieve compounds with adequate thermo-mechanical properties. Then, the compound of the polymeric blends must be melt processed to the final shape with an additional technology, namely the injection molding. The two-stage process the polymeric blends must undergo and the different rheological properties the blends must feature to be suitable to the different processing steps make extremely difficult to engineer the material. Extrusion compounding requires high viscous materials low melt flow index (MFI), while injection molding requires materials with low viscosity (high MFI). To overcome these shortcomings, this manuscript deals with the design of novel biodegradable PLA-based blends that rely on mixing PLA grades with different MFI (i.e. very low for extrusion and high for injection molding), each chosen to feature the rheological characteristics needed for each step of the two-stage transformation process. The ratio of the two PLA-grades inside the blends was the matter of the present investigation. The blends were subsequently tested for the manufacturing of single-use biodegradable and thermal resistant injection molded small cups, specifically designed for brewing of hot beverages. Lastly, the thermo-mechanical performance of the as-is and annealed cups were studied. Experimental evidences show blending of two-different grades of PLA is a promising route to formulate low impact polymeric materials suitable for demanding packaging solutions
Sodium current in periglomerular cells of rat olfactory bulb in vitro
No full textThe capacity of periglomerular cells (PGc) to give fast, Na-dependent action potentials is a crucial and debated issue for the comprehension of how sensory information is processed in the olfactory bulb (OB). Using patchclamp whole cell recording in thin slices of rat OB (P8-P20) we showed that fast sodium conductance is present in all the PGc studied, that this current is sufficiently large to generate action potentials and that action potentials can be evoked in these cells by direct stimulation of the olfactory nerve. A comprehensive kinetic characterization of INa is also presented
NMDA-dependent, network-driven oscillatory activity induced by bicuculline or removal of Mg2+ in rat olfactory bulb neurons
No full textSpontaneous, low-frequency voltage oscillations (LFOs) were observed in the neurons of rat olfactory bulb upon disinhibition with GABAA antagonists and/or removal of Mg2+ from external saline. Ordinarily, LFOs presented a highly organized temporal structure, with bursts recurring regularly at about 0.05 Hz. Slow depolarizing shifts with similar frequencies were observed in all types of bulbar neurons. Simultaneous recordings from mutually independent neurons showed that LFOs were highly synchronized in distinct cells. The occurrence of LFOs was prevented by NMDA, but not AMPA/kainate, receptor antagonists. The oscillations were also halted by Ca2+ antagonists and tetrodotoxin. The pace of the oscillations was reset by stimulation of the olfactory nerve but not by direct injection of depolarizing current into the oscillating cell. Removal of the outer portion of the slice with a cut along the external plexiform layer provided crucial evidence that the bursting activity first initiated in the glomerular region and propagated synaptically downstream towards the inner layers, suggesting an organizing role for olfactory glomeruli
Thermoforming of compostable PLA/PBS blends reinforced with highly hygroscopic calcium carbonate
No full textMineral fillers have always been used in engineered polymers to reduce the cost, promote the thermal and dimensional stability of the material, and contain its shrinkage and deformations generated by the conversion processes. Compounds based on compostable polymers are normally characterized by the presence of high levels of mineral fillers (up to 30 %), although mineral fillers with a limited ability to incorporate moisture are preferred. The bioplastic compounds are, in fact, based mainly on bio-derived polyesters, highly sensitive to hydrolytic degradation at high temperatures. Therefore, in the design of bioplastic compounds, the moisture content is kept strictly under control to avoid the onset of degradation mechanisms. Calcium carbonate is, however, the cheapest mineral filler and is broadly available on the market. It is the most widely used mineral filler in the design of engineered polymers based on polyolefins and polystyrenes. However, the use of calcium carbonate in the bioplastic compound segment is severely limited by the hygroscopicity of the carbonate. In this context, the use of calcium carbonate was studied, as a reinforcement element of binary blends between polylactic acid (PLA) and polybutylene succinate (PBS). In particular, the role of the percentage of the mineral filler on the absorption of moisture in the compound has been studied. The thermo-rheological properties of the compound were also evaluated. Finally, the processability of the compound was studied in the thermoforming process of containers suitable for food contact on a prototype system (machine - mold), specifically designed to transform polyolefins. Experimental results have shown that a correct design of the bioplastic compound, even in the presence of a highly hygroscopic filler, can allow the development of a material suitable for the thermoforming process, without the need to make changes to the conversion plant and to the mold
Inhibitory synapses among interneurons in the glomerular layer of rat and frog olfactory bulbs
No full textThe patch-clamp technique was applied to periglomerular (PG) cells from slices of frog and rat olfactory bulbs to characterize whole cell and single-channel properties of inhibitory synaptic currents. Spontaneous and electrically driven bicuculline-sensitive synaptic events were recorded under ionic conditions that excluded any possible interference of excitatory synapses. The peak amplitude distribution of spontaneous events could be fitted by several Gaussians having the same interpeak distance. Spontaneous currents reversed polarity at the chloride equilibrium potential and were suppressed by 2 mM Co2+; the decay phase could be fitted with a single exponential having a time constant of approximately 10 ms at 0 mV. Bicuculline-sensitive monosynaptic responses could be evoked in PG cells by electrical stimulations delivered at the distance of several glomeruli within the glomerular layer. Finally, in excised outside-out patches, single-channel analysis revealed the presence of typical gamma-aminobutyric acid-A receptor channels, with a single-channel conductance of 28 pS in symmetrical chloride and mean open times of 3-4 ms. The simplest explanation of these data, effectively supported by pristine anatomic findings, is that there could be inhibitory contacts among interneurons in the glomerular layer
