Comparative equilibrium mechanical properties of bovine and lamprey cartilaginous tissues

Constitutive behaviour of paddlefish (Polyodon spathula) cartilage

This study explored the constitutive behaviour of the midline cartilage of the paddlefish (Polyodon spathula) rostrum and examined the properties of the cartilage as a function of stress state and strain rate. The cartilage structure of the paddlefish contributes to the physical characteristics of the unique rostrum, and is of much interest as an inspiration for engineered structures. Low-strain rate testing (∼0·01/s) results indicated an average compressive yield stress of 11·34 ± 3·10 MPa and an average tensile yield stress of 3·62 ± 0·62 MPa. High-strain rate testing (∼100/s) results showed an average compressive yield stress of 25·07 ± 10·86 MPa. A histological study showed that the material is a type of hyaline cartilage. An Ogden hyperelastic model was used for finite-element analysis and fit very well with experimental data. This paper contributes to an overall study examining the electrosensory capabilities, hydrodynamics and structure–property relationships of the rostrum.

Structure and mechanical implications of the pectoral fin skeleton in the Longnose Skate (Chondrichthyes, Batoidea)

Animal propulsion systems are believed to show high energy and mechanical efficiency in assisting movement compared to artificial designs. As an example, batoid fishes have very light cartilaginous skeletons that facilitate their elegant swimming via enlarged wing-like pectoral fins. The aim of this work is to illustrate the hierarchical structure of the pectoral fin of a representative batoid, the Longnose Skate (Raja rhina), and explain the mechanical implications of its structural design. At the macro level, the pectoral fins are comprised of radially oriented fin rays, formed by staggered mineralized skeletal elements stacked end-to-end. At the micro level, the midsection of each radial element is composed of three mineralized components, which consist of discrete segments (tesserae) that are mineralized cartilage and embedded in unmineralized cartilage. The radial elements are wrapped with aligned, unmineralized collagen fibers. This is the first report of the detailed structure of the ray elements, including the observation of a 3-chain mineralized tesserae. Structural analyses demonstrate that this configuration enhances stiffness in multiple directions. A two-dimensional numerical model based on the morphological analysis demonstrated that the tessera structure helps distributing shear, tensile and compressive stress more ideally, which can better support both lift and thrust forces when swimming without losing flexibility.

STATEMENT OF SIGNIFICANCE

Batoid fishes have very light cartilaginous skeletons that facilitate their elegant swimming by applying their enlarged wing-like pectoral fins. Previous studies have shown structural features and mechanical properties of the mineralized cartilage skeleton in various batoid fishes. However, the details of the pectoral fin structure at different length scales, as well as the relationship between the mechanical properties and structural design remains unknown. The present work illustrates the hierarchical structure of the pectoral fin of the Longnose Skate (a representative batoid fish) and verifies the materials configuration and structural design increases the stiffness of fin skeleton without a loss in flexibility. These results have implications for the design of strong but flexible materials and bio-inspired autonomous underwater vehicles (AUVs).

Decrease of the electrical potentials measured on the surface of the knee and produced by cartilage compression during successive loading cycles

Electroarthrography (EAG) is a new technique for measuring electrical potentials appearing on the knee surface during loading that reflects cartilage quality and joint contact force. Our objective was to investigate the evolution of EAG signals during successive loading cycles. The study was conducted on 20 standing subjects who shifted their body weight to achieve knee loading. Their EAG signals were recorded during 10 successive loading cycles, and during a subsequent sequence of 10 cycles recorded after a 15min exercise period. Multiple linear regression models estimated the electro-mechanical ratio (EMR) interpreting the ability of cartilage to generate a certain potential for a given ground reaction force by taking into account this force and the center of pressure displacements during unipedal stance. The results showed that the EMR values slowly decreased with successive cycles: during the initial sequence, the correlation coefficients between EMR values and sequence numbers were significant at 3 of the 4 electrode sites (p<0.05); for the post-exercise sequence, the EMR values still decreased and were significantly lower than during the initial sequence (p<0.001). The reduction of EMR values could arise from muscle activity and habituation of the stretch reflex, and also from the time dependent electromechanical properties of cartilage. In conclusion, refraining from physical activity before the EAG measurements is important to improve measurement repeatability because of the EMR decrease. The electromechanical model confirmed the role of EAG as a natural sensor of the changes in the knee contact force and also improved EAG measurement accuracy.

No bones about it: an enigmatic Devonian fossil reveals a new skeletal framework--a potential role of loss of gene regulation

Palaeospondylus gunni (Devonian, Scotland) is an enigmatic vertebrate, assigned to various jawless and jawed groups since its original description. New sections through the whole body allow description of a novel skeletal tissue for Palaeospondylus, comprising the entire skeleton. This tissue is mineralized cartilage and is characterized by large cell spaces embedded in minimal matrix. Bone is completely absent. Calcium phosphate mineralization has a differential topography of deposition within the cartilage that reflects a biogenic origin, despite subsequent diagenetic modification. This combination of hypertrophied cell spaces surrounded by regionalized mineralized matrix differs from all other cartilage in fossil and extant vertebrates. However, it compares most closely to gnathostome endochondral bone in early developmental stages. For example, Palaeospondylus skeletal histology differs from the Devonian agnathan Euphanerops and extant lamprey cartilage. Comparison with mineralized cartilage of armored fossil agnathans and placoderms shows the histology is not comparable to globular calcified cartilage. It also differs from that in extant chondrichthyan mineralized tesserae, which is restricted to a subperichondral zone. Amongst this diversity of calcified cartilage types we discuss various interpretations, including one that implicates tissue either in developmental stasis, before osteoblasts can deposit bone, or at a phylogenetic stage when this step has not evolved. These very different hypotheses highlight difficulties in interpreting fossil ontogenies when phylogenetic relationships are uncertain. Nevertheless, we propose that the composition of the Palaeospondylus skeleton represents a fossilized ontogenetic stage of endochondral bone, a type of bone characteristic of osteichthyan vertebrates.