Collagen Fiber Network Research Articles

Comparison of various test methods to quantify the deterioration degree of archaeological leather

Quantifying the degree of deterioration is crucial for developing prevention strategies for archaeological leather. In this work, the morphology, chemical compositions, and physical properties of artificially aged leather samples were analyzed using a series of test methods to determine non-destructive or micro-destructive technologies for quantifying the degree of deterioration in archaeological leather. Results show that the hydroxyproline (Hyp) content of leather decreases with the increase of deterioration degree because deterioration leads to the gradual destruction of the collagen fiber network of leather. Moreover, the Hyp content of leather can be micro-destructively determined by high-performance liquid chromatography with fluorescence detection. Therefore, the determination of Hyp content is recommended to quantify the degree of deterioration in archaeological leather.

Restoration of the Ultrastructural Integrity of the Dermal Collagen Network by 12-Week Ingestion of Special Collagen Peptides.

This pilot study investigated the effects of a 12-week administration of a nutritional supplement containing special collagen peptides on the structural and molecular properties of the collagen fiber network in the human skin. For the assessments, the suction blister method and electron microscopical comparisons were used. Three suction blisters were generated on the inner forearm of each test subject before and after the 12-week administration of the nutritional supplement. High-resolution scanning electron microscopy (SEM) was employed to meticulously investigate the structural characteristics of the skin's collagen network, including the length and diameter of collagen fibers within the suction blister roof. Furthermore, the analysis included immunohistochemistry and fluorescence light microscopy to study hyaluronic acid within the extracellular matrix. Additional assessments encompassed changes in various epidermal parameters. Nine female participants within the age range of 43.7-61.8years (mean: 52.5 ± 5.9years) completed the study in accordance with the study protocol. Compared with baseline, the 12-week supplementation regimen led to a statistically significant average increase in the collagen fiber network size of 34.56% (p < 0.0001). Additionally, collagen fiber cross-linking and fiber length were substantially increased. The ingestion of the supplement also resulted in an 18.08% elevation in epidermal hyaluronic acid concentration (p < 0.0001). No adverse events were recorded during the study. Using an innovative approach, this study demonstrated the ability of a targeted nutritional supplement to effectively restore the ultrastructural integrity of the dermal collagen network, which is typically disrupted by the natural aging process of the skin. These findings not only corroborate existing data regarding the positive effects of oral collagen peptides on skin structure and function but also contribute to our understanding of ultrastructural morphological aspects of changes in the skin's collagen network. Supplementation can induce regeneration of the collagen fiber network in the human skin. German Clinical Trials Register, DRKS-ID DRKS00034161- Date of registration: 06.05.2024, retrospectively registered.

Multifunctional polymeric nanocapsules with enhanced cartilage penetration and retention for osteoarthritis treatment

Osteoarthritis (OA) is a prevalent joint disease characterized by cartilage degeneration and subchondral bone homeostasis imbalance. Effective topical OA therapy is challenging, as therapeutic drugs often suffer from insufficient penetration and rapid clearance. We develop miniature polydopamine (PDA) nanocapsules (sub-60 nm), which are conjugated with collagen-binding polypeptide (CBP) and loaded with an anabolic drug (i.e., parathyroid hormone 1–34, PTH 1–34) for efficient OA treatment. Such multifunctional polymeric nanocapsules, denoted as PDA@CBP-PTH, possess deformability when interacting with the dense collagen fiber networks, enabling the efficient penetration into 1 mm cartilage in 4 h and prolonged retention within the joints up to 28 days. Moreover, PDA@CBP-PTH nanocapsules exhibit excellent reactive oxygen species scavenging property in chondrocytes and enhance the anabolism in subchondral bone. The nanosystem, as dual-mode treatment for OA, demonstrates rapid penetration, long-lasting effects, and combinational therapeutic impact, paving the way for reversing the progression of OA for joint health care.

A Mathematical Model for Postimplant Collagen Remodeling in an Autologous Engineered Pulmonary Arterial Conduit.

