MATERIALS FOR ORTHOPEDIC APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 57

TABLE 3.2. Mechanical Properties of Different Hard Tissues of Human System

Tissues Elastic modulus (GPa) Tensile strength (MPa)

Cortical bone 17.7 133

Cancellous bone 0.30 15

Enamel 85 11.5 transverse, 42.2 parallel

Dentine 32.4 44.4

[137,138,139,140] .

TABLE 3.3. Composition of Bone

Organic — Collagen Fibres (Type 1) 16%

Mineral — Hydroxyapatite [Hap - Ca10(PO4)6(OH)2] 60%

Ground Substance 2%

Water 23%

[7] .

Tropocollagen

Osteon

Collagen fibrils

Bone

300 nm

1.5 nm

Hydroxyapatite
crystals

70 nm

Microfibril

1 nm

Figure 3.1. Schematic representation of a bone structure, showing the complexity of bone
structure. (Reproduced from ref. 141 )

vide the framework and architecture of bone, with HAp particles located between
the fi bers. The ground substance is formed from proteins, polysaccharides and
mucopolysaccharides, which together act as cement. Except for these, the living
portion, i.e., osteoblast, osteoclast and osteocytes, are present in the structure and
such cells actually infl uence biological properties to a great extent. The detailed
structure of a cortical bone is shown schematically in Figure 3.1. At the nano
level structure, HAp nanoparticles (20-40 nm) are shown to be adhered and dis-
persed in the collagen matrix. At top level structure hierarchy, the three dimen-
sional schematic of bone structure is also shown (Figure 3.1). It is quite evident
that the synthetic materials cannot mimic such extremely complex structural hi-
erarchy of bone. However, they can provide the bone's external properties to