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Application of soft and compliant joints in grasping mechanisms received an increasing attention during recent years. This article suggests the design and development of a novel bio-inspired compliant finger which is composed of a 3D printed rigid endoskeleton covered by a soft matter. The overall integrated system resembles a biological structure in which a finger presents an anthropomorphic look. The mechanical properties of such structure are enhanced through optimization of the repetitive geometrical structures that constructs a flexure bearing as a joint for the fingers. The endoskeleton is formed by additive manufacturing of such geometries with rigid materials. The geometry of the endoskeleton was studied by finite element analysis (FEA) to obtain the desired properties: high stiffness against lateral deflection and twisting, and low stiffness in the desired bending axis of the fingers. Results are validated by experimental analysis.

Cells form networks in animal tissues through synaptic, chemical and adhesive links. Invertebrate muscle cells often connect to other cells through desmosomes, adhesive junctions anchored by intermediate filaments. To study desmosomal networks, we skeletonised 853 muscle cells and their desmosomal partners in volume electron microscopy data covering an entire larva of the annelidPlatynereis. Muscle cells adhere to each other, to epithelial, glial, ciliated, and bristle-producing cells and to the basal lamina, forming a desmosomal connectome of over 2,000 cells. The aciculae – chitin rods that form an endoskeleton in the segmental appendages – are highly connected hubs in this network. This agrees with the many degrees of freedom of their movement, as revealed by video microscopy. Mapping motoneuron synapses to the desmosomal connectome allowed us to infer the extent of tissue influenced by motoneurons. Our work shows how cellular-level maps of synaptic and adherent force networks can elucidate body mechanics.

In this research, a specimen of arthropod, infraspecies Cormocephalus calcaratus (centipede) is the matter of study for modeling its trunk-limb biomechanics. The endoskeletal system was built to model and approach its passive dynamics motion. The limb’s musculoskeletal system was digitally ’sculpted’ in three-dimension using the planar taxonomic sagittal, ventral and transventral views as metrical references, constrained in scale and geometry. The endoskeleton was modeled by an equivalent network of spring-mass-damper muscles with five joints controlled by two input muscles to manipulate the limb’s tip. The kinematic position equations with their higher-order derivatives and the inner muscles dynamics were deduced for a Newton-based dynamic controller to resemble scramble up motion. Simulations produced realistic controlled motions with expected limb’s dexterity underactuation.

Only the second bored cup of the disparid crinoid Synbathocrinus conicus Phillips is described, infested by a pit of Oichnus paraboloides Bromley. Both bored specimens are from the Mississippian of Salthill Quarry, Clitheroe, Lancashire, UK, although the search for others has extended from northern Europe to North America. The first, described 30 years ago, infested a plate triple-junction of the cup on the presumed up-current side of the crinoid; the new specimen, in contrast, is in the centre of a radial plate, which is inflated as a growth response to infestation. We informally name the producing organism the ‘Salthill bug’. Although unknown, this was a small, unmineralized invertebrate that commonly attached to elevated positions on living crinoids and was likely a filter feeder. It constructed a domicile by boring into the crinoid endoskeleton, and could invade both living and dead crinoid skeletons. On crinoid stems it was commonly gregarious, a habit perhaps favoured by secretions by the first ‘Salthill bug’ to settle, attracting conspecific larvae and similar to the settling patterns of some modern sessile invertebrates. Comparison with Oichnus from Trearne Quarry, Ayrshire, UK, reveals several differences between the pits in infested crinoids at the two sites.

Introduction: AFX is a bifurcated unibody aortic endograft for the treatment of Abdominal Aortic aneurysms. It consists of an inner metallic endoskeleton with multiple metallic struts covered by a polytetrafluoroethylene graft fabric. The endoskeleton is sutured to the outer fabric only at the proximal and distal ends. The unique design of AFX aims at fixation onto the aortic bifurcation while a proximal cuff ensures sealing at the infrarenal level.Areas covered: Since this endograft design by Endologix has undergone significant changes over the last years, the aim of this article is to present its unique structure and deployment method and discuss the relevant clinical results as well as reported complications and associated concerns.Expert commentary: the AFX stent-graft exhibits very satisfactory clinical mid-term results in abdominal aortic aneurysms treated within the instructions-for-use. Its 'active-seal' concept of infrarenal fixation stemming from the loose conjugation of the fabric material to the endoskeleton can accommodate efficiently to challenging necks with thrombus or morphological irregularities, thereby extending the anatomical sealing zone without exerting significant radial outward force. Long-term results are needed to validate the promising performance of AFX.

In current research on soft grippers, pneumatically actuated soft grippers are generally fabricated using fully soft materials, which have the advantage of flexibility as well as the disadvantages of a small gripping force and slow response speed. To improve these characteristics, a novel pneumatic soft gripper with a jointed endoskeleton structure (E-Gripper) is developed, in which the muscle actuating function has been separated from the force bearing function. The soft action of an E-Gripper finger is performed by some air chambers surrounded by multilayer rubber embedded in the restraining fiber. The gripping force is borne and transferred by the rigid endoskeleton within the E-Gripper finger. Thus, the gripping force and action response speed can be increased while the flexibility is maintained. Through experiments, the bending angle of each finger segment, response time, and gripping force of the E-Gripper have been measured, which provides a basis for designing and controlling the soft gripper. The test results have shown that the maximum gripping force of the E-Gripper can be 35 N, which is three times greater than that of a fully soft gripper (FS-Gripper) of the same size. At the maximum charging pressure of 150 kPa, the response time is 1.123 s faster than that of the FS-Gripper. The research results indicate that the flexibility of a pneumatic soft gripper is not only maintained in the case of the E-Gripper, but its gripping force is also obviously increased, and the response time is reduced. The E-Gripper thus shows great potential for future development and applications.

Starfish (order: Asteroidea) possess a complex endoskeleton composed of thousands of calcareous ossicles. These ossicles are embedded in a body wall mostly consisting of a complex collagen fiber array. The combination of soft and hard tissue provides a challenge for detailed morphological and histological studies. As a consequence, very little is known about the general biomechanics of echinoderm endoskeletons and the possible role of ossicle shape in enabling or limiting skeletal movements. In this study, we used high‐resolution X‐ray microscopy to investigate individual ossicle shape in unprecedented detail. Our results show the variation of ossicle shape within ossicles of marginal, reticular and carinal type. Based on these results we propose an additional classification to categorize ossicles not only by shape but also by function into ‘connecting’ and ‘node’ ossicles. We also used soft tissue staining with phosphotungstic acid successfully and were able to visualize the ossicle ultrastructure at 2‐μm resolution. We also identified two new joint types in the aboral skeleton (groove‐on‐groove joint) and between adambulacral ossicles (ball‐and‐socket joint). To demonstrate the possibilities of micro‐computed tomographic methods in analyzing the biomechanics of echinoderm skeletons we exemplarily quantified changes in ossicle orientation for a bent ray for ambulacral ossicles. This study provides a first step for future biomechanical studies focusing on the interaction of ossicles and soft tissues during ray movements.

