Mechanical Properties Of Collagen Fibrils Research Articles

Hyaluronic acid-mediated collagen intrafibrillar mineralization and enhancement of dentin remineralization

Non-collagenous proteins (NCPs) in the extracellular matrix (ECM) of bone and dentin are known to play a critical regulatory role in the induction of collagen fibril mineralization and are embedded in hyaluronic acid (HA), which acts as a water-retaining glycosaminoglycan and provides necessary biochemical and biomechanical cues. Our previous study demonstrated that HA could regulate the mineralization degree and mechanical properties of collagen fibrils, yet its kinetics dynamic mechanism on mineralization is under debate. Here, we further investigated the role of HA on collagen fibril mineralization and the possible mechanism. The HA modification can significantly promote intrafibrillar collagen mineralization by reducing the electronegativity of the collagen surface to enhance calcium ions (Ca2+) binding capacity to create a local higher supersaturation. In addition, the HA also provides additional nucleation sites and shortens the induction time of amorphous calcium phosphate (ACP)-mediated hydroxyapatite (HAP) crystallization, which benefits mineralization. The acceleration effect of HA on intrafibrillar collagen mineralization is also confirmed in collagen hydrogel and in vitro dentin remineralization. These findings offer a physicochemical view of the regulation effect of carbohydrate polymers in the body on biomineralization, the fine prospect for an ideal biomaterial to repair collagen-mineralized tissues.

Characterization of the effect of chromium salts on tropocollagen molecules and molecular aggregates

Though the capability of chromium treatment to improve the stability and mechanical properties of collagen fibrils is well-known, the influence of different chromium salts on collagen molecules (tropocollagen) is not well characterized. In this study, the effect of Cr3+ treatment on the conformation and hydrodynamic properties of collagen was studied using atomic force microscopy (AFM) and dynamic light scattering (DLS). Statistical analysis of contours of adsorbed tropocollagen molecules using the two-dimensional worm-like chain model revealed a reduction of the persistence length (i.e., the increase of flexibility) from ≈72 nm in water to ≈56–57 nm in chromium (III) salt solutions. DLS studies demonstrated an increase of the hydrodynamic radius from ≈140 nm in water to ≈190 nm in chromium (III) salt solutions, which is associated with protein aggregation. The kinetics of collagen aggregation was shown to be ionic strength dependent. Collagen molecules treated with three different chromium (III) salts demonstrated similar properties such as flexibility, aggregation kinetics, and susceptibility to enzymatic cleavage. The observed effects are explained by a model that considers the formation of chromium-associated intra- and intermolecular crosslinks. The obtained results provide novel insights into the effect of chromium salts on the conformation and properties of tropocollagen molecules.

The influence of AGEs and enzymatic cross-links on the mechanical properties of collagen fibrils

Collagen, one of the main building blocks for various tissues, derives its mechanical properties directly from its structure of cross-linked tropocollagen molecules. The cross-links are considered to be a key component of collagen fibrils as they can change the fibrillar behavior in various ways. For instance, enzymatic cross-links (ECLs), one particular type of cross-links, are known for stabilizing the structure of the fibril and improving material properties, while cross-linking AGEs (Advanced-Glycation Endproducts) have been shown to accumulate and impair the mechanical properties of collageneous tissues. However, the reasons for whether and how a given type of cross-link improves or impairs the material properties remain unknown, and the exact relationship between the cross-link properties and density, and the fibrillar behavior is still not well understood. Here, we use coarse-grained steered molecular models to evaluate the effect of AGEs and ECLs cross-links content on the deformation and failure properties of collagen fibrils. Our simulations show that the collagen fibrils stiffen at high strain levels when the AGEs content exceeds a critical value. In addition, the strength of the fibril increases with AGEs accumulation. By analyzing the forces within the different types of cross-links (AGEs and ECLs) as well as their failure, we demonstrate that a change of deformation mechanism is at the origin of these observations. A high AGEs content reinforces force transfer through AGEs cross-links rather than through friction between sliding tropocollagen molecules, which leads to failure by breaking of bonds within the tropocollagen molecules. We show that this failure mechanism, which is associated with lower energy dissipation, results in more abrupt failure of the collagen fibril. Our results provide a direct and causal link between increased AGEs content, inhibited intra-fibrillar sliding, increased stiffness, and abrupt fibril fracture. Therefore, they explain the mechanical origin of bone brittleness as commonly observed in elderly and diabetic populations. Our findings contribute to a better understanding of the mechanisms underlying impaired tissue behavior due to elevated AGEs content and could enable targeted measures regarding the reduction of specific collagen cross-linking levels.

