Nanomechanical Mapping of Hydrated Rat Tail Tendon Collagen I Fibrils

Abstract

Collagen fibrils play an important role in the human body, providing tensile strength to connective tissues. These fibrils are characterized by a banding pattern with a D-period of 67 nm. The proposed origin of the D-period is the internal staggering of tropocollagen molecules within the fibril, leading to gap and overlap regions and a corresponding periodic density fluctuation. Using an atomic force microscope high-resolution modulus maps of collagen fibril segments, up to 80 μm in length, were acquired at indentation speeds around 10(5) nm/s. The maps revealed a periodic modulation corresponding to the D-period as well as previously undocumented micrometer scale fluctuations. Further analysis revealed a 4/5, gap/overlap, ratio in the measured modulus providing further support for the quarter-staggered model of collagen fibril axial structure. The modulus values obtained at indentation speeds around 10(5) nm/s are significantly larger than those previously reported. Probing the effect of indentation speed over four decades reveals two distinct logarithmic regimes of the measured modulus and point to the existence of a characteristic molecular relaxation time around 0.1 ms. Furthermore, collagen fibrils exposed to temperatures between 50 and 62°C and cooled back to room temperature show a sharp decrease in modulus and a sharp increase in fibril diameter. This is also associated with a disappearance of the D-period and the appearance of twisted subfibrils with a pitch in the micrometer range. Based on all these data and a similar behavior observed for cross-linked polymer networks below the glass transition temperature, we propose that collagen I fibrils may be in a glassy state while hydrated.

Quantitative phase measurements of tendon collagen fibres

“…tively [12]. A similar swelling of collagen fibrils has also been observed in pig corneal stroma exposed to temperatures above 60°C [17].…”

“…Nevertheless, the observed changes in fibre diameter with treatment may be of interest. The increased diameter of the thermally treated fibres is expected as collagen molecules begin to denature, causing collagen fibrils to swell [12]. For the collagen fibres from mechanically overloaded tendon, no change in fibre diameter was observed (Figure 4).…”

Molecular Mechanisms of Stress-Responsive Changes in Collagen and Elastin Networks in Skin

“…For example, COL1A1 is the gene which synthesizes the alpha-1 chain of collagen type I, while COL4A6 synthesizes the alpha-6 chain of collagen type IV. These 46 polypeptide chains can combine to form 28 different types of collagen [12,13]. Collagen type I and type III are predominant in skin, and can be found in abundance in the dermal layer, while collagen type V, VI, VII, and XI can also found throughout skin in varying amounts [9,14].…”

Tensile Strength of Single Collagen Fibrils Isolated from Tendons

“…At the fibrillar level, direct mechanical measurements have only recently become possible by atomic force microscopy (AFM) and microelectromechanical systems (MEMS). The mechanical properties of single collagen fibrils have been measured using AFM-based tensile [7][8][9][10], nanoindentation [11][12][13][14][15][16][17][18][19], and bending [20][21][22] tests, and MEMS-based tensile [23][24][25] tests.…”