This study was undertaken to develop a mathematical model of the long-term in vivo remodeling processes in postimplanted pulmonary artery (PA) conduits. Experimental results from two extant ovine in vivo studies, wherein polyglycolic-acid (PGA)/poly-L-lactic acid tubular conduits were constructed, cell seeded, incubated for 4 weeks, and then implanted in mature sheep to obtain the remodeling data for up to two years. Explanted conduit analysis included detailed novel structural and mechanical studies. Results in both studies indicated that the in vivo conduits remained dimensionally stable up to 80 weeks, so that the conduits maintained a constant in vivo stress and deformation state. In contrast, continued remodeling of the constituent collagen fiber network as evidenced by an increase in effective tissue uniaxial tangent modulus, which then stabilized by one year postimplant. A mesostructural constitute model was then applied to extant planar biaxial mechanical data and revealed several interesting features, including an initial pronounced increase in effective collagen fiber modulus, paralleled by a simultaneous shift toward longer, more uniformly length-distributed collagen fibers. Thus, while the conduit remained dimensionally stable, its internal collagen fibrous structure and resultant mechanical behaviors underwent continued remodeling that stabilized by one year. A time-evolving structural mixture-based mathematical model specialized for this unique form of tissue remodeling was developed, with a focus on time-evolving collagen fiber stiffness as the driver for tissue-level remodeling. The remodeling model was able to fully reproduce (1) the observed tissue-level increases in stiffness by time-evolving simultaneous increases in collagen fiber modulus and lengths, (2) maintenance of the constant collagen fiber angular dispersion, and (3) stabilization of the remodeling processes at one year. Collagen fiber remodeling geometry was directly verified experimentally by histological analysis of the time-evolving collagen fiber crimp, which matches model predictions very closely. Interestingly, the remodeling model indicated that the basis for tissue homeostasis was maintenance of the collagen fiber ensemble stress for all orientations, and not individual collagen fiber stresses. Unlike other growth and remodeling models that traditionally treat changes in the external boundary conditions (e.g., changes in blood pressure) as the primary input stimuli, the driver herein is changes to the internal constituent collagen fiber themselves due to cellular mediated cross-linking.

Superamphiphilic aerogels with 2D lamellar structure of gelatin-tuned 3D supramolecular network of collagen fibers for high-performance separation of surfactant-stabilized emulsified oily wastewater

Superwetting aerogel is a promising alternative for the remediation of emulsified oily wastewater for its high porosity combined with extreme wettability enabled high separation performances to emulsion wastewater. However, it remains challenging for superwetting aerogels to accomplish high-performance dual separation to surfactant-stabilized oil-in-water (O/W) and water-in-oil (W/O) emulsions with high stability. Herein, an environmentally benign superamphiphilic composite aerogel was prepared by a green synthesis route that relied on the utilization of natural amphiphilic biomass. Collagen fibers (CFs) were utilized to construct the three-dimensional (3D) supramolecular skeleton of aerogel to provide high storage capacity of water/oil and outstanding capillary effect to boost the mass transfer. The two-dimensional (2D) lamellar structure of gelatin (Gel) was further grown on the skeleton of CFs aerogel to play the role for simultaneously enhanced demulsifying capability and spreading of emulsions. The as-prepared superamphiphilic aerogel enabled the separation of highly stable surfactant-stabilized O/W and W/O emulsions with high separation efficiency and flux. Excellent recycling performances and anti-fouling performance were also confirmed. Our investigations therefore demonstrated that the structural engineering of superamphiphilic aerogel is a promising way to realize high-performance dual separation of surfactant-stabilized O/W and W/O emulsion wastewater.Graphical

Identification of CD44 as a key mediator of cell traction force generation in hyaluronic acid-rich extracellular matrices.

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 integrin cell surface adhesion receptors. In contrast, studies of GAGs in modulating cell-ECM interactions are limited. Here, we present experimental studies on the roles of hyaluronic acid (HA, an unsulfated GAG) 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 adhesion 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.

High angular resolution diffusion imaging (HARDI) of porcine menisci: a comparison of diffusion tensor imaging and generalized q-sampling imaging.