Mechanical properties of collagen fibrils determined by buckling analysis

The mechanical properties of biological nanofibers such as collagen fibrils are important in many applications, ranging from tissue-engineering to cancer treatment. However, mechanical testing is not straightforward at the nanometer scale. Here, we use the theory of column-buckling to determine the bending properties of individual collagen fibrils. To achieve this, fibrils were deposited on a manually pre-stretched foil, which was then released with the fibrils attached. Atomic Force Microscopy (AFM) imaging was used to determine the tensile modulus by measuring the buckling-wavelength and the radius for each fibril. Comparison with data obtained by AFM nanoindentation and other, more sophisticated methods, shows that our results are in very good agreement. The great advantage of this simple approach is that it can be used to quickly determine mechanical properties without force or stress-strain measurements, which are challenging to obtain accurately and at high throughput at the nanoscale. The method could be applied to any nanofibers, not just collagen fibrils. Statement of significanceCollagen fibrils are the main constituent of the extracellular matrix, and alterations of their mechanical properties can have significant effects on cell adhesion and motility. This has, ultimately, implications in age-related diseases and cancer. Furthermore, tuning the mechanical properties of collagen fibrils could be an important tool in the design of artificial cell scaffolds in tissue-engineering. For these reasons, it is important to have methods that can be used to determine the mechanical properties of fibrils at the single-fibril level and, therefore, at the nanometer scale. The method presented here has the advantage of being easy to use and avoids some of the fundamental issues of more established methods.

Stretching Single Collagen Fibrils Reveals Nonlinear Mechanical Behavior

The mechanical properties of collagen fibrils play an important role in cell-matrix interactions and are a manifestation of their molecular structure. Using a, to our knowledge, novel combination of uniaxial, longitudinal straining and radial nanoindentation, we found that type I collagen fibrils show a pronounced nonlinear behavior in the form of strain stiffening at strains from 0 to 15%, followed by strain softening at strains from 15 to 25%. At the molecular scale, this surprising phenomenon can be explained by the combination of unfolding of disordered domains and breaking of native cross-links at different stages of strain. Fibrils cross-linked artificially by glutaraldehyde do not show such a behavior, and nanoindentation allowed us to measure the mechanics of the overlap and gap regions in the D-banding individually. The results could have consequences for our understanding of matrix mechanics and the influence of excessive glycation, which has been linked with age-related diseases such as diabetes. Furthermore, the simplicity of the straining method could be attractive in other areas of biophysics at the nanometer scale because it does not require any bespoke instrumentation and is easy to use.

Measurement of the mechanical properties of collagen fibrils and proteoglycan using atomic force microscope

Measurement of the mechanical properties of collagen fibrils and proteoglycan using atomic force microscope

Unraveling capillary interaction and viscoelastic response in atomic force microscopy of hydrated collagen fibrils.

