Elastin fibers display a versatile microfibril network in articular cartilage depending on the mechanical microenvironments

Effect of Moderate Exercise on the Superficial Zone of Articular Cartilage in Age-Related Osteoarthritis

This study aimed to evaluate the effect of exercise on the superficial zone of the osteoarticular cartilage during osteoarthritis progression. Three-month-old, nine-month-old, and eighteen-month-old Sprague Dawley rats were randomly divided into two groups, moderate exercise and no exercise, for 10 weeks. Histological staining, immunostaining, and nanoindentation measurements were conducted to detect changes in the superficial zone. X-ray and micro-CT were quantitated to detect alterations in the microarchitecture of the tibial subchondral bone. Cells were extracted from the superficial zone of the cartilage under fluid-flow shear stress conditions to further verify changes in vitro. The number of cells and proteoglycan content in the superficial zone increased more in the exercise group than in the control group. Exercise can change the content and distribution of collagen types I and III in the superficial layer. In addition, TGFβ/pSmad2/3 and Prg4 expression levels increased under the intervention of exercise on the superficial zone. Exercise can improve the Young's modulus of the cartilage and reduce the abnormal subchondral bone remodeling which occurs after superficial zone changes. Moderate exercise delays the degeneration of the articular cartilage by its effect on the superficial zone, and the TGFβ/pSmad2/3 signaling pathways and Prg4 play an important role.

Mechanical Properties and Functions of Elastin: An Overview

Human tissues must be elastic, much like other materials that work under continuous loads without losing functionality. The elasticity of tissues is provided by elastin, a unique protein of the extracellular matrix (ECM) of mammals. Its function is to endow soft tissues with low stiffness, high and fully reversible extensibility, and efficient elastic-energy storage. Depending on the mechanical functions, the amount and distribution of elastin-rich elastic fibers vary between and within tissues and organs. The article presents a concise overview of the mechanical properties of elastin and its role in the elasticity of soft tissues. Both the occurrence of elastin and the relationship between its spatial arrangement and mechanical functions in a given tissue or organ are overviewed. As elastin in tissues occurs only in the form of elastic fibers, the current state of knowledge about their mechanical characteristics, as well as certain aspects of degradation of these fibers and their mechanical performance, is presented. The overview also outlines the latest understanding of the molecular basis of unique physical characteristics of elastin and, in particular, the origin of the driving force of elastic recoil after stretching.

Protein-engineered biomaterials for cartilage therapeutics and repair

Cartilage degeneration and injury are major causes of pain and disability that effect millions, and yet treatment options for conditions like osteoarthritis (OA) continue to be mainly palliative or involve complete replacement of injured joints. Several biomaterial strategies have been explored to address cartilage repair either by the delivery of therapeutics or as support for tissue repair, however the complex structure of cartilage tissue, its mechanical needs, and lack of regenerative capacity have hindered this goal. Recent advances in synthetic biology have opened new possibilities for engineered proteins to address these unique needs. Engineered protein and peptide-based materials benefit from inherent biocompatibility and nearly unlimited tunability as they utilize the body's natural building blocks to fabricate a variety of supramolecular structures. The pathophysiology and needs of OA cartilage are presented here, along with an overview of the current state of the art and next steps for protein-engineered repair strategies for cartilage.

Multiscale Strain Transfer in Cartilage

The transfer of stress and strain signals between the extracellular matrix (ECM) and cells is crucial for biochemical and biomechanical cues that are required for tissue morphogenesis, differentiation, growth, and homeostasis. In cartilage tissue, the heterogeneity in spatial variation of ECM molecules leads to a depth-dependent non-uniform strain transfer and alters the magnitude of forces sensed by cells in articular and fibrocartilage, influencing chondrocyte metabolism and biochemical response. It is not fully established how these nonuniform forces ultimately influence cartilage health, maintenance, and integrity. To comprehend tissue remodelling in health and disease, it is fundamental to investigate how these forces, the ECM, and cells interrelate. However, not much is known about the relationship between applied mechanical stimulus and resulting spatial variations in magnitude and sense of mechanical stimuli within the chondrocyte’s microenvironment. Investigating multiscale strain transfer and hierarchical structure-function relationships in cartilage is key to unravelling how cells receive signals and how they are transformed into biosynthetic responses. Therefore, this article first reviews different cartilage types and chondrocyte mechanosensing. Following this, multiscale strain transfer through cartilage tissue and the involvement of individual ECM components are discussed. Finally, insights to further understand multiscale strain transfer in cartilage are outlined.

