Pure dense collagen threads from extrusion to fibrillogenesis stability

In tendons, collagens reach a concentration of 60%–85% of the dry weight of the tissue, collagen I being one of the major structuring agents. Collagen is found under its fibrillated state and organized in a highly anisotropic and hierarchical manner. In a first step to synthetize a mime of a tendon, we built a set up to extrude highly viscous acidic pure molecular collagen solutions (60 mg ml−1) into meters of regular threads of 300 μm to 600 μm in diameter. Eight different extruding and fibrillogenesis buffers were tested for their ability to generate stable anisotropic threads, with collagen fibrils characterized by the 67 nm-D period and optimally aligned parallel to the thread axis. Thanks to a follow up over 15 days, we pinned down one condition for which both diameter and anisotropy of the threads were stable throughout extrusion, fibrillogenesis and storage. The threads presented characteristic collagen fibrils and mechanical tests indicated a Young modulus around 1.7 MPa and an ultimate tensile strength of 0.3 MPa. Since neither chemical cross-linkers nor dehydrating processes were used, our synthesis process raises no biocompatibility or structure preservation concerns for tissue engineering applications, opening routes for further developments.