Biomedical Engineering Reference
In-Depth Information
Table 2.2
Contemporary and Historical Nomenclature for Medical Grades of PEEK
Property
General-Purpose Grade
Medium-Flow Grade
Easy-Flow Grade
Historical Victrex
nomenclature
450
381
150
Invibio nomenclature
OPTIMA LT1
OPTIMA LT2
OPTIMA LT3
Melt flow index
3.4
4.5
36.4
Molecular weight (
M
n
)
115,000
108,000
83,000
LT1 Standard grade
LT2 Optimized grade for melt strength and melt
viscosity
d
recommended for tubing
LT3 High-flow grade for injection molding thin-
walled parts
tribological testing (see Chapter 13). However,
PEK has not been commercialized for
implant
manufacture.
PEKK resins are produced by OPM (Enfield, CT)
and have been marketed under the OXPEKK trade
name since the company was founded in 2000. Both
medical grades and implantable grades of OXPEKK
are available. OPM was acquired by Arkema
(Colombes Cedex, France) in 2009.
Sustainability of biomaterial supply has been
a concern with PAEK resins in the 1980s and 1990s.
With the exception of PEEK-OPTIMA, which can
trace its origins back to 1998, many industrial PAEK
materials have been withdrawn from the market,
either out of concern for liability, patent infringe-
ment, and concerns about viability of a niche market
or due to technical difficulties (
Table 2.1
). Nonethe-
less, to the extent that biomaterials history is not fully
reflected in the literature,
Table 2.1
provides some
guidance as to the current availability of PAEK
materials for industrial and implant use.
The most commonly used grade for PEEK is
OPTIMA LT1, which has flow properties similar to
450. Victrex grades are also designated as PF (fine
powder), P (powder), or G (granulated). Powder
grades are recommended for compounding, whereas
granulated resin is preferred for injection molding.
Although powder grades are produced for industrial
applications, there are no powder grades commer-
cially available for implantable grade PEEK-
OPTIMA, only granules. PEEK-OPTIMA undergoes
a melt filtration step as a quality control measure to
ensure cleanliness and biocompatibility. Following
melt filtration, the polymer is granulated into cylin-
drical pellets (
Fig. 2.2
). Thus, to obtain powder from
PEEK-OPTIMA, it is necessary to mill or grind the
granules to obtain the desired particle size.
Recently, two new resin manufacturers entered the
medical PEEK market. In 2007, Solvay announced
an implantable grade of PEEK marketed under the
Zeniva trade name. In 2009, Evonik began marketing
an implantable grade of PEEK under the VESTA-
KEEP trade name. However, no reports have been
published describing these resins in scientific studies
or how they are used in long-term implants. Publi-
cation of further details about the performance of
Solvay and Evonik materials is anticipated.
PAEK alternatives to PEEK are available from
Invibio and Oxford Performance Materials (OPM).
PEK has been made available by Invibio in experi-
mental quantities as a candidate biomaterial for
2.4 Quality Systems for Medical
Grade Resin Production
PEEK-OPTIMA
biomaterials are manufactured
under a Quality Management System certified to ISO
9001:2000 and ISO 13485:2003. Only fully approved
raw materials are used at the production stages
together with extensive supervision and checks at key
production stages. The recording of key parameters is
performed at all stages.
PEEK-OPTIMA biomaterials are manufactured on
a campaign basis, thus enabling the employment of
contamination risk reduction procedures. Invibio
embraces Good Manufacturing Practice in relation to
