Collagen breaks at weak sacrificial bonds taming its mechanoradicals

Hidden length lets collagen buffer mechanical and chemical stress

Collagen, the most abundant protein in the human body, must withstand high mechanical loads due to its structural role in tendons, skin, bones, and other connective tissue. It was recently found that tensed collagen creates mechanoradicals by homolytic bond scission. We here employ scale-bridging simulations to determine the influence of collagen's mesoscale fibril structure on molecular breakages, combining atomistic molecular dynamics simulations with a newly developed mesoscopic ultra-coarse-grained description of a collagen fibril. Our simulations identify a conserved structural feature, a length difference of the two helices between pairs of crosslinks, to play a critical role. The release of the extra hidden length enables collagen to buffer mechanical stress. At the same time, this topology funnels ruptures such that the potentially harmful mechanoradicals are readily stabilized, buffering the arising oxidative stress. Our results suggest collagen's hidden length to exploit a sweet spot in the trade-off between breakage specificity and strength.

Mineral and cross-linking in collagen fibrils: The mechanical behavior of bone tissue at the nano-scale

The mineralized collagen fibril is the main building block of hard tissues and it directly affects the macroscopic mechanics of biological tissues such as bone. The mechanical behavior of the fibril itself is determined by its structure: the content of collagen molecules, minerals, and cross-links, and the mechanical interactions and properties of these components. Advanced glycation end products (AGEs) form cross-links between tropocollagen molecules within the collagen fibril and are one important factor that is believed to have a major influence on the tissue. For instance, it has been shown that brittleness in bone correlates with increased AGEs densities. However, the underlying nano-scale mechanisms within the mineralized collagen fibril remain unknown. Here, we study the effect of mineral and AGEs cross-linking on fibril deformation and fracture behavior by performing destructive tensile tests using coarse-grained molecular dynamics simulations. Our results demonstrate that after exceeding a critical content of mineral, it induces stiffening of the collagen fibril at high strain levels. We show that mineral morphology and location affect collagen fibril mechanics: The mineral content at which this stiffening occurs depends on the mineral's location and morphology. Further, both, increasing AGEs density and mineral content lead to stiffening and increased peak stresses. At low mineral contents, the mechanical response of the fibril is dominated by the AGEs, while at high mineral contents, the mineral itself determines fibril mechanics.

Advancing Synthetic Hydrogels through Nature-Inspired Materials Chemistry

Synthetic extracellular matrix (ECM) mimics that can recapitulate the complex biochemical and mechanical nature of native tissues are needed for advanced models of development and disease. Biomedical research has heavily relied on the use of animal-derived biomaterials, which is now impeding their translational potential and convoluting the biological insights gleaned from in vitro tissue models. Natural hydrogels have long served as a convenient and effective cell culture tool, but advances in materials chemistry and fabrication techniques now present promising new avenues for creating xenogenic-free ECM substitutes appropriate for organotypic models and microphysiological systems. However, significant challenges remain in creating synthetic matrices that can approximate the structural sophistication, biochemical complexity, and dynamic functionality of native tissues. This review summarizes key properties of the native ECM, and discusses recent approaches used to systematically decouple and tune these properties in synthetic matrices. The importance of dynamic ECM mechanics, such as viscoelasticity and matrix plasticity, is also discussed, particularly within the context of organoid and engineered tissue matrices. Emerging design strategies to mimic these dynamic mechanical properties are reviewed, such as multi-network hydrogels, supramolecular chemistry, and hydrogels assembled from biological monomers.

Productive chemistry induced by mechanochemically generated macroradicals

Large or repeated mechanical loads degrade polymeric materials by accelerating chain fragmentation. This mechanochemical backbone fracture usually occurs by homolysis of otherwise inert C-C, C-O and C-S bonds, generating highly reactive macroradicals. Because backbone fracture is detrimental on its own and the resulting macroradicals can initiate damaging reaction cascades, a major thrust in contemporary polymer mechanochemistry is to suppress it, usually by mechanochemical release of "hidden length" that dissipates local molecular strain. Here we summarize an emerging complementary strategy of channelling mechanochemically generated macroradicals in reaction cascades to form new load-bearing chemical bonds, which enables local self-healing or self-strengthening, and/or to generate mechanofluorescence, which could yield detailed quantitative molecular understanding of how material-failure-inducing macroscopic mechanical loads distribute across the network. We aim to identify generalizable lessons derivable from the reported implementations of this strategy and outline the key challenges in adapting it to diverse polymeric materials and loading scenarios.

