Plantain fibre bundles isolated from Colombian agro-industrial residues

Comestible fruit production from Musaceas plants is an important economical activity in developing countries like Colombia. However, it generates a large amount of agro-industrial residues. Some of them are a potential resource of natural fibres, which can be used as reinforcement for composite materials. In this work, a series of commercial plantain (Musa AAB, cv "Dominico Harton") fibre bundles extracted from pseudostem, leaf sheath and rachis agricultural wastes were analyzed. Mechanical decortication and biological retting processes were used during fiber extraction. No significant differences in composition of vascular bundles were observed for both extraction processes. Gross morphological characteristics and mechanical behavior have been evaluated. Conducting tissues with spiral-like arrangement are observed attached to fibre bundles. This fact suggests a big amount of these tissues in commercial plantain plants. Both used extraction methods are not enough to remove them. Pseudostem fibre bundles have higher specific strength and modulus and lower strain at break than leaf sheath and rachis fibre bundles, having values comparable to other lignocellulosic fibres bundles.     

Imaging cellulose fibre interfaces with fluorescence microscopy and resonance energy transfer

Future developments in cellulosic materials are predicated by the need to understand the fundamental interactions that occur at cellulose fibre interfaces. These interfaces strongly influence the material properties of fibre networks and fibre reinforced composites. This study takes advantage of fluorescence resonance energy transfer (FRET) and fluorescence microscopy to image cellulose interfaces. Steady-state epi-fluorescence microscopy suggests that energy transfer from coumarin dyed fibres to fluorescein dyed fibres is occurring at the fibre–fibre interface. The FRET response for natural spruce fibre interfaces is distinctly different from that observed in synthetic viscose fibres. This approach constitutes a novel methodology for the characterization of soft material interfaces on the molecular scale, and represents a major opportunity for advancing the understanding of fibrous network structures.     

Visualization of satellite cells in living muscle fibres of the frog

Satellite cells were visualized in living muscle fibres of the frog. Single fibres or bundles consisting of a few fibres were isolated after treatment with collagenase, and viewed under the light microscope. Subsequent electron microscopy of identified cells confirmed that they were satellite muscle cells. Under the light microscope, satellite cells appear as fusiform cells, tapering into long fine processes usually orientated parallel to the muscle fibre axis. Horseradish peroxidase injected into the muscle fibre was not transferred to the satellite cells.     

The structure of the scales of Latimeria chalumnae

Scales from four specimens of Latimeria chalumnae were examined in a dissecting microscope and then X-rayed. Some were demineralized and prepared for routine histology. Others were cleared in cedarwood oil. Ground sections of plastic embedded scales were micro-radiographed and electronmicrographs made of araldite embedded frozen scales. Corresponding 1 μm thick serial sections were examined in the light microscope.
The greater part of the scale is composed of layers of unmineralized isopedine surmounted by the exposed portion of the scale which is pigmented and ornamented by a series of denticles of tubular dentine tipped with enameloid. Between these two parts is a thin ridged bone-like layer. In the electron micrographs the isopedine was seen to consist of layers of densely packed collagen fibres; the orientation of which was uniform in each layer but varied markedly from layer to layer. Only few cells were found between the fibre bundles.
The X-rays revealed numerous concentric annulae and, lying approximately at right angles to these, a further series of ridges radiating from the centre of the scales.
It is suggested that the basal unmineralized isopedine and the ridged layer of bone-like tissue covering it represents a highly modified cosmoid scale on which the denticles and pigmented layer have become superimposed.     

Vascular-nervous relationships in the valves of the heart]

Method of silver nitrate impregnation was used in order to study 50 preparations of not-changed atrioventricular valves of the heart of domestic bulls and 30 preparations of the same valves of adult humans. It has been shown that in heart valves there are certain relationships between striated muscle fibres, blood vessels and nerve elements. The nerve structures of the valves are represented by nerve bundles of different thickness. In their composition there are comparatively thin non-myelinated and thicker myelinated fibres. Towards the free edge of cusps the nerve bundles become thinner and the nerve trunks give off separate thin nerve fibres disposed along the vessels of a capillary type and in some places getting around them. In certain portions of cusps the nerve bundles, some of which have zigzag sinuosity, cross blood vessels in different directions. In man the major mass of blood vessels and nerve elements are disposed near the base of the valve cusps, accompanying the muscle fibre bundles penetrating from the base side. In the bull heart valves an amount of blood vessels and nerve elements is found in considerable portions of the cusps not connected with muscle fibres.     

