Collagen Network Research Articles

Mechanical Wear of Degraded Articular Cartilage.

To evaluate the mechanical wear of cartilage with different types of degradation. Bovine osteochondral explants were treated with interleukin-1β (IL-1β) to mimic inflammatory conditions, with chondroitinase ABC (ChABC) to specifically remove glycosaminoglycans (GAGs), orwith collagenase to degrade the collagen network during 5 days of culture. Viscoelastic properties of cartilage were characterized via indentation. Biochemical assays were performed to quantify the cartilage matrix loss to the media during culture and from an accelerated, ex vivo wear test. The coefficient of friction during the wear test was measured. Distribution of GAGs in the tissue was assessed histologically. All three degradative treatments decreased the cartilage modulus values and depleted GAGs in histological sections. However, wear was not uniform among the different treatments. Collagen loss from the tissue due to mechanical wear was only higher with IL-1β and collagenase treatment, while collagen loss due to wear with ChABC treatment was similar to untreated controls. In addition, less GAG was released due to mechanical wear in all degraded groups than the controls, likely because GAGs had already been depleted from these tissues during culture. As no significant differences in the coefficient of friction were observed between groups, changes in wear were attributed to altered tissue composition and structure rather than to changes in frictional forces. Results suggest that cartilage with a degraded collagen network is more susceptible to mechanical wear, but that cartilage wear may be relatively unaffected by the loss of GAGs. Furthermore, exacerbated mechanical wear could be an additional mechanism by which inflammatory cytokines induce cartilage breakdown.

Zonal Characteristics of Collagen Ultrastructure and Responses to Mechanical Loading in Articular Cartilage.

The biomechanical properties of articular cartilage arise from a complex bioenvironment comprising hierarchically organised collagen networks within the extracellular matrix (ECM) that interact with the proteoglycan-rich interstitial fluid. This network features a depth-dependent fibril organisation across different zones. Understanding how collagen fibrils respond to external loading is key to elucidating the mechanisms behind lesion and managing degenerative conditions like osteoarthritis. This study employs polarisation-resolved second harmonic generation (pSHG) microscopy to quantify the ultrastructural organisation of collagen fibrils and their spatial gradient along the depth of bone-cartilage explants at a close-to-in vivo condition. By combining with in-situ loading, we examined the responses of collagen fibrils by quantifying changes in their principal orientation and degree of alignment. The spatial gradient and heterogeneity of collagen organisation were captured at high resolution (1 µm) along the longitudinal plane of explants (0.5 by 2 mm). Zone-specific ultrastructural characteristics were quantified to aid in defining zonal borders, revealing consistent zonal proportions with varying overall thicknesses. Under compression, the transitional zone exhibited the most significant re-organisation of collagen fibrils. It initially allowed large deformation through re-orientation of fibrils, which then tightened fibril alignment to prevent excessive deformation, indicating a dynamic adaptation mechanism in response to increasing strain levels. Our results provide comprehensive, zone-specific baselines of cartilage ultrastructure and micromechanics, crucial for investigating the onset and progression of degenerative conditions, setting therapeutic intervention targets, and guiding cartilage repair and regeneration efforts. STATEMENT OF SIGNIFICANCE: Achieved unprecedented quantification of the spatial gradient and heterogeneity of collagen ultrastructural organisation at a high resolution (1 µm) along the full depth of the longitudinal plane of osteochondral explants (500 by 2000 µm) in close-to-in vivo condition. Suggested new anatomical landmarks based on ultrastructural features for determining zonal borders and found consistent zonal proportions in explants with different overall thicknesses. Demonstrated that collagen fibrils initially respond by re-orientating themselves at low strain levels, playing a significant role in cartilage deformation, particularly within the transitional zone. At higher strain levels, more collagen fibrils changed their alignment, indicating a dynamic shift in the response mechanism at varying strain levels.

