Can a fibrillar interface be stronger and tougher than a non-fibrillar one?

Elasticity analysis and finite element simulations are carried out to study the strength of an elastic fibrillar interface. The fibrils are assumed to be in perfect contact with a rigid substrate. The adhesive interaction between the fibrils and the substrate is modelled by the Dugdale–Barenblatt model (DB). The condition for a fibrillar interface to be stronger than a non-fibrillar one is obtained for two regimes: (i) small fibril or flaw insensitive regime; (ii) large fibril or flaw sensitive regime. The transition between the two regimes is characterized by a dimensionless parameter that incorporates the material constants of the elastic fibrils and interfacial properties. The condition for a fibrillar interface to be tougher is also given. Lateral collapse is found to be detrimental to the strength and toughness of a fibrillar interface.

Evidence against lung galaptin being important to the synthesis or organization of the elastic fibril

Previously it has been suggested that galaptin, an endogenous beta-galactoside-binding lectin, may function in the organization of lung elastic fibres. Galaptin was not present in preparations of rat or porcine lung elastic fibrils, neither did it bind to any of the fibril-associated proteins when these were separated by SDS/polyacrylamide-gel electrophoresis. Elastin and galaptin synthesis and secretion were investigated in lung fibroblast cultures and in anatomically preserved slices from developing rat lung. In both systems the synthesis and secretion of elastin was unmodified by the presence of beta-galactosides or antigalaptin in the culture medium. The synthesis of galaptin was unmodified by the presence of anti-elastin or beta-aminoproprionitrile in the culture medium. Cultured fibroblasts secreted elastin but only trivial amounts of galaptin. When cultures were treated with iodoacetamide (10(-5)M) galaptin synthesis was maintained but elastin synthesis ceased. These results argue against galaptin having an important role in the synthesis, secretion or organization of the elastic fibril.

Ultrastructural localization of fibronectin to different anatomic structures of human skin.

Fibronectin was localized in fetal and adult human skin with affinity-purified antibodies, using a ferritin staining technique. The most common observation was a close association of this fibronectin with thin and thick cross-striated fibrils containing collagens types I and III. Deposits of fibronectin occurred in discrete spots, with some regular distribution, in agreement with a major binding site for this protein on collagen. Fibronectin was also detectable at the periphery of elastic fibrils and in amorphous, non-fibrillar regions of skin. The latter pattern included a close pericellular localization, indicating interactions between fibronectin and plasma membranes. Discrete deposits of fibronectin were also found on the lamina lucida of the basement membrane of the dermal-epidermal junction and around small blood vessels. This widespread distribution of fibronectin suggests that it has a multitude of biologic functions in situ.

The Effect of Salts on the Anal Gills of the Mosquito Larva

The so-called anal gills of the mosquito larvae (Aedes argenteus) are delicate chitinous papillae lined by flattened cells and filled with haemolymph. Externally the cells rest directly upon the chitinous cuticle. Internally they are bounded by a continuous elastic membrane, apparently composed of some "scleroprotein." The faintly granular cytoplasm is crossed vertically by elastic fibrils or membranes. If the gills are cut off in various salt solutions, which can then come in contact with the cells on both their surfaces, the cells swell or contract like other tissues, depending on whether the solutions are hypo- or hypertonic. But if the same solutions are applied to the intact larva, so that they come in contact with the outer surface while the inner surface of the cells is still in contact with the haemolymph, the effects are altogether different: Hypotonic solutions have no visible effect. Hypertonic solutions of salts like NaCl, KBr, etc., in which both ions are monovalent, cause enormous swelling of the cells. This is probably because these salts diffuse through the outer membrane (the cuticle) of the gills into the cells, which then absorb water from the haemolymph by osmosis. If the larva so treated is soon restored to fresh water, the action is reversible; but after a time the elastic filaments in the cells are dissolved and these can no longer contract again. These effects occur equally in the presence of salts with divalent cations. Hypertonic solutions of salts like CaCl2, Na2SO4, etc., in which one or both ions are divalent, extract water from the larva but do not cause swelling of the cells. These salts do not dissolve the elastic filaments. In the presence of hypotonic NaCl, etc. (which by itself has no visible effect), they cause temporary swelling followed by contraction. The cause of the difference between these two groups of salts is discussed. Dilute alkalis (N/50 NaOH) applied to the isolated gill or the intact larva dissolve the cells and cause extreme swelling, but do not dissolve the cuticle or the inner membrane. This action is accentuated by NaCl, etc., and by Na2SO4, etc., but is partially inhibited by CaCl2. Dilute acids (N/100 HCl) cause precipitation of the nuclei, slight swelling of the cells, and complete separation from the cuticle. In the presence of hypertonic Na2SO4 or CaCl2 the separation does not occur. All these effects are peculiar to the gills; no other part of the surface of the larvae is affected by these reagents.1

THE BEHAVIOR OF ELASTIC TISSUE IN THE POSTFETAL OCCLUSION AND OBLITERATION OF THE DUCTUS ARTERIOSUS (BOTALLI) IN SUS SCROFA

A study of the histogenesis of elastic tissue in the embryonic ductus arteriosus of Sus scrofa is in accord with the theory that elastic fibrils are directly differentiated in the outlying portion of the protoplasm of the early connective tissue cell. In the occlusion of the postfetal ductus arteriosus of Sus scrofa there is early a hypertrophy of the internal elastic membrane. Subsequently there takes place a marked delamination of the thickened internal elastic membrane in the production of new and independent elastic fibers and lamellæ. The formation of new elastic fibers from preformed elastic tissue is most abundant where the postfetal contraction of the ductus arteriosus is least marked. These new elastic fibers play an important part in the occlusion of the lumen of the postfetal ductus. Aside from the extensive formation of elastic fibers from preformed elastic tissue, in the occlusion of the lumen of the postfetal ductus arteriosus of Sus scrofa, there are also some elastic fibrils formed from non-elastic elements, apparently from connective tissue cells. In some recent preliminary work on ligations of the common carotid artery there was found, after an interval of from eight to twelve days, at some points between the ligatures, a slight but obvious cellular thickening of the so-called subendothelial stratum. Some of these connective tissue cells may have wandered from the other coats of the vessel, through the inner elastic membrane into the subendothelial stratum; others may have proliferated from cells in situ. Specific stains revealed near the periphery of some of these cells, i. e., in the outlying portion of the exoplasm, very delicate elastic fibrils, apparently the product of protoplasmic activity.