Myosin-ATPase fibre typing of chemically skinned muscle fibres

Summary The efficacy of myosin (M)-ATPase fibre typing to differentiate fibre types in chemically (EGTA) skinned muscle fibres was investigated. Cryosections or single fibres from isolated bundles of chemically skinned rat extensor digitorum longus (EDL) and soleus (SOL) muscles were stained for M-ATPase activity. The results indicate that two major fibre types (type I and II, Brooke & Kaiser, 1970) can be indentified, as well as subgrouping of the type II fibres into types IIa and IIb. Thus, chemically skinning muscle fibres appears to have no detrimental effects on subsequent M-ATPase fibre typing.     

Electron microscopy of neurosecretory nerve fibres in the neural lobe of the embryonic mouse

Summary Nerve fibres of the neurosecretory hypothalamo-hypophyseal tract were studied in embryonic C3H mouse neural lobes; at least four glands at each gestational day 15–19 were examined.Single axons and small bundles of fibres are visible at gestational days 15 and 16. By day 17 large fibre bundles penetrate between glial cells. They increase in number during the next two days.Electron-lucent and electron-dense vesicles are seen in the fibres of the 15th and 16th gestational days. In the 17–19 day-old embryos development is characterized by a successive rise in the number of the two types of vesicles. The mean diameter of the electron-lucent vesicles is approximately unchanged in all the stages examined (50 nm). The electron-dense vesicles increase in size from approximately 80–90 nm at days 15–16 to 140 nm at the 19th gestational day.By day 19 contacts between neurosecretory fibre terminals and the outer basement membrane of internal and peripheral capillaries are occasionally observed. The possibly adrenergic nature of a few terminals contacting peripheral vascular structures in 17 and 18 day-old embryos is suggested.This investigation was supported by grant No. 2180-020 from the Swedish Natural Science Research Council. The skilful technical assistance of Mrs. Ulla Wennerberg is gratefully acknowledged.     

The fin musculature of cuttlefish and squid (Mollusca, Cephalopoda): morphology and mechanics

The lateral fins of cuttlefish and squid consist of a tightly packed three-dimensional array of musculature that lacks bony skeletal support or fluid-filled cavities for hydrostatic skeletal support. During swimming and manoeuvring, the fins are bent upward and downward in undulatory waves. The fin musculature is arranged in three mutually perpendicular planes. Transverse muscle bundles extend parallel to the fin surface from the base of the fin to the fin margin. Dorso-ventral muscle bundles extend from dorsal and ventral connective tissue fasciae to a median connective tissue fascia. A layer of longitudinal muscle bundles is situated adjacent to both the dorsal and ventral surface of the median fascia. The muscle fibres are obliquely striated and include a core of mitochondria. A zone of muscle fibres with a more extensive core of mitochondria is present in both the dorsal and the ventral transverse muscle bundles. It is hypothesized that these muscle masses include two fibre types with different aerobic capacity. A network of connective tissue fibres is present in the transverse and dorso-ventral muscle masses. These fibres, probably collagen, are oriented at 45 to the long axes of the transverse and dorsoventral muscle fibres in transverse planes.
A biomechanicayl analysis of the morphology suggests that support for fin movements is provided by simultaneous contractile activity of muscles of specific orientations in a manner similar to that proposed for other 'muscular-hydrostats'. The musculature therefore provides both the force and support for movement. Connective tissue fibres may aid in providing support and may also serve for elastic energy storage.     

Effects of Na-octanoate on potassium contractures in normal and denervated frog tonic fibres

In frog twitch muscle fibres, Na-octanoate (NaC8) shifted the relation between potassium induced tension and membrane potential to the right. The present study has been carried out to investigate the effect of this fatty acid on frog tonic fibres. Potassium contractures measured on bundles of 30-40 fibres of ileofibularis muscles were less decreased by NaC8 (2.5-10 mmol/l) than those of twitch fibre bundles. In denervated muscles the sensitivity to NaC8 was increased, probably due to the development of sodium channels in the membranes. Experiments with mixed fibre bundles also showed a lower influence of NaC8 on potassium contracture of tonic fibres. On the other hand, tonic fibres showed a lower threshold of the potassium induced tension as well as a lower K+ concentration for maximal activation. This lower threshold was further lowered by NaC8, corresponding to a shift of the relation between potassium concentration and tension to the left. The membrane resting potentials were -58 +/- 9 mV in tonic fibres and -83 +/- 5 mV in twitch fibres. Five mmol/l NaC8 only induced depolarization of the membrane of tonic fibres. This depolarization (by about 20 mV) may be responsible for the threshold shift to lower K+ concentration in NaC8-exposed tonic fibres. In addition to the effects of NaC8 on sodium channels, interactions with Ca2+ binding sites are discussed.     

