in length. The fibrils are wrapped with proteins and assemble into fibers of about
60 nm in diameter. These fibers further assemble into bundles. The bundles then
arrange themselves parallel to each other and form horizontal planes. These planes
are stacked in a helicoid fashion, creating a twisted plywood structure. A stack of
layers that have completed a 180
rotation is referred to as a Bouligand structure.
These structures repeat to form the exocuticle and endocuticle. The same Bouligand
structure is also characteristic of collagen networks in compact bone, cellulose
fibers in plant cell walls, and other fibrous materials. In crab exoskeletons, the
minerals are in the form of calcite or amorphous calcium carbonate, deposited
within the chitin–protein matrix.
In the direction normal to the surface (the z-direction), there are well-developed,
high-density pore canals containing long, flexible tubules penetrating through the
exoskeleton. These tubules play an important role in the transport of ions and
nutrition during the formation of the new exoskeleton after the animals molt.
The crab exoskeleton is a three-dimensional composite comprising brittle
chitin–protein bundles arranged in a Bouligand pattern (the x–y plane) and ductile
pore canal tubules in the direction normal to the surface (the z-direction). The pore
canal tubules possess ductile mechanical properties even in a dry condition.
The structure and mechanical properties of arthropod exoskeletons have been much
studied. It is important for materials scientists to understand the design of natural
composites, in order to develop novel composite materials with enhanced properties.
6.3 Hierarchical Structure of Calcium Phosphate-Based
Biomineral
6.3.1 Zebrafish Bone
The zebrafish (Danio rerio) has proved to be an important system for studying
vertebrate-specific problems of development because it is a powerful model organism for embryology, developmental biology, and genetics. Related researches
utilizing the zebrafish system have been involved in many areas, such as developmental neurobiology, cardiovasology, etc.
Bone is a type of mineralized material with highly complex hierarchical structure. Weiner has described the seven levels of hierarchical organization of human
long bone. The basic building block of the bone materials is the mineralized
collagen fibril (level 2), which is composed of very hard material, the mineral
and much softer material, the collagen fibrils (level 1). Mineralized collagen fibrils
are always present in bundles or arrays aligned along their length (level 3). These
fibril arrays organize into four common patterns: arrays of parallel fibrils, woven
fiber structure, plywood-like structure, and radial fibril arrays (level 4). At a higher
level of organization, the initially deposited primary bone undergoes internal
remodeling and forms the secondary bone with a central canal for blood vessels
164
Q. Feng
60 nm in diameter. These fibers further assemble into bundles. The bundles then
arrange themselves parallel to each other and form horizontal planes. These planes
are stacked in a helicoid fashion, creating a twisted plywood structure. A stack of
layers that have completed a 180
rotation is referred to as a Bouligand structure.
These structures repeat to form the exocuticle and endocuticle. The same Bouligand
structure is also characteristic of collagen networks in compact bone, cellulose
fibers in plant cell walls, and other fibrous materials. In crab exoskeletons, the
minerals are in the form of calcite or amorphous calcium carbonate, deposited
within the chitin–protein matrix.
In the direction normal to the surface (the z-direction), there are well-developed,
high-density pore canals containing long, flexible tubules penetrating through the
exoskeleton. These tubules play an important role in the transport of ions and
nutrition during the formation of the new exoskeleton after the animals molt.
The crab exoskeleton is a three-dimensional composite comprising brittle
chitin–protein bundles arranged in a Bouligand pattern (the x–y plane) and ductile
pore canal tubules in the direction normal to the surface (the z-direction). The pore
canal tubules possess ductile mechanical properties even in a dry condition.
The structure and mechanical properties of arthropod exoskeletons have been much
studied. It is important for materials scientists to understand the design of natural
composites, in order to develop novel composite materials with enhanced properties.
6.3 Hierarchical Structure of Calcium Phosphate-Based
Biomineral
6.3.1 Zebrafish Bone
The zebrafish (Danio rerio) has proved to be an important system for studying
vertebrate-specific problems of development because it is a powerful model organism for embryology, developmental biology, and genetics. Related researches
utilizing the zebrafish system have been involved in many areas, such as developmental neurobiology, cardiovasology, etc.
Bone is a type of mineralized material with highly complex hierarchical structure. Weiner has described the seven levels of hierarchical organization of human
long bone. The basic building block of the bone materials is the mineralized
collagen fibril (level 2), which is composed of very hard material, the mineral
and much softer material, the collagen fibrils (level 1). Mineralized collagen fibrils
are always present in bundles or arrays aligned along their length (level 3). These
fibril arrays organize into four common patterns: arrays of parallel fibrils, woven
fiber structure, plywood-like structure, and radial fibril arrays (level 4). At a higher
level of organization, the initially deposited primary bone undergoes internal
remodeling and forms the secondary bone with a central canal for blood vessels
164
Q. Feng