Fig. 4
A schematic representation depicting the molecular structures of (A) Lys, (B) tannic acid (TA), (C) hydroxyapatite (HA), (D) the TApHs@HA forming process, and (E) the fabrication of (TA@HA/Lys)n. (1) The substrate was initially coated with PEI, then (2) TA@HA, and (3) Lys were deposited; (4) this process was repeated a desired number of times for (2) and (3).