The oldest three-dimensionally preserved vertebrate neurocranium.

The neurocranium is an integral part of the vertebrate head, itself a major evolutionary innovation1,2. However, its early history remains poorly understood, with great dissimilarity in form between the two living vertebrate groups: gnathostomes (jawed vertebrates) and cyclostomes (hagfishes and lampreys)2,3. The 100 Myr gap separating the Cambrian appearance of vertebrates4-6 from the earliest three-dimensionally preserved vertebrate neurocrania7 further obscures the origins of modern states. Here we use computed tomography to describe the cranial anatomy of an Ordovician stem-group gnathostome: Eriptychius americanus from the Harding Sandstone of Colorado, USA8. A fossilized head of Eriptychius preserves a symmetrical set of cartilages that we interpret as the preorbital neurocranium, enclosing the fronts of laterally placed orbits, terminally located mouth, olfactory bulbs and pineal organ. This suggests that, in the earliest gnathostomes, the neurocranium filled out the space between the dermal skeleton and brain, like in galeaspids, osteostracans and placoderms and unlike in cyclostomes2. However, these cartilages are not fused into a single neurocranial unit, suggesting that this is a derived gnathostome trait. Eriptychius fills a major temporal and phylogenetic gap in our understanding of the evolution of the gnathostome head, revealing a neurocranium with an anatomy unlike that of any previously described vertebrate.

A new Meckel's cartilage from the Devonian Hangenberg black shale in Morocco and its position in chondrichthyan jaw morphospace.

Fossil chondrichthyan remains are mostly known from their teeth, scales or fin spines only, whereas their cartilaginous endoskeletons require exceptional preservational conditions to become fossilized. While most cartilaginous remains of Famennian (Late Devonian) chondrichthyans were found in older layers of the eastern Anti-Atlas, such fossils were unknown from the Hangenberg black shale (HBS) and only a few chondrichthyan teeth had been found therein previously. Here, we describe a Meckel's cartilage from the Hangenberg black shale in Morocco, which is the first fossil cartilage from these strata. Since no teeth or other skeletal elements have been found in articulation, we used elliptical Fourier (EFA), principal component (PCA), and hierarchical cluster (HCA) analyses to morphologically compare it with 41 chondrichthyan taxa of different size and age and to evaluate its possible systematic affiliation. PCA and HCA position the new specimen closest to some acanthodian and elasmobranch jaws. Accordingly, a holocephalan origin was excluded. The jaw shape as well as the presence of a polygonal pattern, typical for tessellated calcified cartilage, suggest a ctenacanth origin and we assigned the new HBS Meckel's cartilage to the order Ctenacanthiformes with reservations.

The combined cartilage growth - calcification patterns in the wing-fins of Rajidae (Chondrichthyes): A divergent model from endochondral ossification of tetrapods.

The relationship between cartilage growth - mineralization patterns were studied in adult Rajidae with X-ray morphology/morphometry, undecalcified resin-embedded, heat-deproteinated histology and scanning electron microscopy. Morphometry of the wing-fins, nine central rays of the youngest and oldest specimens documented a significant decrement of radials mean length between inner, middle and outer zones, but without a regular progression along the ray. This suggests that single radial length growth is regulated in such a way to align inter-radial joints parallel to the wing metapterygia curvature. Trans-illumination and heat-deproteination techniques showed polygonal and cylindrical morphotypes of tesserae, whose aligned pattern ranged from mono-columnar, bi-columnar, and multi-columnar up to the crustal-like layout. Histology of tessellated cartilage allowed to identify of zones of the incoming mineral deposition characterized by enhanced duplication rate of chondrocytes with the formation of isogenic groups, whose morphology and topography suggested a relationship with the impending formation of the radials calcified column. The morphotype and layout of radial tesserae were related to mechanical demands (stiffening) and the size/mass of the radial cartilage body. The cartilage calcification pattern of the batoids model shares several morphological features with tetrapods' endochondral ossification, that is, (chondrocytes' high duplication rate, alignment in rows, increased volume of chondrocyte lacunae), but without the typical geometry of the metaphyseal growth plates. RESEARCH HIGHLIGHTS: 1. The wing-fins system consists of stiff radials, mobile inter-radial joints and a flat inter-radial membrane adapted to the mechanical demand of wing wave movement. 2. Growth occurs by forming a mixed calcified-uncalcified cartilage texture, developing intrinsic tensional stresses documented by morphoanatomical data.

