Biomedical Engineering Reference
In-Depth Information
originated in the metal coating and then propagated
into the substrate, decreasing specimens' fatigue
limit. On the other hand, the carbon fibers have
a toughening effect, strongly hindering crack
propagation even in Ti-coated samples.
In conclusion, coatings can be successfully
associated with PEEK substrate if a proper
conservative design is used by considering working
section reduction, elongation decrease, lowering of
fatigue limit, and device strains in exercise. CFR-
PEEK showed a more tolerant behavior when
coated.
This chapter has summarized the performance and
limitations of coating technologies for PEEK
medical devices, so that implant designers can select
the appropriate coating and substrate combination for
a specific application. In vivo tests as well as
preliminary clinical feedback thus far show prom-
ising results for pioneers currently in the market with
coated PEEK devices.
References
[1] B. Christianson, Pioneering CFR-PEEK for
spinal cages, in: Proceedings, MD&M confer-
ence, Minneapolis, Minnesota, USA, October
12
e
14, 2010.
[2] S. Capps, PEEK cages and spacers in cervical
spine fusion applications: review of published
literature, Spinal News Int. Sept. 4 (2007).
[3] Q.B. Bao, M. Songer, K. Pimenta, D. Werner,
A. Reyes-Sanchez, M. Balsano, et al., NUBAC
intradiscal arthroplasty: preclinical studies and
preliminary safety and efficacy evaluations,
SAS J. 1 (1) (2007) 36
e
45.
[4] J.N. Devine, Developing PEEK polymer as
a bearing material for implants, MDDI Online
(May 1, 2006).
[5] H. Austin, M. Harper, J. Medley, PEEK-on-
PEEK for application in cervical disc arthro-
plasty? in: Proceedings, 8th World Biomaterials
Congress, Amsterdam, The Netherlands, May
28
e
June 1, 2008.
[6] M. Hawkins, Design and development of the
epoch stem, in: Proceedings, MD&M confer-
ence, Minneapolis, Minnesota, USA, October
12
e
14, 2010.
[7] N. Pace, M. Marinelli, S. Spurio, Technical and
histologic analysis of a retrieved carbon fiber-
d
PEEK composite alumina bearing liner
28 months after implantation, J. Arthroplasty 23
(2008) 151.
[8] J. Nevelos, Design of PEEK orthopaedic bear-
ings, in: Proceedings, MD&M conference, Min-
neapolis, Minnesota, USA, October 12
e
14, 2010.
[9] J.N. Devine, S.C.Scholes, A. Unsworth,
Tribology of a pitch carbon fiber PEEK against
CoCrMo unicondylar knee bearing, in: Proceed-
ings, Society for Biomaterials Annual Meeting,
San Antonio, Texas, USA, April 22
e
25, 2009.
[10] T.M. Grupp, S. Utzschneider, C. Schroder,
J. Schwiesan, B. Fritz, A. Maas, et al., Bio-
tribology of alternative bearing materials for
9.8 Summary and Conclusions
Surface functionalization of medical devices made
of PEEK or CFR-PEEK is an essential requirement
when a direct osteointegration between implants and
host tissues is desired. Plasma spray coating was
investigated as one potentially successful method for
accomplishing this target. Among several available
plasma spray technologies, VPS and air plasma
spraying (APS) were shown to be suitable for osteo-
conductive materials apposition, although preserving
substrate chemical
e
physical characteristics.
Titanium and hydroxyapatite are the most
frequently applied materials for this purpose. For
implant applications, Ti or HA coatings must succeed
in reaching quantitative performances like controlled
thickness and roughness, specific composition and
porosity, adhesion and shear strength, fatigue endur-
ance, abrasion resistance, and so on. Limits for coat-
ings performance are given in ISO and ASTM
standards as well as through FDA guidance if applied
onto metallic substrates. However, with selected
plasma spray process tuning and controlled analyses,
such limits can also be successfully reachedwith PEEK
substrates.
The Eurocoating experience was successful in
reaching high adhesion values for HA and Ti coatings
on several substrates made of PEEK or CFR-PEEK.
Static mechanical characterization performed on
coated samples confirmed that bulk strength is unaf-
fected by coatings application. The fatigue limit at 1
million cycles for CFR-PEEK was unaffected as well.
On the other hand, ductility and fatigue strength for
neat PEEK are reduced after coating. Different failure
behaviors of coatings are involved during fatigue
cycling, depending on coating nature (HA or Ti),
substrate (PEEK or CFR-PEEK), and strain values.
