Biomedical Engineering Reference
In-Depth Information
8.5.4.7.3 Chitosan-Calcium Phosphate Composite
Calcium phosphate, the main inorganic component of bone, is of superior biocompatibil-
ity, insolubility, and mechanical stability, and has been proven to be suitable for enzyme
immobilization. Compared with silica, the common material in immobilized enzymes,
calcium phosphate has good biocompatibility and can be prepared in mild conditions.
A novel kind of calcium phosphate-mineralized chitosan-alginate microcapsule was
prepared through a bioinspired process for efficient encapsulation of yeast alcohol dehy-
san droplets were added into a phosphate-containing solution of alginate, a thin
chitosan-alginate film formed immediately around the microcapsules coupled with
in
situ
precipitation of calcium phosphate. The biomineralization of calcium phosphate was
mimicked by the counter diffusion system in which Ca
2+
ions and phosphate ions migrated
into the chitosan-alginate film from opposite directions, respectively. YADH encapsu-
lated in the microcapsules exhibited significantly higher activity and recycling stability
in a broader temperature range than the free YADH. These hybrid materials will find
promising applications in enzyme encapsulation and drug delivery systems [153].
8.5.4.7.4 Chitosan-Silica-K
3
Fe(CN)
6
Hybrid Film
Li et al. developed a simple and effective strategy for the fabrication of hydrogen peroxide
(H
2
O
2
) biosensors by entrapping HRP in chitosan-silica sol-gel hybrid membranes
(CSHMs) doped with potassium ferricyanide (K
3
Fe(CN)
6
) and GNPs on platinum elec-
trode surface. The hybrid membranes are prepared by cross-linking chitosan with APTES,
while the presence of GNPs improved the conductivity of CSHMs, and the Fe(CN)
6
3−/4−
was
used as a mediator to transfer electrons. K
3
Fe(CN)
6
, the most widely used inorganic
electron mediator, has been extensively used in biosensors because of its excellent electron
transferability and high degree of reversibility. Moreover, due to the possible control over
pore size and hydrophobicity, the mediators could be attached specifically to the composite
+
+
+
HPO
4
Ca
+
-
-
+
Ca
E
HPO
4
E
+
Ca
+
+
+
+
Ca
-
E
+
Alginate
Ca
+
-
Ca
+
HPO
2-
+
Ca
Ca
+
E
+
+
+
E
+
+
+
+
Ca
E
+
Ca
-
+
Calcium
phosphate
Ca
+
-
Alginate/chitosan
+
Ca
2+
HPO
2-
-
Chitosan
Alginate
E
Enzyme
Ca
HPO
4
+
-
Figure 8.15
Schematic representation of the formation process of calcium phosphate-mineralized chitosan-alginate micro-
capsules. (From Jiang, Y. J. et al. 2008.
Ind Eng Chem Res
47: 2495-2501. With permission.)
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