Mechanism Of Fiber Formation Research Articles

Turbidimetric and morphological studies of type I collagen fibre self assembly in vitro and the influence of fibronectin

Collagen undergoes several stages of self assembly including turbidimetric lag, growth and plateau steps. The later stages of type I collagen self assembly were studied by turbidity—time measurements, low angle laser light scattering and by determination of the birefringence retardation of collagen fibres formed in vitro. These studies were conducted in the presence and absence of fibronectin to evaluate the effect of fibronectin on the kinetics and extent of type I collagen fibrillogenesis. The results of these studies indicate that the collagen fibres observed at the end of the lag phase appear to be identical to fibres seen in the growth phase of turbidity—time curves based on fibre diameter and birefringence retardation measurements. Birefringence retardation measurements suggest that the diffracting unit may be the collagen fibril and that the volume fraction of fibrils in fibres is about 0.95 using a model developed for a series of parallel ellipsoids. Morphological observations suggest that the distribution of fibre diameters formed in vitro during the growth phase is narrow and appears to be independent of time with only the mass of collagen in fibres increasing during the growth phase. During the growth phase, layers of parallel fibres are formed with alternating layers appearing almost orthogonal. In the presence of fibronectin the mechanism of fibre formation appeared unchanged. It was concluded that fibronectin appeared to modify the kinetics of self assembly by preventing collisions between collagen molecules.

Scanning electron microscopy of the structural reconstruction of the abdominal wall after experimental paramedian incision

The various healing stages of experimental paramedian incisions in the right rectus sheath of 36 albino rats were examined by utilizing the scanning electron and the light microscope. The successive reconstruction processes were visualized stereoscopically at a cellular level. During the inflammatory stage (7 days) various inflammatory cells accumulated around a wide network of trabeculae which traversed the gap of the wound. The fibrillogenetic stage increased in the period between the 2nd and 12th weeks postoperatively. Various stages of fiber maturation were visualized. Mechanisms of fiber formation, maturation, and junction between the newly formed fibers and the old healthy ones at the wound margin were also seen three dimensionally and described. The newly formed fibers were always arranged parallel to each other in a definite direction. This direction had a constant angular relationship to the long axis of the wound, i.e., the line of incision, regardless of the direction of the incision itself. This constant relationship might prove to be useful to the surgeon while choosing his incision in the anterior abdominal wall.

A criterion for craze formation

AbstractA general criterion for craze formation is presented. Crazes are deformation zones that are common to both glassy and semicrystalline polymers. Crazes are composed primarily of fibrils. This paper attempts to describe the process that transforms unoriented glassy and semicrystalline polymeric solids into a fibrous state. The criterion for crazing discussed is a local phase transition. The transition occurs at the draw temperature. Unoriented solid‐phase macromolecules, at local high‐stress regions, undergo a transition to the elastomeric phase. Rapid extension and accompanying resolidification produce the fibrous morphology of craze fibrils. Cavitation of the deforming rubber phase ocurs because the local length increase is riot compensated for by an overall area decrease. Craze formation in glassy polymers has long been suspected to involve a local solid‐to‐rubber phase change. To relate crazes in glassy and semicrystalline polymers, one can assume that a solid‐to‐rubber phase change is required to produce craze fibrils in semicrystalline polymers. The transient melt phase would undergo rapid elongation, causing the formation of extended chain crystallites. These subsequently nucleate the remaining melt, which then crystallizes epitaxially as lamellae. Crystallization during flow would, therefore, be the mechanism of fiber formation.

