Calcification alters the viscoelastic properties of tendon fascicle bundles depending on matrix content

Quantification of 3D microstructures in Achilles tendons during in situ loading reveals anisotropic fiber response

While the number of studies investigating Achilles tendon pathologies has grown exponentially, more research is needed to gain a better understanding of the complex relation between its hierarchical structure, mechanical response, and failure. At the microscale, collagen fibers are, with some degree of dispersion, primarily aligned along the principal loading direction. However, during tension, rearrangements and reorientations of these fibers are believed to occur. As 3D micro-movements are hard to capture, the precise nature of this fiber reorganization remains unknown. This study aimed to visualize and quantify the intricate fiber changes occurring within rat Achilles tendons under tension. Rat tendons were in situ loaded with concurrent synchrotron phase contrast microCT imaging. The results are heterogenous and show that collagen fibers' response to loading is nonuniform and depends on anatomical orientation. Furthermore, damage propagation could be visualized, revealing that in the presence of heterotopic ossification, damage proceeds within the ossified deposits rather than at the interface between hard and soft tissues. Our approach could effectively capture the microstructural changes occurring during loading and shows promise in understanding the relation between microstructure and mechanical response for ex-vivo Achilles tendons and other biological tissues. STATEMENT OF SIGNIFICANCE: Achilles tendons endure high mechanical loads during daily motion and physical activities. Understanding the structural and mechanical responses of Achilles tendons to such loads is vital for elucidating their function in health and pathology. We have combined the use of synchrotron phase contrast microCT with in situ mechanical loading to contribute to a better understanding of the relation between microstructural response and organ scale mechanical properties. The proposed methodology will be valuable for future research into the interplay between structure, mechanics, and pathology of tendons, and for the development of more effective strategies to preserve tendon function and possibly mitigating musculoskeletal disorders.

Viscoelastic Mechanics: From Pathology and Cell Fate to Tissue Regeneration Biomaterial Development

Viscoelasticity is the mechanical feature of living tissues and the cellular extracellular matrix (ECM) and has been recognized as an essential biophysical cue in cell function and fate regulation, tissue development and homeostasis maintenance, and disease progression. These findings provide new insights for the development of biomaterials with comparable viscoelastic properties as native ECMs and the tissue matrix, displaying promising applications in regeneration medicine. In this review, the relationship between matrix viscoelasticity and tissue functions (e.g., development and regeneration) in physiological conditions and disease progression (e.g., aging, degenerative, fibrosis, and tumor) in pathological conditions will be especially highlighted to figure out the potential therapeutic target for disease treatment and inspiration for tissue regeneration related biomaterial development. Furthermore, findings and an understanding of the cell response to ECM viscoelasticity and the mechanism behind it are comprehensively summarized to provide a pathophysiological basis for viscoelastic biomaterials design. The advances of viscoelastic biomaterials on defect tissue repair are also reviewed, suggesting the significance of the native matrix matchable microenvironment on tissue regeneration. Although challenging, tunable viscoelastic biomaterials that match the mechanical properties of native tissues and ECMs show great promise. They could promote tissue regeneration, treat degenerative diseases, and support the development of organoids and artificial organs.

Deciphering mechanical cues in the microenvironment: from non-malignant settings to tumor progression

The tumor microenvironment functions as a dynamic and intricate ecosystem, comprising a diverse array of cellular and non-cellular components that precisely orchestrate pivotal tumor behaviors, including invasion, metastasis, and drug resistance. While unraveling the intricate interplay between the tumor microenvironment and tumor behaviors represents a tremendous challenge, recent research illuminates a crucial biological phenomenon known as cellular mechanotransduction. Within the microenvironment, mechanical cues like tensile stress, shear stress, and stiffness play a pivotal role by activating mechanosensitive effectors such as PIEZO proteins, integrins, and Yes-associated protein. This activation initiates cascades of intrinsic signaling pathways, effectively linking the physical properties of tissues to their physiological and pathophysiological processes like morphogenesis, regeneration, and immunity. This mechanistic insight offers a novel perspective on how the mechanical cues within the tumor microenvironment impact tumor behaviors. While the intricacies of the mechanical tumor microenvironment are yet to be fully elucidated, it exhibits distinct physical attributes from non-malignant tissues, including elevated solid stresses, interstitial hypertension, augmented matrix stiffness, and enhanced viscoelasticity. These traits exert notable influences on tumor progression and treatment responses, enriching our comprehension of the multifaceted nature of the microenvironment. Through this innovative review, we aim to provide a new lens to decipher the mechanical attributes within the tumor microenvironment from non-malignant contexts, broadening our knowledge on how these factors promote or inhibit tumor behaviors, and thus offering valuable insights to identify potential targets for anti-tumor strategies.