Morphological association between muscle attachments and ossification sites in the late cartilaginous skull of tuatara embryos.

During development, the embryonic cartilaginous skull in most vertebrates is partially replaced by bones with endochondral and perichondral ossifications. Muscle attachments are thought to influence the patterns of ossification and, hence, the differentiation of the skull. To investigate the association between muscle attachments and early ossifications of reptilian embryos, we conducted digital 3D reconstructions of the cranium, the head, and the neck musculature from a histological section series of a late term embryonic tuatara, Sphenodon punctatus, with a total body length of 52 mm. As the sole living rhynchocephalian species, it is an important outgroup in comparative studies of squamate evolution. We found that head and neck muscles are largely associated with early ossification of the basal plate and the palatoquadrate, and with three other ossifications in an older specimen with a total body length of 72 mm. These results suggest that tensile forces resulting from embryonic muscle contraction are largely, but not exclusively, correlated with the area of endochondral ossification in the chondrocranium and palatoquadrate in tuatara. Beyond little-known genetic factors, the complexity of chondrocranial architecture, the progress of its development, and the effect of multiple muscle transmitting forces in the chondrocranium must be considered to provide a more comprehensive discussion of the mechanical properties of the embryonic skull.

Phylogenetic significance of clasper morphology of electric rays (Chondrichthyes: Batoidea: Torpediniformes).

Torpediniformes (electric rays) is a monophyletic group strongly supported by morphological and molecular phylogenetic studies. The claspers of electric rays, however, are poorly documented in comparation to the clasper of other batoids, especially skates, and the knowledge of their anatomical variation is restricted to the description of a few species. The present article analyzes the external and skeletal clasper anatomy of electric rays and reports newly discovered characters that can be useful for taxonomic diagnoses and higher-level systematic studies. The family Torpedinidae exclusively presents the integumental flap, a poorly calcified clasper skeleton, and a dorsal marginal cartilage with a medial flange on its distal portion. Derived or diagnostic characters were not found in the clasper of the reportedly nonmonophyletic families Narcinidae and Narkidae; however, the claspers of species and genera of narcinids and narkids present different anatomical patterns that can be useful for taxonomic and phylogenetic studies.

Elucidating the early signaling cues involved in zebrafish chondrogenesis and cartilage morphology.

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.

Cryogenic sequenced layering for the 3D reconstruction of biological objects.

Three-dimensional (3D) visualization is applied throughout many specialities, prompting an important breakthrough in accessibility and modeling of data. Experimental rendering and computerized reconstruction of objects has influenced many scientific achievements, facilitating one of the greatest advancements in medical education since the first illustrated anatomy book changed specialist training forever. Modern medicine relies on detailed, high quality virtual models for educational, experimental and clinical purposes. Almost all current virtual visualization methods rely on object slicing producing serial sections, which can then be digitalized or analyzed manually. The tendency to computerize serial sections roots from convenience, accessibility, decent visualization quality and automation capabilities. Drawbacks of serial section imaging is tissue damage occurring within each consequent sectioning. To utilize the important aspects of real-life object reconstruction, and maintain integrity of biological structures, we suggest a novel method of low-temperature layering of objects for digitization and computerized virtual reconstruction. Here we show the process of consequent imaging of each novel layer of a biological object, which provides a computer with high quality data for virtual reconstruction and creation of a multidimensional real-life model. Our method prevents tissue deformation and biodegradation due to specific methods used in preparation of the biological object. The resulting images can be applied in surgical training, medical education and numerous scientific fields for realistic reconstruction of biological objects.

