Calcium Orthophosphate-Based Biocomposites and Hybrid Biomaterials - Calcium Orthophosphates: Applications in Nature, Biology and Medicine - page 583

Table 6.1 The biochemical composition * of bones [36].

Inorganic phases Wt.% Bioorganic phases Wt. %

Calcium
orthophosphates
(biological apatite)

~ 60 Collagen type I ~ 20

Water ~ 9 Non-collagenous

proteins: osteocalcin,
osteonectin, osteopontin,
thrombospondin,
morphogenetic proteins,
sialoprotein, serum proteins

~ 3

Carbonates ~ 4 Other traces:

polysaccharides, lipids,
cytokines

balance

Citrates ~ 0.9 Primary bone cells:

osteoblasts, osteocytes,
osteoclasts

balance

Sodium ~ 0.7

Magnesium ~ 0.5

Other traces: Cl − , F − , K +
Sr 2+ , Pb 2+ , Zn 2+ , Cu 2+ ,
Fe 2+

Balance

*

The composition varies from species to species and from bone to bone.

It remains a great challenge to design the ideal bone graft
that emulates nature's own structures or functions. Certainly, the
successful design requires an appreciation of the structure of bone.
According to expectations, the ideal bone graft should be benign,
available in a variety of forms and sizes, all with sufficient mechanical
properties for use in load-bearing sites, form a chemical bond at the
bone/implant interface, as well as be osteogenic, osteoinductive,
osteoconductive, biocompatible, completely biodegradable at the
expense of bone growth and moldable to fill and restore bone defects
[29, 40, 43]. Further, it should resemble the chemical composition of
bones (thus, the presence of calcium orthophosphates is mandatory),
exhibit contiguous porosity to encourage invasion by the live host
tissue, as well as possess both viscoelastic and semi-brittle behavior,
as bones do [44-47]. Moreover, the degradation kinetics of the