Diffusion magnetic resonance imaging (MRI) allows for the quantification of water diffusion properties in soft tissues. The goal of this study was to characterize the 3D collagen fiber network in the porcine meniscus using high angular resolution diffusion imaging (HARDI) acquisition with both diffusion tensor imaging (DTI) and generalized q-sampling imaging (GQI). Porcine menisci (n=7) were scanned ex vivo using a three-dimensional (3D) HARDI spin-echo pulse sequence with an isotropic resolution of 500 µm at 7.0 Tesla. Both DTI and GQI reconstruction techniques were used to quantify the collagen fiber alignment and visualize the complex collagen network of the meniscus. The MRI findings were validated with conventional histology. DTI and GQI exhibited distinct fiber orientation maps in the meniscus using the same HARDI acquisition. We found that crossing fibers were only resolved with GQI, demonstrating the advantage of GQI over DTI to visualize the complex collagen fiber orientation in the meniscus. Furthermore, the MRI findings were consistent with conventional histology. HARDI acquisition with GQI reconstruction more accurately resolves the complex 3D collagen architecture of the meniscus compared to DTI reconstruction. In the future, these technologies have the potential to nondestructively assess both normal and abnormal meniscal structure.

Biomechanical analysis of the human derived soft tissue graft Epiflex for use in oral soft tissue augmentation

PurposeThis study aimed to investigate the biomechanical properties, cell migration, and revascularization of the acellular dermal matrix Epiflex. As a decellularized, freeze–dried human skin graft, Epiflex has broad applications in medical fields, particularly in implantology and dentistry. Understanding its biomechanical characteristics is crucial for its clinical adoption as a novel soft tissue graft option.MethodsEpiflex (n = 3) was evaluated in comparison to palatal tissue from body donors (n = 3). Key metrics, such as elongation and tear resistance, were quantified. Both graft types underwent histological analysis and scanning electron microscopy. Additionally, the healing properties of Epiflex were assessed using a Chorioallantoic Membrane (CAM) Assay.ResultsBiomechanically, Epiflex (mean = 116.01 N) demonstrated the ability to withstand greater forces (p = 0.013) than human palatal tissue (mean = 12.58 N). When comparing the elongation, no significant difference was measured (ASG mean = 9.93 mm, EF mean = 9.7 mm). Histologically, Epiflex exhibited a loosely connected network of collagen fibers with a dense upper layer. The CAM Assay indicated efficient revascularization.ConclusionEpiflex appears to be a viable option for soft tissue augmentation, particularly appealing to patient groups who avoid all or specific animal-derived products due to ethical or religious reasons.Graphical

Salmonella-driven intestinal edema in mice is characterized by tensed fibronectin fibers.

Intestinal edema is a common manifestation of numerous gastrointestinal diseases and is characterized by the accumulation of fluid in the interstitial space of the intestinal wall. Technical advances in laser capture microdissection and low-biomass proteomics now allow us to specifically characterize the intestinal edema proteome. Using advanced proteomics, we identify peptides derived from antimicrobial factors with high signal intensity, but also highlight major contributions from the blood clotting system, extracellular matrix (ECM) and protease-protease inhibitor networks. The ECM is a complex fibrillar network of macromolecules that provides structural and mechanical support to the intestinal tissue. One abundant component of the ECM observed in Salmonella-driven intestinal edema is the glycoprotein fibronectin, recognized for its structure-function interplay regulated by mechanical forces. Using mechanosensitive staining of fibronectin fibers reveals that they are tensed in the edema, despite the high abundance of proteases able to cleave fibronectin. In contrast, fibronectin fibers increasingly relax in other cecal tissue areas as the infection progresses. Co-staining for fibrin(ogen) indicates the formation of a provisional matrix in the edema, similar to what is observed in response to skin injury, while collagen staining reveals a sparse and disrupted collagen fiber network. These observations plus the absence of low tensional fibronectin fibers and the additional finding of a high number of protease inhibitors in the edema proteome could indicate a critical role of stretched fibronectin fibers in maintaining tissue integrity in the severely inflamed cecum. Understanding these processes may also provide valuable functional diagnostic markers of intestinal disease progression in the future.

Analysis of fibrocalcific aortic valve stenosis: computational pre-and-post TAVR haemodynamics behaviours.