Introduction: The deep-sea asteroid species of Brisingida have a nearly global distribution but have remained poorly understood due to their deep bathymetric distributions and fragile skeletons. Objective: To describe the external and internal morphology of Midgardia xandaros including the skeletal arrangement, through multifocal and SEM techniques. Methods: We examined a total of 21 specimens, including 27 arm fragments, from the Gulf of Mexico and Honduras. Two specimens were dissected. Results: Detailed descriptions of pedicellariae, abactinal, intercostal, inferomarginal, adambulacral, ambulacral, odontophore, and oral ossicles, and their spines are provided, emphasizing the articulations and muscle attachments. C-shaped valves pedicellariae and small pedicellariae valves with shorter denticulation areas were recognized. Conclusions: The morphological description of M. xandaros is expanded, providing the most extensive description of abactinal, first adambulacral, first and subsequent inferomarginal ossicles, abactinal spines, and C-shaped, crossed pedicellariae, as well as the distal arm plates, for a brisingid species using SEM to date. Resumen Introducción: Las estrellas de mar de profundidad del orden Brisingida tienen una distribución casi global, sin embargo, han sido poco estudiadas debido a su profunda distribución batimétrica y esqueleto frágil. Objetivo: Describir la morfología externa e interna de Midgardia xandaros incluyendo el arreglo de las placas del esqueleto mediante técnicas de microscopía multifocal y electrónica de barrido (MEB). Métodos: Se examinó un total de 21 ejemplares, incluyendo 27 fragmentos de brazos, provenientes del Golfo de México y Honduras. Dos de estos ejemplares fueron disectados. Resultados: Se presenta la descripción de pedicelarios; placas abactinales, intercostales, inferomarginales, adambulacrales, ambulacrales, orales y odontóforo, y sus espinas, enfatizando los sitios de articulaciones e inserción de músculos. Se reconocieron pedicelarios con valvas con forma de C, y pequeños pedicelarios cuyas valvas poseen áreas de denticulación cortas. Conclusiones: La descripción morfológica de M. xandaros es ampliada, presentado por primera vez la morfología de las placas abactinales, primera adambulacrales, primera y subsecuentes inferomarginales, espinas abactinales y pedicelarios con valvas con forma de “C”, así como las placas distales de los brazos para una especie del orden Brisingida.

Purpose: Bridging stents undergo millions of cycles during respiratory movements of the kidneys throughout the patient’s life. Thus, understanding the response of fabric and endoskeleton of the stent to cyclic loading over the time is crucial. In this study, we compare the fatigue resistance of the Viabahn Balloon-Expandable stent-graft (VBX) with the widely used Advanta V12/iCast under prolonged stress induction. Materials and Methods: A polyester test sheet with 10 fenestrations was used simulating a fenestrated endograft. Five 6×59 mm VBX stent-grafts and five 6×58 mm Advanta stent-grafts were implanted into 6×6 mm fenestrations. The stents were flared with a 10×20 mm PTA (percutaneous transluminal angioplasty) catheter and connected with a fatigue stress machine. All stent-grafts were evaluated by microscopy and radiography at baseline and after regular intervals until 50,000,000 cycles were applied, simulating a life span of approximately 75 months. Freedom from fracture (FF), freedom from initial polytertafluoroethylene (PTFE) changes (FIC), and from PTFE breakpoint (FBP, all-layer defect) were calculated. Results: Digital radiographic images did not show any stent fracture in both groups after 50,000,000 cycles. The VBX stent-graft was free from any all-layer defects at the conclusion of 50,000,00 cycles resulting in a significant higher FBP compared with Advanta V12 (50,000,000 vs 33,400,000; pConclusions: In fatigue tests simulating respiration movements, VBX and Advanta V12 performed equally well in terms of fracture resistance and freedom from initial PTFE changes. VBX maintained freedom from PTFE breakpoint throughout the full 50,000,000 cycles. All-layers defects were detected only in Advanta and were mainly caused by penetration of the nitinol ring through the PTFE.

Growing evidence indicates that reduced uterine perfusion pressure (RUPP) triggers the cascade of events leading to preeclampsia. Edaravone is a powerful free radical scavenger used for the treatment of ischemia/reperfusion diseases due to its anti-oxidative stress and anti-inflammatory properties. Here we investigate the effect of edaravone (3 mg/kg) on different maternal and fetal outcomes of RUPP-induced placental ischemia mice model. RUPP surgery was performed on gestation day (GD) 13 followed by edaravone injection from GD14 to GD18, sacrifice day. The results showed that edaravone injection significantly decreased the maternal blood pressure (113.2 ± 2.3 mmHg) compared with RUPP group (131.5 ± 1.9 mmHg). Edaravone increased fetal survival rate (75.4%) compared with RUPP group (54.4%), increased fetal length, weights, and feto-placental ratio (7.2 and 5.7 for RUPP and RUPP-Edaravone groups, respectively) compared with RUPP group. In addition, RUPP resulted in many fetal morphological abnormalities as well as severe delayed ossification, however edaravone decreased the morphological abnormalities and increased the ossification of the fetal endoskeleton. Edaravone improved the histopathological structure of the maternal kidney and heart as well as decreased the elevated blood urea and creatinine levels (31.5 ± 0.15 mg/dl (RUPP), 25.6 ± 0.1 mg/dl (RUPP+edaravone) for urea and 5.4 ± 0.1 mg/dl (RUPP), 3.5 ± 0.1 mg/dl (RUPP+edaravone) for creatinine) and decreased cleaved caspase-3 expression in the maternal kidney. In conclusion, this study demonstrated that our RUPP mice model recapitulated preeclampsia symptoms and edaravone injection ameliorated most of these abnormalities suggesting its effectiveness and potential application in preeclampsia treatment regimes. Supplementary Information The online version contains supplementary material available at 10.1186/s12958-021-00707-2.

Reptiles are the only amniotes that maintain the capacity to regenerate appendages. This study presents the first anatomical and histological evidence of tail repair with regrowth in an archosaur, the American alligator. The regrown alligator tails constituted approximately 6–18% of the total body length and were morphologically distinct from original tail segments. Gross dissection, radiographs, and magnetic resonance imaging revealed that caudal vertebrae were replaced by a ventrally-positioned, unsegmented endoskeleton. This contrasts with lepidosaurs, where the regenerated tail is radially organized around a central endoskeleton. Furthermore, the regrown alligator tail lacked skeletal muscle and instead consisted of fibrous connective tissue composed of type I and type III collagen fibers. The overproduction of connective tissue shares features with mammalian wound healing or fibrosis. The lack of skeletal muscle contrasts with lizards, but shares similarities with regenerated tails in the tuatara and regenerated limbs in Xenopus adult frogs, which have a cartilaginous endoskeleton surrounded by connective tissue, but lack skeletal muscle. Overall, this study of wild-caught, juvenile American alligator tails identifies a distinct pattern of wound repair in mammals while exhibiting features in common with regeneration in lepidosaurs and amphibia.

Background As rhinoplasty techniques have evolved to more extensive dissections, the incidence of iatrogenic deformities, such as alar rim retraction, has risen. Its mechanism is presently unknown. This study examined the microscopic anatomy of the nasal ala to define architectural support elements at the histologic level to determine why rhinoplasty dissection creates such deformities. Methods Eight cadaveric noses were harvested and sectioned through the soft triangle and ala. Various tissue stains were performed. Slides were examined using light microscopy. Anatomical features pertaining to cartilage, skin, mucosa, elastic fibers, and muscle were documented. Results Four male and four female noses were sectioned. The median cadaver age was 64 years (range, 47 to 83 years). On Elastica van Gieson stain, distinct elastic fibers span from the vestibular lining to the caudal margin of the lower lateral cartilage, and from the caudal edge of the lower lateral cartilage to the external alar skin. In the nasal ala midsection, trichrome stains reveal that skeletal muscle is located far beyond the lower lateral cartilage, close to the free alar margin. The soft triangle shows a distinct microanatomical structure, with heavy longitudinal condensations of elastin. These histologic findings have not been previously reported. Conclusions A distinct anatomical alar wall endoskeleton has been identified. It is obligatorily disrupted by specific rhinoplasty maneuvers when dissection is carried out over the lateral crura and into areas without cartilaginous support. This microanatomy may explain factors that contribute to postoperative alar wall retraction. Leaving this area undisturbed or performing adjunctive measures with rhinoplasty can provide structural support to the external valves, thus minimizing the risk of deformity.

