DOS BULLETIN - Dansk Ortopædisk Selskab

2010-378_DOS nr. 3 2010 29/09/10 10:08 Side 109
The Wear Effect of Hydrophilic Coatings on Hard
Implants
Sune Lund Sporring, Jes Bruun Lauritzen,
Povl Brøndsted, Kion Norrman
Bispebjerg Hospital; DTU-Risø
Background: A serious limiting factor in implant lifetime is wear. Many
methods, including ceramic, MoM and highly polishable products, contribute
to reducing wear, however other surface treatments are also accessible.
Lubricating films often contribute very low friction in many non- medical
applications, and could therefore possibly reduce the wear in implants.
Purpose: During development of an interpositional intraarticular implant
device, experimentation was done with introducing a water film covalently
bonded directly to the polymeric implant surfaces. This study is concerned
with quantifying the coating and its effect in reducing wear.
Methods: Poly(vinyl pyrolidone) (PVP) was coated uniformly on a
poly(ethylene) implant (as well as simplified discs) in a custom made plasma
coating chamber with 3 electrodes employing 0-600V, and using dried
vinyl pyrrolidone monomer. Several techniques were used to quantify the
PVP coating: TOF-SIMS, XPS, CLSM, Photomicrography, ATR-FTIR and
Pin on disc.
Findings: Using a Pin on disc investigation, results were obtained quantifying
frictional coefficients. The discs were tested at a constant speed of 0,01
m/s and loads corresponding roughly to the normal walking forces in a hip
joint at 37°C ± 1° C. 1) The coefficient of friction was in all cases found to
be in the range of 0.12 to 0.18. 2) No significant difference can be seen
between PVP coated and not- coated discs. This was later verified in a 3D
hip joint test rig at Risø. 3) The coating was removed or compressed due to
wear (supported by the observation that the surface properties changed from
hydrophilic to hydrophobic). 4) The results did not differ when changing
track diameter, loads or sampling frequency (1Hz to 10Hz).
Conclusion: Adding a thin (