Fibro-calcific aortic valve (AV) diseases are characterized by calcium growth or accumulation of fibrosis in the AV tissues. Fibrocalcific aortic stenosis (FAS) rises specifically in females, like calcification-induced aortic stenosis (CAS), may eventually necessitate valve replacement. Fluid-structure-interaction (FSI) computational models for severe CAS and FAS patients were developed using lattice Boltzmann method and multi-scale finite elements (FE). Three parametric AV models were introduced: pathology-free of non-calcified tri-and-bicuspid AVs with healthy collagen fibre network (CFN), a FAS model incorporated a thickened CFN with embedded small calcification volumes, and a CAS model employs healthy CFN with embedded high calcification volumes. The results indicate that the interaction between calcium deposits, adjacent tissue and fibres crucially influences haemodynamics and structural reactions. A fourth model of transcatheter aortic valve replacement (TAVR) post-procedure outcomes was created to study both CAS and FAS. TAVR-CAS had a higher maximum contact pressure and lower anchoring area than TAVR-FAS, making it prone to aortic tissue damage and migration. Finally, although the TAVR-CAS offered a larger opening area, its paravalvular leakage was higher. This may be attributed to a similar thrombogenicity potential characterizing both models. The computational framework emphasizes the significance of mechanobiology in FAS and underscores the requirement for tissue modelling at multiple scales.

Abstract C020: Unconvering the hidden immunosuppressive landscape in pancreatic ductal adenocarcinoma

Abstract Pancreatic ductal adenocarcinoma (PDA) is one of the deadliest forms of cancer with an extremely low survival rate. Despite the success of therapeutic T cells in hematologic cancers, many solid tumors, including PDA, remain unresponsive with such therapies, partly due to its mechanically complex, dense, and immunosuppressive stroma. Therefore, understanding the dynamic interplay between therapeutic T cells and the tumor microenvironment (TME) is crucial for revealing engineering targets for next-generation immunotherapies. We approach this problem with genetically engineered KPC (KrasLSL-G12D/+; Trp53LSL-R172H/+; Pdx-1-Cre) mouse models that recapitulates PDA disease progression and stromal dynamics. Within live tumor slices from primary tumors, we are defining how stromal components such as dense collagen fiber networks and tumor-associated macrophages (TAMs) orchestrate an immunosuppressive landscape. We employ multiphoton laser scanning microscopy (MPLSM) to generate multiphoton excitation of fluorescence (cell dyes and immunofluorescence) and second harmonic generation (SHG) for collagen fibers to acquire multidimensional data (x, y, z, c, t) of T cell migration and interaction within the TME. We subsequently reveal T cell migration and interaction as a function of its physical and biological ECM components using advanced computer vision and machine learning algorithms based on the Clustered Random Convolutional Kernel Transform (cROCKET), revealing a hidden landscape in the feature space. Perturbations to the TME in KPC mice with CCR2 inhibitor CCX598 (in vivo) and clodronate liposomes (ex vivo) deplete CD11b+ myeloid cells, resulting in altered behaviors of the infiltrating T cells. Anti-PD-1 monoclonal antibody neutralizes the PD-1/PD-L1 axis in T cells, resulting in enhanced migration and infiltration in tumor slices. Citation Format: Guhan Qian, Hongrong Zhang, Aine Knott, Jon Zettervall, Ingunn Stromnes, Paolo Provenzano. Unconvering the hidden immunosuppressive landscape in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C020.

Review on Causes and Management of Ganglion Cyst after Anterior Cruciate Ligament Reconstruction

The gelatinous fluid within a ganglion is rich in hyaluronic acid and other mucopolysaccharides, and the lesion itself is surrounded by a dense network of collagen fibres and fibrocytes. By restoring knee stability, the procedure aims to enhance the patient’s quality of life. Historically, individuals who underwent anterior cruciate ligament (ACL) surgery were able to resume their prior level of athletic involvement in 75%–90% of cases. ACL ganglion cysts are associated with serious clinical symptoms. Some people’s discomfort and stiffness from immobility due to large ganglia prohibit them from fully extending. Such individuals should have an arthroscopy or a computed tomography (CT) scan to decompress the ganglion, which offers immediate relief. ACL surgeries are becoming more and more common, and ganglion cysts may be present in individuals who have pain at the extremes of both flexion and extension has a clinical history. Radiologists must be conversant with these therapies and the adverse effects that go with them. While arthroscopic treatment offers quick discomfort alleviation without compromising ligament integrity, when it comes to radiological diagnostics, nothing beats magnetic resonance imaging (MRI). With an MRI, any other relevant intraarticular abnormalities may be ruled out. Safe CT scan-guided suction was used to successfully cure this patient’s ACL ganglion cyst symptoms.