The visible skeleton 2.0: phenotyping of cartilage and bone in fixed vertebrate embryos and foetuses based on X-ray microCT.

For decades, clearing and staining with Alcian Blue and Alizarin Red has been the gold standard to image vertebrate skeletal development. Here, we present an alternate approach to visualise bone and cartilage based on X-ray microCT imaging, which allows the collection of genuine 3D data of the entire developing skeleton at micron resolution. Our novel protocol is based on ethanol fixation and staining with Ruthenium Red, and efficiently contrasts cartilage matrix, as demonstrated in whole E16.5 mouse foetuses and limbs of E14 chicken embryos. Bone mineral is well preserved during staining, thus the entire embryonic skeleton can be imaged at high contrast. Differences in X-ray attenuation of ruthenium and calcium enable the spectral separation of cartilage matrix and bone by dual energy microCT (microDECT). Clearing of specimens is not required. The protocol is simple and reproducible. We demonstrate that cartilage contrast in E16.5 mouse foetuses is adequate for fast visual phenotyping. Morphometric skeletal parameters are easily extracted. We consider the presented workflow to be a powerful and versatile extension to the toolkit currently available for qualitative and quantitative phenotyping of vertebrate skeletal development.

Incorporating prior knowledge via volumetric deep residual network to optimize the reconstruction of sparsely sampled MRI.

For sparse sampling that accelerates magnetic resonance (MR) image acquisition, non-linear reconstruction algorithms have been developed, which incorporated patient specific a prior information. More generic a prior information could be acquired via deep learning and utilized for image reconstruction. In this study, we developed a volumetric hierarchical deep residual convolutional neural network, referred to as T-Net, to provide a data-driven end-to-end mapping from sparsely sampled MR images to fully sampled MR images, where cartilage MR images were acquired using an Ultra-short TE sequence and retrospectively undersampled using pseudo-random Cartesian and radial acquisition schemes. The network had a hierarchical architecture that promoted the sparsity of feature maps and increased the receptive field, which were valuable for signal synthesis and artifact suppression. Relatively dense local connections and global shortcuts were established to facilitate residual learning and compensate for details lost in hierarchical processing. Additionally, volumetric processing was adopted to fully exploit spatial continuity in three-dimensional space. Data consistency was further enforced. The network was trained with 336 three-dimensional images (each consisting of 32 slices) and tested by 24 images. The incorporation of a priori information acquired via deep learning facilitated high acceleration factors (as high as 8) while maintaining high image fidelity (quantitatively evaluated using the structural similarity index measurement). The proposed T-Net had an improved performance as compared to several state-of-the-art networks.

Pulse Lavage Fails to Significantly Reduce Bone Marrow Content in Osteochondral Allografts: A Histological and DNA Quantification Study.

BACKGROUND: Current clinical practice calls for pulse lavage of fresh osteochondral allografts (OCAs) to reduce immunogenicity; however, there is limited evidence of its effectiveness in reducing allogenic bone marrow elements. PURPOSE: To evaluate the effectiveness of pulse lavage in removing marrow elements from trabecular bone in fresh OCA transplantation. STUDY DESIGN: Controlled laboratory study. METHODS: The authors evaluated 48 fresh OCA plugs with 4 different common sizes (14- and 24-mm diameter, 6- and 10-mm thickness). Within each size group, half of the samples underwent pulse lavage (n = 6) with saline solution and half were left untreated (no lavage; control group, n = 6). For each treatment and size group, 3 samples were analyzed for DNA content as an indicator of the number of residual nucleated cells; the other 3 samples were histologically analyzed to assess the presence and distribution of cells within subchondral bone pores in 3 specific locations within the plug: peripheral, intermediate, and core. RESULTS: Osteochondral plugs treated with pulse lavage did not show a significant decrease in DNA content in comparison with untreated plugs. Overall, histological analysis did not show a significant difference between the treated and untreated groups (P = .23). Subgroup analysis by size demonstrated decreased marrow content in treated versus untreated groups in the thinner plug sizes (14 × 6 mm and 24 × 6 mm). Histological evaluation by zone demonstrated a significant difference between groups only in the peripheral zone (P = .04). CONCLUSION: Pulse lavage has limited effectiveness in removing marrow elements, in particular in plugs that are larger in diameter and, more importantly, in thickness. Better techniques for subchondral bone treatment are required for more thorough removal of potentially immunogenic marrow elements. CLINICAL RELEVANCE: OCA transplantation has become an established treatment modality. Unfortunately, OCA is not without limitations, chiefly its mode of failure through inadequate integration of the allograft subchondral bone with subsequent collapse. In an effort to improve integration, current clinical practice calls for pulse lavage to remove allogenic bone marrow from the subchondral bone in hopes of decreasing the immunogenicity of the graft and facilitating revascularization.

