Figure 1.

Schematic illustration of the proposed highly tunable injectable oligomeric collagen-fibril matrix system, using a well-established tooth slice model: (a) tooth slice, (b) concentrically injected collagen matrices (the low-stiffness matrix is purposely dyed in red), and (c) interface adaptation between the two matrices evidenced by reflectance microscopy. For the preparation of concentric collagen matrices, an endodontic fiber post (1.3 mm in diameter, 3MESPE, St. Paul, MN) was placed and stabilized inside the tooth slice. The collagen solution of 2.88 mg/mL (800 Pa) containing DPSC and BMP2 was injected using a needle to the area surrounding the fiber post. Once the matrix is polymerized, the fiber post was lifted and the lumen was injected with a collagen solution (1.37 mg/mL, 235 Pa) containing DPSC and VEGF165 and was allowed to polymerize. The volume ratio of the collagen solutions (1.37 and 2.88 mg/mL) was adjusted to 2:1, which compares with the anatomical features of a root canal. The fibril density and interface adaptation between the two collagen matrices of lower and higher stiffness are shown.