Extrusion blow molding of environmentally friendly bottles in biodegradable polyesters blends
No full textIncreasing awareness of the environmental impact of oil-relying plastic materials is prompting Academia and manufacturing industry to develop eco-friendly materials and alternative technological solutions. Blown bottles and containers represent a significant share of the worldwide plastic market and great environmental concern is arising about their disposal. Generally, blown plastic bottles are made of three different materials: (i) a cap manufactured from High Density Polyethylene (HDPE), (ii) a bottle body manufactured from Polyethylene Terephthalate (PET), (iii) a label manufactured from printed Low Density Polyethylene (LDPE). The disposal of blown bottles requires, therefore, the separation of the different materials and, then, their individual recovery. An eco-friendly alternative to multi-material blown bottles is the development of a bottle entirely made from a biodegradable polymeric blend, designed to be suitable for manufacturing both the cap, the bottle body and the label. In this framework, the present manuscript deals with the design and development of novel biodegradable blends based on bio-based polyesters. The blends are herewith specialized for extrusion blow molding of the bottle body, although they could be further customized for both the cap and the label. Twin-screw co-rotating extrusion of the compounds, extrusion blow molding of the compounds for bottle manufacturing and the evaluation of the thermo-physical and mechanical properties of the bottles are hereinafter reported. The novel polymeric blends are found to be suitable for extrusion blow molding of the bottle body, also exhibiting valuable performances in terms of mechanical strength and impact resistance as well as protection against gas permeation and light transmission
Graphene reinforced UV-curable epoxy resins: Design, manufacture and material performance
No full textGraphene and its derivatives (graphene oxide, reduced graphene, functionalised graphene oxide, and functionalised reduced graphene oxide) are found to improve the mechanical properties of the polymers in which they are dispersed. In the present work, the potential of graphene and its derivatives in terms of their anti-scratch performance is thus investigated. In particular, graphene oxides, as-is graphene nano-platelets and reduced graphene oxides that were functionalised with amino-propyl triethoxy silane (APTES) were blended as reinforcing phases in UV curable epoxy coatings on polycarbonates, and the resulting performances were comparatively evaluated. Additionally, UV curable epoxy coatings covalently bonded to amino-functionalised silica-nanoparticles were studied.The experimental analyses involved FT-IR spectroscopy to study the chemical interactions that occurred among the different compounds in the investigated mixtures, progressive and constant load scratch tests and SEM images of the residual scratch patterns to evaluate the micro-mechanical response and scratch visibility of the coatings. APTES-functionalised reduced-graphene oxide was found to be able to reduce the scratch visibility, thus revealing its suitability to promote the effective anti-scratch properties of UV-curable bis cyclo-aliphatic epoxy resins deposited on polycarbonate. © 2015 Elsevier B.V
Advances in design and manufacturing of environmentally friendly and biocide-free antifouling/foul-release coatings: replacement of fluorinate species
No full textAmphiphilic coatings are nowadays described as the most promising strategy for the achievement of an effective and eco-friendly antifouling marine paint, based on a physical principle. Nevertheless, most of the preparations imply the introduction of fluorinate chemicals for the formation of the hydrophobic moieties, which are potentially toxic for the marine environment in the case of an accidental release. The present work evaluates the possibility of removing fluorinate species for the implementation of such coatings and their replacement with analogous long-alkyls. In particular, this work presents an easily implementable procedure for the manufacturing of an amphiphilic system that exploits the reactivity of a commercially available –OH-rich hybrid polysiloxane resin. The resin was first modified through sol–gel chemistry that was used in the grafting of a silane-bearing hydrophobic long-alkyl chain, while the introduction of the hydrophilic moieties was conducted contextually to the curing process, through the reaction with a commercially available PEG-ilate isocyanate hardener. The effective persistence of the amphiphilic character with respect to the replacement of the fluorinate silane by the alkylsilane was ensured by the measurement of the hysteresis contact angle. The effectiveness of the persistence of the antifouling/foul-release properties was assessed through testing against the adhesion and deposition of egg white, as a proteinaceous probe, Mytilus edulis (mussel) and Ulva intestinalis (algae). All the tests indicated that the amphiphilic coating prepared from long-alkyl silane performed even better than fluorinate silane-containing samples in this hybrid coating system resulting from the fusion of a xerogel and a resin. The results suggested that the use of a long alkyl silane was an effective alternative to the use of potentially noxious fluorinate silanes, with advantages that boost the ecological benefits and also include the performance of the coating
Graphene-modified poly(lactic acid) for packaging: Material formulation, processing and performance
No full textManufacturing of plastics by compostable polymers is of crucial relevance to limit the environmental impact and reduce oil consumption. Performance of compostable polymers is often mediocre, although they could be improved by physical and chemical routes. In this work, Poly(Lactic Acid) (PLA) is modified for improved performance by two different routes: (1) by physically dispersing Graphene Nano-Platelets (GNP) in the organic matrix; (2) by the physical dispersion and covalent bonding of PLA and Amino-Functionalized Nano-Silica (A-fSiO2). Functionalization of the PLAs after compounding and pelletizing was assessed by combined Fourier Transform Infrared (FT-IR). In addition, thermal analysis was performed by Differential Scanning Calorimetry (DSC). Mechanical response was evaluated on compression molded flat slabs of the modified PLAs by Pencil and progressive and constant load scratch tests. Chemical endurance was evaluated on compression molded flat slabs of the modified PLAs by dipping in aggressive acidic, basic, and saline environments. Finally, the modified PLAs were successfully injection molded to manufacture high performance coffee capsules, whose thermal stability and suitability to coffee brewing were demonstrated. © 2015 Wiley Periodicals, Inc
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