High Resolution and Labeling Free Studying the 3D Microstructure of the Pars Tensa-Annulus Unit of Mice

Hearing loss is a serious illness affecting people’s normal life enormously. The acoustic properties of a tympanic membrane play an important role in hearing, and highly depend on its geometry, composition, microstructure and connection to the surrounding annulus. While the conical geometry of the tympanic membrane is critical to the sound propagation in the auditory system, it presents significant challenges to the study of the 3D microstructure of the tympanic membrane using traditional 2D imaging techniques. To date, most of our knowledge about the 3D microstructure and composition of tympanic membranes is built from 2D microscopic studies, which precludes an accurate understanding of the 3D microstructure, acoustic behaviors and biology of the tissue. Although the tympanic membrane has been reported to contain elastic fibers, the morphological characteristic of the elastic fibers and the spatial arrangement of the elastic fibers with the predominant collagen fibers have not been shown in images. We have developed a 3D imaging technique for the three-dimensional examination of the microstructure of the full thickness of the tympanic membranes in mice without requiring tissue dehydration and stain. We have also used this imaging technique to study the 3D arrangement of the collagen and elastic fibrillar network with the capillaries and cells in the pars tensa-annulus unit at a status close to the native. The most striking findings in the study are the discovery of the 3D form of the elastic and collagen network, and the close spatial relationships between the elastic fibers and the elongated fibroblasts in the tympanic membranes. The 3D imaging technique has enabled to show the 3D waveform contour of the collagen and elastic scaffold in the conical tympanic membrane. Given the close relationship among the acoustic properties, composition, 3D microstructure and geometry of tympanic membranes, the findings may advance the understanding of the structure—acoustic functionality of the tympanic membrane. The knowledge will also be very helpful in the development of advanced cellular therapeutic technologies and 3D printing techniques to restore damaged tympanic membranes to a status close to the native.

Metalloelastase-12 is involved in the temporomandibular joint inflammatory response as well as cartilage degradation by aggrecanases in STR/Ort mice

Temporomandibular joint dysfunction (TMJD) is characterised by clinical symptoms involving both the masticatory muscles and the temporomandibular joint (TMJ). Disc internal derangement and osteoarthritis (OA) are the most common forms of TMJD. Currently, the molecular process associated with degenerative changes in the TMJ is unclear. Our previous study showed that elastin-digested peptides act on human TMJ synovial cells and lead to upregulation of interleukin-6 (IL-6) and metalloelastase-12 (MMP-12; an elastin-degrading enzyme) in vitro. However, there is limited information regarding the involvement of elastin-degradation by MMP-12 in the processes of inflammatory responses and cartilage degradation in vivo. STR/Ort mice were used as a model of TMJ OA in the present study. Significant articular cartilage degeneration was observed starting at 20 weeks of age in the STR/Ort mice and this progressed gradually until 40 weeks, compared with the age-matched CBA mice. Immunostaining analysis showed that MMP-12 and IL-6 were expressed in the chondrocytes in the superficial zones of the cartilage. Immunostaining also showed that aggrecanases [a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 and ADAMTS-5] were expressed in the chondrocytes in the superficial zones of the cartilage. These findings suggest that an inflammatory and degradative process was initiated in the TMJ. Harmful mechanical stimuli, particularly pressure, may cause damage to the elastin fibres in the most elastin-rich superficial layer of the articular cartilage. Elastin-digested peptides are then generated as endogenous warning signals and they initiate a pro-inflammatory cascade. This leads to upregulation of pro-inflammatory mediators, such as IL-6 and MMP-12, which further trigger tissue damage resulting in elevated levels of elastin-digested peptides. IL-6 increases expression of the aggrecanases ADAMTS-4 and ADAMTS-5, following cartilage degradation. This leads to the establishment of a positive feedback loop and may result in chronic inflammation and cartilage degradation of the TMJ in vivo.

