Biorheology - Volume 2, issue 1 - Journals

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Three analogies to explain the mechanical properties of bone

Article Type: Research Article

Abstract: 1. The mechanical properties of bone are described. It is shown that these properties are not explicable on the assumption that the apatite and the collagen of bone are acting as a compound bar, such as reinforced concrete. 2. Knese ’s hypothesis that bone is a prestressed material, explaining some of the anomalous properties of bone, is discussed. It is shown that: (a) There is no good evidence that bone is prestressed. (b) It is difficult to see how the very large initial prestresses could be applied. (c) For the prestressing to be effective in increasing the …apparent tensile strength of the apatite sufficiently would mean that during compression the apatite would be subjected to a load higher than it can probably bear. 3. It is suggested that bone is a two-phase material, like fibreglass. Similarities between bone and engineering two-phase materials are discussed. The apatite crystals are very small, so dangerous flaws could form in them only with difficulty, and any running crack would immediately come to the edge of the crystal and run into collagen, which would deform but not split. 4. The possible occurrence of other two-phase materials in nature is discussed. The mechanical properties of bone are described. It is shown that these properties are not explicable on the assumption that the apatite and the collagen of bone are acting as a compound bar, such as reinforced concrete. Knese ’s hypothesis that bone is a prestressed material, explaining some of the anomalous properties of bone, is discussed. It is shown that: There is no good evidence that bone is prestressed. It is difficult to see how the very large initial prestresses could be applied. For the prestressing to be effective in increasing the apparent tensile strength of the apatite sufficiently would mean that during compression the apatite would be subjected to a load higher than it can probably bear. It is suggested that bone is a two-phase material, like fibreglass. Similarities between bone and engineering two-phase materials are discussed. The apatite crystals are very small, so dangerous flaws could form in them only with difficulty, and any running crack would immediately come to the edge of the crystal and run into collagen, which would deform but not split. The possible occurrence of other two-phase materials in nature is discussed. Show more

DOI: 10.3233/BIR-1964-2101

Citation: Biorheology, vol. 2, no. 1, pp. 1-10, 1964

Price: EUR 27.50

The sequence of hepatic microcirculatory and rheological events induced by shock in the rat

Authors: Michel, A.G. | Shoemaker, W.C.

Article Type: Research Article

Abstract: Hepatic microcirculatory alterations were observed in rats after shock from hemorrhage and exposure. The time sequence of events was described and criteria were proposed for evaluating the degree of the microcirculatory defect as a basis for comparison with histological studies. A plasma dye, T–1824, was used to distinguish closely packed, aggregated red cell masses from blood containing a relatively normal proportion of plasma. The relation of hepatic cellular aggregation to previously described hepatic morphologic lesion and to the development of increased organ resistance was discussed.

DOI: 10.3233/BIR-1964-2102

Citation: Biorheology, vol. 2, no. 1, pp. 11-14, 1964

Price: EUR 27.50

Sap movements in trees

Authors: Zimmermann, M.H.

Article Type: Review Article

Abstract: Water and dissolved mineral nutrients are taken up by the roots and ascend via the xylem (the wood) into the leaves, where most of the water is lost by transpiration. Transpiration from leaves pulls up the water; movement is presumably along a gradient of negative pressures (tensions). The conducting tissues are uniquely adapted to negative pressures, for they contain rigid tubes which acquire a strong cellulose and lignin re-inforced wall during growth. Conducting cells die before they become functional. The whole water-conduction tissue is continuous throughout the plant. Rapid movement takes place through xylem tubes, slow movement through walls of …all cells, even living ones. The transpiration stream is very low in concentration (< 0.5% w/v). However the rapid rate of movement (up to around 50 m/hr), and loss of water by transpiration from leaves, carry sufficient quantities of mineral nutrients into the leaves.—Growth of flowers, fruits, branches, stem and roots can only take place if building materials (photosynthetic products) are translocated from the leaves to these places. This type of long-distance transport takes place in the phloem (the inner bark) mainly in a downward direction. The conducting channels are living but enucleate cells. Velocities of translocation are of the order of 1 m/hr, the concentration of the moving solution is much higher than in the xylem (10–20% w/v, mostly sugars), and the pressures in the system are positive. Cross transfer between the two transport systems enables plants to circulate materials throughout their body. Show more

DOI: 10.3233/BIR-1964-2103

Citation: Biorheology, vol. 2, no. 1, pp. 15-27, 1964

Price: EUR 27.50

The wettability of fibrinized surfaces and of living vascular endothelium by blood

Authors: Copley, A.L. | Glover, F.A. | Scott Blair, G.W.