The mechanical properties of collagen fibrils depend on the amount and the distribution of water molecules within the fibrils. Here, we use atomic force microscopy (AFM) to study the effect of hydration on the viscoelastic properties of reconstituted type I collagen fibrils in air with controlled relative humidity. With the same AFM tip, we investigate the same area of a collagen fibril with two different force spectroscopy methods: force-distance (FD) and amplitude-phase-distance (APD) measurements. This allows us to separate the contributions of the fibril's viscoelastic response and the capillary force to the tip-sample interaction. A water bridge forms between the tip apex and the surface, causing an attractive capillary force, which is the main contribution to the energy dissipated from the tip to the specimen in dynamic AFM. The force hysteresis in the FD measurements and the tip indentation of only 2 nm in the APD measurements show that the hydrated collagen fibril is a viscoelastic solid. The mechanical properties of the gap regions and the overlap regions in the fibril's D-band pattern differ only in the top 2 nm but not in the fibril's bulk. We attribute this to the reduced number of intermolecular crosslinks in the reconstituted collagen fibril. The presented methodology allows the mechanical surface properties of hydrated collagenous tissues and biomaterials to be studied with unprecedented detail on the nanometer scale.

Mechanical properties of collagen fibrils isolated from tendons and ligaments of knee joint

Mechanical properties of collagen fibrils isolated from tendons and ligaments of knee joint

Investigation of the mechanical properties of collagen fibrils under the influence of low power red laser irradiation

The low level red laser has been increasingly used for medical applications over the last decade. Despite the recorded positive effects of low level red laser in various medical treatments, the exact collagen—red light interaction mechanism still remains unknown. Hence, in this paper, thin collagen films were irradiated using red low power laser in order to investigate the effects of red light on collagen nanoscale features and mechanical properties. The results demonstrated that the red light did not induce statistically significant changes on nanoscale collagen topography features. The topography of the alternating sequence of overlapping and gap regions (D-band periodicity) and the surface roughness were not affected. However, significant changes on the mechanical properties of the collagen fibrils were recorded. In particular, the red light induced major changes in the mechanical heterogeneity of the fibrils due to the D-band periodicity. The above results provide new information about the red light-collagen interaction mechanism and are a step forward towards to the clarification of the impact of red light on collagen nanoscale features.

The effects of UV irradiation on collagen D-band revealed by atomic force microscopy.

The objective of this paper was to investigate the influence of UV irradiation on collagen D-band periodicity by using the AFM imaging and nanoindentation methods. It is well known than UV irradiation is one of the main factors inducing destabilization of collagen molecules. Due to the human's skin chronic exposure to sun light, the research concerning the influence of UV radiation on collagen is of great interest. The impact of UV irradiation on collagen can be studied in nanoscale using Atomic Force Microscopy (AFM). AFM is a powerful tool as far as surface characterization is concerned, due to its ability to relate high resolution imaging with mechanical properties. Hence, high resolution images of individual collagen fibrils and load-displacement curves on the overlapping and gap regions, under various time intervals of UV exposure, were obtained. The results demonstrated that the UV rays affect the height level differences between the overlapping and gap regions. Under various time intervals of UV exposure, the height difference between overlaps and gaps reduced from ~3.7 nm to ~0.8 nm and the fibril diameters showed an average of 8-10% reduction. In addition, the irradiation influenced the mechanical properties of collagen fibrils. The Young's modulus values were reduced per 66% (overlaps) and 61% (gaps) compared to their initial values. The observed alterations on the structural and the mechanical properties of collagen fibrils are probably a consequence of the polypeptide chain scission due to the impact of the UV irradiation.

C218 真皮および腱より摘出したコラーゲン原線維の力学的性質(C2-4 細胞外マトリクス)

C218 真皮および腱より摘出したコラーゲン原線維の力学的性質(C2-4 細胞外マトリクス)

The effect of point mutations on structure and mechanical properties of collagen-like fibril: A molecular dynamics study

