Biomedical Engineering Reference
In-Depth Information
with traces of magnesium, carbonate, hydroxyl, chloride,
fluoride, and citrate ions. Hence calcium phosphates
occur naturally in the body, but they occur also within
nature as mineral rocks, and certain compounds can be
synthesized in the laboratory.
Table 3.2.10-7
summarizes
the mineral name, chemical name and composition of
various phases of calcium phosphates.
Within the past 20-30 years interest has intensified in
the use of calcium phosphates as biomaterials, but only
certain compounds are useful for implantation in the body
since both their solubility and speed of hydrolysis increase
with a decreasing calcium-to-phosphorus ratio. Driessens
(1983) stated that those compounds with a Ca/P ratio of
less than 1:1 are not suitable for biological implantation.
The main crystalline component of the mineral phase
of bone is a calcium-deficient carbonate HA, and various
methods have been investigated to produce synthetic
HA. The commercial routes are based on aqueous pre-
cipitation or conversion from other calcium compounds.
Aqueous precipitation is most often performed in one of
two ways: a reaction between a calcium salt and an al-
kaline phosphate (Collin, Hayek and Newsley, 1963;
Eanes
et al.
, 1965; Bonel
et al.,
1987; Young and
Holcomb, 1982; Denissen
et al.
, 1980b; Jarcho
et al.
,
1976; Kijima and Tsutsumi, 1979) or a reaction between
calcium hydroxide or calcium carbonate and phosphoric
acid (Mooney and Aia, 1961; Irvine, 1981; Rao and
Boehm, 1974; McDowell
et al.
, 1977; Akao
et al
., 1981).
Other routes include solid-state processing (Monma
et al.
, 1981; Fowler, 1974; Young and Holcomb, 1982;
Rootare
et al.
, 1978; Lehr
et al.
, 1967); hydrolysis
(Schleede
et al.
, 1932; Morancho
et al.
, 1981; Young and
Holcomb, 1982); hydrothermal synthesis (Young and
Holcomb, 1982; Fowler, 1974; Roy, 1971; Skinner, 1973;
Arends
et al.
, 1979).
105
90
Cement fixation
(after Park)
75
60
Bioglass
bioactive
fixation
Healed certical
bone
45
30
Morphologic
fixation
Biologic
fixation
15
3
6
9
12151821242730
Weeks
Fig. 3.2.10-7 Time dependence of interfacial bond strength of
various fixation systems in bone. (After Hench, 1987.)
Calcium phosphate ceramics
Bone typically consists, by weight of 25% water, 15%
organic materials and 60% mineral phases. The mineral
phase consists primarily of calcium and phosphate ions,
Table 3.2.10-6 Present uses of bioceramics
Orthopedic load-bearing
applications Al
2
O
3
Coatings for tissue ingrowth
(cardiovascular, orthopedic,
dental and maxillofacial
prosthetics)
Al
2
O
3
Coatings for chemical bonding
(Orthopedic, dental and
maxillofacial prosthetics)
HA
Bioactive glasses
Bioactive glass-ceramics
Temporary bone space fillers
Tricalcium phosphate
Calcium and phosphate salts
Dental implants
Al
2
O
3
HA
Bioactive glasses
Periodontal pocket obliteration
HA
HA-PLA composite
Trisodium phosphate
Calcium and phosphate salts
Bioactive glasses
Table 3.2.10-7 Calcium phosphates
Ca:P Mineral
name
Formula
Chemical name
Alveolar ridge augmentations
Al
2
O
3
HA
HA-autogenous bone composite
HA-PLA composite
Bioactive glasses
Maxillofacial reconstruction
Al
2
OHA
HA-PLA composite
Bioactive glasses
1.0
Monetite
CaHPO
4
Dicalcium phosphate
(DCP)
1.0
Brushite
CaHPO
4
$
2H
2
O
Dicalcium phosphate
dihydrate (DCPD)
1.33
d
Ca
8
(HPO
4
)
2
(PO
4
)
4
$
5H
2
O
Octocalcium phosphate
(OCP)
Otolaryngological
Al
2
O
3
HA
Bioactive glasses
Bioactive glass-ceramics
Percutaneous access devices
Bioactive glasses
Bioactive composites
1.43
Whitlockite
Ca
10
(HPO
4
)(PO
4
)
6
1.5
d
Ca
3
(PO
4
)
2
Tricalcium phosphate
(TCP)
Artifical tendon and ligament
PLA-carbon fiber composite
Orthopedic fixation devices
PLA-carbon fibers
PLA-calcium/phosphorus-base
glass fibers
1.67
Hydroxyapatite
Ca
10
(PO
4
)
6
(OH)
2
2.0
Ca
4
P
2
O
9
Tetracalcium phosphate