Figure 2.

Midsection of fibers pulled from solutions of (A) atelo-collagen and (B) telo-collagen observed under 1× phosphate-buffered saline (PBS). (C) Drawing a fiber from a prepolymerized droplet of telo-collagen (held under silicone oil to prevent evaporation and maintain pH and ionic strength). Preassembled collagen fibrils adhered to a glass microneedle and allowed a fiber to be drawn from the assembled network. The arrows identify the location from where the fiber was drawn. (D) Midsection of the fiber drawn from the preformed collagen network clearly shows the disorganization and poor spatial packing that resulted from pulling out an entangled network. The fiber morphology was far different than that observed in A or B, which indicated that triggering polymerization via extensional strain was a uniquely different process than drawing a fiber from an already formed network. This observation suggests that even cellular manipulation of an already polymerized network is unlikely to result in highly aligned fibrillar structures without further fibril modification.⁴² TEM images of the (E) atelo- and (F) telo-collagen droplet surface (preserved by quick freezing then replicated following deep-etching by rotary shadowing with platinum) at the time when a fiber would be drawn (150 s). Generally, the surfaces of the collagen droplet were enriched with a high concentration of monomers that have not yet assembled into larger hierarchical structures.