Across the teleost skeleton, cartilages are diverse in their composition suggesting subtle differences in their developmental mechanisms. This study aims to elucidate the regulatory role of bone morphogenetic protein (BMPs) during the morphogenesis of two cartilage elements in zebrafish: the scleral cartilage in the eye and the caudal fin endoskeleton. Zebrafish larvae were exposed to a BMP inhibitor (LDN193189) at a series of timepoints preceding the initial appearance of the scleral cartilage and caudal fin endoskeleton. Morphological assessments of the cartilages in later stages, revealed that BMP-inhibited fish harbored striking disruptions in caudal fin endoskeletal morphology, regardless of the age at which the inhibitor treatment was performed. In contrast, scleral cartilage morphology was unaffected in all age groups. Morphometric and principal component analysis, performed on the caudal fin endoskeleton, revealed differential clustering of principal components one and two in BMP-inhibited and control fish. Additionally, the expression of sox9a and sox9b were reduced in BMP-inhibited fish when compared to controls, indicating that LDN193189 acts via a Sox9-dependent pathway. Further examination of notochord flexion also revealed a disruptive effect of BMP inhibition on this process. This study provides a detailed characterization of the effects of BMP inhibition via LDN193189 on zebrafish cartilage morphogenesis and development. It highlights the specific, localized role of the BMP-signaling pathways during the development of different cartilage elements and sheds some light on the morphological characteristics of fossil teleosts that together suggest an uncoupling of the developmental processes between the upper and lower lobes of the caudal fin.

The ontogeny of the paired appendages has been extensively studied in lungfishes and tetrapods, but remains poorly known in coelacanths. Recent work has shed light on the anatomy and development of the pectoral fin in Latimeria chalumnae. Yet, information on the development of the pelvic fin and girdle is still lacking. Here, we described the development of the pelvic fin and girdle in Latimeria chalumnae based on 3D reconstructions generated from conventional and X-ray synchrotron microtomography, as well as MRI acquisitions. As in other jawed vertebrates, the development of the pelvic fin occurs later than that of the pectoral fin in Latimeria. Many elements of the endoskeleton are not yet formed at the earliest stage sampled. The four mesomeres are already formed in the fetus, but only the most proximal radial elements (preaxial radial 0-1) are formed and individualized at this stage. We suggest that all the preaxial radial elements in the pelvic and pectoral fin of Latimeria are formed through the fragmentation of the mesomeres. We document the progressive ossification of the pelvic girdle, and the presence of a trabecular system in the adult. This trabecular system likely reinforces the cartilaginous girdle to resist the muscle forces exerted during locomotion. Finally, the presence of a preaxial element in contact with the pelvic girdle from the earliest stage of development onward questions the mono-basal condition of the pelvic fin in Latimeria. However, the particular shape of the mesomeres may explain the presence of this element in contact with the girdle.

The purpose of this study was to evaluate the changes in pulse wave velocity and left ventricular dimensions in patients undergoing stent-graft treatment for aortic arch aneurysm. From July 2008 to February 2019, 86 patients underwent thoracic endovascular aortic repair of an aortic arch aneurysm. Changes in pulse wave velocity (PWV), echocardiogram findings, and long-term outcomes were compared between endoskeleton type (n = 60) and exoskeleton type stent-graft (n = 26). There was no significant difference in patient demographics except for diabetes which was more observed in endoskeleton type (p = 0.017). There was a significant increase in PWV in exoskeleton type after surgery, which further progressed at a median follow-up of 32 months (before: 2047 cm/s vs. after: 2259 cm/s vs. follow-up: 2486 cm/s, p = 0.010, p = 0.017). No significant difference was observed in endoskeleton type (before: 1980 cm/s vs. after: 2058 cm/s, vs. follow-up: 2042 cm/s, p = 0.25, p = 0.34). Echocardiogram performed at a median period of 46.3 months, revealed a significant increase in left ventricular diastolic volume (LVDV) (before: 107.4 ± 20.6 ml vs. follow-up: 127.7 ± 27.5 ml, p = 0.003) and decrease in e′ (before: 5.5 ± 1.78 cm/s vs. follow-up: 4.7 ± 1.72 cm/s, p = 0.012) in exoskeleton type, while no significant change was observed in endoskeleton type (LVDV: before: 102.6 ± 32.3 ml vs. follow-up: 96.9 ± 35.4 ml, p = 0.74; e′: before: 4.4 ± 1.21 cm/s vs. follow-up: 4.8 ± 1.40 cm/s, p = 0.68). At the median period of 61.3 months, there was no significant difference in long-term mortality (p = 0.89). However, the endoskeleton type was associated with a lower incidence of a cardiac event (p = 0.034) and cerebrovascular event (p = 0.029). Types of endoprosthesis might affect differently on physiological changes and its accommodated risk factors after surgery.

While it is well known that the notochord of bony fishes changes over developmental time, less is known about how it varies across different body regions. In the development of the Atlantic salmon, Salmo salar L., cranial and caudal ends of the notochord are overlaid by the formation of the bony elements of the neurocranium and caudal fin, respectively. To investigate, we describe how the notochord of the cranium and caudal fin changes from embryo to spawning adult, using light microscopy, SEM, TEM, dissection, and CT scanning. The differences are dramatic. In contrast to the abdominal and caudal regions, at the ends of the notochord vertebrae never develop. While the cranial notochord builds a tapering, unsegmented cone of chordal bone, the urostylic notochordal sheath never ossifies: adjacent, irregular bony elements form from the endoskeleton of the caudal fin. As development progresses, two previously undescribed processes occur. First, the bony cone of the cranial notochord, and its internal chordocytes, are degraded by chordoclasts, an undescribed function of the clastic cell type. Second, the sheath of the urostylic notochord creates transverse septae that partly traverse the lumen in an irregular pattern. By the adult stage, the cranial notochord is gone. In contrast, the urostylic notochord in adults is robust, reinforced with septae, covered by irregularly shaped pieces of cellular bone, and capped with an opistural cartilage that develops from the sheath of the urostylic notochord. A previously undescribed muscle, with its origin on the opistural cartilage, inserts on the lepidotrich ventral to it. publishedVersion

Levantine scraper, Capoeta damascina is a candidate species for future stock assessments, conservation studies, and hatchery efforts. Herein, we documented embryonic and early larval development, from egg activation to the exogenous feeding period, using morphological and histological landmarks. Embryos were obtained by in vitro fertilization from hormonally induced wild-caught broodstock, and subsequent development was monitored at temperatures coinciding with native conditions. Embryonic development from fertilization to hatch lasted ~105-110 hr. Larvae emerged with unpigmented eyes and body morphology, as well as an undifferentiated digestive tract. The mouth was closed at hatch by the oropharyngeal membrane and opened by the early endogenous feeding period. Trabeculae cartilage, quadrate bone, and Meckel's cartilage of the endoskeleton were present during the endogenous feeding period. During this period, the larvae underwent considerable changes in craniofacial morphology, locomotion, and organogenesis of the digestive tract. The cartilaginous floor of the neurocranium developed and the first four ceratobranchials appeared simultaneously at the end of endogenous feeding period. The digestive tract was differentiated into buccopharynx, esophagus, and small intestine during the endogenous feeding period. The intestinal valve and numerous longitudinal folds at the posterior region of the intestine formed together by the endo-exogenous feeding period. Major developmental events in retinogenesis occurred during the endogenous feeding period. When larvae entered exogenous feeding the mouth was fully-functional. Additionally, liver size and eye diameter increased. Our analysis of embryonic and early larval development in Levantine scraper aligned with other freshwater fishes.

The large carnivorous ray-finned fish Birgeria liui Jin, 2001 from the Middle Triassic marine Zhuganpo Member, was previously briefly described based on an incomplete specimen, which lacked the skull and the anterior part of the body, hence with many of its morphological characteristics missing or misidentified. Herein, we report a new well preserved specimen of B. liui from the early Late Ladinian of South China, which shows the most complete and articulated postcranial skeleton for an adult specimen of Birgeria. The new informations relate to the number of neural arches and their changes along the vertebral column, the articulation between the neighboring haemal spines in the caudal region, the presence of ribs, the endoskeleton and the pattern of lepidotrichia of all fins and the covering of scales. We also update some characters of the postcranial skeleton of a few of other Birgeria species, based on direct observations.

