Biomedical Engineering Reference
In-Depth Information
Chapter 12
Porosity in Polyaryletheretherketone
Marcus Jarman-Smith, Mark Brady, Steven M. Kurtz, Nicholas M. Cordaro, and William R. Walsh
12.1 Introduction
Porosity is currently employed in medical device
applications through various routes:
Connective tissues are complex composite mate-
rials of cellular and extracellular matrix components
that together confer specific biological and structural
properties. Permanent solid biomaterials, such as
polyaryletheretherketone (PEEK), mainly serve as
a replacement for the structural properties. Materials
and devices with porosity are primarily cited as
having improved integration with the body and aiding
a more natural biological and physical functioning.
Porosity gives biomaterials the ability to allow tissue
infiltration and integration. A structural biomaterial
becomes a physical form that more closely replicates
the natural tissue and allows the integration with the
cellular component. This improved physical rela-
tionship between biomaterial and cells manifests
itself as better cell functioning and enhanced fixation
of devices with adjacent tissue. This is still a phys-
ical/mechanical relationship with no chemical bond.
Porous biomaterials can also incorporate additional
factors (e.g., BMP-2) that encourage cell ingrowth or
physicochemical bonding. Other drivers for the
development of a permanent porous biomaterial
include closer structural replication of the host tissue.
The material properties of solid PEEK are already
considered useful to produce flexible implants, and
the introduction of porosity may provide a transi-
tional zone between the bone and biomaterial, further
reducing stress shielding in load-bearing applica-
tions. Other historic drivers in orthopedics have
included the quest for uncemented fixation, as
demonstrated in several studies examining the role of
pore size for bone integration [1 e 3] . Further, the use
of bone graft substitutes has previously provided
naturally “macroporous” (cancellous bone) and
“micro” or “nano” porous (cortical bone) structures.
l Use of completely porous structural materials
such as porous tantalum (trabecular metal, Zim-
mer) and porous titanium alloy (Regenerex ,
Biomet)
l Cell support scaffolds (e.g., collagen, PET
meshes)
l Osteoconductive filler materials (e.g., calcium
phosphates)
l Surface coatings (e.g., porous titanium beads,
cobalt chrome beads, hydroxyapatite coatings).
Regardless of its end application, creating
a biomaterial with porosity can allow the opportunity
for the material to better integrate or interact with the
surrounding
tissue. Reasons
for
incorporating
porosity into an implant include:
l Better integration of implant with body;
l Orientation of cells in configuration closer to
nature d more conducive to correct functioning;
l Enhanced fixation of device, preventing device
migration
or movement
causing
abrasive
damage to adjacent tissue; and
l Porosity of correct type may trigger or direct
tissue repair.
PEEK biomaterials are an attractive platform for
research on incorporating porosity as an alternative to
established porous polymers, metals, and ceramics.
The natural radiolucency of PEEK allows imaging
compatibility for the visualization of any bony
ingrowth from a radiographic point of view as well as
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