Figure 1. Schematic of experimental principles.

Left) 2D diffraction patterns from tendons are dominated by the meridional Bragg reflections corresponding to ∼67.5 nm and harmonic frequencies of this spacing. Right) This pattern results from the quarter-stagger model of collagen. More simply, this can be seen as “gap” and “overlap” regions with high and low electron dense areas that scatter X-rays as wide periodic slits [63]. Middle) The meridional intensities were integrated over azimuthal (θ) sectors, which resulted in 1-D intensity profiles, I [a.u.] vs. q [nm⁻¹]. The peak positions or correspondingly the distance between peaks) were used to calculate the length of the periodicity (Bragg's law) during tensile experiments. Changes of the peak spacing served then as averaged measure for collagen fibril elongation: absolute deformation (D) and relative fibril strain).