The early actinopterygianMesopoma plantiis reassigned to a new genus on the basis of data obtained from high-resolution computed tomography (CT) scans of an unusually well-preserved specimen from the Early Pennsylvanian of Lancashire, UK. The formerM. plantiis joined by two furtherMesopomaspecies from the Late Mississippian of Scotland. CT scans of the keyplantispecimen bring to light new details of the dermal skull, pectoral girdle and fin. Among the cranial features, CT data reveal a specialised, anteriorly projecting preopercular bone, the location of the spiracular duct opening, presence of a so-called coronoid process on the lower jaw and the full three-dimensional shape of the snout. Of the pectoral girdle and fin, for the first time in a Palaeozoic actinopterygian it has been possible to complete a three-dimensional reconstruction of the entire endoskeleton in articulation. The fin presents new diversity within a conservative general pattern, revealing for the first time a double propterygium. Girdle shape shows that the fin orientation is derived: rotated with the leading edge dorsalmost. These details are used to identify unexploited character states for use in phylogenetic analyses, while functional implications of the fin and girdle suggest advanced locomotory control emerging among different groups of post-Devonian ray-finned fishes.

The body wall of starfish is composed of magnesium calcite ossicles connected by collagenous tissue and muscles and it exhibits remarkable variability in stiffness, which is attributed to the mechanical mutability of the collagenous component. Using the common European starfish Asterias rubens as an experimental animal, here we have employed a variety of techniques to gain new insights into the structure of the starfish body wall. The structure and organisation of muscular and collagenous components of the body wall were analysed using trichrome staining. The muscle system comprises interossicular muscles as well as muscle strands that connect ossicles with the circular muscle layer of the coelomic lining. The collagenous tissue surrounding the ossicle network contains collagen fibres that form loop‐shaped straps that wrap around calcite struts near to the surface of ossicles. The 3D architecture of the calcareous endoskeleton was visualised for the first time using X‐ray microtomography, revealing the shapes and interactions of different ossicle types. Furthermore, analysis of the anatomical organisation of the ossicles indicates how changes in body shape may be achieved by local contraction/relaxation of interossicular muscles. Scanning synchrotron small‐angle X‐ray diffraction (SAXD) scans of the starfish aboral body wall and ambulacrum were used to study the collagenous tissue component at the fibrillar level. Collagen fibrils in aboral body wall were found to exhibit variable degrees of alignment, with high levels of alignment probably corresponding to regions where collagenous tissue is under tension. Collagen fibrils in the ambulacrum had a uniformly low degree of orientation, attributed to macrocrimp of the fibrils and the presence of slanted as well as horizontal fibrils connecting antimeric ambulacral ossicles. Body wall collagen fibril D‐period lengths were similar to previously reported mammalian D‐periods, but were significantly different between the aboral and ambulacral samples. The overlap/D‐period length ratio within fibrils was higher than reported for mammalian tissues. Collectively, the data reported here provide new insights into the anatomy of the body wall in A. rubens and a foundation for further studies investigating the structural basis of the mechanical properties of echinoderm body wall tissue composites.

Infection of the hip after implant fixation is an uncommon yet devastating complication that results in poor long-term outcome. The gold standard treatment for chronic infection after hip arthroplasty is a two-stage protocol: eradication of infection, follow by re-implantation arthroplasty. The use of interim antibiotic-laden cement spacer has become a popular procedure to maintain hip joint function and provide antibiotic elution simultaneously before re-implantation. However, antibiotic cement spacer is mechanically weak and breaks if overloaded. Therefore, we designed a cement mould with metallic endoskeleton with the aim of creating a stronger, inexpensive, antibiotic-impregnated spacer resembling a unipolar arthroplasty. We report two cases of severe hip joint infection after implant fixation (bipolar hemiarthroplasty, screw fixation neck of femur). Both patients had undergone first stage surgery of debridement and articulating antibiotic cement insertion using our design. Although the second stage surgery was planned for these patients, both patients delayed the operation in view of good functional status after a year walking with the antibiotic cement spacer. These cases showed that the mechanical property of the new antibiotic cement spacer was promising but further mechanical studies upon this new endoskeleton design are required.

Pulse wave velocity (PWV), which measures vascular stiffness, is a powerful predictor of cardiovascular event. Treatment of aneurysms with endovascular prosthesis has been reported to increase PWV. The purpose of this study was to evaluate whether an endoskeleton stent graft design has less effect on PWV than the exoskeleton stent graft design. Between July 2008 and September 2016, 74 patients underwent endovascular treatment of aortic arch aneurysm in our institution. PWV before and after surgery were compared between those who underwent treatment with Najuta, an endoskeleton stent graft (n = 51), and those treated with other commercially available exoskeleton stent grafts (n = 23). Preoperative PWV (endoskeleton: 2004 ± 379.2 cm/s vs. exoskeleton: 2083 ± 454.5 cm/s, p = 0.47) was similar between the two groups. Factors that were associated with preoperative PWV were age (r = 0.37, 95% CI 0.15–0.56, p = 0.002) and mean arterial pressure (r = 0.53, 95% CI 0.34–0.68, p

Ninety per cent of animals do not have a spine. In the adult state it exists only in chordates. Among them, only vertebrates (0.8% of the biomass) have a cartilaginous or osseous endoskeleton with this type of axial structure around which the symmetry of the body is organized. It is involved in the maintenance of posture and locomotion. In most aquatic vertebrates the spinal column alone provides most of these functions. In terrestrial vertebrates, from amphibians to primates, the limbs assume a role in movement. Its coupling with the limbs, thanks to the pelvis, allows it to play an essential role in the postural balance and movements in vertebrates.

International audience; The monobasal pectoral fins of living coelacanths and lungfishes are homologous to the forelimbs of tetrapods and are thus critical to investigate the origin thereof. However, it remains unclear whether the similarity in the asymmetrical endoskeletal arrangement of the pectoral fins of coelacanths reflects the evolution of the pectoral appendages in sarcopterygians. Here, we describe for the first time the development of the pectoral fin and shoulder girdle in the extant coelacanth Latimeria chalumnae, based on the tomographic acquisition of a growth series. The pectoral girdle and pectoral fin endoskeleton are formed early in development with a radially outward growth of the endoskeletal elements. The visualization of the pectoral girdle during development shows a reorientation of the girdle between the fetus and pup 1 stages, creating a contact between the scapulocoracoids and the clavicles in the ventro‐medial region. Moreover, we observed a splitting of the pre‐ and post‐axial cartilaginous plates in respectively pre‐axial radials and accessory elements on one hand, and in post‐axial accessory elements on the other hand. However, the mechanisms involved in the splitting of the cartilaginous plates appear different from those involved in the formation of radials in actinopterygians. Our results show a proportional reduction of the proximal pre‐axial radial of the fin, rendering the external morphology of the fin more lobe‐shaped, and a spatial reorganization of elements resulting from the fragmentation of the two cartilaginous plates. Latimeria development hence supports previous interpretations of the asymmetrical pectoral fin skeleton as being plesiomorphic for coelacanths and sarcopterygians.

The dermoskeleton of the earliest vertebrates is well known but their endoskeleton is thought to have been largely cartilaginous until the Late Silurian. We confirm that the dermal plates of Astraspis are three-layered, with a superficial layer of enameloid and orthodentine, a middle layer of aspidin and a basal layer of lamellar acellular bone. This dermoskeleton is found in association with globular calcified cartilage, indicating the presence of a partially mineralized endoskeleton. In addition to the classical three-layered organization, some dermal plates exhibit alignments of chondrocyte-like lacunae, very similar to a pattern typical of chondroid metaplastic bone, previously unknown in early vertebrates. This discovery implies the presence of a proliferative cartilage, hitherto only known in Osteichthyans. This discovery indicates that a pattern similar to the first step of endochondral ossification was already present in the earliest vertebrates.