Aging-Induced Discrepant Response of Fracture Healing is Initiated from the Organization and Mineralization of Collagen Fibrils in Callus.

Fracture healing is a complex process during which the bone restores its structural and mechanical integrity. Collagen networks and minerals are the fundamental components to rebuild the bone matrix in callus. It has been recognized that bone quality could be impaired during aging. However, how the structural and mechanical recovery of fracture healing is influenced by aging, particularly from the perspective of organization and mineralization of the collagen network in callus, remains unclear. A tibial fracture model was established for both the young (5 weeks) and aged mice (68 weeks). On the 21st day postfracture, the characteristics of the collagen network, mineralization, and the nanoscale mechanical properties of the callus were assessed. The results indicated that aging postpones the fracture healing process, leading to incomplete microstructure, less mineral content and mineralization, and weaker mechanical properties of callus. In the aged mice, the internal fixation and mechanical immobilization promoted the mineralization of callus by increasing mineral crystal length and mineral-to-matrix ratio by 48 and 42% compared to the internal fixation and free movement control group, respectively. By contrast, in the young mice, the internal fixation and mechanical immobilization induced disordered collagen fibrils and decreased the crystal length and mineral-to-matrix ratio by 32 and 36%, compared to the internal fixation and free movement control group, respectively. The present findings suggested that the aging-induced structure and mechanical differences of callus during fracture healing initiate from the organization and mineralization of collagen fibrils. Multiscale structural and mechanical analysis suggested mechanical immobilization is beneficial to the structure, composition, and mechanics of callus in the aged mice while impairing the organization and mineralization of collagen fibril in the callus of the young mice. These findings suggested that different mechanical intervention strategies should be adopted for fracture healing at different ages, which provides valuable insights for the clinical treatment of bone fracture.

Decellularized Liver Matrices for Expanding the Donor Pool-An Evaluation of Existing Protocols and Future Trends.

Liver transplantation is the only curative option for end-stage liver disease and is necessary for an increasing number of patients with advanced primary or secondary liver cancer. Many patient groups can benefit from this treatment, however the shortage of liver grafts remains an unsolved problem. Liver bioengineering offers a promising method for expanding the donor pool through the production of acellular scaffolds that can be seeded with recipient cells. Decellularization protocols involve the removal of cells using various chemical, physical, and enzymatic steps to create a collagenous network that provides support for introduced cells and future vascular and biliary beds. However, the removal of the cells causes varying degrees of matrix damage, that can affect cell seeding and future organ performance. The main objective of this review is to present the existing techniques of producing decellularized livers, with an emphasis on the assessment and definition of acellularity. Decellularization agents are discussed, and the standard process of acellular matrix production is evaluated. We also introduce the concept of the stepwise assessment of the matrix during decellularization through decellularization cycles. This method may lead to shorter detergent exposure times and less scaffold damage. The introduction of apoptosis induction in the field of organ engineering may provide a valuable alternative to existing long perfusion protocols, which lead to significant matrix damage. A thorough understanding of the decellularization process and the action of the various factors influencing the final composition of the scaffold is essential to produce a biocompatible matrix, which can be the basis for further studies regarding recellularization and retransplantation.

Interpenetrating networks of fibrillar and amorphous collagen promote cell spreading and hydrogel stability.

