Biomedical Engineering Reference
In-Depth Information
In practice, controlling the colloidal assembly could be employed to define
a template for creating two-dimensional (2D)/three-dimensional (3D) periodic
structures for applications in photonic devices [
26
,
27
], biological and chemical
sensors [
28
], and tunable lasers [
29
]. Recently, the controlled colloidal assembly
has been utilized to mimic the structural color created by animals, i.e., butterfly
wings,etc.[
30
,
31
].
The purpose of this chapter is to provide an overview on the recent progress in
the experimental simulations of crystallization processes, in particular biomineral-
ization processes, by controlled colloidal assembly. Our attention will be focused
on the following two aspects: the electrically controlled colloidal crystallization
as a well-controlled and quantitative modeling system to simulate the kinetics
of crystallization, i.e., biomineralization, and structural color biomimetics. As the
thermodynamic driving force in crystallization can be tuned directly from altering
the strength and/or frequency of the applied electric field, some most essential issues
in biomineralization, i.e., nucleation kinetics, the multistep/phase crystallization,
the ordered crystallites assembly, etc., which are often observed in hard tissues,
can be examined quantitatively by the electrically controlled colloidal assembly in
a combination of microscopic visualization. The results obtained will provide the
most up-to-date knowledge on crystallization at the individual growth unit level.
On the other hand, we will also review that, practically, the controlled colloidal
assembly can be adopted to produce templates in engineering photonic crystals in
mimicking structural colors from the animal kingdom. In this regard, some examples
of structural color biomimetics and the application to textiles will be given. This may
pave the new silk road in the years to come.
7.2
Thermodynamic Driving Force of Colloidal
Crystallization and Assembly
As crystallization in most cases is a first-order phase transition, without thermo-
dynamic driving force, crystallization (including biomineralization) will not take
place. Therefore, to examine the kinetics of crystallization (including biominer-
alization) in a quantitative way, the well-controlled thermodynamic driving force
is the precondition. Furthermore, exercising the control of crystallization should
demonstrate the capability of controlling the thermodynamic driving force for the
theoretical analysis. Regarding the colloidal crystallization, the interactions among
colloidal particles play a key role in this analysis. The most general equation of the
total free-energy difference (
G
) between particles at a separation
H
is obtained by
adding these contributions:
att
rep
rep
G
D
G
.
vanderWaals
/
C
G
.
shortrange
/
C
G
.
electrostatic
/
rep
C
G
.
steric
/
C
G.
othereffects
/
(7.1)