Collagen Induces Anisotropy in Fingertip Subcutaneous Tissues During Contact.

The subcutaneous mechanical response of the fingertip is highly anisotropic due to the presence of a network of collagen fibers linking the outer skin layer to the bone. The impact of this anisotropy on the fingerpad deformation, which had not been studied until now, is here demonstrated using a two-dimensional finite element model of a transverse sectionof the finger. Different distributions of fiber orientations are considered: radial (physiologic), circumferential, and random (isotropic). The three variants of the model are assessed using experimental observations of a finger pressed on a flat surface. Predictions relying on the physiological orientation of fibers best reproduce experimental trends. Our results show that the orientation of fibers significantly influences the distribution of internal strains and stresses. This leads to a sudden change in the profile of contact pressure when transitioning from sticking to slipping. Interpreted in terms of tactile perception or sensation, these variations might represent important sensory cues for partial slip detection. This is also valuable information for the development of haptic devices.

A Stretchable and Strain‐Limiting, Bio‐Inspired Nanofiber‐Reinforced Microfiber for Wearable Electronics

AbstractWith existing fiber‐based approaches for wearable electronics, devices with limited stretchability are not fully protected against large stretching when the wearer is participating in vigorous activities. A network of elastin and collagen fibers makes biological tissues elastic at low strains and strain‐limiting at high strains, showing a J‐shaped stress‐strain behavior. Stretchable systems can replicate a “J‐shaped stress‐strain/strain‐limiting” mechanical behavior of biological tissues under deformations and provide mechanical compliance and comfort to wearers. For mimicking this mechanical behavior of biological tissues, he developed a combined microfiber and nanofiber (NF)‐based approach. The soft polyurethane (PU) microfiber mimicking elastin of biological tissue is wrapped with stiff poly(vinylidene fluoride)(PVDF) NFs, mimicking collagen in tissue, and dip coated in polydimethylsiloxane (PDMS). Confocal images during stretching confirmed that the PU microfiber maintained stretchability, while the stiff PVDF NFs played a role in the strain‐limiting characteristics. By tailoring a loading ratio of the PVDF NFs on the PU microfiber, the elastic modulus is matched well with those of biological tissues. The stretchable conducting coating and temperature sensor on the bio‐inspired microfiber showed a negligible difference in a current‐time (I‐T) response during static and dynamic stretching which indicated the efficient absorption of stress by the bio‐inspired microfiber.

Zirconium ion ligand Cross-Linked carbon nanotubes and leather collagen fibers for Flexible, Stable, and highly efficient underwater sensors

Flexible sensing materials have recently found widespread applications in integrating various underwater sensors. In this study, we adopted oil-tanned sheepskin as a “structural template” and harnessed its distinctive three-dimensional collagen fiber network. By leveraging the coordination complexation of zirconium ions (Zr4+), we brided collagen fibers with carbon nanotubes (CNTs) to enhance the bonding fastness of the two. We finally constructed a double cross-linked network to produce a new flexible conductive leather called CNTs@Zr@OTL. This material is the basis for preparing leather bio-based piezoresistive sensors （LBPS） and further developing leather biosensing systems (LBS). Experimental outcomes revealed that when CNTs were employed at a concentration of 8.5 %, CNTs@Zr@OTL exhibited an electrical resistivity of approximately 7.4 Ω·cm and a shrinkage temperature of around 74.5 °C. Furthermore, this material demonstrated remarkable characteristics, including 24-hour biodegradability, a broad sensing range (20 %-120 %), and high sensitivity (with response and recovery times of 300 ms and 100 ms, respectively). Based on multiple cross-linked networks, we propose for the first time the underwater sensing mechanism of “Submarine Tunnel” to achieve strong stability in the water environment. Finally, we simulated the LBPS's response to minor external stimuli, including rainwater exposure, multiangle reactions, and water depth sensitivity. By interfacing with wireless modules and mobile phones, the LBS enabled the execution of emergency SOS signals, highlighting its potential applications in underwater motion monitoring and urgent rescue operations.