A composite scaffold of Wharton's jelly and chondroitin sulphate loaded with human umbilical cord mesenchymal stem cells repairs articular cartilage defects in rat knee

To evaluate the performance of a composite scaffold of Wharton's jelly (WJ) and chondroitin sulfate (CS) and the effect of the composite scaffold loaded with human umbilical cord mesenchymal stem cells (hUCMSCs) in repairing articular cartilage defects, two experiments were carried out. The in vitro experiments involved identification of the hUCMSCs, construction of the biomimetic composite scaffolds by the physical and chemical crosslinking of WJ and CS, and testing of the biomechanical properties of both the composite scaffold and the WJ scaffold. In the in vivo experiments, composite scaffolds loaded with hUCMSCs and WJ scaffolds loaded with hUCMSCs were applied to repair articular cartilage defects in the rat knee. Moreover, their repair effects were evaluated by the unaided eye, histological observations, and the immunogenicity of scaffolds and hUCMSCs. We found that in vitro, the Young's modulus of the composite scaffold (WJ-CS) was higher than that of the WJ scaffold. In vivo, the composite scaffold loaded with hUCMSCs repaired rat cartilage defects better than did the WJ scaffold loaded with hUCMSCs. Both the scaffold and hUCMSCs showed low immunogenicity. These results demonstrate that the in vitro construction of a human-derived WJ-CS composite scaffold enhances the biomechanical properties of WJ and that the repair of knee cartilage defects in rats is better with the composite scaffold than with the single WJ scaffold if the scaffold is loaded with hUCMSCs.

Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.

Protein and Polysaccharide-Based Magnetic Composite Materials for Medical Applications

The combination of protein and polysaccharides with magnetic materials has been implemented in biomedical applications for decades. Proteins such as silk, collagen, and elastin and polysaccharides such as chitosan, cellulose, and alginate have been heavily used in composite biomaterials. The wide diversity in the structure of the materials including their primary monomer/amino acid sequences allow for tunable properties. Various types of these composites are highly regarded due to their biocompatible, thermal, and mechanical properties while retaining their biological characteristics. This review provides information on protein and polysaccharide materials combined with magnetic elements in the biomedical space showcasing the materials used, fabrication methods, and their subsequent applications in biomedical research.

Elastic materials for tissue engineering applications: Natural, synthetic, and hybrid polymers

Elastin and collagen are the two main components of elastic tissues and provide the tissue with elasticity and mechanical strength, respectively. Whereas collagen is adequately produced in vitro, production of elastin in tissue-engineered constructs is often inadequate when engineering elastic tissues. Therefore, elasticity has to be artificially introduced into tissue-engineered scaffolds. The elasticity of scaffold materials can be attributed to either natural sources, when native elastin or recombinant techniques are used to provide natural polymers, or synthetic sources, when polymers are synthesized. While synthetic elastomers often lack the biocompatibility needed for tissue engineering applications, the production of natural materials in adequate amounts or with proper mechanical strength remains a challenge. However, combining natural and synthetic materials to create hybrid components could overcome these issues. This review explains the synthesis, mechanical properties, and structure of native elastin as well as the theories on how this extracellular matrix component provides elasticity in vivo. Furthermore, current methods, ranging from proteins and synthetic polymers to hybrid structures that are being investigated for providing elasticity to tissue engineering constructs, are comprehensively discussed.

STATEMENT OF SIGNIFICANCE

Tissue engineered scaffolds are being developed as treatment options for malfunctioning tissues throughout the body. It is essential that the scaffold is a close mimic of the native tissue with regards to both mechanical and biological functionalities. Therefore, the production of elastic scaffolds is of key importance to fabricate tissue engineered scaffolds of the elastic tissues such as heart valves and blood vessels. Combining naturally derived and synthetic materials to reach this goal proves to be an interesting area where a highly tunable material that unites mechanical and biological functionalities can be obtained.

Resection-Induced Leveling of Elevated Plug Cartilage in Osteochondral Autologous Transplantation of the Knee Achieves Acceptable Clinical Results

BACKGROUND

Plug protuberance occasionally occurs in osteochondral autologous transplantation (OAT). The incongruity of plugs results in poor clinical outcomes, especially in cases of protuberance. However, a surgical procedure to deal with this problem has not been reported. Purpose/Hypothesis: The purpose was to evaluate the efficacy and safety of cartilage resection of elevated plugs, with the hypothesis that patients whose elevated plugs were resected and leveled would achieve clinical outcomes equivalent to those of patients with flush plugs.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Cases (group P) included 22 patients who underwent OAT of the knee and whose plugs showed protuberance greater than 1 mm that was resected with a scalpel to obtain smooth congruity, while controls (group C) included 22 background-matched patients who did not require plug resection. The International Knee Documentation Committee (IKDC) subjective score, IKDC objective grade, and Japanese Orthopaedic Association score for knee osteoarthritis (JOA knee score) were used preoperatively and at the final follow-up (mean ± SD, 49.3 ± 18.1 months). International Cartilage Repair Society (ICRS) Cartilage Repair Assessment was used to evaluate lesion healing during the second-look arthroscopy.