Defining the extracellular matrix in non-cartilage soft-tissues in osteoarthritis: a systematic review

Aims

Extracellular matrix (ECM) is a critical determinant of tissue mechanobiology, yet remains poorly characterized in joint tissues beyond cartilage in osteoarthritis (OA). This review aimed to define the composition and architecture of non-cartilage soft joint tissue structural ECM in human OA, and to compare the changes observed in humans with those seen in animal models of the disease.

Methods

A systematic search strategy, devised using relevant matrix, tissue, and disease nomenclature, was run through the MEDLINE, Embase, and Scopus databases. Demographic, clinical, and biological data were extracted from eligible studies. Bias analysis was performed.

Results

A total of 161 studies were included, which covered capsule, ligaments, meniscus, skeletal muscle, synovium, and tendon in both humans and animals, and fat pad and intervertebral disc in humans only. These studies covered a wide variety of ECM features, including individual ECM components (i.e. collagens, proteoglycans, and glycoproteins), ECM architecture (i.e. collagen fibre organization and diameter), and viscoelastic properties (i.e. elastic and compressive modulus). Some ECM changes, notably calcification and the loss of collagen fibre organization, have been extensively studied across osteoarthritic tissues. However, most ECM features were only studied by one or a few papers in each tissue. When comparisons were possible, the results from animal experiments largely concurred with those from human studies, although some findings were contradictory.

Conclusion

Changes in ECM composition and architecture occur throughout non-cartilage soft tissues in the osteoarthritic joint, but most of these remain poorly defined due to the low number of studies and lack of healthy comparator groups.

Unveiling the role of hydroxyapatite and hydroxyapatite/silver composite in osteoblast-like cell mineralization: An exploration through their viscoelastic properties

Mechanical properties are becoming fundamental for advancing the comprehension of cellular processes. This study addresses the relationship between viscoelastic properties and the cellular mineralization process. Osteoblast-like cells treated with an osteogenic medium were employed for this purpose. Additionally, the study explores the impact of hydroxyapatite (HA) and hydroxyapatite/silver (HA/Ag) composite on this process. AFM relaxation experiments were conducted to extract viscoelastic parameters using the Fractional Zener (FZ) and Fractional Kelvin (FK) models. Our findings revealed that the main phases of mineralization are associated with alterations in the viscoelastic properties of osteoblast-like cells. Furthermore, HA and HA/Ag treatments significantly influenced changes in the viscoelastic properties of these cells. In particular, the HA/Ag treatment demonstrated a marked enhancement in cell fluidity, suggesting a possible role of silver in accelerating the mineralization process. Moreover, the study underscores the independence observed between fluidity and stiffness, indicating that modifications in one parameter may not necessarily correspond to changes in the other. These findings shed light on the factors involved in the cellular mineralization process and emphasize the importance of using viscoelastic properties to discern the impact of treatments on cells.

Biochemical and morpho-mechanical properties, and structural organization of rat tail tendon collagen in diet-induced obesity model

We have investigated the impact of obesity on the structural organization, morpho-mechanical properties of collagen fibers from rat tail tendon fascicles (RTTFs). Polarized Raman microspectroscopy showed that the collagen bands 855, 875, 938, and 960 cm-1 as well as those 1631 and 1660 cm-1 were affected by diet. Mechanical properties exhibited an increase in the yield strength from control (CTRL) to high fat (HF) diet (9.60 ± 1.71 and 13.09 ± 1.81 MPa) (p < 0.01) and ultimate tensile strength (13.12 ± 2.37 and 18.32 ± 2.83 MPa) (p < 0.05) with no significant change in the Young's Modulus. During mechanical, the band at 875 cm-1 exhibited the most relevant frequency shift (2 cm-1). The intensity of those at 855, 875, and 938 cm-1 in HF collagen displayed a comparable response to mechanical stress as compared to CTRL collagen with no significant diet-related changes in the Full Width at Half Maximum. Second harmonic generation technique revealed i) similar fiber straightness (0.963 ± 0.004 and 0.965 ± 0.003) and ii) significant changes in fibers diameter (1.48 ± 0.07 and 1.52 ± 0.08 μm) (p < 0.05) and length (22.06 ± 2.38 and 29.00 ± 3.76 μm) (p < 0.001) between CTRL and HF diet, respectively. The quantification of advanced glycation end products (AGEs) revealed an increase in both carboxymethyl-lysine and total fluorescence AGEs from CTRL to HF RTTFs.