Multiscale analysis of a 3D fibrous collagen tissue

Collagen fibers, a primary structural protein in the extracellular matrix, provides essential scaffolding for tissues. Functionally, these fibers are essential for providing mechanical support, ensuring tissues like tendons effectively transfer force from muscles to bones. Moreover, collagen is a dynamic component that plays a crucial role in mediating cell signaling, influencing various cellular behaviors and functions.The intricate network of collagen fibers in tissues forms a highly interconnected system, highlighting the tissue's structural resilience. This complexity, especially when considering interactions between collagen fibers or with cells, presents challenges for detailed analyses.Our study introduces a homogenization framework for 3D collagen networks with diverse number of connectivity (C ∼ 7 and 4), bridging micro-to-macro scale behaviors. We employed a numerical strategy to homogenize the RVE, incorporating boundary periodicity and uniaxial loading to determine elastic properties. Systematic evaluations yielded a stress-stretch curve, reflecting micro-scale material behavior. This behavior aligned with hyperelastic models for both highly and moderately connected collagen networks, mirroring experimental findings. Collectively, these insights enhance our understanding of collagen mechanics, setting the stage for more nuanced analyses, particularly in cellular interactions within collagen matrices.

The morphology of the interfacial tissue between bighorn sheep horn and bony horncore increases contact surface to enhance strength and facilitate load transfer from the horn to the horncore

The horns of bighorn sheep rams are permanent cranial appendages used for high energy head-to-head impacts during interspecific combat. The horns attach to the underlying bony horncore by a layer of interfacial tissue that facilitates load transfer between the impacted horn and underlying horncore, which has been shown to absorb substantial energy during head impact. However, the morphology and mechanical properties of the interfacial tissue were previously unknown. Histomorphometry was used to quantify the interfacial tissue composition and morphology and lap-shear testing was used to quantify its mechanical properties. Histological analyses revealed the interfacial tissue is a complex network of collagen and keratin fibers, with collagen being the most abundant protein. Sharpey's fibers provide strong attachment between the interfacial tissue and horncore bone. The inner horn surface displayed microscopic porosity and branching digitations which increased the contact surface with the interfacial tissue by approximately 3-fold. Horn-horncore samples tested by lap-shear loading failed primarily at the horn surface, and the interfacial tissue displayed non-linear strain hardening behavior similar to other soft tissues. The elastic properties of the interfacial tissue (i.e., low- and high-strain shear moduli) were comparable to previously measured values for the equine laminar junction. The interfacial tissue contact surface was positively correlated with the interfacial tissue shear strength (1.23 ± 0.21 MPa), high-strain shear modulus (4.5 ± 0.7 MPa), and strain energy density (0.38 ± 0.07 MJ/m3). Statement of significanceThe bony horncore in bighorn sheep rams absorbs energy to reduce brain cavity accelerations and mitigate brain injury during head butting. The interfacial zone between the horn and horncore transfers energy from the impacted horn to the energy absorbing horncore but has been largely neglected in previous models of bighorn sheep ramming since interfacial tissue properties were previously unknown. This study quantified the morphology and mechanical properties of the horn-horncore interfacial tissue to better understand structure-property relationships that contribute to energy transfer during ramming. Results from this study will improve models of bighorn sheep ramming used to study mechanisms of brain injury mitigation and may inspire novel materials and structures for brain injury prevention in humans.

Melatonin Exerts Prominent, Differential Epidermal and Dermal Anti-Aging Properties in Aged Human Eyelid Skin Ex Vivo.

