Keywords

Paper information

Toshiro MATSUMOTO and Ei YAMAMOTO, “Preface”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 4 (2009), pp.480-480 . doi:10.1299/jbse.4.480

Using the basic building blocks of collagens, elastins and proteoglycans, the human body is capable of manufacturing our large range of different structural tissues. Understanding how these structural components combine to create such widely varying tissues with diverse mechanical characteristics is a topic of interest for a range of research areas. However, probing the sub-structural mechanics to investigating these structure-function relationships is complex, as the series of hierarchical levels in connective tissues range in size from the Angstrom to millimeter level. Tendon has received considerable interest, as its simple aligned structure provides a promising route for investigating structure-function relationships. Tendon is an aligned, multi-level fibre composite structure, built predominantly from the collagen molecule to make a material with excellent tensile strength. The paper reviews the current state of research relating to tendon structure-function behaviour throughout the tendon hierarchy, building from the collagen molecule at the nano scale to the complete tendon.

Keywords

Tendon, Nano-Mechanics, Micro-Mechanics, Strain, Cell, Stress, Hierarchy, Structure

Paper information

Hazel R.C. SCREEN, “Hierarchical Approaches to Understanding Tendon Mechanics”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 4 (2009), pp.481-499 . doi:10.1299/jbse.4.481

The liver is one of the injury regions impacted by the steering wheel during a traffic accident. Therefore, in the field of impact biomechanics, the study of the liver has attracted considerable interest. We consider the case of abdominal compression by a steering wheel and perform quasi-static compression tests using a full-scale porcine liver that is not shaped into a cylinder or a cube in order to determine the basic mechanical properties of an unaltered liver. A human liver and a porcine liver have different structures; the former is divided into two regions (right and left lobe), while the latter is divided into four regions (right medial, right lateral, left medial, and left lateral lobe). Therefore, we compared the compressive properties of the four regions of the porcine liver using a cylindrical indenter to simulate the effect of the steering wheel of a passenger car. No significant differences were observed among the four porcine liver regions. Next, we compared the differences in mechanical properties, behaviors, and injury patterns of the porcine liver by using four compressive indenter profiles. The indenters were made from an acrylic resin. Although the injury patterns were different, yield loads were observed under an approximately constant compressive ratio regardless of the compressive indenter profile.

Keywords

Liver, Steering Wheel, Compressive Characteristics, Indenter Profile, Compressive Ratio

Paper information

Yutaku KANETA, Hisashi OHKAWA, Yushi SUZUKI, Toshiaki HARA, Yoshihiro YAMAMOTO, Shinichi TAKAYAMA, Koichi KAMIJI and Tsuyoshi YASUKI, “Compressive Characteristics of Porcine Whole Liver”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 4 (2009), pp.500-509 . doi:10.1299/jbse.4.500

Intermittent pattern of mechanical stimulation has been demonstrated to possess different regulatory effects on cell metabolism in many connective tissues, but little is known about tenocyte responses. A previous study has shown that the application of a small number of continuous cyclic strain inhibited collagen synthesis by tenocytes in explants, whereas a large number of strain cycles upregulated the synthesis. Thus, the present study tested the hypothesis that collagen synthesis is influenced by cyclic tensile strain provided in an intermittent manner. A total of 43,200 cycles of tensile strain, with a 3% amplitude superimposed on a 2% static strain was provided in four different intermittent patterns with different strain/unstrain periods: 10 minutes, 1 hour, 6 hours, and 12 hours. The amount of newly synthesised collagen, both those retained in strained fascicles and released into culture media, were not significantly altered by the application of different patters of intermittent cyclic strain. The present findings may suggest that, unlike other connective tissue cells, tenocyte responses are predominantly regulated by the total number of strain cycles.

Keywords

Tendon, Fascicle, Cyclic Strain, Collagen, Tenocyte, Metabolism

Paper information

Eijiro MAEDA, Julia C. SHELTON, Dan L. BADER and David A. LEE, “Effect of Intermittent Cyclic Tensile Strain on Collagen Synthesis by Tenocytes in Isolated Fascicles”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 4 (2009), pp.510-517 . doi:10.1299/jbse.4.510