Morphogenesis of the femur at different stages of normal human development.

The present study aimed to better characterize the morphogenesis of the femur from the embryonic to the early fetal periods. Sixty-two human fetal specimens (crown-rump length [CRL] range: 11.4-185 mm) from the Kyoto Collection were used for this study. The morphogenesis and internal differentiation process of the femur were analyzed in 3D using phase-contrast X-ray computed tomography and magnetic resonance imaging. The cartilaginous femur was first observed at Carnegie stage 18. Major anatomical landmarks were formed prior to the initiation of ossification at the center of the diaphysis (CRL, 40 mm), as described by Bardeen. The region with very high signal intensity (phase 5 according to Streeter's classification; i.e., area described as cartilage disintegration) emerged at the center of the diaphysis, which split the region with slightly low signal intensity (phase 4; i.e., cartilage cells of maximum size) in fetuses with a CRL of 40.0 mm. The phase 4 and phase 5 regions became confined to the metaphysis, which might become the epiphyseal cartilage plate. Femur length and ossified shaft length (OSL) showed a strong positive correlation with CRL. The OSL-to-femur length ratio rapidly increased in fetuses with CRL between 40 and 75 mm, which became moderately increased in fetuses with a CRL of ≥75 mm. Cartilage canal invasion occurred earlier at the proximal epiphysis (CRL, 62 mm) than at the distal epiphysis (CRL, 75 mm). Morphometry and Procrustes analysis indicated that changes in the femur shape after ossification were limited, which were mainly detected at the time of initial ossification and shortly after that. In contrast, femoral neck anteversion and torsion of the femoral head continuously changed during the fetal period. Our data could aid in understanding the morphogenesis of the femur and in differentiating normal and abnormal development during the early fetal period.

Accelerating anatomical 2D turbo spin echo imaging of the ankle using compressed sensing.

INTRODUCTION: To assess the feasibility and diagnostic value of compressed sensing for accelerating two-dimensional turbo spin echo imaging of the ankle. MATERIALS AND METHODS: Ankles of 20 volunteers were scanned (mean age 30.2 ±â€¯7.3 years, 13 men) at 3 T MRI. Coronal and sagittal intermediate-weighted (IM) sequences with fat saturation as well as axial T2- and coronal T1-weighted sequences were acquired using parallel imaging based on sensitivity encoding (SENSE) only as well as with a combination of compressed sensing (CS) and SENSE. Compressed sensing is a technique that acquires less data through k-space random undersampling and enables a reduction in total acquisition time by 20%. All images were reviewed by two radiologists, image quality was graded using a 5-point Likert scale and signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of different anatomical structures of the ankle were assessed and compared between sequences with SENSE only and with the combination of CS and SENSE using Wilcoxon signed-rank tests and Cohen's kappa. RESULTS: There was a substantial to perfect agreement for the rating between the images acquired with SENSE only and with the combination of CS and SENSE when assessing cartilage, subchondral bone and ligaments (κ = 0.75 - 0.89). SNR was slightly higher for the combination of CS and SENSE sequences compared to the sequences acquired with SENSE only, yet this finding was not significant (P = 0.18-0.62). Moreover, CNR of cartilage/fluid, subchondral bone/cartilage, ligaments/fluid and ligaments/fat did not show significant differences between the sequences acquired with SENSE only and the combination of CS and SENSE (P > 0.05). The interreader agreement was substantial to excellent for both techniques (κ=0.75 - 0.89). CONCLUSIONS: Compressed sensing reduced the acquisition time of conventional MR imaging of the ankle by 20% without decreasing diagnostic image quality, SNR and CNR.