Males of many Psylloidea are known to possess a characteristic structure at the functional hub of their reproductive apparatus, between afferent and efferent passage of seminal fluid. The structure is a squat, cylindrical endoskeleton consisting of two sections. Classical authors named them as ‘sperm pump’ and ‘ejaculatory duct’, based on superficial resemblance to a spring-loaded, thimble-shaped cylinder, encircled by smooth, vertical columns interpreted to be muscles which, when contracted, compress the cylinder and affect seminal fluid discharge. The discovery of numerous spherules of unknown composition and function in and around the columns of the Asian citrus psyllid male genitalia invoked rigorous scrutiny of the classical literature for evidence to support its claims, and determined that the grounds for vetting the structure as a sperm pump were fully teleological. This paper raises several objections to modern acceptance of this classical interpretation, presenting them as problematic, thought-provoking, and sometimes controversial anatomical features. The two sections are herein called ‘drum’ and ‘spout’. As an endoskeleton, the sections are an invagination of the exoskeleton and therefore cannot receive seminal fluid into their hollow. A phallus is identified inside an aedeagal tube, indicating that it is the ejaculatory duct—the tube, drum, and spout are considered its housing. A sheath envelopes the drum and is directly continuous with the spout hypodermis, another problematical feature raising the question of whether it is detached from adherence to the drum cuticles. Also, there are four afferent tubes but only two openings in the drum to receive their seminal fluids.

With aim to report the ontogeny of the osseous elements of the carapace in Peurodiras, 62 embryos and 43 nestlings of Podocnemis expansa were collected and submitted to the clearing and staining technique of bones and cartilages and study of serial histological slices. The carapace has mixed osseous structure of endo and exoskeleton, formed by 8 pairs of costal bones associated with ribs, 7 neural bones associated with neural arches, 11 pairs of peripheral bones, 1 nuchal, 1 pygal and 1 suprapygal. This structure begins its formation in the beginning of stage 16 with the ossification of the periosteal collar of the ribs. With exception of the peripheral bones, the other ones begin their ossification during the embrionary period. In histologic investigation it was found that the costal bones and neural bones have a close relation to the endoskeleton components, originating themselves as intramembranous expansions of the periosteal collar of the ribs and neural arches, respectively. The condensation of the mesenchyme adjacent to the periosteal collar induces the formation of spikes that grow in trabeculae permeated by fibroblasts below the dermis. The nuchal bone also ossifies in an intramembranous way, but does not show direct relation to the endoskeleton. Such information confirms those related to the other Pleurodira, mainly with Podocnemis unifilis, sometimes with conspicuous variations in the chronology of the ossification events. The formation of dermal plates in the carapace of Pleurodira and Criptodira follow the same pattern. Resumo: Com objetivo de relatar a ontogenia dos elementos ósseos da carapaça em Pleurodiras, coletaram-se 62 embriões e 43 filhotes de Podocnemis expansa que foram submetidos à técnica de clareamento e coloração dos ossos e cartilagens e pelo estudo cortes histológicos seriados. A carapaça possui estrutura óssea mista de endo e exoesqueleto, sendo formada por 8 pares de ossos costais associados às costelas, 7 ossos neurais associados aos arcos vertebrais, 11 pares de ossos periféricos, 1 nucal, 1 pigal e 1 supra-pigal. Esta estrutura começa sua formação no início do estágio 16 com a ossificação do colar periostal das costelas. Com exceção dos ossos periféricos, os demais iniciam sua ossificação durante o período embrionário. A investigação histológica explicitou que os ossos costais e neurais possuem uma estreita relação com componentes do endoesqueleto, originando-se como expansões intramembranosas do colar periostal das costelas e dos arcos neurais, respectivamente. A condensação do mesenquima adjacente ao colar periostal induz a formação de espiculas que crescem em trabéculas permeadas por fibroblastos abaixo da derme. O osso nucal, também se ossifica de maneira intramembranosa mas não apresenta relação direta com o endoesqueleto. Tais informações corroboram àquelas relatadas para os demais Pleurodiras, principalmente com Podocnemis unifilis, outrora com variações conspícuas na cronologia dos eventos de ossificação. A formação das placas dérmicas da carapaça em Pleurodira e Criptodira seguem um mesmo padrão.

Rehabilitation engineering plays an important role in designing various autonomous robots to provide better therapeutic exercise to disabled patients. Hence it is necessary to study human musculoskeletal system and also needs to be presented in scientific manner in order to describe and analyze the biomechanics of human body motion. This review focuses on lower appendicular musculoskeletal structure of human body to represent joints and links architectures; to identify muscle attachments and functions; and to illustrate muscle groups which are responsible for a particular joint movement. Firstly, human lower skeletal structure, linking systems, joint mechanisms, and their functions are described with a conceptual representation of joint architecture of human skeleton. This section also represents joints and limbs by comparing with mechanical systems. Characteristics of ligaments and their functions to construct skeletal joints are also discussed briefly in this part. Secondly, the study focuses on muscular system of human lower limbs where muscle structure, functions, roles in moving endoskeleton structure, and supporting mechanisms are presented ellaborately. Thirdly, muscle groups are tabulated based on functions that provide mobility to different joints of lower limbs. Finally, for a particular movement action of lower extremity, muscles are also grouped and tabulated to have a better understanding on functions of individual muscle. Basically the study presents an overview of the structure of human lower limbs by characterizing and classifying skeletal and muscular systems.KEYWORDS: Musculoskeletal system; Human lower limbs; Muscle groups; Joint motion; Biomechatronics; Rehabilitation.

Due to their cartilaginous endoskeleton and the continuous tooth replacement, the chondrichthyan fossil record predominantly consists of isolated teeth, which offer diagnostic features for taxonomic identifications, but only provide very limited information of an organism's life history. In contrast, the calcified vertebral centra of elasmobranchs (sharks, skates and rays) yield important information about ecological and biological traits that can be utilized for constructing age-structured population dynamic models of extant species and palaeoecological reconstructions of such aspects in extinct groups. Here, we describe two large shark vertebrae from the Santonian (Upper Cretaceous) of Spain, which show a unique combination of characters (asterospondylic calcification pattern, with concentric lamellae and numerous parallel bands that are oriented perpendicular) that is only known from ptychodontid sharks, a distinct, extinct group of giant durophagous sharks of the Cretaceous era. Based on linear regression models for large extant sharks a total length between 430 and 707cm was estimated for the examined specimen. Our results indicate that ptychodontid sharks were large viviparous animals, with slow growth rates, matured very late and, therefore, show typical traits for K-selected species. These traits combined with a highly specialized feeding ecology might have played a crucial role for the success but also, eventually, extinction of this group.

This paper describes the regeneration of the caudal axial skeleton after amputation of the tail, including about 20 vertebrae, in the gymnotoid fish Eigenmannia virescens. Seven days after amputation, a regeneration blastema developed and soft tissues degenerated. A cylinder of cartilage developed at the end of the notochord. When this cartilage was about 10 mm long (21 days), perichondral ossification began. The cartilage continued to elongate and ossification increased while osteoclasts began to destroy the cartilage ventrally. Finally, a bony rod formed and at its tip the cartilage persisted as a rod, 2 to 3 mm long. The anal fin also regenerated: Endoskeletal cartilage developed first, following by differentiation of the lepidotrichia, and finally ossification of the endoskeleton.

