Biomimetic Preparation and Biomineralization of Bioceramics - Advanced Bioactive Inorganic Materials for Bone Regeneration and Drug Delivery - page 128

biomineralization is the biologically controlled mineralization. However, the
concept has been “misused” or widened. Any mineralization process that
forms minerals with biological morphology or biological effect has been called
“biomineralization,” even if there is no “bio-stuff” involved in the whole pro-
cess. In this chapter, the concept of biomineralization covers both real biologi-
cally controlled and nonbiological, or self-assembled, mineralization.
Biomineralization of bioceramics can be considered to form bonelike apa-
tite on their surfaces via a biologically or nonbiologically controlled precipi-
tation process. Hench (1991) first reported the formation of an apatite layer
on the bioglass surface. It is not just a biomineralization process, but bonds
between bone and bioactive materials and avoids soft tissue surrounding an
artificial biomaterial.
There are two possible ways of crystallizations via a biomineralization
process (Colfen and Mann 2003). One is thermodynamic control and another
is kinetic control (see Figure 5.1). Thermodynamic crystallization is a one-
step process. The fast growing faces have high surface energies and they will
vanish in the final morphology and vice versa. The kinetic crystallization
is based on the modification of the activation-energy barriers of nucleation,
growth, and phase transformation. It often involves an initial amorphous

ermodynamic
A

∆ G

∆ G n(B) + ∆ G g(B)

∆ G n(A) + ∆ G g(A)

Solution
(M aq + X aq )

∆ G t1

+ -

Amorphous

∆ G t2

B
Kinetic

∆ G t3

Final Mineral
(crystalline)

FIGURE 5.1
Crystallization pathways under thermodynamic and kinetic control. Whether a system fol-
lows a one-step route to the final mineral phase (pathway A) or proceeds by sequential precipi-
tation (pathway B), depends on the free energy of activation (DG) associated with nucleation
(n), growth (g), and phase transformation (t). Amorphous phases are common under kinetic
conditions. (From H. Colfen and S. Mann, Angewandte Chemie-International Edition 42(21): 2350-
2365, 20 03.)