RESULTS

IKDC subjective scores of group C (82.5 ± 11.8) and group P (82.1± 15.1) showed no difference at the final follow-up. On postoperative IKDC objective grading, 86% of group C and 82% of group P patients were graded as "nearly normal" or better ( P = .639). The mean JOA knee scores of group C (90.9 ± 8.9) and group P (90.1 ± 9.5) did not differ significantly ( P = .647). Nine second-look arthroscopies were performed in group C versus 8 in group P, and all patients had plugs that were graded as "nearly normal" or better by the ICRS Cartilage Repair Assessment. Larger plugs tended to be used in those patients who required resection.

CONCLUSION

Resection of the elevated plug surface did not negatively affect patient outcomes in the midterm follow-up period.

Stratification of knee osteoarthritis: two major patient subgroups identified by genome-wide expression analysis of articular cartilage

Introduction

Osteoarthritis (OA) is a heterogeneous and complex disease. We have used a network biology approach based on genome-wide analysis of gene expression in OA knee cartilage to seek evidence for pathogenic mechanisms that may distinguish different patient subgroups.

Methods

Results from RNA-Sequencing (RNA-Seq) were collected from intact knee cartilage at total knee replacement from 44 patients with OA, from 16 additional patients with OA and 10 control patients with non-OA. Results were analysed to identify patient subsets and compare major active pathways.

Results

The RNA-Seq results showed 2692 differentially expressed genes between OA and non-OA. Analysis by unsupervised clustering identified two distinct OA groups: Group A with 24 patients (55%) and Group B with 18 patients (41%). A 10 gene subgroup classifier was validated by RT-qPCR in 16 further patients with OA. Pathway analysis showed increased protein expression in both groups. PhenomeExpress analysis revealed group differences in complement activation, innate immune responses and altered Wnt and TGFβ signalling, but no activation of inflammatory cytokine expression. Both groups showed suppressed circadian regulators and whereas matrix changes in Group A were chondrogenic, in Group B they were non-chondrogenic with changes in mechanoreceptors, calcium signalling, ion channels and in cytoskeletal organisers. The gene expression changes predicted 478 potential biomarkers for detection in synovial fluid to distinguish patients from the two groups.

Conclusions

Two subgroups of knee OA were identified by network analysis of RNA-Seq data with evidence for the presence of two major pathogenic pathways. This has potential importance as a new basis for the stratification of patients with OA for drug trials and for the development of new targeted treatments.

Enhanced nutrient transport improves the depth-dependent properties of tri-layered engineered cartilage constructs with zonal co-culture of chondrocytes and MSCs

Biomimetic design in cartilage tissue engineering is a challenge given the complexity of the native tissue. While numerous studies have generated constructs with near-native bulk properties, recapitulating the depth-dependent features of native tissue remains a challenge. Furthermore, limitations in nutrient transport and matrix accumulation in engineered constructs hinders maturation within the central core of large constructs. To overcome these limitations, we fabricated tri-layered constructs that recapitulate the depth-dependent cellular organization and functional properties of native tissue using zonally derived chondrocytes co-cultured with MSCs. We also introduced porous hollow fibers (HFs) and HFs/cotton threads to enhance nutrient transport. Our results showed that tri-layered constructs with depth-dependent organization and properties could be fabricated. The addition of HFs or HFs/threads improved matrix accumulation in the central core region. With HF/threads, the local modulus in the deep region of tri-layered constructs nearly matched that of native tissue, though the properties in the central regions remained lower. These constructs reproduced the zonal organization and depth-dependent properties of native tissue, and demonstrate that a layer-by-layer fabrication scheme holds promise for the biomimetic repair of focal cartilage defects.

STATEMENT OF SIGNIFICANCE

Articular cartilage is a highly organized tissue driven by zonal heterogeneity of cells, extracellular matrix proteins and fibril orientations, resulting in depth-dependent mechanical properties. Therefore, the recapitulation of the functional properties of native cartilage in a tissue engineered construct requires such a biomimetic design of the morphological organization, and this has remained a challenge in cartilage tissue engineering. This study demonstrates that a layer-by-layer fabrication scheme, including co-cultures of zone-specific articular CHs and MSCs, can reproduce the depth-dependent characteristics and mechanical properties of native cartilage while minimizing the need for large numbers of chondrocytes. In addition, introduction of a porous hollow fiber (combined with a cotton thread) enhanced nutrient transport and depth-dependent properties of the tri-layered construct. Such a tri-layered construct may provide critical advantages for focal cartilage repair. These constructs hold promise for restoring native tissue structure and function, and may be beneficial in terms of zone-to-zone integration with adjacent host tissue and providing more appropriate strain transfer after implantation.