Understanding sequence dependent mechanical and structural properties of collagen fibrils is important for the development of artificial biomaterials for medical and nanotechnological applications. Moreover, point mutations are behind many collagen associated diseases, including Osteogenesis Imperfecta (OI). We conducted a combination of classical and steered atomistic molecular dynamics simulations to examine the effect of point mutations on structure and mechanical properties of short collagen fibrils which include mutations of glycine to alanine, aspartic acid, cysteine, and serine or mutations of hydroxyproline to arginine, asparagine, glutamine, and lysine. We found that all mutations disrupt structure and reduce strength of the collagen fibrils, which may affect the hierarchical packing of the fibrils. The glycine mutations were more detrimental to mechanical strength of the fibrils (WT>Ala>Ser>Cys>Asp) than that of hydroxyproline (WT>Arg>Gln>Asn>Lys). The clinical outcome for glycine mutations agrees well with the trend in reduction of fibril's tensile strength predicted by our simulations. Overall, our results suggest that the reduction in mechanical properties of collagen fibrils may be used to predict the clinical outcome of mutations.

Nanoscale characterization of acid and thermally treated collagen fibrils

Type I collagen is a major extracellular matrix component and its hierarchical structure plays an essential role in the regulation of cellular behavior. Here, we have analyzed the changes in the morphological, chemical, and mechanical properties of collagen fibrils induced by acidic and thermal treatments and the influence on the cellular response of MC3T3-E1 cells. Morphological changes induced by the disintegration of the fibrillar structure of collagen were observed using atomic force microscopy. The changes in the surface chemistry due to the disassembly of native collagen fibrils were observed using time-of-flight secondary ion mass spectroscopy (ToF-SIMS). ToF-SIMS spectra were very sensitive to changes in the molecular configuration of the collagen fibrils induced by acidic and thermal treatments due to the extreme surface specificity. In addition, ToF-SIMS showed clear and reproducible changes in the surface amino acid composition corresponding to the acidic and thermal treatments of collagen fibrils. Based on the quantitative map of surface elastic modulus measured by contact-resonance force microscopy, acid and thermally treated collagen showed a lower elastic modulus than native collagen fibrils. Compared with native collagen fibrils, reduced cell spreading and decreased viability of MC3T3-E1 cells were observed on both the acid and thermally treated collagen.

Mechanical Properties of Type I Collagen: Insights From Molecular Dynamics Simulations

Fibrous collagens are present in all mammalian species where they form the structural basis for connective tissue, including those in the heart, vasculature, skin, cornea, bones, and tendons. While the general features of the structure of type I collagen have been known for a long time, the specific packing arrangement of collagen molecules was identified only recently (Orgel et al., PNAS, 103:9001, 2006). Each collagen molecule is approximately 300 nm long and 1.5 nm in diameter. It is made up of three polypeptide chains, called alpha chains, each containing about 1000 amino acids. These alpha helices are twisted together into a right-handed triple helix, a cooperative quaternary structure presumably stabilized by inter-chain hydrogen bonding and other non-bonded interactions. The individual collagen molecules are then arranged to form a super twisted (discontinuous) right-handed microfibril that interdigitates with neighboring microfibrils. In order to better understand the nature of the intermolecular interactions in collagen at an atomic level, and to understand how observed mechanical properties of collagen emerge from these interactions, we have run a series of molecular dynamics simulations. Our calculations are the first set of atomistic simulations of individual collagen molecules. The data from the simulations provide valuable insights into the origin of the mechanical properties of collagen fibrils, that in some ways are different from those obtained using simulations and experiments of collagen analogues.

Tensile Properties of Human Collagen Fibrils and Fascicles Are Insensitive to Environmental Salts

