Biomedical Engineering Reference
In-Depth Information
encapsulated and isolated within the polymer matrix
(see patent application US 2005/0004340)
[30]
. This
circumvents any concerns over whether porogen is
inadequately removed from the material since the
resultant biomaterial showed that it had levels of
sodium and chloride equal to the unfilled natural
PEEK polymer. All other polymer characterization
testing (e.g., FTIR, GPC, and DSC) demonstrated
that the processed polymer was still essentially the
same as for the natural PEEK controls. The incor-
poration of a filler material allows machining of
a near net shape prior to leaching. This benefits
cleanliness and sterility in that machining is not
occurring when the material is already porous.
The surface of the porous material and the solid
unfilled PEEK was compared using microscopy
(
Fig. 12.2
). Even subtle changes between injection
molded or machined surfaces have been shown to
Figure 12.1
Porous PEEK construct for soft tissue
application. The first FDA 510 (k) approved rotator
cuff repair device PROcuff from Synovis (US). Image
courtesy of J. Brunelle (Synovis, USA).
to be applied to soft tissue applications (
Fig. 12.1
).
This device combines the strength of the PEEK mesh
with crosslinked equine collagen sheets to confer
a biological influence.
12.5 Case Study 1dPorosity
Through Porogen Leaching at
Production Scale
(a)
12.5.1 Material Manufacture
In this case study, a medical grade porous PEEK-
OPTIMA was studied by SeaSpine (USA). The
material was fabricated by Invibio (UK) using an
industrial relevant and scaled method of twin screw
compounding PEEK with a pharmaceutical grade
porogen filler (70 wt% sodium chloride). The
manufacturing process, detailed in patent application
WO/2010/007424, generated pellets of highly filled
compound that were sufficiently versatile to be
subsequently used for molding or for melting and
processing into a stock shape such as a bar or rod
[29]
. For this study, the compound was subsequently
molded to near net ingot shapes that were machined
to finished shape. To remove the filler, the material
was subjected to an extraction with deionized water
at supercritical temperatures and pressures and by
using alternative high-temperature extraction
methods such as microwave. With supercritical water
extraction, the water is heated to approximately
180
C under 7
e
10 bar of pressure. The higher
temperature allowed the ions to have an increased
solubility in the solvent and the PEEK polymer
matrix is made more mobile through being held
above its glass transition temperature (
T
g
(b)
143
C).
This particular process allows water to enter more
readily through the PEEK polymer and dissolve the
filler. This allows the water solvent to penetrate
through to the sodium chloride whether the filler is
openly accessible
ΒΌ
Figure 12.2
Showing the difference in the surface pre-
sented to the tissue for machined solid PEEK and
porous PEEK.
through interconnectivity or
