Biomedical Engineering Reference
In-Depth Information
regions of the mold, or by building up layers of the
PEEK-soluble glass blend over solid PEEK inserts.
The presence of a solid PEEK structural zone
combined with a covering zone of porosity formed in
this way is shown in Fig. 12.6 . Micro-CT analysis of
the thin porous zone on these hybrids revealed
a mean pore size of 490 m m, closer still to that of
trabecular bone (678 m m), and a connective density
equivalent to that of trabecular bone (7 mm 3 )
( Fig. 12.17 ).
It is envisaged that solid e porous PEEK hybrids
will provide both the structural integrity demanded of
such materials in potential load-bearing applications,
along with the ability for osseoconductivity.
Evidence in the literature suggests that bone
ingrowth into porous materials of the order of
a couple of millimeters may be sufficient to signifi-
cantly increase implant fixation. Although far from
being proven, the use of hybrid solid e porous PEEK
constructs may find their place, not in direct
competition with existing porous metals, but in
applications where a reduced material stiffness and
imaging may be beneficial.
Figure 12.15 Porous PEEK is interconnected, porous,
and also radiolucentdallowing visualization of bony
ingrowth. Image courtesy of D. Jaekel, Drexel University,
USA.
mean pore size of 369 m m( n ΒΌ
3), confirming its
characteristics as lying somewhere between those
samples described in case study 2.
As expected, the additional porosity and inter-
connectivity of this material had adverse implications
for the compressive strength (15 MPa). Such
mechanical properties would likely preclude the use
of a wholly porous material in a load-bearing predi-
cate application (e.g., spinal cage). Therefore,
a hybrid solid e porous structure was examined. This
can be manufactured using the described approach
or, alternatively, the process can be modified to build
up the mix of the materials layer by layer, ensuring
full melt of each layer before the subsequent layer is
added and molten ( Fig. 12.16 ).
Regions of solid PEEK can be created through
addition of PEEK-OPTIMA microgranules alone to
12.8 Conclusions
Incorporating porosity into PEEK opens a wide
range of opportunities for research and biomaterials
development. Many avenues for creating porous
PEEK biomaterials are currently under investigation,
as illustrated by the three case studies described in
this chapter. It appears that the challenge for porous
PEEK materials is the engineering of a material with
pores that are sufficiently large to satisfy literature
recommendations for bone ingrowth, yet also able to
retain desirable structural properties. In addition,
considerations around cost, scaleability of produc-
tion, and the versatility of the technology to be
absorbed into existing manufacturing routes must be
made. Specifically, the case studies chosen here
considered factors such as demonstrating a measur-
able benefit for ingrowth, predicate mechanical
requirements, the ability to machine the material
postproduction, and subsequent sterilization and
retention of cleanliness of the material.
The best application for a porous PEEK is not yet
clear, although most intellectual property activity is
around spinal applications. It is possible that the
successful use of PEEK in spine will additionally
utilize this new form if the mechanical requirements
Figure 12.16 Mid-sized porous PEEK is intercon-
nected and should permit infiltration of surrounding
tissue. Image courtesy of Invibio Ltd.
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