To carry out realistic in vitro mechanical testing on anatomical tissue, a choice has to be made regarding the buffering environment. Therefore, it is important to understand how the environment may influence the measurement to ensure the highest level of accuracy. The most physiologically relevant loading direction of tendon is along its longitudinal axis. Thus, in this study, we focus on the tensile mechanical properties of two hierarchical levels from human patellar tendon, namely: individual collagen fibrils and fascicles. Investigations on collagen fibrils and fascicles were made at pH 7.4 in solutions of phosphate-buffered saline at three different concentrations as well as two HEPES buffered solutions containing NaCl or NaCl + CaCl 2. An atomic force microscope technique was used for tensile testing of individual collagen fibrils. Only a slight increase in relative energy dissipation was observed at the highest phosphate-buffered saline concentration for both the fibrils and fascicles, indicating a stabilizing effect of ionic screening, but changes were much less than reported for radial compression. Due to the small magnitude of the effects, the tensile mechanical properties of collagen fibrils and fascicles from the patellar tendon of mature humans are essentially insensitive to environmental salt concentration and composition at physiological pH.

0439 成長過程にあるマウス尾腱より摘出したコラーゲン原線維の力学的性質(OS7:腱・靭帯のバイオメカニクス)

0439 成長過程にあるマウス尾腱より摘出したコラーゲン原線維の力学的性質(OS7:腱・靭帯のバイオメカニクス)

Deformation micromechanisms of collagen fibrils under uniaxial tension.

Collagen, an essential building block of connective tissues, possesses useful mechanical properties due to its hierarchical structure. However, little is known about the mechanical properties of collagen fibril, an intermediate structure between the collagen molecule and connective tissue. Here, we report the results of systematic molecular dynamics simulations to probe the mechanical response of initially unflawed finite size collagen fibrils subjected to uniaxial tension. The observed deformation mechanisms, associated with rupture and sliding of tropocollagen molecules, are strongly influenced by fibril length, width and cross-linking density. Fibrils containing more than approximately 10 molecules along their length and across their width behave as representative volume elements and exhibit brittle fracture. Shorter fibrils experience a more graceful ductile-like failure. An analytical model is constructed and the results of the molecular modelling are used to find curve-fitted expressions for yield stress, yield strain and fracture strain as functions of fibril structural parameters. Our results for the first time elucidate the size dependence of mechanical failure properties of collagen fibrils. The associated molecular deformation mechanisms allow the full power of traditional material and structural engineering theory to be applied to our understanding of the normal and pathological mechanical behaviours of collagenous tissues under load.

Vascular Smooth Muscle Cell Response to Transglutaminase 2 Cross-linked Collagen Fibril Thin Films

Tissue transglutaminase 2 (TG2) is a ubiquitous protein thought to play an important role in both the normal and abnormal progression of the wound healing response through extracellular matrix (ECM) cross-linking. However, how TG2 cross-linking of ECM affects cell behavior is still ill-defined. Here we use a model ECM system to show that vascular smooth muscle cell (vSMC) spreading, proliferation, actin polymerization, and myosin activation increase with increasing exposure of type 1 collagen fibrils to TG2 activity. A10 vSMC ligate fibrillar type 1 collagen through beta(1) integrins, and beta(1) integrin ligation appeared to be identical before and after TG2 cross-linking of collagen. This result suggests that the observed changes in cell response were not induced by changes in surface chemistry or receptor recognition. Atomic force microscopy (AFM) studies show that untreated fibrils are more susceptible to lateral movement on the surface than cross-linked fibrils, which suggest that the observed cell response is solely due to TG2-induced changes in the mechanical properties of collagen fibrils. The results provide valuable insight into a mechanism by which TG2-modified ECM proteins can influence cell behavior.

A108 マウス尾腱より摘出したコラーゲン原線維の微細構造と力学的性質に及ぼすコラゲナーゼの影響(A1-2 組織・器官のバイオメカニクス1)

A108 マウス尾腱より摘出したコラーゲン原線維の微細構造と力学的性質に及ぼすコラゲナーゼの影響(A1-2 組織・器官のバイオメカニクス1)

A104 マウス尾腱より摘出したコラーゲン原線維の力学的性質に及ぼすコラゲナーゼの影響(細胞・分子工学)

A104 マウス尾腱より摘出したコラーゲン原線維の力学的性質に及ぼすコラゲナーゼの影響(細胞・分子工学)