Longitudinal growth of polymer crystals from flowing solutions. VIII. Mechanism of fiber formation on rotor surface

A study has been made of the mechanism of the fibrous crystallization process of high-molecular-weight polyethylene from dilute solution subjected to Couette flow. Fiber growth has been observed to take place in a gel layer adhering to the surface of the rotating inner cylinder. The fiber is both taper and ribbonlike shaped, which suggests that growth occurs primarily on the lateral surfaces. The crystal growth rate, as determined by measurements of the fiber cross section, is found to depend on the roughness and the chemical nature of the rotor surface, and is independent of the take-up speed. These observations have led to the following conclusions concerning the mechanism. Long-chain molecules adsorb onto the rotor surface. By reptation an entanglement network is formed. It has long relaxation times due to the tendency of the supercooled chains to form embryonic crystallites upon slight orientation. This network is stretched by the entanglement formation with the cilia of a seed crystal, followed by shear stresses. Stretching will lead to further crystallization. The elastically active chain parts between entanglements will lead to the extended-chain backbone crystals. Inelastic chain parts will crystallize as folded platelets of the shish kebab.

Conformational changes in the hemoglobin S system as seen by proton binding.

The proton binding behavior of the carbon monoxy derivatives of hemoglobins A and S, the respective beta-subunits (in the native form and with the cysteines combined with p-mercuribenzoate), and the respective beta (1-55) peptides have been measured. The results show that in the systems obtained from hemoglobin S there is a group which shifts its pK from about 7.0 to 8.35 in the beta-subunits that were reacted with p-mercuribenzoate and to more than 9.0 in the beta (1-55) peptide. Proton nuclear magnetic resonance measurements indicate that in the peptide beta (1-55) from hemoglobin S this residue is the histidine at beta 2. It is proposed that this pK shift is due to the formation of a salt bridge between beta 2 His and beta 7 Glu. This structure would disrupt the first turn of the A helix of the beta s-subunits. Its stabilization by extramolecular contacts may be relevant to the mechanism of fiber formation of hemoglobin S.

Hydrodynamically induced formation of cellulose fibers. I. Observations on the formation of cellulose fibers from stirred solutions

AbstractLike synthetic polymers, a natural polymer such as cellulose may crystallize in fibrous form from stirred solutions. In the present work, it is demonstrated that cellulose fibers can be formed by precipitation from dimethyl sulfoxide/paraformaldehyde solutions by two methods that involve different mechanisms of fiber formation, viz., (A) precipitation of cellulose by addition of nonsolvent to the stirred cellulose solution, and (B) precipitation of cellulose by coagulation of droplets of cellulose solution in a stirred precipitant. Both processes yield fibers with properties depending on the stirring speed and the coagulant strength. The molecular orientation and tensile strength of the fibers produced by method A was low, but increased with the stirring speed, while some fibers formed by method B reached extremely high orientation, depending on the thickness of the fibers. The two mechanisms of fiber formation are discussed on the basis of the experimental observations.

“Bishydrazid A2”: A new semiaromatic film and fiber-forming polymer based on bisacid A2

We report the preparation of the dihydrazide of bisacid A2 (“bisdihidrazide A2”). Its composition and structure have been verified by elemental analysis and by means of infrared and NMR spectra. This material was then converted into a polyhydrazide (“bishydrazid A2”) in an HCl-accepting solvent. The polymer was converted to fiber by wet spinning the dope obtained during the polycondensation reaction without prior neutralization or dilution. Film was cast from a solution of the precipitated and washed polymer which had an inherent viscosity of about 0.8; mechanical tests on the film—both before and after treatment with formic acid—were carried out. Differential scanning calorimetry showed an α/β transition comparable to that shown by bisacid A2 polyaramides and described in preceding papers1,2. Wide-angle x-ray scattering showed that the polymer is amorphous. Scanning electron micrographs revealed the physical structure of wet-spun fiber and the probable mechanism of fiber formation by dope extrusion into a water bath.

THE STRUCTURE OF HIGH-TENACITY VISCOSE FIBRES

High-tenacity viscose fibres are shown to possess a homogeneous surface layer (or cuticle), and a dye-retentive (or skin-like) region which forms the central part of the fibres; this region contains innumerable cavities. The evidence is in agreement with a mechanism of fibre formation previously published.