The finless porpoise has characteristic tubercles on its dorsal ridge. These tubercles are supposed to have biological and mechanical functions. In the former, specific nerve endings and fibers exist in the tubercles indicating its function as a sensory organ. In the latter, tubercles provide fluid dynamic functions such as underwater drag reduction or inhibition of wave or spray drag while breathing at the sea surface. This research focuses on the latter function aiming at the application to the drag reduction in moving vehicles. Small projection models, or tubercle models were fabricated with resin and tested in the wind tunnel to investigate the effect on the lift and the drag characteristics of an airplane model with the tubercle models attached on the wing-fuselage connection. In consequence, it was shown that the tubercles effectively delayed the wing stall at high angles of attack without largely degrading the wing performance. The oil flow experiments also clarified that this delay of wing stall was caused by the inhibition of flow separation on the wing surface. The tubercles then had a positive influence on the flow around the wing or fuselage effectively inhibiting the flow separation and thus may be a useful device to reduce drag, noise, or vibration of moving vehicles.
The purpose of the present study is to determine the tensile properties of the single collagen fibrils with various diameters using our original tensile test method. The fibrils were directly isolated from mouse tail tendons. The both ends of the fibril were wound onto the tips of microneedles several times using micromanipulators. The fibril and tips were immersed in physiological saline solution. Then, the fibril was stretched to failure by moving the microneedle. The tensile properties of the 26 fibrils with various diameters ranging from 140 to 490 nm were determined. The stress-strain curves of these fibrils were almost linear or upward convex at the large strain region. These fibrils showed the tensile strength of 47-310 MPa, the strain at failure of 7.3-81 %, and the tangent modulus of 160-1600 MPa. The tensile strength and tangent modulus decreased significantly with increasing the diameter. On the other hand, the strain at failure increased significantly with increasing the diameter.
Understanding the intervertebral disc response to mechanical loads is important to prevent back injuries. The experimental and the finite element methods are widely used for that purpose but methodological triangulation is deficient due to lack of a complementary method. This study aims at choosing theories and assumptions that could be used to develop an analytical model for stress analysis of intervertebral discs. Thin-shell and beam-on-elastic-foundation theories are used in conjunction with an iterative method to account for large deformation of the disc. The model simulates an axial compression load acting on a simplified axisymmetric disc composed of a multi-shell linear and isotropic structure surrounding a pressurized cavity. The highly deformable lamellae are idealized by either circular or parabolic arches in the sagittal plane, and their effect on stress and strain response are compared. The circumferential and longitudinal stresses are compared to those of a simplified finite element model. The comparison shows that the analytical approach is promising and allows to identify improvements for future studies. The use of a parabolic profile is advantageous and allows to account for the interactive support of the lamellae near the endplates. The method should be adapted to improve bulge deformation obtained across the thickness of anulus fibrosus, and the model should include material anisotropy and hyperelasticity.
Adherent cells generate traction forces, which are generated by and transmitted along the actin cytoskeleton to the underlying external substrate via focal adhesions. These cell generated forces are fundamental for maintaining cell shape and driving cell migration as well as triggering signaling pathways to promote processes such as differentiation and proliferation. Here we investigate how mechanical stretch affects traction forces. Following moderate mechanical stretching and release, traction forces are increased and then return to basal levels. However, when cells are stretched with relatively large strains, >10%, traction forces fail to return to basal levels and are attenuated. In this study, we investigate whether cells experiencing attenuated traction forces, following a large strain, can still respond to subsequent mechanical stretching. Traction forces were measured in cells following a consecutive 12% increase in mechanical stretch. We show that, even after traction force attenuation occurs, cells are able to respond to consecutive mechanical stretching by increasing traction force. Visualization of stress fibers, with GFP-actin, indicates that the attenuation of traction force is accompanied by a decrease in stress fiber integrity during mechanical stretching. The ability of cells to increase traction force during a second round of stretching, following attenuation, maybe generated by intact stress fibers that escape damage.
Bone tissue is a composite structure of apatite particles distributed in collagen fibril matrix on a nano-size scale. Mechanical properties of cortical bone are determined by the apatite-collagen composition. The amount and specific orientation of apatite crystals strongly affect the mechanical properties of macroscopic bone tissue such as anisotropic elastic modulus and fracture toughness. The progression of mineralization with tissue aging results in a reduction of fracture toughness due to embrittlement of tissue caused by excessive increase of apatite density. This study focused on the change of impact fracture characteristics of cortical bone tissue with reduction of apatite concentration (demineralization). A compact-sized impact loading device for Charpy tests was developed to measure the absorbed energy for impact fracture of bone specimens in the 0.5 and 1.0 J input energy range. Cortical bone specimens of 3 × 3 × 30 mm were prepared from shaft of bovine femurs. Differences relating to the anisotropy in axial and circumferential direction of the femur were observed in the absorbed energy values. The values of the axial specimens were greater than the circumferential specimens. Axial bone specimens were demineralized in ethylenediaminetetraacetic acid (EDTA) solution at 5°C. The demineralization progressed slowly from surfaces of the specimen. The 24-hour demineralization created a collagen layer at the surface of specimen and the demineralized specimen showed higher absorbed energy than unprocessed specimens. The absorbed energy in defective specimens with a square shaped small slit of 0.5 × 0.5 mm increased after local demineralization process. The time for effective demineralization could be reduced to 2 hours in the case of 37°C condition. The demineralization process improved the fracture characteristics of both intact and defective cortical bone tissue.
Cancer vaccine therapy is a novel treatment method which uses an extra-fine (0.53 mm in diameter (25 G)) needle to deliver a tumor-specific vaccine directly into a tumor. This method is expected to deliver an effective treatment with few side effects. However, the procedure is very difficult to perform because of needle deflection. We intend to develop a needle insertion robot to combat this deflection and deliver the vaccine successfully. The key features of the robot were developed to minimize needle tip deflection while traversing complex tissues which is composed of various tissues. In this paper, as targeted to lower abdomen, we propose a control method for minimizing needle tip deflection during insertion through vibration and axial rotation. The effectiveness of the proposed method was evaluated in artificial and biomaterial tissues found in the lower abdomen (muscle, bowel, and skin). Results demonstrated that the effectiveness of vibration and rotation was changed depending on the kind of the tissues. The rotation was effective to the thick tissues (muscle and skin) and the vibration was effective to membranous tissues (bowel). Based on the results, our method used vibration and rotation when the needle is inserted into the skin and muscle and only vibration when traversing through soft tissue such as the bowel. In conclusion, the proposed method can minimize needle tip deflection robustly in a lower abdomen phantom.
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