Hydrogels composed of collagen, the most abundant protein in the human body, are widely used as scaffolds for tissue engineering due to their ability to support cellular activity. However, collagen hydrogels with encapsulated cells often experience bulk contraction due to cell-generated forces, and conventional strategies to mitigate this undesired deformation often compromise either the fibrillar microstructure or cytocompatibility of the collagen. To support the spreading of encapsulated cells while preserving the structural integrity of the gels, we present an interpenetrating network (IPN) of two distinct collagen networks with different crosslinking mechanisms and microstructures. First, a physically self-assembled collagen network preserves the fibrillar microstructure and enables the spreading of encapsulated human corneal mesenchymal stromal cells. Second, an amorphous collagen network covalently crosslinked with bioorthogonal chemistry fills the voids between fibrils and stabilizes the gel against cell-induced contraction. This collagen IPN balances the biofunctionality of natural collagen with the stability of covalently crosslinked, engineered polymers. Taken together, these data represent a new avenue for maintaining both the fiber-induced spreading of cells and the structural integrity of collagen hydrogels by leveraging an IPN of fibrillar and amorphous collagen networks. STATEMENT OF SIGNIFICANCE: Collagen hydrogels are widely used as scaffolds for tissue engineering due to their support of cellular activity. However, collagen hydrogels often undergo undesired changes in size and shape due to cell-generated forces, and conventional strategies to mitigate this deformation typically compromise either the fibrillar microstructure or cytocompatibility of the collagen. In this study, we introduce an innovative interpenetrating network (IPN) that combines physically self-assembled, fibrillar collagen-ideal for promoting cell adhesion and spreading-with covalently crosslinked, amorphous collagen-ideal for enhancing bulk hydrogel stability. Our IPN design maintains the native fibrillar structure of collagen while significantly improving resistance against cell-induced contraction, providing a promising solution to enhance the performance and reliability of collagen hydrogels for tissue engineering applications.

The Precise Synthesis of Ultradense Bottlebrush Polymers Unearths Unique Trends in Lyotropic Ordering.

Biomacromolecular networks with multiscale fibrillar structures are characterized by exceptional mechanical properties, making them attractive architectures for synthetic materials. However, there is a dearth of synthetic polymeric building blocks capable of forming similarly structured networks. Bottlebrush polymers (BBPs) are anisotropic graft polymers with the potential to mimic and replace biomacromolecules such as tropocollagen for the fabrication of synthetic fibrillar networks; however, a longstanding limitation of BBPs has been the lack of rigidity necessary to access the lyotropic ordering that underpins the formation of collagenous networks. While the correlation between BBP rigidity and grafting density is well established, synthetic approaches to rigidify BBPs by increased grafting density are underdeveloped. To address this gap in synthetic capability, we report the synthesis of novel macroinitiators that provide well-defined BBPs with an unprecedentedly high grafting density. A suite of light scattering techniques are used to correlate macromolecular rigidity with grafting architecture and density and demonstrate for the first time that poly(norbornene) BBPs exhibit long-range lyotropic ordering as a result of their rodlike character. Specifically, the newly reported ultradensely grafted structures, preparable on multigram scale, form hexagonal arrays while conventional BBPs do not, despite showing long-range spatial correlations. These results implicate the central role of density and entanglement in the solution phase assembly of BBPs and provide new fundamental insight that is broadly relevant to the fabrication and performance of BBP-derived materials, spanning biomedical research to photonic materials and thermal management technologies. Furthermore, these newly reported liquid crystalline BBPs provide a structural template to explore the untapped potential of the bottom-up assembly of semiflexible networks and are ultimately intended to provide a modular route to hierarchically structured biomimetic materials.

Collagen deposition in lung parenchyma driven by depletion of interstitial Lyve-1+ macrophages prevents cigarette smoke-induced emphysema and loss of airway function.