Bone is a defining characteristic of the vertebrate skeleton, and while chondrichthyans (sharks, skates, and other cartilaginous fishes) are vertebrates, they are hypothesized to have lost the ability to make bone during their evolution. Multiple descriptions of a bone-like tissue in neural arches of vertebrae in various shark species (selachians), however, challenge this hypothesis. Here, we extend this argument by analyzing vertebrae of two members of the batoids (the little skate Leucoraja erinacea and Eaton's skate Bathyraja eatonii), the sister group to selachians within elasmobranchs. Micro-CT images showed a bone-like mineralization pattern in neural arches of each skate species, and histological analyses confirmed that this bone-like tissue surrounded a cartilage core, exactly as described in sharks. Another mineralization pattern identified in skate vertebrae was distinct from the polygonal tesseral and areolar patterns that classically are associated with the chondrichthyan endoskeleton. Many regions of the vertebrae, including the neural spine and transverse processes, showed this perichondral mineralization pattern, termed here trabecular tesseral. Other than the cartilage core of the neural arch, all mineralized tissues in skate vertebrae had flattened cells surrounded by matrix with bone-like histology. Analyses of quantitative microstructural parameters revealed that, compared to rat vertebrae, the bone-like mineralization pattern in the neural arches of skate vertebrae was more similar to compact bone than trabecular bone. In contrast, the thickness of the trabecular tesseral pattern was more similar to trabecular bone than compact bone of rat vertebrae. In conclusion, a bone-like tissue in neural arches of skate vertebrae appears to be a novel elasmobranch synapomorphy. We propose that the trabecular tesseral mineralization pattern in the skate might have deep homology to the mineralization pattern utilized in trabecular bone. STATEMENT OF SIGNIFICANCE: Mineralization patterns of skeletal tissues have not been investigated thoroughly in all vertebrate clades. Despite their designation as 'cartilaginous fish', chondrichthyans clearly evolved from ancestral vertebrates that made bone. The consensus that chondrichthyans lost the ability to make bone during their evolution, however, is challenged by reports of bone and bone-like tissues in the neural arches of vertebrae in extant sharks (selachians). Here, we provide evidence from micro-CT imaging and histological analyses to support our hypothesis that a bone-like tissue is present in the neural arches of batoids (the sister group to selachians within elasmobranchs). These results argue strongly that the neural arch bone-like tissue is a previously unknown synapomorphy of elasmobranchs. In addition to the bone-like mineralization pattern identified in the neural arches, micro-CT images also showed a novel mineralization pattern which we described as trabecular tesseral. Quantitative microstructural features shared between trabecular tesseral pattern and trabecular bone (from homologous rat vertebrae) suggest that both patterns might derive from an ancestral gene network driving trabecular mineralization (i.e., deep homology).

The ATP-binding cassette transporter 6 (ABCC6) gene encodes a cellular transmembrane protein transporter (MRP6) that is involved in the regulation of tissue calcification in mammals. Mutations in ABCC6 are associated with human ectopic calcification disorders. To gain insight into its evolution and involvement in tissue calcification we conducted a comparative analysis of the ABCC6 gene and the related gene ABCC1 from invertebrates to vertebrates where a bony endoskeleton first evolved. Taking into consideration the role of ABCC6 in ectopic calcification of human skin we analysed the involvement of both genes in the regeneration of scales, mineralized structures that develop in fish skin. The ABCC6 gene was only found in bony vertebrate genomes and was absent from Elasmobranchs, Agnatha and from invertebrates. In teleost fish the abcc6 gene duplicated but the two genes persisted only in some teleost genomes. Six disease causing amino acid mutations in human MRP6 are a normal feature of abcc6 in fish, suggesting they do not have a deleterious effect on the protein. After scale removal the abcc6 (5 and 10 days) and abcc1 (10 days) gene expression was up-regulated relative to the intact control skin and this coincided with a time of intense scale mineralization.

The paired appendages (fins or limbs) of jawed vertebrates contain an endoskeleton consisting of nodules, bars and, in some groups, plates of cartilage, or bone arising from replacement of cartilaginous templates. The generation of the endoskeletal elements occurs by processes involving production and diffusion of morphogens, with, variously, positive and negative feedback circuits, adhesion, and receptor dynamics with similarities to the mechanism for chemical pattern formation proposed by Alan Turing. This review presents a unified interpretation of the evolution and functioning of these mechanisms. Studies are described indicating that protocondensations, compacted mesenchymal cell aggregates that prefigure the appendicular skeleton, arise through the adhesive activity of galectin-1, a matricellular protein with skeletogenic homologs in all jawed vertebrates. In the cartilaginous and lobe-finned fishes (and to a variable extent in ray-finned fishes) it additionally cooperates with an isoform of galectin-8 to constitute a self-organizing network capable of generating arrays of preskeletal nodules, bars and plates. Further, in the tetrapods, a putative galectin-8 control module was acquired that may have enabled proximodistal increase in the number of protocondensations. In parallel to this, other self-organizing networks emerged that acted, via Bmp, Wnt, Sox9 and Runx2, as well as transforming factor-β and fibronectin, to convert protocondensations into skeletal tissues. The progressive appearance and integration of these skeletogenic networks over evolution occurred in the context of an independently evolved system of Hox protein and Shh gradients that interfaced with them to tune the spatial wavelengths and refine the identities of the resulting arrays of elements.

Although relationships among the major groups of living gnathostomes are well established, the relatedness of early jawed vertebrates to modern clades is intensely debated. Here, we provide a new description of Gladbachus , a Middle Devonian (Givetian approx. 385-million-year-old) stem chondrichthyan from Germany, and one of the very few early chondrichthyans in which substantial portions of the endoskeleton are preserved. Tomographic and histological techniques reveal new details of the gill skeleton, hyoid arch and jaws, neurocranium, cartilage, scales and teeth. Despite many features resembling placoderm or osteichthyan conditions, phylogenetic analysis confirms Gladbachus as a stem chondrichthyan and corroborates hypotheses that all acanthodians are stem chondrichthyans. The unfamiliar character combination displayed by Gladbachus , alongside conditions observed in acanthodians, implies that pre-Devonian stem chondrichthyans are severely under-sampled and strongly supports indications from isolated scales that the gnathostome crown group originated at the latest by the early Silurian (approx. 440 Ma). Moreover, phylogenetic results highlight the likely convergent evolution of conventional chondrichthyan conditions among earliest members of this primary gnathostome division, while skeletal morphology points towards the likely suspension feeding habits of Gladbachus , suggesting a functional origin of the gill slit condition characteristic of the vast majority of living and fossil chondrichthyans.

In recent years in Japan, over half of all workers suffered from lower back pain. This has become a social problem that needs to be addressed. To reduce its occurrence, we developed a flexible, high-output waist assist suit called “AB-Wear” in a previous study. The AB-Wear suit can assist human motion and reduce muscular fatigue of the waist. However, the assistive forces of the device generate compressive forces on the backbone, which have adverse effects on the body. Hence, in this study, we propose an exoskeleton-type AB-Wear equipped with a compressive force reduction mechanism, called “semi-endoskeleton-type AB-Wear”. This device has a reduction mechanism similar to a flexible flat spring behind the upper body. Because of this structure, this device can generate an effective assistive force. First, we explain the difference between the semi-endoskeleton-type AB-Wear and the previous device. Then, we model the semi-endoskeleton-type AB-Wear because the model is used for its operation. Moreover, its effectiveness is confirmed using musculoskeletal simulation. Finally it is evaluated by measuring surface electromyography (EMG) on a subject's body to confirm its effectiveness with a real body. The EMGs of the wearer with and without the suit are compared. The usefulness of the AB-Wear is confirmed by simulation and experiment.

Soft limbs with anisotropic stiffness are common in nature and enable animals to solve a variety of tasks, including locomotion and manipulation. This mixture of hardness and softness enables animals to efficiently control the unpredictable contact forces that occur while performing such tasks. A challenge for soft robotics is to create artificial limbs that mimic natural mixtures of hardness and softness for use as a building block for soft, adaptable robots. This article presents the design of a novel pneumatic limb module with adjustable length and anisotropic stiffness. The artificial limb is designed with a rigid telescopic endoskeleton inside a rubber bellow, which we show is able to resist buckling, while remaining externally soft. Finally, we present the design of a hexapod walker based on the limb units.

