Fig. 1. Schematic representation of the deck-of-cards model of mineralized collagen.

The model considers the collagen fibril to comprise staggered molecular layers and the gap regions to contain rectangular shaped channels (a)^1,11,13. In that model the HAp crystals nucleate in the gap regions (b), where they are epitaxially templated by charged functional groups (inset in b)^9,18. They subsequently develop into platelets that are embedded between the collagen layers as shown in c. A 3D array of oriented parallel platelets eventually forms, as shown in d.