Collagen is essential for maintaining lung structure and function and its remodeling has been associated with respiratory diseases including chronic obstructive pulmonary disease (COPD). However, the cellular mechanisms driving collagen remodeling and the functional implications of this process in the pathophysiology of pulmonary diseases remain poorly understood. To address this question, we employed Lyve1wt/cre ; Csf1rflox/flox mice with specific depletion of Lyve-1+ macrophages and assessed the content, types and organization of collagen in lung compartments at steady state and after chronic exposure to cigarette smoke (CS). Using this mouse model, we found that the absence of this subpopulation of tissue resident macrophage led to the deposition of type I collagen fibers around the alveoli and bronchi at steady state. Further analysis by polarized light microscopy and Sircol collagen assay revealed that the collagen fibers accumulating in the lungs depleted of Lyve-1+ macrophages were thicker and crosslinked. A decrease in MMP-9 gene expression and proteolytic activity together with an increase in Col1a1, Timp-3 and Lox expression accompanied the collagen alterations. Next, we investigated the effect of the collagen remodeling on the pathophysiology of COPD and airway function in mice lacking Lyve-1+ macrophages exposed chronically to cigarette smoke (CS), a well-established animal model of COPD. We found that deposition of collagen prior CS exposure protected these mice against destruction of alveoli (emphysema), and bronchi thickening and prevented loss of airway function. Thus, we uncover that interstitial Lyve-1+ macrophages regulate the composition, amount, and architecture of collagen network in the lungs at steady state and that such collagen remodeling functionally impacts the development of COPD. This study further supports the potential of targeting collagen as promising approaches to treat respiratory diseases.

SiRNA Treatment Enhances Collagen Fiber Formation in Tissue-Engineered Meniscus via Transient Inhibition of Aggrecan Production.

The complex collagen network of the native meniscus and the gradient of the density and alignment of this network through the meniscal enthesis is essential for the proper mechanical function of these tissues. This architecture is difficult to recapitulate in tissue-engineered replacement strategies. Prenatally, the organization of the collagen fiber network is established and aggrecan content is minimal. In vitro, fibrochondrocytes (FCCs) produce proteoglycans and associated glycosaminoglycan (GAG) chains early in culture, which can inhibit collagen fiber formation during the maturation of tissue-engineered menisci. Thus, it would be beneficial to both specifically and temporarily block deposition of proteoglycans early in culture. In this study, we transiently inhibited aggrecan production by meniscal fibrochondrocytes using siRNA in collagen gel-based tissue-engineered constructs. We evaluated the effect of siRNA treatment on the formation of collagen fibrils and bulk and microscale tensile properties. Specific inhibition of aggrecan production by fibrochondrocytes via siRNA was successful both in 2D monolayer cell culture and 3D tissue culture. This inhibition during early maturation of these in vitro constructs increased collagen fibril diameter by more than 2-fold. This increase in fibril diameter allowed these tissues to distribute strains more effectively at the local level, particularly at the interface of the bone and soft tissue. These data show that siRNA can be used to modulate the ECM to improve collagen fiber formation and mechanical properties in tissue-engineered constructs, and that a transient decrease in aggrecan promotes the formation of a more robust fiber network.

Biologically inspired bioactive hydrogels for scarless corneal repair.

Corneal injury-induced fibrosis occurs because of corneal epithelial basement membrane (EBM) injury and defective regeneration. Corneal fibrosis inhibition and transparency restoration depend on reestablished EBM, where the collagen network provides structural stability and heparan sulfate binds corneal epithelium-derived cytokines to regulate homeostasis. Inspired by this, bioactive hydrogels (Hep@Gel) composed of collagen-derived gelatins and highly anionic heparin were constructed for scarless corneal repair. Hep@Gel resembled the barrier function of the EBM regarding surface-confined binding, long-time sequestration, and progressive degradation of IL-1, TGF-β, and PDGF-BB, which robustly inhibited the apoptosis and myofibroblast transition of keratocytes. Animal models of rabbits and nonhuman primates confirmed that Hep@Gel effectively limited the influx of inflammatory and fibrotic cytokines from the epithelium into the stroma to down-regulate the wound healing cascade, contributing to better vision quality with 73% reduced fibrosis. Hep@Gel offers a solution for preventing corneal injury-induced scarring and substituting for lamellar keratoplasty to remove scarring.

