Fig. 4

Picrosirius red-enhanced collagen birefringence in non-aligned collagen gels and aligned tendon collagen. a, b Bright field (left) and polarised light microscopy (right) of PSR-stained cryosections cut from reconstituted collagen gels (a) and rat tail tendon (b). c, d Atomic force microscopy (AFM) height maps of collagen gels (c) and tendon (d). Collagen alignment and periodicity (white arrows) can be readily determined from fast fourier transform (FFT) of AFM amplitude images. Inset position of the fast fourier transform (FFT) signals corresponding to collagen periodicity (diffuse circles for the gel and discrete lines for the tendon) are indicated by arrows. e AFM-derived collagen periodicity. f Micro-mechanical stiffness (modulus (MPa)) of in vitro (gel) (255 kPa ± 0.91) and in vivo (tendon) assembled collagen (869 kPa ± 0.90, p <0.005)