The development of upper limb prostheses had a great growth with the proliferation of additive manufacturing technologies. This article suggests the design and development of a novel Bio-inspired compliant finger which is composed of a 3D printed rigid endoskeleton covered by soft matter, to apply to body actuated upper limb prostheses. We demonstrate the design and implementation of this finger and show how such finger can improve the hands functionality substantially. The hand performance is evaluated against a comprehensive grasp list that contains 33 grasps that humans perform in daily tasks. While the previous version of the body-actuated hand could perform only 5 of these 33 grasps, the updated version of the hand with soft fingers could perform 23 grasps.

Most adult vertebrate animals have bony skeletons, with cartilage mostly restricted to joints and flexible structures. In contrast, the Chondrichthyes (sharks, batoids, and chimaeras) have endoskeletons made entirely of cartilage. Moreover, in sharks and batoids, most of the skeletal cartilage is tessellated, covered with mineralized, subperichondral blocks called tesserae. There are several other forms of cartilage found in the bodies of these fishes that likely serve distinct functional and metabolic roles. The structure and development of chimaeroid cartilage is essentially unknown.

Summary Vertebrates have both more than one skeleton and multiple skeletal systems reflecting origins from two germ layers (mesoderm and neural crest), locations of skeletal elements as external or internal (exo- and endoskeleton), and separate craniofacial, axial and appendicular skeleton systems. Current studies reinforce the exoskeleton as consisting of bone and dentine to the exclusion of cartilage. The endoskeleton is based in cartilage, which, depending on lineage may be replaced by bone. Current understanding of the nature of the exo- and endoskeletons, modes of ossification (intramembranous, endochondral, perichondral), and the contributions of mesodermal and neural crest cells to the skeleton(s) is summarized and then discussed in more depth using fin rays in paired and unpaired fins as examples. Recent studies demonstrating that fin rays and scales are mesodermal and not neural crest in origin are reviewed and whether trunk neural crest cells have skeletogenic potential is considered. These results are discussed in the context of whether scales and fin rays should continue to be regarded as components of the exoskeleton. The conclusion is that they should, thereby separating germ layer of origin from classification of skeletal elements as exo- or endoskeletal; germ layer of origin does not provide unambiguous evidence for classification of elements as parts of the exo- or endoskeletons. Recent studies indicating that turtle shells are mesodermal in origin provides further evidence of the contribution of mesoderm to skeletal elements traditionally regarded as part of the exoskeleton. Therefore, exoskeleton is not synonymous with neural crest origin. These studies on fish fin rays/scales and turtle shells herald a new paradigm in which germ layer of origin (mesoderm or neural crest) does not equate with classification of elements as parts of the endo- or exoskeleton.

The sea urchin larva is shaped by a calcite endoskeleton. That skeleton is built by 64 primary mesenchyme cells (PMCs) in Lytechinus variegatus. The PMCs originate as micromeres due to an unequal fourth cleavage in the embryo. Micromeres are specified in a well-described molecular sequence and enter the blastocoel at a precise time using a classic epithelial–mesenchymal transition. To make the skeleton, the PMCs receive signaling inputs from the overlying ectoderm, which provides positional information as well as control of the growth of initial skeletal tri-radiates. The patterning of the skeleton is the result both of autonomous inputs from PMCs, including production of proteins that are included in the skeletal matrix, and of non-autonomous dynamic information from the ectoderm. Here, we summarize the wealth of information known about how a PMC contributes to the skeletal structure. The larval skeleton is a model for understanding how information encoded in DNA is translated into a three-dimensional crystalline structure.

The locomotory appendages of vertebrates have undergone significant changes during evolution, which likely promoted a wide range of adaptive strategies. These appendages first evolved as unpaired finfolds in the dorsal midline of early chordates, more than 500 million years ago. Later on, during vertebrates' radiation, two sets of locomotory appendages emerged, developing from both sides of the latero-ventral body wall. The morphology of these paired fins in fishes at different phylogenetic positions suggests an evolutionary tendency for increasing elaboration of the endoskeleton and concomitant reduction of the distal dermoskeleton. This evolutionary process culminated with the origin of limbs in the lineages leading to tetrapods. The developmental programs responsible for the evolution of vertebrate appendages have been a major topic for evolutionary developmental biology recently. Gene expression comparisons performed in chordates explored how these mechanisms were transferred from a midline to latero-ventral position. On another front, gene function assays have begun to test classical hypotheses concerning the transition from fish fins to tetrapod limbs. In this review, we highlight these recent findings on the evolution of vertebrate fin development. First, we discuss new perspectives on the transition from midline to paired appendages focus on (i) origin and molecular regionalization of the lateral plate mesoderm and (ii) novel ectodermic competency zones for fin induction. Next, we review recent work exploring how tetrapod limbs evolved from fish fins, considering (i) molecular and structural changes in the distal ectoderm of fins and (ii) modulation of 5'HoxD transcription during fin endoskeleton development.

Functional knockdown of zebrafish tbx5a causes hypoplasia or aplasia of pectoral fins. This study aimed to assess developmental pectoral fin anomalies in tbx5a morpholino knockdown zebrafish embryos. The expression of cartilage-related genes in the tbx5a morphant was analyzed by DNA microarray, immunostaining, and thin-section histology to examine the detailed distribution of the extracellular matrix (ECM) during different pectoral fin developmental stages. Chondrogenic condensation (CC) in the tbx5a morpholino knockdown group was barely recognizable at 37 h postfertilization (hpf), the process from CC to endoskeleton formation was disrupted at 48 hpf, and the endoskeleton was only loosely formed at 72 hpf. Microarrays identified 18 downregulated genes in tbx5a-deficient embryos, including 2 fin morphogenesis-related (cx43, bbs7), 4 fin development-related (hoxc8a, hhip, axin1, msxb), and 12 cartilage development-related (mmp14a, sec23b, tfap2a, slc35b2, dlx5a, dlx1a, tfap2b, fmr1, runx3, cdh2, lect1, acvr2a, mmp14b) genes, at 24 and 30 hpf. The increase in apoptosis-related proteins (BAD and BCL2) in the tbx5a morphant influenced the cellular component of pectoral fins and resulted in chondrocyte reduction throughout the different CC phases. Furthermore, tbx5a knockdown interfered with ECM formation in pectoral fins, affecting glycosaminoglycans, fibronectin, hyaluronic acid (HA), and N-cadherin. Our results provide evidence that the pectoral fin phenotypic anomaly induced by tbx5a knockdown is related to disruption of the mesoderm and ECM, consequently interfering with mesoderm migration, CC, and subsequent endoskeleton formation.

Despite recent publications indicating billowing (aneurysmal degeneration of the outer fabric material manifesting as a bulging sac of contained contrast due to weakening of the fabric material between the metal struts) as a benign finding, we present a unique case of billowing that resulted in aneurysmal rupture with the AFX2® stent graft (Endologix, Inc., Irvine, CA). AFX2® consists of an inner metallic endoskeleton with multiple metallic struts covered by a polytetrafluoroethylene graft fabric. It allows the flow of blood or contrast beyond the border of the metallic endoskeleton without evidence of endoleak or rupture secondary to the outer cover being anchored to the endoskeleton with polypropylene sutures only at the proximal and distal ends. Our report raises the concern that although billowing may be a relatively common manifestation with Endologix stent grafts, clinicians have to be diligent as the phenomenon may progress to abdominal aortic aneurysm rupture.

