Properties Of Threads Research Articles

Bacterial Macrofibers and Bionites: Materials of Natural and Synthetic Design

ABSTRACTTwo fiber forms can be obtained from cells of the rod-shaped bacterium,Bacillus subtilis, one called macrofibers, the other bacterial thread. Macrofibers are highly organized, multicellular structures, millimeters in length that selfassemble in a unique way. Each fiber is essentially a single chain of cells linked end-to-end that has repeatedly folded upon itself and twisted into helical form. The growth of individual cells yields both the material of the macrofiber and the forces required for its assembly. The forces involved stem from twisting motions caused by cell growth geometry. The folding process is akin to negative supercoiling. New approaches have been used to estimate the magnitude of forces. Torque generated by single filaments has been estimated from snapopening motions resulting from aborted attempts at folding to be in the range of 10−10to10−8dyne-cm. In contrast, multifilament fibers carrying small wires in their loops must have generated a torque of at least 10−5dyne-cm and a supercoiling force of at least 10−5dyne in order to have moved the wires in viscous solutions at the rates observed. The second bacterial fiber form, bacterial thread, and its mineralized derivatives, called bionites, are man-made materials. They are produced by the drawing and drying of bacterial cell filaments from cultures grown in the form of a textile-like web. The material properties of bacterial thread reflect primarily those of the strength-bearing cell wall polymer, peptidoglycan. A variety of new fiber-like materials have been produced by mineralizing the cell walls in situ in web cultures and drawing the products. Iron, copper, calcium, and potassium phosphate-containing bionites have been obtained in this manner. We are currently searching for order in the bionite crystal forms that may reflect the electrostatic nature of the wall polymer structural templates.

Mechanical properties of Bacillus subtilis cell walls: effects of removing residual culture medium

Experiments are described in which the tensile strength, the initial (Youngs') modulus, and other mechanical properties of the bacterial cell wall were obtained as functions of relative humidity (RH) in the range of 20 to 95%. These properties were deduced from tensile tests on bacterial thread, a fiber consisting of many highly aligned cells of Bacillus subtilis, from which residual culture medium had been removed by immersion in water. Reasons are given to support the idea that the mechanical properties of bacterial thread relate directly to those of the cylinder wall and that they are not influenced by septa, cytoplasm, or the thread assembly. The data show that the cell wall, like many other heteropolymers, is visco-elastic. When dry, it behaves like a glassy polymer with a tensile strength of about 300 MPa and a modulus of about 13 GPa. When wet, its behavior is more like a rubbery polymer with a tensile strength of about 13 MPa and a modulus of about 30 MPa. Thus, the cell wall is stronger than previously reported. Walls of this strength would be able to bear a turgor pressure of 2.6 MPa (about 26 atm). The dynamic behavior suggests a wide range of relaxation times. The way in which mechanical behavior depends strongly on humidity is discussed in terms of possible hydrogen bond density and the ordering of water molecules. Cell walls in threads containing residual culture medium TB are, except at low RH, 10 times more flexible and about 4 times less strong. All of their mechanical properties appear to vary with change in RH in a manner similar to those of walls from which the culture medium has been washed, but with a downshift of about 18% RH.

Effect of prevulcanisation of natural rubber latex on the chemical and physical properties of latex thread

AbstractThe effect of prevulcanisation on the processing properties and network structure of a series of latex compounds containing conventional and efficient vulcanisation (E.V. systems) systems for the manufacture of latex thread was evaluated. Prevulcanisation was effected at 70°C and the extent of crosslinks formed and compound viscosity at various periods of heating were studied. It is observed that the vulcanisation systems studied have a profound effect on the extent of crosslink formation during prevulcanisation. The network structure of the vulcanisate was also studied and found that polysulphidic content is high as the extent of prevulcanisation of the latex compound increases. Latex threads were also prepared from typical latex compounds which were prevulcanised to different degrees and their chemical and physical properties were evaluated. It is observed that the extent of prevulcanisation affects the aged and unaged physical properties of latex threads.

Thermal Properties of Spider's Thread

Thermal properties of drag lines collected from Nephila clavata, Yaginumia sia and Argiope amoena were studied by differential scanning calorimetry (DSC) and thermogravimetry (TG) at temperatures from 20°C to 600°C. The DSC thermograms obtained for N. clavata showed an endothermic peak at ca. 100°C and exothermic peaks at ca. 300, 340, 500 and 580°C. The former could be ascribed to the desorption of water from the protein constituting drag lines and the latter to decomposition of the protein. Tce spider's silk thread was stable even above 200°C but completely decomposed at ca. 600°C. The thermal properties of drag lines were found to change with season and depended on the sex as well as species of the spider. Such difference in the thermal properties may be ascribed to the differences not only in the physical properties such as the morphology of silks, the molecular weight and density but also in the chemical structure such as the amino acid composition.