Age-related remodeling of the vocal fold extracellular matrix composition, structure, and biomechanics during tissue maturation

ABSTRACT Purpose The vocal folds (VFs) are among the most mechanically active connective tissues, vibrating between 80 and 250 hz during speech. Overall VF function is determined by the composition and structure of their extracellular matrix (ECM). During tissue maturation, the VFs remodel from a monolayer of collagen fibers to a tri-layered structure, affecting tissue biomechanics. However, age-related VF ECM remodeling remains poorly understood since few studies have explored the proteins governing collagen fibrillogenesis or the non-collagenous ECM components critical for VF elasticity. Materials and Methods VFs from immature, sexually mature, and skeletally mature rats were evaluated by endoscopy, histology, and electron microscopy for cellular and biochemical composition, ECM organization, and proteoglycan distribution. Nanoindentation modulus was determined by atomic force microscopy. Results Collagen fiber abundance, maturity, and alignment are low in immature rats but show an age-dependent increase during tissue maturation. Lumican and fibromodulin, which regulate early-stage collagen fibril formation, are distributed throughout the VFs, and their abundance decreases with age. Decorin, involved in collagen organization, is concentrated just beneath the epithelium and increases with age. Elastin levels increase during tissue maturation, but hyaluronic acid abundance and distribution remain consistent with age. VF nanoindentation modulus trends toward a decrease with age. Conclusion This work identifies changes in VF ECM composition and organization during tissue maturation, focusing on proteins that regulate collagen fibrillogenesis, fiber assembly, and VF biomechanics. These findings may inform the development of pro-reparative therapies designed to influence collagen network structure and overall ECM dysregulation in a number of laryngeal pathologies.

Monocytes use protrusive forces to generate migration paths in viscoelastic collagen-based extracellular matrices.

Circulating monocytes are recruited to the tumor microenvironment, where they can differentiate into macrophages that mediate tumor progression. To reach the tumor microenvironment, monocytes must first extravasate and migrate through the type-1 collagen rich stromal matrix. The viscoelastic stromal matrix around tumors not only stiffens relative to normal stromal matrix, but often exhibits enhanced viscous characteristics, as indicated by a higher loss tangent or faster stress relaxation rate. Here, we studied how changes in matrix stiffness and viscoelasticity, impact the three-dimensional migration of monocytes through stromal-like matrices. Interpenetrating networks of type-1 collagen and alginate, which enable independent tunability of stiffness and stress relaxation over physiologically relevant ranges, were used as confining matrices for three-dimensional culture of monocytes. Increased stiffness and faster stress relaxation independently enhanced the 3D migration of monocytes. Migrating monocytes have an ellipsoidal or rounded wedge-like morphology, reminiscent of amoeboid migration, with accumulation of actin at the trailing edge. Matrix adhesions and Rho-mediated contractility were dispensable for monocyte migration in 3D, but migration did require actin polymerization and myosin contractility. Mechanistic studies indicate that actin polymerization at the leading edge generates protrusive forces that open a path for the monocytes to migrate through in the confining viscoelastic matrices. Taken together, our findings implicate matrix stiffness and stress relaxation as key mediators of monocyte migration and reveal how monocytes use pushing forces at the leading edge mediated by actin polymerization to generate migration paths in confining viscoelastic matrices.

Implementation of the UNRES/SUGRES-1P Coarse-Grained Model of Heparin for Simulating Protein/Heparin Interactions.

Heparin is a natural highly sulfated unbranched periodic polysaccharide that plays a critical role in regulating various cellular events through interactions with its protein targets such as growth factors and cytokines. Although all-atom simulations of heparin-containing systems provide valuable insights into their structural and dynamical properties, long chains of heparin participate in many biologically relevant processes at much bigger scales and longer times than the ones which all-atom MD is able to effectively deal with. Among these processes is the establishment of chemokine gradients, amyloidogenesis, or collagen network organization. To address this limitation, coarse-grained models simplify these systems by reducing the number of degrees of freedom, allowing for the efficient exploration of structural changes within protein/heparin complexes. We introduce and validate the accuracy of a new coarse-grained physics-based model designed for studying protein/heparin interactions, which has been incorporated into the UNRES software package. The effective energy functions from UNRES and SUGRES-1P have been employed for the protein and heparin components, respectively. A good agreement between the obtained coarse-grained simulation results and experimental data confirms the suitability of the combined coarse-grained UNRES and SUGRES-1P model for in silico analysis of complex biological phenomena involving heparin, spanning time scales and molecular system sizes not attainable by conventional atomistic molecular dynamics simulations.