Human skin aging is associated with functional deterioration on multiple levels of physiology, necessitating the development of effective skin senotherapeutics. The well-tolerated neurohormone melatonin unfolds anti-aging properties in vitro and in vivo, but it remains unclear whether these effects translate to aged human skin ex vivo. We tested this in organ-cultured, full-thickness human eyelid skin (5-6 donors; 49-77 years) by adding melatonin to the culture medium, followed by the assessment of core aging biomarkers via quantitative immunohistochemistry. Over 6 days, 200 µM melatonin significantly downregulated the intraepidermal activity of the aging-promoting mTORC1 pathway (as visualized by reduced S6 phosphorylation) and MMP-1 protein expression in the epidermis compared to vehicle-treated control skin. Conversely, the transmembrane collagen 17A1, a key stem cell niche matrix molecule that declines with aging, and mitochondrial markers (e.g., TFAM, MTCO-1, and VDAC/porin) were significantly upregulated. Interestingly, 100 µM melatonin also significantly increased the epidermal expression of VEGF-A protein, which is required and sufficient for inducing human skin rejuvenation. In aged human dermis, melatonin significantly increased fibrillin-1 protein expression and improved fibrillin structural organization, indicating an improved collagen and elastic fiber network. In contrast, other key aging biomarkers (SIRT-1, lamin-B1, p16INK4, collagen I) remained unchanged. This ex vivo study provides proof of principle that melatonin indeed exerts long-suspected but never conclusively demonstrated and surprisingly differential anti-aging effects in aged human epidermis and dermis.

Multiscale mechanical analysis of the elastic modulus of skin

The mechanical properties of the skin determine tissue function and regulate dermal cell behavior. Yet measuring these properties remains challenging, as evidenced by the large range of elastic moduli reported in the literature—from below one kPa to hundreds of MPa. Here, we reconcile these disparate results by dedicated experiments at both tissue and cellular length scales and by computational models considering the multiscale and multiphasic tissue structure. At the macroscopic tissue length scale, the collective behavior of the collagen fiber network under tension provides functional tissue stiffness, and its properties determine the corresponding elastic modulus (100–200 kPa). The compliant microscale environment (0.1–10 kPa), probed by atomic force microscopy, arises from the ground matrix without engaging the collagen fiber network. Our analysis indicates that indentation-based elasticity measurements, although probing tissue properties at the cell-relevant length scale, do not assess the deformation mechanisms activated by dermal cells when exerting traction forces on the extracellular matrix. Using dermal-equivalent collagen hydrogels, we demonstrate that indentation measurements of tissue stiffness do not correlate with the behavior of embedded dermal fibroblasts. These results provide a deeper understanding of tissue mechanics across length scales with important implications for skin mechanobiology and tissue engineering. Statement of SignificanceMeasuring the mechanical properties of the skin is essential for understanding dermal cell mechanobiology and designing tissue-engineered skin substitutes. However, previous results reported for the elastic modulus of skin vary by six orders of magnitude. We show that two distinct deformation mechanisms, related to the tension–compression nonlinearity of the collagen fiber network, can explain the large variations in elastic moduli. Furthermore, we show that microscale indentation, which is frequently used to assess the stiffness perceived by cells, fails to engage the fiber network, and therefore cannot predict the behavior of dermal fibroblasts in stiffness-tunable fibrous hydrogels. This has important implications for how to measure and interpret the mechanical properties of soft tissues across length scales.

Mechanical Characterization of Collagen Hydrogels by Quasistatic Uniaxial Tensile Experiments

Collagen serves as an essential structural material in the human body. Despite the complex mechanical conditions surrounding the collagen hydrogels, previous studies mostly focus on analyzing the mechanical behavior under dynamically varying compressive or shear loads, but the tensile properties at the quasistatic time scale are relatively less studied. This work aims to investigate the quasistatic tensile behavior of reconstituted collagen hydrogels under uniaxial tensile stresses. The evolution of the collagen fiber network structures with straining is visually observed using the confocal microscope equipped with the tensile strain actuator. While the unfolding of the initially undulated fibers accommodates the early‐stage strains, the deformation mechanism continuously changes to the stretching of fibers through the network alignment to the tensile direction. This transition commences with the buckling of a fiber lying transverse to the loading direction, which otherwise locks the rotation of adjacent fibers.