A new mineralized tissue in the early vertebrate Astraspis.

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.

Screening of the Maturity Status of the Tibial Tuberosity by Ultrasonography in Higher Elementary School Grade Schoolchildren.

This study aimed to obtain screening data on the maturity status of the tibial tuberosity in schoolchildren of higher elementary school grades for risk management of Osgood-Schlatter disease (OSD). The maturity stages and cartilage thicknesses at the tibial tuberosity were determined by ultrasonography on the occasion of a school-based musculoskeletal examination for 124 grade 5-6 elementary schoolchildren, and their associations with the students' demographic characteristics and OSD were examined. The time-dependent changes of the maturity status of the tibial tuberosity were also examined in grade 5 students (n = 26) by a longitudinal survey. The cross-sectional survey showed that the epiphyseal stage was reached in 89% of girls and 35% of boys. The girls who had experienced menarche (n = 28) were all in the epiphyseal stage and had a decreased cartilage thickness (p = 0.004, after adjusting maturity stages). Students with OSD (n = 5) were all girls in the epiphyseal stage, and only two of them had an increased cartilage thickness. During the longitudinal survey, a marked increase in cartilage thickness from the previous measurement was observed in three boys (without clinical symptoms) and a girl who newly developed OSD. Two students with OSD without chronic pain had thin cartilage. In conclusion, for schoolchildren of higher elementary school grades, the risk of OSD is higher among girls with the epiphyseal stage. Cartilage thickness may not contribute to the diagnosis of OSD, since thick cartilage is not very common in OSD. However, cartilage thickness may reflect the status of OSD.

Studying airflow structures in periodic cylindrical hills of human tracheal cartilaginous rings.

The objective of this study is to assess tracheobronchial flow features with the cartilaginous rings during a light exercising. Tracheobronchial is part of human's body airway system that carries oxygen-rich air to human's lungs as well as takes carbon dioxide out of the human's lungs. Consequently, evaluation of the flow structures in tracheobronchial is important to support diagnosis of tracheal disorders. Computational Fluid Dynamics (CFD) allows evaluating effectiveness of tracheal cartilage rings in human body under different configurations. This study utilizes Large Eddy Simulation (LES) to model an anatomically-based human large conducting airway model with and without cartilaginous rings at the breathing conditions at Reynolds number of 5,176 in trachea region. It is observed that small recirculating areas shaped between rings cavities. While these recirculating areas are decaying, similar to periodic 2D-hills, the cartilaginous rings contribute to the construction of a vortical flow structure in the main flow. The separated vortically-shaped zone creates a wake in the flow and passes inside of the next ring cavity and disturb its boundary layer. At last, the small recirculation flow impinges onto tracheal wall. The outcome of this impinge flow is a latitudinal rotating flow perpendicular to the main flow in a cavity between the two cartilaginous rings crest which appear and disappear within a hundredth of a second. Kelvin-Helmholtz instability is observed in trachea caused by shear flow created behind of interaction between these flow structures near to tracheal wavy wall and main flow. A comparison of the results between a smooth wall model named simplified model and a rough wall model named modified model shows that these structures do not exist in simplified model, which is common in modeling tracheobronchial flow. This study proposes to consider macro surface roughness to account for the separating and rotating instantaneous flow structures. Finally, solving trachea airflow with its cartilages can become one of major issues in measuring the validity and capability of solving flow in developing types of sub-grid scale models as a turbulence studies benchmark.

Glycosaminoglycans and vitamin C affect broiler bone parameters.