Identification of CD44 as a key engager to hyaluronic acid-rich extracellular matrices for cell traction force generation and tumor invasion in 3D

Mechanical properties of the extracellular matrix (ECM) critically regulate a number of important cell functions including growth, differentiation and migration. Type I collagen and glycosaminoglycans (GAGs) are two primary components of ECMs that contribute to mammalian tissue mechanics, with the collagen fiber network sustaining tension, and GAGs withstanding compression. The architecture and stiffness of the collagen network are known to be important for cell-ECM mechanical interactions via cell surface adhesion receptor integrin. In contrast, studies of GAGs in modulating cell-ECM interactions are limited. Here, we present experimental studies on the roles of hyaluronic acid (HA) in single tumor cell traction force generation using a recently developed 3D cell traction force microscopy method. Our work reveals that CD44, a cell surface receptor to HA, is engaged in cell traction force generation in conjunction with β1-integrin. We find that HA significantly modifies the architecture and mechanics of the collagen fiber network, decreasing tumor cells’ propensity to remodel the collagen network, attenuating traction force generation, transmission distance, and tumor invasion. Our findings point to a novel role for CD44 in traction force generation, which can be a potential therapeutic target for diseases involving HA rich ECMs such as breast cancer and glioblastoma.

Investigating the effect of water on collagen triple helix stability

Collagen provides essential structural support to diverse body tissues through its unique triple helix structure. Collagen stability is crucial for proper tissue function and any disruptions in its stability can lead to various health issues. Prior research has identified multiple factors affecting collagen stability. However, despite its fundamental presence in biological systems, the influence of water remains inadequately explored. Here, we performed molecular dynamics simulations on collagen model peptides (CMPs) with varying experimental stability profiles to investigate the influence of water on collagen stability. Our simulations revealed variations in both the hydrogen bonding (H-bonding) patterns between the CMPs and surrounding water molecules, as well as the water networks formed around CMPs. We noted that water molecules form H-bonds with collagen residues which enhance its structural stability. Additionally, water molecules assemble around the collagen and form topological water networks (TWNs) through intermolecular H-bonding. These TWNs further stabilizes the collagen structure. Overall, this research provides insight into the role of water molecules in preserving the stability of the collagen triple helix.

Quantitative structural organization of the sclera in chicks after deprivation myopia measured with second harmonic generation microscopy.

Visual deprivation causes enhanced eye growth and the development of myopia, which is associated with a change in the arrangement of collagen fibers within the sclera. A second harmonic generation (SHG) microscope has been used to image the collagen fibers of unstained scleral punches from the posterior part of chicken eyes. We aimed to analyze the fibrous scleral tissue and quantify the changes in collagen organization in relation to the extent of induced deprivation myopia. The scleral architecture was assessed with the Radon transform (RT) through the parameter called structural dispersion (SD) that provides an objective tool to quantify the level of organization of the collagen network. We found that final refraction and axial length changes were linearly correlated. However, no significant differences in scleral thickness were found for different amounts of induced myopia. In contrast, a significant correlation between SD and refraction was demonstrated, ranging from a non-organized (in the control sclerae) to a quasi-aligned distribution (with a dominant direction of the fibers, in the sclera of myopic chicks). These findings demonstrate a remodeling process of the scleral collagen associated with myopia progression that can be measured accurately combining SHG imaging microscopy and RT algorithms.

Self-Assembly and Wound Healing Activity of Biomimetic Cycloalkane-Based Lipopeptides.