Three dimensional microstructural network of elastin, collagen, and cells in Achilles tendons

Similar to most biological tissues, the biomechanical, and functional characteristics of the Achilles tendon are closely related to its composition and microstructure. It is commonly reported that type I collagen is the predominant component of tendons and is mainly responsible for the tissue's function. Although elastin has been found in varying proportions in other connective tissues, previous studies report that tendons contain very small quantities of elastin. However, the morphology and the microstructural relationship among the elastic fibres, collagen, and cells in tendon tissue have not been well examined. We hypothesize the elastic fibres, as another fibrillar component in the extracellular matrix, have a unique role in mechanical function and microstructural arrangement in Achilles tendons. It has been shown that elastic fibres present a close connection with the tenocytes. The close relationship of the three components has been revealed as a distinct, integrated and complex microstructural network. Notably, a "spiral" structure within fibril bundles in Achilles tendons was observed in some samples in specialized regions. This study substantiates the hierarchical system of the spatial microstructure of tendon, including the mapping of collagen, elastin and tenocytes, with 3-dimensional confocal images. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1203-1214, 2017.

High-resolution study of the 3D collagen fibrillary matrix of Achilles tendons without tissue labelling and dehydrating

Knowledge of the collagen structure of an Achilles tendon is critical to comprehend the physiology, biomechanics, homeostasis and remodelling of the tissue. Despite intensive studies, there are still uncertainties regarding the microstructure. The majority of studies have examined the longitudinally arranged collagen fibrils as they are primarily attributed to the principal tensile strength of the tendon. Few studies have considered the structural integrity of the entire three-dimensional (3D) collagen meshwork, and how the longitudinal collagen fibrils are integrated as a strong unit in a 3D domain to provide the tendons with the essential tensile properties. Using second harmonic generation imaging, a 3D imaging technique was developed and used to study the 3D collagen matrix in the midportion of Achilles tendons without tissue labelling and dehydration. Therefore, the 3D collagen structure is presented in a condition closely representative of the in vivo status. Atomic force microscopy studies have confirmed that second harmonic generation reveals the internal collagen matrix of tendons in 3D at a fibril level. Achilles tendons primarily contain longitudinal collagen fibrils that braid spatially into a dense rope-like collagen meshwork and are encapsulated or wound tightly by the oblique collagen fibrils emanating from the epitenon region. The arrangement of the collagen fibrils provides the longitudinal fibrils with essential structural integrity and endows the tendon with the unique mechanical function for withstanding tensile stresses. A novel 3D microscopic method has been developed to examine the 3D collagen microstructure of tendons without tissue dehydrating and labelling. The study also provides new knowledge about the collagen microstructure in an Achilles tendon, which enables understanding of the function of the tissue. The knowledge may be important for applying surgical and tissue engineering techniques to tendon reconstruction.

Biomimetic collagen/elastin meshes for ventral hernia repair in a rat model

Ventral hernia repair remains a major clinical need. Herein, we formulated a type I collagen/elastin crosslinked blend (CollE) for the fabrication of biomimetic meshes for ventral hernia repair. To evaluate the effect of architecture on the performance of the implants, CollE was formulated both as flat sheets (CollE Sheets) and porous scaffolds (CollE Scaffolds). The morphology, hydrophylicity and in vitro degradation were assessed by SEM, water contact angle and differential scanning calorimetry, respectively. The stiffness of the meshes was determined using a constant stretch rate uniaxial tensile test, and compared to that of native tissue. CollE Sheets and Scaffolds were tested in vitro with human bone marrow-derived mesenchymal stem cells (h-BM-MSC), and finally implanted in a rat ventral hernia model. Neovascularization and tissue regeneration within the implants was evaluated at 6weeks, by histology, immunofluorescence, and q-PCR. It was found that CollE Sheets and Scaffolds were not only biomechanically sturdy enough to provide immediate repair of the hernia defect, but also promoted tissue restoration in only 6weeks. In fact, the presence of elastin enhanced the neovascularization in both sheets and scaffolds. Overall, CollE Scaffolds displayed mechanical properties more closely resembling those of native tissue, and induced higher gene expression of the entire marker genes tested, associated with de novo matrix deposition, angiogenesis, adipogenesis and skeletal muscles, compared to CollE Sheets. Altogether, this data suggests that the improved mechanical properties and bioactivity of CollE Sheets and Scaffolds make them valuable candidates for applications of ventral hernia repair.