Seasonal Change in Color of Spiders' Silk

The optical properties of spiders' threads in different seasons were studied by optical reflectance in the range of wavelength from 400 to 700nm. It was found that the color of threads from female spiders Nephila clavata collected in the same area changed seasonally from white or semitransparent in summer to yellow in autumn according to the seasonal change in the environment This change in color was concluded to be ascribed to the seretions from the mature female spiders Nephila clavata and to play an important role not only in protecting spiders from predators but also in capturing preys.

Elastic properties and beta-sheet structure of connectin threads.

Connectin is a very long and flexible protein of striated muscle, linking myosin filaments to z discs in a sarcomere. Isolated native connectin in solution frequently forms elastic threads upon concentration of the solution, by side-by-side association of molecules. An X-ray diffraction study was performed to examine the presence of beta-sheet structure in artificially prepared threads. The elastic properties of such threads were measured at various temperatures. Negative temperature dependence of the elastic coefficient suggests that the elasticity of connectin threads is due to deformation of the three-dimensional structure and not to rubber-like behavior.

Biomechanics of bacterial walls: studies of bacterial thread made from Bacillus subtilis.

Bacterial threads of up to 1 m in length have been produced from filaments of separation-suppressed mutants of Bacillus subtilis. Individual threads may contain 20,000 cellular filaments in parallel alignment. The tensile properties of bacterial threads have been examined by using conventional textile engineering techniques. The kinetics of elongation at constant load are indicative of a viscoelastic material. Both Young's modulus and breaking stress are highly dependent upon relative humidity. By extrapolation to 100% relative humidity, it appears that cell walls may be able to bear only internal osmotic pressures of about 2 atmospheres (2.03 X 105(5) Pa) in living cells. Similarly, the strength of wall material limits the amount of cell-surface charge permissible to only a small fraction of that known to be carried by the negatively charged wall polymers.

Limitations in the use of actomyosin threads as model contractile systems.

Recent studies have suggested that actomyosin threads may provide a useful model for studying the properties of contractile systems. The development of highly sensitive positional feedback transducers has enabled the properties of these threads to be measured reproducibly. Potential applications include such systems as ventricle, smooth muscle and non-muscle preparations, from which it is difficult to obtain suitable fibres for mechanical studies. In addition, studies with chemically modified myosins may provide new insights into the relationships between the biochemical and mechanical events in the cross-bridge cycle. However, there are indications that the mechanical properties of actomyosin threads differ from those of intact fibres in several important respects. For example, contraction velocity is proportional to isometric tension in threads, but is independent of filament density in intact fibres. We have now determined the force-velocity characteristics of actomyosin threads prepared from muscles with known differences in their physiological contraction velocities. No direct relationships could be found between the velocity characteristics of the threads and those of intact muscle. We conclude that the measured velocities of threads reflect properties of the actomyosins other than cross-bridge cycling times, thus severely limiting the usefulness of this technique for comparative purposes.

The change in viscoelastic properties of thread on forming

An examination has been made of the general laws of deformation of artificial fibres in their formation. A dependence is introduced between the reversible and irreversible deformations at various stages of the thread formation with constant stress and also the dependence of the stress on the value of the designated deformation.

Contractile properties of actomyosin threads and bands prepared from dogs' hearts.

The experiments deal with the results obtained on the contraction of actomyosin from dogs' hearts, using a newly developed ‘null-seeking’ device for measuring and recording ATP-induced isometric, isontonic and afterloaded contractions. A comparison was made of the relative shortening of actomyosin a) when the relative shortening of actomyosin threads was plotted against the load, b) when relative shortening of the threads was expressed as a function of their specific nitrogen content, c) when this relationship was determined for compressed actomyosin bands rather than threads. In several experiments, the tension developed during isometric contraction was related to specific nitrogen content. Results demonstrate that the scatter of observation was reduced by compression of the fibers to bands and by mounting the bands in a horizontal position when recording their contractions. Using afterloaded contractions, a definite inverse relationship was found in bands between shortening and load/unit of nitrogen.

Effect of ultrasonic energy on fibrous materials: Newsletter for Wool Textile Executives, Vol. 5, No.

Pineapple leaf fibre of certain varieties is widely used in Philippines for making apparels. In Indian subcontinent, pineapple leaves are wasted after harvesting the fruit, because of technology gap exists in the efficient extraction and lack of knowledge of subsequent processes for value addition to the fibre. Agricultural practices and seed varieties used in Indian subcontinent is also widely different from those of Philippines. An attempt has been made to extract and soften pineapple leaf fibre by decortication of leaves followed by water retting. The retting time was optimized at 7 days. The retted fibres were then degummed and bleached for better processibility and aesthetic look. The physio-chemical properties of fibres were analysed for its different uses. The degummed and bleached fibres were then successfully converted into textile quality thread of 90 tex through suitable mechanical processing system. Mechanical properties of thread were found to be suitable to make sustainable novelty fabrics for apparel.