The self-assembly of lipopeptide (peptide amphiphile) molecules bearing single linear lipid chains has been widely studied, as has their diverse range of bioactivities. Here, we introduce lipopeptides bearing one or two cycloalkane chains (cycloheptadecyl or cyclododecyl) conjugated to the collagen-stimulating pentapeptide KTTKS used in Matrixyl formulations. The self-assembly of all four molecules is probed using fluorescence probe measurements to detect the critical aggregation concentration (CAC), and cryogenic-TEM and small-angle X-ray scattering (SAXS) to image the nanostructure. The peptide conformation is studied using circular dichroism (CD) and FTIR spectroscopies. All the cycloalkane lipopeptides show excellent compatibility with dermal fibroblasts. The compounds bearing one or two cyclododecyl chains (denoted as DKT and DDKT, respectively) show wound healing in diabetic rats, the improvement being markedly enhanced for DDKT. Interestingly, the revival of hair follicles and blood vessels in the dermis were observed, which are the critical markers of effective wound repair. Analysis of H&E-stained tissue images (from a rat model) shows that the rat groups treated with DDKT and DKT displayed a significantly increased amount of regenerated hair follicles, indicating a faster healing process for DDKT compared to the control group. Collagen deposition was also enhanced, especially for DDKT, and by day 20, the DDKT-treated groups had developed a dense collagen network accompanied by a regenerated epidermis. At the same time, the number of blood vessels in DDKT-treated diabetic wounds was significantly higher than in control groups and neovascularization was substantially enhanced, as assayed using α-SMA (a marker for vascular smooth muscle cells) and CD31 (a marker specific to vascular endothelial cells). These results suggest that the lead lipopeptide DDKT exhibits a remarkable pro-vascularization capability and shows great promise for future application as a wound-healing biomaterial.

Cellular solids and prestressed affine networks as models of the elastic behavior of soft biological structures.

We reviewed two microstructural models, cellular solid models and prestressed affine network models, that have been used previously in studies of elastic behavior of soft biological materials. These models provide simple and mathematically transparent equations that can be used to interpret experimental data and to obtain quantitative predictions of the elastic properties of biological structures. In both models, volumetric density and elastic properties of the microstructure are key determinants of the macroscopic elastic properties. In the prestressed network model, geometrical rearrangement of the microstructure (kinematic stiffness) is also important. As examples of application of these models, we considered the shear behavior of the cytoskeleton of adherent cells, of the collagen network of articular cartilage, and of the lung parenchymal network since their ability to resist shear is important for their normal biological and physiological functions. All three networks carry a pre-existing stress (prestress). We predicted their shear moduli using the microstructural models and compared those predictions with existing experimental data. Prestressed network models of the cytoskeleton and of the lung parenchyma provided a better correspondence to experimental data than cellular solid models. Both cellular solid and prestressed network models of the cartilage collagen network provided reasonable agreements with experimental values. These findings suggested that the kinematic stiffness and material stiffness of microstructural elements were both important determinants of the shear modulus of the cytoskeleton and of the lung parenchyma, whereas elasticity of collagen fibrils had a predominant role in the cartilage shear behavior.

Evaluating facial dermis aging in healthy Caucasian females with LC-OCT and deep learning

Recent advancements in high-resolution imaging have significantly improved our understanding of microstructural changes in the skin and their relationship to the aging process. Line Field Confocal Optical Coherence Tomography (LC-OCT) provides detailed 3D insights into various skin layers, including the papillary dermis and its fibrous network. In this study, a deep learning model utilizing a 3D ResNet-18 network was trained to predict chronological age from LC-OCT images of 100 healthy Caucasian female volunteers, aged 20 to 70 years. The AI-based protocol focused on regions of interest delineated between the segmented dermal-epidermal junction and the superficial dermis, exploiting complex patterns within the collagen network for age prediction. The model achieved a mean absolute error of 4.2 years and exhibited a Pearson correlation coefficient of 0.937 with actual ages. Furthermore, there was a notable correlation (r = 0.87) between quantified clinical scoring, encompassing parameters such as firmness, elasticity, density, and wrinkle appearance, and the ages predicted by deep learning model. This strong correlation underscores how integrating emerging imaging technologies with deep learning can accelerate aging research and deepen our understanding of how alterations in skin microstructure are related to visible signs of aging.

