Biomedical Engineering Reference
In-Depth Information
2
Biogenesis of Cellulose Nanofibrils
by a Biological Nanomachine
Candace H. Haigler and Alison W. Roberts
2.1
Introduction
Cellulose is synthesized by diverse organisms including prokaryotes, protists, animals,
and plants. However, cellulose achieves its natural dominance within plants, where
ß-1,4-linked glucan chains form long, semi-crystalline fibrils with nanoscale lateral
dimensions. Although these fibrils have been conventionally called 'microfibrils', the
term 'nanofibril' may be a more appropriate name in the age of nanoscience and nan-
otechnology (1).
1 . 5and
25 nm in different cells) and the importance of surface properties in the chemistry and
biological roles of cellulose. A main feature of nanomaterials (with 1-100 nm dimen-
sions) is unique properties that: (a) often arise from a high surface-to-volume ratio; and
(b) bridge between the molecular mechanics that applies to the molecular scale and the
Newtonian physics that applies to larger objects (2, 3). The surface interactions of cellu-
lose with other molecules are major determinants of its role as a scaffold for deposition
of other wall components and the coherence and physical properties of the composite
cell wall.
In the plant cell wall, the cellulose nanofibrils are commonly 2-6 nm in diameter, with
the larger nanofibrils usually occurring in secondary walls. All plant cells contain about
This term would reflect the fibril width (ranging between
15% cellulose in the thin, extensible primary walls that surround growing cells. In this
role, the cellulose nanofibrils are able to constrain the direction of plant cell expansion
(as driven by isodiametric turgor pressure). This function derives from the high breaking
strain energy (5
GN/m 2 ) of cellulose fibrils, in
the same range as high tensile steel. In proportion to its density, which is lower than steel,
10 6
J/m 3 ) and tensile strength (
50
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