Movie S6.

FIB-SEM images (SE) and 3D reconstruction of a distal tendon containing an interface between unmineralized and mineralized tissue zones. The specimen is viewed in transverse profile to the longitudinal direction of the tissue prepared by protocol 2. The region consists of collagen fibril bundles, one more heavily mineralized (right half of image and in white) than the others (left half of image). Bundles are separated by a continuous dark, narrow space representing the sheath about the mineralized bundle. The more heavily mineralized bundle contains some fibrils yet to mineralize and which appear rather compact with indistinct borders. Fibrils comprising the less mineralized bundles are clearly separated from their neighbors by dark spaces which might be secondary channels. These same fibrils are not as compact as their counterpart unmineralized fibrils in the more heavily mineralized bundle. On 3D rendering of a portion of a less mineralized bundle, individual collagen fibrils (wine) of similar diameter, estimated to be ∼250 nm, and unfused with each other are found with mineral deposits (blue) both within (intra-) and outside (interfibrillar) the fibrils.