Enhanced Compliant Adhesive Design and Fabrication with Dual-Level Hierarchical Structure

<正> Synthetic dry adhesives inspired by the nano-and micro-scale hairs found on the feet of geckos and some spiders have beendeveloped for almost a decade. Elastomeric single level micro-scale mushroom shaped fibres are currently able to function evenbetter than natural dry adhesives on smooth surfaces under normal loading. However, the adhesion of these single level syntheticdry adhesives on rough surfaces is still not optimal because of the reduced contact surface area. In nature, contact area ismaximized by hierarchically structuring different scales of fibres capable of conforming surface roughness. In this paper, weadapt the nature's solution arid propose a novel dual-level hierarchical adhesive design using Polydimethylsiloxane (PDMS),which is tested under peel loading at different orientations. A negative macro-scale mold is manufactured by using a laser cutterto define holes in a Poly(methyl methacrylate) (PMMA) plate. After casting PDMS macro-scale fibres by using the obtainedPMMA mold, a previously prepared micro-fibre adhesive is bonded to the macro-scale fibre substrate. Once the bondingpolymer is cured, the micro-fibre adhesive is cut to form macro scale mushroom caps. Each macro-fibre of the resulting hierarchicaladhesive is able to conform to loads applied in different directions. The dual-level structure enhances the peel strengthon smooth surfaces compared to a single-level dry adhesive, but also weakens the shear strength of the adhesive for a given areain contact. The adhesive appears to be very performance sensitive to the specific size of the fibre tips, and experiments indicatethat designing hierarchical structures is not as simple as placing multiple scales of fibres on top of one another, but can requiresignificant design optimization to enhance the contact mechanics and adhesion strength.     

Developmental changes in cell wall structure of phloem fibres of the bamboo Dendrocalamus asper

BACKGROUND AND AIMS: Bamboo culms have excellent physical and mechanical properties, which mainly depend on their fibre content and anatomical structure. One of the features which is known to contribute to the high tensile strength in bamboo is the multilayered structure of the fibre cell wall. The aim of this study was to characterize the development of the layered structure in fibre cell walls of developing and maturing culms of Dendrocalamus asper. METHODS: Cell wall development patterns were investigated in phloem fibre caps of vascular bundles in the inner culm wall areas of Dendrocalamus asper of three different age classes (<6 months old, 1 year old, 3 years old). A combination of light microscopy and image analysis techniques were employed to measure cell wall thickness and to determine number of cell wall layers, as well as to describe the layering structure of fibre walls. Two-dimensional maps showing the distribution pattern of fibres according to the number of cell wall layers were produced. KEY RESULTS: The cell walls of fibres in phloem fibre caps located in the inner part of the culm wall of D. asper developed rapidly during the first year of growth. Six different fibre types could be distinguished based upon their cell wall layering and all were already present in the young, 1-year-old culm. In the mature stage (3 years of age) the multilayering was independent of the cell wall thickness and even the thinner-walled fibres could have a large number of wall layers. The multilayered nature of cell wall structure varied considerably between individual cells and was not exclusively related to the cell wall thickness. Nevertheless, fibres at the periphery of the fibre bundles and immediately adjacent to the phloem elements exhibited a consistent and high degree of layering in their cell walls. CONCLUSIONS: The multilayered structure of fibre cell walls was formed mainly during the first year of growth by the deposition of new wall layers of variable thickness, resulting in a high degree of heterogeneity in the layering patterns amongst individual fibres. A degree of 'order' in the distribution of multilayered fibres within the caps does exist, however, with multilayered cell walls common in fibres adjacent to phloem elements and around the edge of the fibre cap. These findings confirm the observations, primarily in Phyllostachys viridi-glaucescens. The layering structure was not found to be specifically related to the thickness of the cell wall.     