The evolutionary origin of the autopod involved a loss of the fin-fold and associated dermal skeleton with a concomitant elaboration of the distal endoskeleton to form a wrist and digits. Developmental studies, primarily from teleosts and amniotes, suggest a model for appendage evolution in which a delay in the AER-to-fin-fold conversion fuelled endoskeletal expansion by prolonging the function of AER-mediated regulatory networks. Here, we characterize aspects of paired fin development in the paddlefishPolyodon spathula(a non-teleost actinopterygian) and catsharkScyliorhinus canicula(chondrichthyan) to explore aspects of this model in a broader phylogenetic context. Our data demonstrate that in basal gnathostomes, the autopod markerHoxA13co-localizes with the dermoskeleton componentAnd1to mark the position of the fin-fold, supporting recent work demonstrating a role forHoxA13in zebrafish fin ray development. Additionally, we show that in paddlefish, the proximal fin and fin-fold mesenchyme share a common mesodermal origin, and that components of the Shh/LIM/Gremlin/Fgf transcriptional network critical to limb bud outgrowth and patterning are expressed in the fin-fold with a profile similar to that of tetrapods. Together these data draw contrast with hypotheses of AER heterochrony and suggest that limb-specific morphologies arose through evolutionary changes in the differentiation outcome of conserved early distal patterning compartments.

The endoskeleton of elasmobranchs (sharks and rays) is comprised largely of unmineralized cartilage, differing fundamentally from the bony skeletons of other vertebrates. Elasmobranch skeletons are further distinguished by a tessellated surface mineralization, a layer of minute, polygonal, mineralized tiles called tesserae. This ‘tessellation’ has defined the elasmobranch group for more than 400 million years, yet the limited data on development and ultrastructure of elasmobranch skeletons (e.g. how tesserae change in shape and mineral density with age) have restricted our abilities to develop hypotheses for tessellated cartilage growth. Using high-resolution, two-dimensional and three-dimensional materials and structural characterization techniques, we investigate an ontogenetic series of tessellated cartilage from round stingray Urobatis halleri, allowing us to define a series of distinct phases for skeletal mineralization and previously unrecognized features of tesseral anatomy. We show that the distinct tiled morphology of elasmobranch calcified cartilage is established early in U. halleri development, with tesserae forming first in histotroph embryos as isolated, globular islets of mineralized tissue. By the sub-adult stage, tesserae have increased in size and grown into contact with one another. The intertesseral contact results in the formation of more geometric (straight-edged) tesseral shapes and the development of two important features of tesseral anatomy, which we describe here for the first time. The first, the intertesseral joint, where neighboring tesserae abut without appreciable overlapping or interlocking, is far more complex than previously realized, comprised of a convoluted bearing surface surrounded by areas of fibrous attachment. The second, tesseral spokes, are lamellated, high-mineral density features radiating outward, like spokes on a wheel, from the center of each tessera to its joints with its neighbors, likely acting as structural reinforcements of the articulations between tesserae. As tesserae increase in size during ontogeny, spokes are lengthened via the addition of new lamellae, resulting in a visually striking mineralization pattern in the larger tesserae of older adult skeletons when viewed with scanning electron microscopy (SEM) in backscatter mode. Backscatter SEM also revealed that the cell lacunae in the center of larger tesserae are often filled with high mineral density material, suggesting that when intratesseral cells die, cell-regulated inhibition of mineralization is interrupted. Many of the defining ultrastructural details we describe relate to local variation in tissue mineral density and support previously proposed accretive growth mechanisms for tesserae. High-resolution micro-computed tomography data indicate that some tesseral anatomical features we describe for U. halleri are common among species of all major elasmobranch groups despite large variation in tesseral shape and size. We discuss hypotheses about how these features develop, and compare them with other vertebrate skeletal tissue types and their growth mechanisms.

In the sea urchin morphogenesis follows extensive molecular specification. The specification controls the many morphogenetic events and these, in turn, precede patterning steps that establish the larval body plan. To understand how the embryo is built it was necessary to understand those series of molecular steps. Here an example of the historical sequence of those discoveries is presented as it unfolded over the last 50 years, the years during which major progress in understanding development of many animals and plants was documented by CTDB. In sea urchin development a rich series of experimental studies first established many of the phenomenological components of skeletal morphogenesis and patterning without knowledge of the molecular components. The many discoveries of transcription factors, signals, and structural proteins that contribute to the shape of the endoskeleton of the sea urchin larva then followed as molecular tools became available. A number of transcription factors and signals were discovered that were necessary for specification, morphogenesis, and patterning. Perturbation of the transcription factors and signals provided the means for assembling models of the gene regulatory networks used for specification and controlled the subsequent morphogenetic events. The earlier experimental information informed perturbation experiments that asked how patterning worked. As a consequence it was learned that ectoderm provides a series of patterning signals to the skeletogenic cells and as a consequence the skeletogenic cells secrete a highly patterned skeleton based on their ability to genotypically decode the localized reception of several signals. We still do not understand the complexity of the signals received by the skeletogenic cells, nor do we understand in detail how the genotypic information shapes the secreted skeletal biomineral, but the current knowledge at least outlines the sequence of events and provides a useful template for future discoveries.

Biomineralization in sea urchin embryos is a crystal growth process that results in oriented single-crystalline spicules with a complex branching shape and smoothly curving surfaces. Uniquely, the primary mesenchyme cells (PMCs) that construct the endoskeleton can be cultured in vitro. However, in the absence of morphogenetic cues secreted by other cells in the embryo, spicules deposited in PMC culture lack the complex branching behavior observed in the embryo. Herein we demonstrate that recombinant sea urchin vascular endothelial growth factor (rVEGF), a signaling molecule that interacts with a cell-surface receptor, induces spiculogenesis and controls the spicule shape in PMC culture. Depending on the rVEGF concentration, PMCs deposit linear, "h"- and "H"-shaped, or triradiate spicules. Remarkably, the change from linear to triradiate occurs with a switch from bidirectional crystal growth parallel to the calcite c axis to growth along the three a axes. This finding has implications for our understanding of how cells integrate morphogenesis on the multi-micrometer scale with control over lattice orientation on the atomic scale. The PMC model system is uniquely suited to investigate this mechanism and develop biotechnological approaches to single-crystal growth.

We investigated tissue responses to endoskeleton stent grafts for saccular abdominal aortic aneurysms (AAAs) in canines. Saccular AAAs were made with Dacron patch in 8 dogs, and were excluded by endoskeleton stent grafts composed of nitinol stent and expanded polytetrafluoroethylene graft. Animals were sacrificed at 2 months (Group 1; n = 3) or 6 months (Group 2; n = 5) after the placement, respectively. The aortas embedding stent grafts were excised en bloc for gross inspection and sliced at 5 to 8 mm intervals for histopathologic evaluation. Stent grafts were patent in all except a dog showing a thrombotic occlusion in Group 2. In the 7 dogs with patent lumen, the graft overhanging the saccular aneurysm was covered by thick or thin thrombi with no endothelial layer, and the graft over the aortic wall was completely covered by neointima with an endothelial layer. Transgraft cell migration was less active at an aneurysm than at adjacent normal aorta. In conclusion, endoskeleton stent grafts over saccular aneurysms show no endothelial coverage and poor transgraft cell migration in a canine model.

Background: Through developmental and evolutionary time, organisms respond variably to their environment not only in terms of size and shape but also in terms of timing. Developmental plasticity can potentially act on various aspects of the timing of developmental events (i.e., appearance, cessation, duration, sequence). In this study, we address the developmental plasticity of median fin endoskeleton by using exercise training on newly-hatched Arctic charr (Salvelinus alpinus). Results: Developmental progress of cartilage formation (i.e., chondrification) in all fins is less influenced than ossification by an increase of water velocity. The most responsive elements, meaning those elements with greater onset plasticity owing to a water velocity increase, differ in terms of early versus late developmental events. The most responsive elements are those that chondrify and to a greater extent ossify later in the development. Conclusions: Plasticity is documented for the timing of appearance (i.e., onset) and the timing of transition from cartilage to bone (i.e., transitions of skeletal states) rather than the order of events within a sequence. Similarities of plastic response in developmental patterns could be used as a powerful criterion to strengthen the identification of phenotypic modules. Developmental Dynamics 241:1507–1524, 2012. © 2012 Wiley Periodicals, Inc.