The Added Value of T2 Mapping in Assessment of Chondromalacia Patellae and Patellofemoral Osteoarthritis in Patients with Anterior Knee Pain

Abstract Background Cartilage mapping using Magnetic Resonance Imaging T2 is a functional non- invasive scanning procedure delivering cartography of the cartilage T2 relaxation time without using any contrast. It is tissue anisotropy sensitive, and compositional data on the collagen network of cartilage, content of water and concentration of proteoglycans are provided by it. Aim of the Work there is limited studies for evaluation the T2 mapping role in detection of chondromalacia and osteoarthritis in knee pain patients, therefore the aim of this work is to evaluate the additional value of T2 mapping overusing a baseline standard knee MRI to detect patellofemoral cartilage lesions including chondromalacia patella and knee osteoarthritis in patients presented with anterior knee pain. Patients and Methods This Cross-Sectional Study was conducted at Ain Shams University Hospital, Radio diagnosis department on 35 patients with anterior knee pain for at least 6 months. Results Among the study population 27 (77.1 %) of patients were diagnosed with OA by conventional MRI & T2 mapping with accuracy 85.7%, while only 13 (37.1%) of patients were diagnosed with chondromalacia by MRI & T2 mapping with accuracy 74.3%. In the comparison between conventional MRI & MRI T2 mapping to detect OA & chondromalacia lesions the sensitivity and specificity for OA 84.4% & 100%, while it was 59.1% & 100% for chondromalacia respectively. Conclusion T2 mapping may offer added value in the assessment of knee joint conditions such as OA and chondromalacia, with higher sensitivity and accuracy rates compared to conventional MRI. T2 mapping may be particularly useful in detecting early degenerative changes in the knee joint, which may allow for earlier intervention and management of these conditions.

Morphophysiological Assessment of the Cervix during the Reproductive Cycle and Early Pregnancy in Does Using Computed Tomography and Oxytocin Receptor Immunohistochemistry.

This study aimed to elucidate the morphophysiology and oxytocin receptor (OXTR) expression in the cervix of doe goats during various reproductive stages to enhance reproductive management strategies. A total of 40 cervical samples were categorized into follicular (n = 15), luteal (n = 10), and early pregnancy (n = 15) stages. Utilizing advanced imaging based on functional and morphological markers, the study employed computed tomography (CT) scans, histochemical staining (Masson trichrome and alcian blue), immunohistochemistry, Western blotting, and quantitative PCR (qPCR) to assess structural changes in the cervix and in OXTR expression during the estrous cycle and early pregnancy. CT scans revealed consistent cervical folds and a significant reduction in cervical width during pregnancy, suggesting structural adaptations for gestational integrity. Histochemical analyses indicated a well-organized collagen network and presence of mucins, essential for cervical function and integrity. Immunohistochemistry and Western blotting demonstrated elevated OXTR protein levels during the follicular stage, which were markedly reduced during pregnancy, indicating a role in facilitating cervical relaxation and sperm transport during estrus and maintaining cervical closure during gestation. qPCR analysis showed stable OXTR mRNA levels during follicular and luteal stages with a slight, non-significant increase during pregnancy, pointing towards posttranscriptional regulatory mechanisms. In conclusion, this study demonstrates that cervical morphology and OXTR expression in doe goats undergo significant changes across reproductive stages, with elevated OXTR protein levels during the follicular phase and notable reductions in cervical width and OXTR protein levels during pregnancy, indicating structural and functional adaptations for both reproductive processes and gestational integrity.