Figure 4. De novo nucleation of hydroxyapatite by P₁₁-4 in vitro. (a) Transmission electron micrographs (unstained) showing needle-like electron-dense deposits in the body of a self-assembled P₁₁-4 gel following 7 days’ incubation at 35°C in "mineralizing" solution (22 mM NaHCO₃, 3.75 mM CaCl₂, 1.67 mM Na₂HPO₄, pH 7.4). (b) Electron diffraction patterns of needle-like deposits. Lattice planes 110 (A); 002 (B); 211 (C), camera focal length 400 mm; 100 (D); 200 (E); and 102 (F), camera focal length 575 mm, are indicated. (c) EDX spectrum of needle-like deposits.