Collagen Fibril Alignment and Deformation during Tensile Strain of Leather: A Small-Angle X-ray Scattering Study

Abstract

The distribution and effect of applied strain on the collagen fibrils that make up leather may have an important bearing on the ultimate strength and other physical properties of the material. While sections of ovine and bovine leather were being subjected to tensile strain up to rupture, synchrotron-based small-angle X-ray scattering (SAXS) spectra were recorded edge-on to the leather at points from the corium to the grain. Measurements of both fibril orientation and collagen d spacing showed that, initially, the fibers reorient under strain, becoming more aligned. As the strain increases (5-10% strain), further fibril reorientation diminishes until, at 37% strain, the d spacing increases by up to 0.56%, indicating that significant tensile forces are being transmitted to individual fibrils. These changes, however, are not uniform through the cross-section of leather and differ between leathers of different strengths. The stresses are taken up more evenly through the leather cross-section in stronger leathers in comparison to weaker leathers, where stresses tended to be concentrated during strain. These observations contribute to our understanding of the internal strains and structural changes that take place in leather under stress.

Poisson's ratio of collagen fibrils measured by small angle X-ray scattering of strained bovine pericardium

“…This shows that the strain in the tissue is taken up partly by the strain in the collagen fibrils, as has been observed with light scattering 28 and partly by the tissue strain being transferred to interfibrillar sliding or rearrangement of the fibrils. By contrast, in weak ovine leather (data taken from published work 19 ), our calculations of fibril strain versus leather strain give 10% d-spacing strain to whole tissue strain for leather. The collagen fibrils in leather are less aligned than in pericardium, allowing more possibility for realignment.…”

“…For collagen in bovine pericardium, at low strain, the Poisson's ratio appears to have a very high value (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27), but for strain above 0.09, the Poisson's ratio is in the range 2.1-2.8. For the total strain (from 0 to 0.25), the change in d-spacing and diameter gives 0 ¼ 2.1 6 0.7 (these values of 0 can be calculated from Fig.…”

“…19 A linear motor, Linmot PS01 48 Â 240/30 Â 180-C (NTI AG, Switzerland), was mounted on a purpose-built frame. Clamps to hold the pericardium were fitted between the linear motor and a L6D OIML single-point loadcell (Hangzhou Wanto Precision Technology Co., Zhejiang, China).…”

“…18 In leather, where there is very little crimp, the reorientation of fibrils may be an important mechanism for absorbing strain. 19,20 Here, the behavior of individual fibrils of collagen I as strain is applied is studied using small angle X-ray scattering (SAXS) to simultaneously measure the fibril length extension and fibril diameter contraction. Bovine pericardium is used as a model material for this work because it is elastic and strong and has application in medical devices.…”

Age Dependent Differences in Collagen Alignment of Glutaraldehyde Fixed Bovine Pericardium

“…The orientation of collagen measured edge on (alignment in plane) has been shown in bovine and ovine skin to be correlated with strength [15, 16]. This correlation extends across a range of mammal species with a strength range of over a factor of five [17].…”