The purpose of this study was to determine if in ovo feeding and rearing with glycosaminoglycans and vitamin C could influence bone and cartilage macroscopy, mineral composition, mineral density and surface area, bone breaking strength, and bone histology in broilers. Fertile eggs from breeders (Cobb) were either uninjected or injected with 4 µg of additive/100 µL water on day 4 of incubation. Every 100 g of in ovo additive contained 30 g of chondroitin sulfate, 30 g of glucosamine, and 5 g of vitamin C. After hatching, the chicks from both incubation treatments were submitted to additional treatments during the growth phase from 1 to 42 D of age (diet without and with 0.74 g of additive/kg of feed). Every 100 kg of feed contained 30 g of glucosamine sulfate, 24 g of chondroitin sulfate, and 20 g of vitamin C. A completely randomized factorial design (2 × 2) was applied. The data were submitted to variance analysis using the general linear model procedure of SAS (SAS Institute). In ovo feeding with 4 µg of additive plus dietary supplementation with 0.74 g of additive/kg of feed resulted in the highest cartilage weight of the femur proximal epiphysis in birds (P = 0.0098). The highest ash, phosphorus and calcium percentage, mineral density and mineral composition were identified for femur and tibia in the following treatments: in ovo feeding plus diet without additive during rearing, or uninjected eggs plus dietary supplementation during rearing. In ovo feeding with 4 µg of the additive reduced (P = 0.0008) the number of chondrocytes in the proximal epiphysis of the tibia cartilage and increased (P < 0.0001) the number of osteocytes in the tibia diaphysis of broilers. We conclude that in ovo feeding or dietary supplementation during broiler rearing with glycosaminoglycans (chondroitin sulfate and glucosamine sulfate) and vitamin C benefits the development of bird bones and cartilage, and may represent a solution to bone problems in broilers.

The effect of articular geometry features identified using statistical shape modelling on knee biomechanics.

Articular geometry in the knee varies widely among people which has implications for risk of injury and pathology. The goals of this work were to develop a framework to systematically vary geometry in a multibody knee model and to use this framework to investigate the effect of morphological features on dynamic knee kinematics and contact mechanics. A statistical shape model of the tibiofemoral and patellofemoral joints was created from magnetic resonance images of 14 asymptomatic knees. The shape model was then used to generate 37 unique multibody knee models based on -3 to +3 standard deviations of the scores for the first six principal components identified. Each multibody model was then incorporated into a lower extremity musculoskeletal model and the Concurrent Optimization of Muscle Activations and Kinematics (COMAK) routine was used to simulate knee mechanics for overground walking. Changes in articular geometry affected knee function, resulting in differences up to 17° in orientation, 8 mm in translation, 0.7 BW in contact force, and 2.0 MPa in mean cartilage contact pressure. Understanding the relationship between shape and function in a joint could provide insight into the mechanisms behind injury and pathology and the variability in response to treatment.

Evolution and development of the cartilaginous skull: From a lancelet towards a human face.

Chrondrocranium, the cartilaginous skull, is one of the major innovations that underlie evolution of the vertebrate head. Control of the induction and shaping of the cartilage is a key for the formation of the facial bones and largely defines facial shape. The appearance of cartilage in the head enabled many new functions such as protection of central nervous system and sensory structures, support of the feeding apparatus and formation of muscle attachment points ensuring faster and coordinated jaw movements. Here we review the evolution of cartilage in the cranial region and discuss shaping of the chondrocranium in different groups of vertebrates.

Mechanical, Cellular, and Proteomic Properties of Laryngotracheal Cartilage.

The larynx sometimes requires repair and reconstruction due to cancer resection, trauma, stenosis, or developmental disruptions. Bioengineering has provided some scaffolding materials and initial attempts at tissue engineering, especially of the trachea, have been made. The critical issues of providing protection, maintaining a patent airway, and controlling swallowing and phonation, require that the regenerated laryngotracheal cartilages must have mechanical and material properties that closely mimic native tissue. These properties are determined by the cellular and proteomic characteristics of these tissues. However, little is known of these properties for these specific cartilages. This review considers what is known and what issues need to be addressed.