Micromechanical bending of single collagen fibrils using atomic force microscopy

Abstract

A new micromechanical technique was developed to study the mechanical properties of single collagen fibrils. Single collagen fibrils, the basic components of the collagen fiber, have a characteristic highly organized structure. Fibrils were isolated from collagenous materials and their mechanical properties were studied with atomic force microscopy (AFM). In this study, we determined the Young's modulus of single collagen fibrils at ambient conditions from bending tests after depositing the fibrils on a poly(dimethyl siloxane) (PDMS) substrate containing micro-channels. Force-indentation relationships of freely suspended collagen fibrils were determined by loading them with a tip-less cantilever. From the deflection-piezo displacement curve, force-indentation curves could be deduced. With the assumption that the behavior of collagen fibrils can be described by the linear elastic theory of isotropic materials and that the fibrils are freely supported at the rims, a Young's modulus of 5.4 +/- 1.2 GPa was determined. After cross-linking with glutaraldehyde, the Young's modulus of a single fibril increases to 14.7 +/- 2.7 GPa. When it is assumed that the fibril would be fixed at the ends of the channel the Young's moduli of native and cross-linked collagen fibrils are calculated to be 1.4 +/- 0.3 GPa and 3.8 +/- 0.8 GPa, respectively. The minimum and maximum values determined for native and glutaraldehyde cross-linked collagen fibrils represent the boundaries of the Young's modulus.

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.…”

Tension tests on mammalian collagen fibrils

“…Originally, limits on displacement of the piezo-actuated devices used to perform the tests did not allow excursion into the large strain region of the stress-strain curve [29], and therefore the ultimate strength of the fibrils was not determined. More recently, by using stiffer cantilevers, a greater range of strain was achieved and fracture tensile tests were performed [30,31].…”

Untitled

“…In the application then of manual techniques designed to purportedly 'release' fascia or 'myofascia' through the application of external therapeutic loads, whether applied across the skin or by axial or appendicular leverage, the time constants and initial tissue strain derived from the work of Shen et al [27] & Yang et al [28] would appear to be an important biomaterial characteristic worthy of clinical consideration. As previously stated, 2 minutes may be the appropriate time over which to consider the application of a fixed strain to a myofascial structure.…”