Biomedical Engineering Reference
In-Depth Information
Figure 11.2
Schematic diagram showing a
more detailed description of processinge
structureeproperty relationships (
Fig.
11.1
) key to the design of calcium
phosphate-reinforced PEEK composites
for biomedical devices.
DEVICE PERFORMANCE
PROCESSING
PROPERTIES
BIOLOGICAL
• biocompatibility
• bioactivity
• bioresorption
• osteoconductivity
• osteoinductivity
MATERIALS
PAEK
• polymerization
• compounding
• size fractioning
STRUCTURE
MOLECULAR (PAEK)
• composition
• molecular weight
• conformation
• configuration
• crystallinity
• orientation
CALCIUM
PHOSPHATE
REINFORCEMENTS
FUNCTIONAL
• formability
• permeability
• radiopacity
• cost
• availability
• solid state reaction
(high temperature)
• chemical solutions
(low temperature)
CRYSTALLINE
(calcium phosphate)
• stoichiometry
• composition
• size
• morphology
SHAPE FORMING
MECHANICAL
• elastic modulus
• tensile strength
• compressive strength
• fracture toughness
• fatigue life
• compression molding
• injection molding
• pressureless sintering
• selective laser sintering
• particle leaching
• machining
MICROSTRUCTURE
(composite)
• phase fractions
• porosity
• orientation
• gradation
opportunities to design and manufacture bioactive
composites with tailored properties (
Fig. 11.2
).
(OXPEKK-C), has also been investigated
[27
e
30]
.
PEEK products are also currently available from
Evonik Industries (VESTAKEEP
) and Solvay
Advanced Polymers (KetaSpire
and Zeniva
)but
have not yet been used in published reports for
bioactive composites. The crystallinity of all the
above products is generally in the range of 30
e
35%
as-received. The crystallinity after molding will be
discussed further in Section
11.2.3
.
11.2 ProcessingeStructure
Relationships
11.2.1 PAEK Synthesis and
Structure
The processing of PAEK beads and powders of
varying composition, molecular weight, size, and
crystallinity has been reviewed in detail in preceding
chapters of this topic and elsewhere
[3]
. Investigations
of bioactive PAEK composites to date have primarily
utilized commercial polyetheretherketone (PEEK)
beads and powders
[11
e
26,30
e
35]
manufactured by
Victrex (150XF, 150PF, and 450G), and their subsid-
iary Invibio Biomaterial Solutions under the trade
name PEEK-OPTIMA
(LT1PF and LT3UF) (
Table
11.1
). The 150 and LT3 grades have a number average
molecular weight (
11.2.2 Bioactive Reinforcement
Synthesis and Structure
Bioactive reinforcements or fillers have primarily
utilized crystalline calcium orthophosphates,
including stoichiometric HA
[11
e
20,34]
, calcium-
deficient HA
[25
e
31]
, and
b
-TCP
[21
e
24]
(
Table
11.1
). However, strontium-substituted HA
[32]
,
amorphous calcium silicate
[33]
, and Bioglass 45S5
[23,35]
have also been investigated. These and a wide
variety of other calcium phosphates are available for
use as bioactive reinforcements (
Table 11.2
). A key
aspect of selection is the solubility of a particular
composition or stoichiometry, which influences bio-
logical properties and will be discussed further in
Section
11.3.1
.
High-temperature synthesis
d
including solid-state
reactions, molten salt synthesis, and spray drying with
calcination
d
generally leads to stoichiometric phases
M
n
) of 83,000, while the 450 and
LT1 grades have a number average molecular weight
of 115,000. Powder grade PF, XF, and UF have a mass
average particle diameter (
D
50
) of 50, 25, and 10
m
m,
respectively. A polyetherketoneketone
(PEKK)
powder with a mean particle size of 70
m
m, manu-
factured
by Oxford
Performance Materials