The structure of the nerve fibre layer and neurocord in the enteropneusts

Summary The nerve fibre layer and the neurocord of the Enteropneusts Saccoglossus horsti, Harrimania kupfferi and Ptychodera flava have been examined with the electron microscope. The nerve fibres vary in diameter between 0.15 to 10 m. The majority of the fibres are of the smaller diameters. The nerve fibre layer is intraepidermal, and is divided by processes running radially from the epithelial cells to the basement membrane that separates the nerve fibre layer from the muscle cells.The cells of origin of these nerve fibres are situated mainly in the innermost layers of the epidermal cells. The nerve fibre profiles contain numerous vesicles of very varied diameter and contents, together with larger granular inclusions that are also found in the nerve cell bodies.Morphologically recognisable synapses are rare, but the majority of fibres are in intimate contact with one another. Sometimes the mass of fibres is divided into bundles by the epithelial cell processes. The majority of giant fibres are situated near to the basement membrane of the neurocord. The giant fibres also have a varied content of vesicles as well as neurofilaments and neurotubules.The central canal in Ptychodera flava and the remnants of the central canal in Saccoglossus horsti are both lined by columnar cells that bear microvilli as well as cilia with the typical 9 + 2 pattern of tubules. Scattered amongst these cells are mucus secreting cells which open into the cavity of the canal.I (P.N.D.) should like to thank Professor J. Z. Young, F. B. S. for much advice and encouragement. Dr. R. Bellairs generously provided the electron microscope facilities, and Dr. R. Newell kindly collected and identified the Saccoglossus specimens. Mr. R. Moss, Mrs. J. Hamilton and Mr. A. Aldrich gave excellent technical and photographic assistance.     

Mechanical design of polypterid fish integument for energy storage during recoil aspiration

Polypterid fishes ventilate their lungs by recoil aspiration. Active exhalation compresses the bony scale jacket; inhalation occurs when the scale jacket recoils to its original shape. Exhalation and loading of the integument are powered by contraction of striated muscle in the lung walls. The integument of polypterid fishes consists of interlocking rhomboid scales held together by collagen fibre strands. The scales imbricate with bevelled edges, so that when the fish is at rest, its integument is circular in cross-section and the overlapping scale edges are parallel. During exhalation, the hemicircular shape of the ventral integument is deformed, and the scales rotate slightly. As the overlapping scale edges become non parallel, the scales act as tiny levers to stretch the collagen fibres between them. When the fish opens its glottis to inhale, the stretched collagen fibres return to their rest lengths and pull the scale jacket back into a circular shape, sucking air into the lungs. Thus, despite the deformation of the integument as a whole in compression, strain energy is stored in tensile elements.     

Localization of urotensin I- and corticotropin-releasing factor-like immunoreactivity in the central nervous system of Catostomus commersoni

The distribution of urotensin I (UI) and corticotropin-releasing factor (CRF) immunoreactive (IR) structures was studied in the central nervous system (CNS) of the white sucker using the peroxidase-antiperoxidase immunocytochemical procedure. The close sequence homology between both peptides resulted in a high degree of crossreactivity. This was resolved by saturating the antisera solutions with heterologous antigens and specificity tests were done by adding excess of homologous peptides. UI immunoreactivity was seen in all of the identifiable caudal spinal cord neurosecretory cells, in their processes projecting to the urophysis, in thin beaded fibres coursing along the spinal cord, in brain stem, hypothalamus, proximal pars distalis and, especially, in the telencephalon. Some IR-UI specific and IR-CRF specific parvocellular neurons were also identified in the caudo-ventral tuberal region and ventral telencephalon. The IR-CRF was mainly present in parvocellular and magnocellular perikarya of the nucleus preopticus and in the preoptic-neurohypophysial pathway. Dense networks of IR-CRF reacting beaded fibres were also located in the lateral and posterior recessus nuclei. In the pituitary, IR-CRF fibre bundles were seen mainly in the neurointermediate lobe and in the rostral pars distalis. The cells of origin of the extraurophyseal system of IR-UI fibres in the sucker CNS have not been identified. The distribution of CRF immunostaining correlates well with the documented knowledge of CNS structures involved in the control of ACTH secretion in the goldfish. The probability of the occurrence of two UI-CRF related molecules, or of two different forms resulting from a common precursor molecule, forming two separate neuronal systems in the sucker CNS seems likely.     