Mechanical properties of human aortic aneurysm tissues were measured with a biaxial tensile tester. Fifteen-mm-square specimens were obtained from thoracic aortic aneurysms of various origins and from undilated aortas adjacent to the aneurysms during aneurysmectomy, and were stored frozen until the measurement. Each specimen was stretched biaxially in physiological saline at room temperature at the rate of ?0.2 mm/sec. Although the ordered displacement was set equal for both directions, real strain applied to the specimens was not equibiaxial. The stress-strain curves under equibiaxial stretch were obtained by fitting measured curves with a strain energy function considering material anisotropy. Effects of freezing and ambient temperature on the mechanical properties were evaluated with porcine thoracic aortas. The mechanical properties of the frozen-stored specimens at 23°C were almost similar to those of the fresh specimens at 37 °C. Elastic modulus at zero load averaged for both directions Hmi = (Hxi+Hyi)/2 was higher (P < 0.01) in the aneurysm tissues (1450 ± 250 kPa, mean ± SEM, n = 26) than in the undilated tissues (650 ± 140 kPa, n = 10). Anisotropy index K = |Hxi-Hyi|/Hmi was not significantly different between the aneurysm (20 ± 3%) and the undilated tissues (12 ± 3%) for all specimens. For the specimens whose elastic modulus Hmi was smaller than 1 MPa, however, the index K was significantly higher (P < 0.05) in the aneurysm specimens (23.1 ± 5.3%, n = 14) than the undilated tissues (9.5 ± 2.5%, n = 8). These results indicate aneurysm tissues are not only stiffer but also more anisotropic than the nonaneurysmal tissues.

Keywords

True Aneurysm, Dissecting Aneurysm, Annulo Aortic Ectasia, Post-Stenotic Dilatation, Marfan's Syndrome, Mechanical Properties, Tensile Test, Anisotropy, Elastic Modulus

Paper information

Takeo MATSUMOTO, Tomohiro FUKUI, Toshihiro TANAKA, Naoko IKUTA, Toshiro OHASHI, Kiichiro KUMAGAI, Hiroji AKIMOTO, Koichi TABAYASHI and Masaaki SATO, “Biaxial Tensile Properties of Thoracic Aortic Aneurysm Tissues”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 4 (2009), pp.518-529 . doi:10.1299/jbse.4.518

The mechanical and morphological properties of patellar tendons were in vivo measured during isometric knee extension contractions in ten male subjects using ultrasonography. The subjects were accustomed to various exercise and training. The stiffness, cross-sectional area, and tangent modulus of the patellar tendons were positively correlated with the quadriceps strength. The enhancement of contractile forces induced by exercise and training increases the quadriceps strength. Since the primary role of patellar tendons is the transmission of contractile forces from quadriceps to tibia, the contractile forces are directly applied to the patellar tendons. Therefore, in the subjects with the larger quadriceps strength, the forces applied to the patellar tendons during exercise and training may be larger, and the force enhancement may induce the increases in the stiffness, cross-sectional area, and tangent modulus of the patellar tendons.

Keywords

Mechanical Properties, Patellar Tendon, Quadriceps Strength, Ultrasonography

Paper information

Noritaka YAMAMOTO and Takashi OTA, “Relationships between the Mechanical Properties of Patellar Tendons and Quadriceps Strength in Humans”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 4 (2009), pp.530-538 . doi:10.1299/jbse.4.530

Incomplete or subfailure injuries of tendons occur more frequently than their complete ruptures. However, the mechanical behavior of the incompletely injured tissues is poorly understood. In the present study, we quantified the mechanical properties, microstructure, and ultrastructure of rabbit patellar tendons subjected to non-destructive overloading. No significant changes in the mechanical properties were observed in the tendon specimens which were applied a subfailure stretch equivalent to 80% of the failure stress of the control tendons at a low strain rate (1.67 %/sec). There was a significant decrease not in the tensile strength but in the tangent modulus of the specimens when they were subjected to 90% of the control failure stress at the low rate. For the same level of overloading at a high strain rate (16.7 %/sec), both the modulus and strength of the overloaded specimens were significantly lower than those of the control ones. Microstructually, irrespective of the strain rate, crimped collagen fibers in the overloaded tendons were straightened by the 90% overloading. In contrast, adverse alterations in the ultrastructure were induced by the 90% overloading only at the high rate. These results indicate that tendinous tissues have potential capacities to maintain the original strength if a relatively high overload is monotonically applied at lower strain rates. However, it is possible that subfailure overloads delivered at higher strain rates produce more severe changes in the properties and structures of the tissues.

Keywords

Biomechanics, Patellar Tendon, Subfailure Injury, Overloading, Tensile Property, Strain Rate Effect, Crimp Structure, Collagen Fibril

Paper information

Ei YAMAMOTO and Kousuke OHTA, “Effects of Non-Destructive Overloading on the Mechanical Properties, Microstructure and Ultrastructure of Rabbit Patellar Tendons”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 4 (2009), pp.539-549 . doi:10.1299/jbse.4.539