STATEMENT OF SIGNIFICANCE

Due to the elevated annual number of ventral hernia repair in the US, the lack of successful grafts, the design of innovative biomimetic meshes has become a prime focus in tissue engineering, to promote the repair of the abdominal wall, avoid recurrence. Our meshes (CollE Sheets and Scaffolds) not only showed promising mechanical performance, but also allowed for an efficient neovascularization, resulting in new adipose and muscle tissue formation within the implant, in only 6weeks. In addition, our meshes allowed for the use of the same surgical procedure utilized in clinical practice, with the commercially available grafts. This study represents a significant step in the design of bioactive acellular off-the-shelf biomimetic meshes for ventral hernia repair.

Structure and function of the septum nasi and the underlying tension chord in crocodylians

A long rostrum has distinct advantages for prey capture in an aquatic or semi-aquatic environment but at the same time poses severe problems concerning stability during biting. We here investigate the role of the septum nasi of brevirostrine crocodilians for load-absorption during mastication. Histologically, both the septum nasi and the septum interorbitale consist of hyaline cartilage and therefore mainly resist compression. However, we identified a strand of tissue extending longitudinally below the septum nasi that is characterized by a high content of collagenous and elastic fibers and could therefore resist tensile stresses. This strand of tissue is connected with the m. pterygoideus anterior. Two-dimensional finite element modeling shows that minimization of bending in the crocodilian skull can only be achieved if tensile stresses are counteracted by a strand of tissue. We propose that the newly identified strand of tissue acts as an active tension chord necessary for stabilizing the long rostrum of crocodilians during biting by transforming the high bending stress of the rostrum into moderate compressive stress.

Changes in tissue directionality reflect differences in myelin content after demyelination in mice spinal cords

Changes in myelin integrity are key manifestations of many neurological diseases including multiple sclerosis but precise measurement of myelin in vivo is challenging. The goal of this study was to evaluate myelin content in histological images obtained from a lysolecithin mouse model of demyelination, using a new quantitative method named structure tensor analysis. Injury was targeted at the dorsal column of mice spinal cords. We obtained 16 histological images stained with luxol fast blue for myelin from 9 mice: 9 images from lesion epicenter and 7 from a distant area 500-μm away from the epicenter. In each image, we categorized 3 tissue types: healthy, completely demyelinated, and partially demyelinated. Structure tensor analysis was applied to quantify the coherency (anisotropy), energy (trace of dominant directions), and angular entropy (degree of disorder) of each tissue. We found that completely demyelinated lesions had significantly lower coherency and energy but higher angular entropy than partially demyelinated and healthy tissues at both the epicenter and distant areas of the injury. In addition, the coherency of healthy tissue was greater than partially demyelinated tissue at each site. Within tissue category, we did not find differences in any measure between spinal cord locations. Our findings suggest that greater myelin integrity is associated with better tissue anisotropy, independent of injury location. Structure tensor analysis may serve as a new tool for quantitative measurement of myelin content in white matter, and this may help understand disease mechanisms and development in MS and other demyelinating disorders.

High-resolution measurements of the multilayer ultra-structure of articular cartilage and their translational potential

Current musculoskeletal imaging techniques usually target the macro-morphology of articular cartilage or use histological analysis. These techniques are able to reveal advanced osteoarthritic changes in articular cartilage but fail to give detailed information to distinguish early osteoarthritis from healthy cartilage, and this necessitates high-resolution imaging techniques measuring cells and the extracellular matrix within the multilayer structure of articular cartilage. This review provides a comprehensive exploration of the cellular components and extracellular matrix of articular cartilage as well as high-resolution imaging techniques, including magnetic resonance image, electron microscopy, confocal laser scanning microscopy, second harmonic generation microscopy, and laser scanning confocal arthroscopy, in the measurement of multilayer ultra-structures of articular cartilage. This review also provides an overview for micro-structural analysis of the main components of normal or osteoarthritic cartilage and discusses the potential and challenges associated with developing non-invasive high-resolution imaging techniques for both research and clinical diagnosis of early to late osteoarthritis.