Biomedical Engineering Reference
In-Depth Information
TABLE 9.1
Typical Mechanical Properties of Bioceramics
Fracture
Toughness
(MPa√m)
Compressive
Strength(MPa)
Tensile(T)/Bending(B)
Strength(MPa)
Young'sModulus
(GPa)
Bioceramic
Firstgeneration(notbioactive)
Alumina (Al
2
O
3
)
3000
260-300 (T)
380
3-5
Zirconina (ZrO
2
)
2000
248 (T)
200
4-12
Secondandthirdgeneration(bioactive)
Bioactive glass
(Bioglass
®
)
~1000
42 (T)
~100
~3
Bioactive glass-
ceramic (A/W glass)
1080
215 (B)
118
2
Hydroxyapatite (HA)
~1000
40 (T)
100-200
~ 3
Calcium phosphates
20-900
30-200 (T)
30-103
< 1
Naturaltissue
Cortical bone
130-180
50-151 (T)
12-18
6-8
new paradigm where bioactive ceramics (second-generation bioceramics) elicited a specific
biological interfacial bonding responses while maintaining the structural integrity at the
host tissue site. In addition, their surfaces could be designed to be either resorbable, where
the material interface was replaced with host tissue, or nonresorbable (Figure 9.3). Since
the discovery of Hench's composition, various second-generation bioceramics, bioactive
glasses, and glass-ceramics have been developed. Resorbable materials include bioactive
glass (e.g., 45S5 composition), glass-ceramics (e.g., A-W glass, Ceravital
®
), bioactive, porous
sol-gel glasses (e.g., 58S—see Table 9.5), and calcium phosphates. Hydroxyapatite (HA) is
an example of a nonresorbable bioecramic. Recently, biodriven bioactive glass develop-
ment has focused on engineering surface reaction conditions (including the controlled
release of ionic dissolution products into the local interfacial aqueous microenvironment
and engineering nanoscopic surface features) that genetically stimulate bone regenera-
tion. These have been termed third-generation bioceramics (Figure 9.3). It is hoped that
genetic bases for bone regeneration will represent the next paradigm shift in biomaterials
development.
Development of resorbable glasses and glass-ceramics has been limited due to their
intrinsic characteristics (e.g., fracture toughness, elastic moduli, and compressive strength
lower than cancellous and cortical bone for porous bioactive ceramics) verses specific chemi-
cal compositions to be bioactive. However, the nucleation and growth of crystalline phases
in glass-ceramics has resulted in improved mechanical properties that are closer to corti-
cal bone (Table 9.2). The advantage of densification of bioactive ceramics results in materi-
als that are much stiffer than bone. However, the disadvantage is that stiffer implanted
materials can usually fail due to local implant loosening caused by stress-shielding.
First-Generation Bioceramics
The first total hip replacement was carried out using an ivory implant in 1890. In the
1960s, metals and polymers were used in devices to replace hips (femoral steam and ball;
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