Multiscale and multidisciplinary analysis of aging processes in bone

The world population is increasingly aging, deeply affecting our society by challenging our healthcare systems and presenting an economic burden, thus turning the spotlight on aging-related diseases: exempli gratia, osteoporosis, a silent disease until you suddenly break a bone. The increase in bone fracture risk with age is generally associated with a loss of bone mass and an alteration in the skeletal architecture. However, such changes cannot fully explain increased fragility with age. To successfully tackle age-related bone diseases, it is paramount to comprehensively understand the fundamental mechanisms responsible for tissue degeneration. Aging mechanisms persist at multiple length scales within the complex hierarchical bone structure, raising the need for a multiscale and multidisciplinary approach to resolve them. This paper aims to provide an overarching analysis of aging processes in bone and to review the most prominent outcomes of bone aging. A systematic description of different length scales, highlighting the corresponding techniques adopted at each scale and motivating the need for combining diverse techniques, is provided to get a comprehensive description of the multi-physics phenomena involved.

Mineral and cross-linking in collagen fibrils: The mechanical behavior of bone tissue at the nano-scale

The mineralized collagen fibril is the main building block of hard tissues and it directly affects the macroscopic mechanics of biological tissues such as bone. The mechanical behavior of the fibril itself is determined by its structure: the content of collagen molecules, minerals, and cross-links, and the mechanical interactions and properties of these components. Advanced-Glycation-Endproducts (AGEs) cross-linking between tropocollagen molecules within the collagen fibril is one important factor that is believed to have a major influence on the tissue. For instance, it has been shown that brittleness in bone correlates with increased AGEs densities. However, the underlying nano-scale mechanisms within the mineralized collagen fibril remain unknown. Here, we study the effect of mineral and AGEs cross-linking on fibril deformation and fracture behavior by performing destructive tensile tests using coarse-grained molecular dynamics simulations. Our results demonstrate that after exceeding a critical content of mineral, it induces stiffening of the collagen fibril at high strain levels. We show that mineral morphology and location affect collagen fibril mechanics: The mineral content at which this stiffening occurs depends on the mineral's location and morphology. Further, both, increasing AGEs density and mineral content lead to stiffening and increased peak stresses. At low mineral contents, the mechanical response of the fibril is dominated by the AGEs, while at high mineral contents, the mineral itself determines fibril mechanics.

Effects of aging and diabetes on the deformation mechanisms and molecular structural characteristics of collagen fibrils under daily activity

Crosslinking plays an important role in collagen-based tissues since it affects mechanical behavior and tissue metabolism. Aging and diabetes affect the type and density of crosslinking, effectively altering tissue properties. However, most studies focus on these effects under large stress rather than daily activities. We focus on the deformation mechanisms and structural change at the binding sites for integrins, proteoglycans, and collagenase in collagen fibrils using a fully atomistic model. We show that high-connectivity enzymatic crosslinking (our "HC" model, representing normal tissues) and advanced-glycation end-products (our "Glucosepane" model, which increase in diabetes) result in uniform deformation under daily activity, but low-connectivity enzymatic crosslinking (our "LC" model, representing aging tissues) does not. In particular, the HC model displays more sliding, which may explain the ability of healthy tissues to absorb more strain energy. In contrast, AGEs induce instability in the structures near the binding sites, which would affect the tissue metabolism of the collagen molecule. Our results provide important insights into the molecular mechanisms of collagen and a possible explanation for the role of crosslinking in tissues undergoing daily activity.

Shock-Induced Degradation of Guanosine and Uridine Promoted by Nickel and Carbonate: Potential Applications

Experimental studies of the degradation of two ribonucleosides (guanosine and uridine) were carried out by making use of mechanochemistry. Mechanochemical experiments reveal the decomposition of guanosine and uridine, promoted by nickel(II) and carbonate ions, into guanine and uracil, respectively. These nucleobases were identified by HPLC and 1H NMR spectroscopy (this applied only to uracil). Additionally, density-functional theory (DFT) methodologies were used to probe the energetic viability of several degradation pathways, including in the presence of the abovementioned ions. Three mechanisms were analysed via ribose ring-opening: dry, single-molecule water-assisted, and metal-assisted, wherein the last two mechanisms confirmed the mechanochemical degradation of both ribonucleosides into respective nucleobase moieties. These results can contribute to an astrobiological interpretation of the extraterrestrial sample's contents.

An overview of the material science and knowledge of nanomedicine, bioscaffolds, and tissue engineering for tendon restoration

Tendon wounds are a worldwide health issue affecting millions of people annually. Due to the characteristics of tendons, their natural restoration is a complicated and lengthy process. With the advancement of bioengineering, biomaterials, and cell biology, a new science, tissue engineering, has developed. In this field, numerous ways have been offered. As increasingly intricate and natural structures resembling tendons are produced, the results are encouraging. This study highlights the nature of the tendon and the standard cures that have thus far been utilized. Then, a comparison is made between the many tendon tissue engineering methodologies proposed to date, concentrating on the ingredients required to gain the structures that enable appropriate tendon renewal: cells, growth factors, scaffolds, and scaffold formation methods. The analysis of all these factors enables a global understanding of the impact of each component employed in tendon restoration, thereby shedding light on potential future approaches involving the creation of novel combinations of materials, cells, designs, and bioactive molecules for the restoration of a functional tendon.