Article Type: Research Article

Abstract: There are no significant differences between the surface tensions of blood, plasma and serum. On glass, blood wets very slightly better than plasma which wets very slightly better than serum. The wettability of these materials on fibrin is in the same order as that on glass. No appreciable difference has been detected between the wetting of glass and fibrin surfaces by blood, plasma or serum. Our investigations demonstrate that no relation exists between the wettability of a surface with blood and the coagulation of the blood; since fibrin surfaces, which we found to be wettable, have previously been shown …by one of us (A.L.C.) to act as anticoagulants both extracorporeally and in vivo . Our experiments with air emboli in the microcirculation of the hamster’s cheek pouch and of the mesentery of guinea pigs and of rats show that living vascular endothelium, contrary to the generally held contention, is wettable. Show more

DOI: 10.3233/BIR-1964-2104

Citation: Biorheology, vol. 2, no. 1, pp. 29-35, 1964

Price: EUR 27.50

Zur Mechanik schnell rotierender elastischer Schrauben

Authors: Jarosch, R.

Article Type: Research Article

Abstract: Die vorliegende Arbeit geht aus von der Vorstellung, dass die Bewegung des Protoplasmas einer Verschiebung entlang rotierender Schrauben entspricht. (1) Unter der nach elektronenmikroskopischen Befunden wahrscheinlichen Annahme von 300 Å für die Ganghöhe ergeben sich aus der Geschwindigkeit der Protoplasmaströmung Werte für die Rotationsgeschwindigkeit der Schrauben, die im Bereich von 0 bis etwa 500 Umdrehungen pro Sekunde liegen. (2) Modellversuche mit schnell rotierenden Schraubenfedern aus Stahldraht zeigten unter anderen folgendes: (a) Bei jeder rotierenden Schraube tritt eine “Primärschwingung” auf, deren Frequenz der Drehzahl pro Sekunde entspricht. Diese Schwingung führt zur Bildung stehender Wellen. (b) Jede lokale Berührung erhöht …die Schwingungsfrequenz der ganzen Schraube. (“Sekundärschwingung”). (c) Bei der Rotation einer frei in ein flüssiges Medium hängenden Schraube wird die Wellengeschwindigkeit der Schwingung mit der Rotationsgeschwindigkeit vergrössert. (d) Die Wellengeschwindigkeit ist um so grösser, je grösser der Neigungswinkel der Schraube ist. (e) Die stehenden Wellen verursachen Unterschiede in der Teilchenkonzentration des die Schraube umgebenden Mediums. (3) Für einige wichtige physiologische Phänomene (Periodik, Erregung und Erregungsleitung, Formbildung) werden Erklärungen auf schraubenmechanischer Grundlage versucht. Unter der nach elektronenmikroskopischen Befunden wahrscheinlichen Annahme von 300 Å für die Ganghöhe ergeben sich aus der Geschwindigkeit der Protoplasmaströmung Werte für die Rotationsgeschwindigkeit der Schrauben, die im Bereich von 0 bis etwa 500 Umdrehungen pro Sekunde liegen. Modellversuche mit schnell rotierenden Schraubenfedern aus Stahldraht zeigten unter anderen folgendes: Bei jeder rotierenden Schraube tritt eine “Primärschwingung” auf, deren Frequenz der Drehzahl pro Sekunde entspricht. Diese Schwingung führt zur Bildung stehender Wellen. Jede lokale Berührung erhöht die Schwingungsfrequenz der ganzen Schraube. (“Sekundärschwingung”). Bei der Rotation einer frei in ein flüssiges Medium hängenden Schraube wird die Wellengeschwindigkeit der Schwingung mit der Rotationsgeschwindigkeit vergrössert. Die Wellengeschwindigkeit ist um so grösser, je grösser der Neigungswinkel der Schraube ist. Die stehenden Wellen verursachen Unterschiede in der Teilchenkonzentration des die Schraube umgebenden Mediums. Für einige wichtige physiologische Phänomene (Periodik, Erregung und Erregungsleitung, Formbildung) werden Erklärungen auf schraubenmechanischer Grundlage versucht. Show more

DOI: 10.3233/BIR-1964-2105

Citation: Biorheology, vol. 2, no. 1, pp. 37-53, 1964

Price: EUR 27.50