Arrangement of connective tissue fibres in the musculus lateralis of the spiny dogfish,Squalus acanthias L. (chondrichthyes)

Summary In the m. lateralis of Selachii a well-developed perimysium is found, while a similar structure is lacking in Teleostei. The Selachian perimysial fibres are arranged in distinct planes. In such planes two predominant fibre directions are found; the angle between each of them and the body-axis is 60–70°. Additionally the myosepts contain fibre bundles which are arranged in oblique loops. These myoseptal fibre-loops are present in Squalus, well as in the Teleosts we examined. In order to investigate the functional significance of these fibre arrangements we constructed a model, consisting of a steel strip representing the axial skeleton and a bundle of stretched rubber tubes representing the lateral musculature. Both components of this model have to be firmly interconnected. This is easily achieved by winding oblique loops of cotton thread around them, thus tying them to each other. When we now release the stretched rubber tubes, they contract, resulting in a proper bending of the model. An optimal value for the angle between the body-axis and the direction of the fibres is found.On the basis of the morphological similarity between the perimysial and the myoseptal loop fibres on the one hand and the cotton thread loops on the other, it is suggested that a functional similarity exists as well. So it is suggested that the functional significance of the perimysial fibre system, and of the myoseptal fibre loops, is the achievement of a firm contact between the lateral muscle mass and the axial skeleton.     

The lattice arrangement of the collagen fibres in the submucosa of the rat small intestine: scanning electron microscopy

Summary The three-dimensional architecture of the submucosal collagen fibres of the rat (3 weeks old) small intestine was examined by scanning electron microscopy using a selective microdissection method. The main framework of the submucosa was composed of two arrays of collagen fibre bundles running diagonally around the intestinal wall, one set in a clockwise direction, the other counterclockwise. These fibre bundles were about 5 m in diameter and were oriented at a range of angle ± 30°–50° to the longitudinal axis of the intestine. With the advantage of the SEM observation it was demonstrated that these fibres in different arrays did not constitute two separate layers but interwove to form a unified lattice sheet. An irregular network of fine collagen fibrils over the main framework was also seen. The significance of their arrangement is discussed with respect to the skeletal function of the submucosa in the intestine.     

Electron microscopic study on the elastic and elastic related fibres in the human fascia transversalis at different ages

An electron microscopic study of the elastic fibre and elastic related fibres of the fascia transversalis of the human inguinal triangle was performed in 20 male patients aged 13 to 81 a with right indirect inguinal hernia submitted to surgical repair. The 3 fibre types comprising the elastic system (oxytalan, elaunin, and elastic fibres) tend to be ordered in a precise manner and sequence among the fibrils, fibres, and collagen fibre bundles, respectively. The present findings show that with aging, there is a decrease in the oxytalan fibres and an increase in the amorphous substance of the elastic fibres. The authors concluded that the decrease in oxytalan fibres as a function of age may be responsible for alteration in the resistance of the transversalis fascia.     

On the relation between fibre diameter and conduction velocity in myelinated nerve fibres

Myelinated fibres less than 1 micrometer in diameter are rare in the peripheral nervous system; but fibres down to 0.2 micrometer in diameter exist in the central nervous system. These observations are consistent with Rushton's theory on the effects of fibre size on conduction in myelinated nerve when the different processes of myelination in the peripheral and central nervous systems are taken into account.     

Fibres and Fibre-sclereids in Wild-typeArabidopsis thaliana

Examination of the fibre system in roots and shoots ofArabidopsisthaliana(L.) Heynh. revealed three types of fibres, distinguishedaccording to their site of differentiation: (1) short fibre-sclereidsin the secondary phloem of roots and shoots at the rosette level;(2) long fibres in the secondary xylem of the main root; and(3) very long fibres in the xylem of the inflorescence stems.These three types are in addition to the small number of primaryphloem fibres that are formed even in smallA. thalianaindividuals.These findings provide a basis for the use ofArabidopsis thalianaasa model system to study the processes leading to fibre differentiationin dicotyledons. Arabidopsis thaliana; differentiation; fibre-sclereids; inflorescences; phloem fibres; xylem     

Ultrastructural observations on the central innervation of the guinea-pig pineal gland

Summary In the present study the central innervation of the guinea-pig pineal gland was investigated. The habenulae and the pineal stalk contain myelinated and non-myelinated nerve fibres with few dense-cored and electron-lucent vesicles. Some myelinated fibres leave the main nerve fibre bundles, lose their myelin-sheaths and terminate in the pineal gland. Although direct proof is lacking, the non-myelinated fibres appear to end near the site where the bulk of the myelinated fibres are located. Here a neuropil area exists where synapses between non-myelinated fibre elements are abundant. Neurosecretory fibres were also seen. The results support the concept of functional interrelationships between hypothalamus, epithalamus and the pineal gland.