2008 Journal of biomedical materials research. Part B, Applied biomaterials Mechanism / Preclinical Inhalation
2008 · Hill — Preliminary tribological evaluation of nanostructured diamond coatings against ultra-high molecular weight polyethylene.
Super-Abstract
This in-vitro materials science study evaluated nanostructured diamond (NSD) coatings on titanium alloy as a potential counterface for polyethylene in joint replacement implants. Hydrogen-rich and helium-rich feedgas mixtures were used in the deposition process. Wear factors were comparable to cobalt-chromium alloy, suggesting NSD could be a viable alternative implant material. (Journal of Biomedical Materials Research B, 2008.)
Commentary
This is a biomaterials engineering study about wear-resistant coatings for orthopaedic joint implants. The connection to H₂ is purely technical: hydrogen gas was used as one of the feedgas components in the plasma chemical vapor deposition (CVD) process to manufacture the diamond coatings (H-NSD = hydrogen-rich nanostructured diamond). This is a manufacturing process gas, not a therapeutic application of H₂. The study does not investigate any biological effects of hydrogen. Its presence in an H₂ database is a false positive due to the use of hydrogen in the industrial coating deposition process.
Key quotes
- „Nanostructured Diamond (NSD) coatings were deposited onto Ti6Al4V by microwave plasma-assisted chemical vapor deposition, with both hydrogen-rich (H-NSD) and helium-rich (He-NSD) feedgas mixtures.“ — H₂ here is a manufacturing process gas — not therapeutic
- „No significant differences in wear factors were found between polyethylene on H-NSD, He-NSD, and CoCr, despite higher roughness and friction coefficients for the He-NSD and H-NSD coatings, compared with CoCr.“ — the main tribological finding: NSD wear performance comparable to cobalt-chromium
- „NSD-coated Ti6Al4V produced wear factors comparable to CoCr in the present pin-on-disk tests, a promising step towards its use in joint replacement bearing applications.“ — conclusion: NSD is a viable candidate material for joint replacement
Our assessment
This paper has no relevance to therapeutic molecular hydrogen (H₂). Hydrogen gas appears only as a component of the industrial CVD process used to fabricate the diamond coatings. The study is solid orthopaedic biomaterials engineering. Its inclusion in an H₂ therapy database is a false positive due to process-chemistry keyword overlap.
Study design
- Type: in-vitro materials science study (tribological pin-on-disk wear testing) · Model: Ti6Al4V coated with NSD; polyethylene pins; serum lubrication at body temperature · H₂ connection: none therapeutic (H₂ = CVD feedgas for coating deposition only)
- Result: H-NSD and He-NSD wear factors comparable to CoCr; higher roughness/friction for NSD vs. CoCr; surface becomes more hydrophilic after wear; NSD considered promising for joint replacement bearing applications
Abstract
BACKGROUND: Some loss of joint prostheses has been attributed to osteolytic loosening associated with debris from wear of polyethylene articulating against metal alloys. Reduced polyethylene wear has been reported with ceramics serving as an alternative counterface. METHODS: Nanostructured Diamond (NSD) coatings were deposited onto Ti6Al4V by microwave plasma-assisted chemical vapor deposition, with both hydrogen-rich (H-NSD) and helium-rich (He-NSD) feedgas mixtures. Pin-on-disk wear tests of polyethylene against NSD and CoCr were performed in serum lubrication at body temperature. Scanning electron microscopy was used to examine surface morphology, and nanoindentation was used to determine hardness and modulus of the polyethylene wear surfaces. Raman spectroscopy, surface roughness, and wettability analyses of the NSD coatings were performed. RESULTS: Raman spectroscopy confirmed sp(2) and sp(3) bonded carbon in the NSD coatings. No significant differences in wear factors were found between polyethylene on H-NSD, He-NSD, and CoCr, despite higher roughness and friction coefficients for the He-NSD and H-NSD coatings, compared with CoCr. Contact angles for the diamond coatings were reduced following the wear tests, indicating that these surfaces became more hydrophilic. Numerous small protuberances were observed on pins articulated against CoCr, and a single, large protuberance was observed in polyethylene-on-NSD. These features were conjectured to be reconsolidated polyethylene particles. Nanoindentation modulus and hardness of the worn polyethylene surfaces were lower for polyethylene-on-diamond than for polyethylene-on-CoCr. CONCLUSIONS: As a counterface to polyethylene, NSD-coated Ti6Al4V produced wear factors comparable to CoCr in the present pin-on-disk tests, a promising step towards its use in joint replacement bearing applications.
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