Bioinspired Encapsulation of Living Cells within Inorganic Nanoshells - Cell Surface Engineering: Fabrication of Functional Nanoshells - page 63

4.4 Artificial Shells Inspired by Biosilicification
Certain unicellular organisms, such as diatoms, radiolaria, and synur-
ophytes, and multicellular glass sponges produce siliceous exoskeletons,
which have exquisite hierarchical structures and superior mechanical
properties (Figures 4.11a and b), 96-98 whereas most cells in Nature do not
have siliceous shells to protect their cytoplasm from the external environ-
ment. In biological systems, peptides or proteins play a pivotal role as
structure-directing agents in the accumulation of mineral ions and in the

d n 8 y 4 n g | 8

.

Figure 4.11 SEM micrographs of (a) Stephanopyxis turris cell walls (scale bar:

10 mm, 5 mm for the inset) and (b) The glass sponge, Euplectella,
showing the basket-like cage structure. (c) Chemical structure of
silan-1A 1 from Cylindrotheca fusiformis. (d) The catalytically essen-
tial moieties in a serine-hydrolase active site (top), and Ribbon model
of silicatein-a from an energy minimization program (INSIGHT II)
with green highlights for the catalytic site (bottom).
Reproduced with permission from Wiley (Copyright 2006), 97 the

Nature Publishing Group (Copyright 2003), 98 the Royal Society of

Chemistry (Copyright 2004), 102 the National Academy of Sciences,

USA (Copyright 2006). 126