Amorphous Carbon Coatings for Total Knee Replacements—Part II - Tribological Behavior
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-06-05 |
| Journal | Polymers |
| Authors | Benedict Rothammer, Max Marian, Kevin Neusser, Marcel Bartz, Thomas Böhm |
| Institutions | University Hospital Heidelberg, Heidelberg University |
| Citations | 41 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Amorphous Carbon Coatings for Total Knee Replacements
Section titled “Technical Documentation & Analysis: Amorphous Carbon Coatings for Total Knee Replacements”Executive Summary
Section titled “Executive Summary”This analysis focuses on the tribological performance of amorphous carbon (DLC) coatings applied to Total Knee Arthroplasty (TKA) components, demonstrating the potential of advanced carbon materials in high-wear biomedical applications.
- Core Achievement: DLC coatings significantly reduced Ultra-High Molecular Weight Polyethylene (UHMWPE) wear, achieving reductions up to 77% when paired with coated Ti64 pins and 49% with coated CoCr pins.
- Material Integrity: The coatings exhibited continuous, slow wear without catastrophic failure mechanisms such as delamination or spalling of large particles, which is crucial for minimizing particle-induced aseptic loosening.
- Clinical Relevance: Numerical Elastohydrodynamic Lubrication (EHL) modeling validated that the pin-on-disk test conditions were representative of harsh, mixed lubrication regimes found in TKAs.
- Friction Trade-off: The higher surface roughness (Ra) of the coated specimens led to an increase in the Coefficient of Friction (COF), indicating a need for subsequent polishing steps to optimize performance.
- Future Material Potential: The DLC-coated Ti64 pairing outperformed the uncoated CoCr reference, suggesting that coated Ti64 alloys bear the potential to supplant traditional CoCr as the preferred implant material.
- Methodology: The study employed a rigorous combination of experimental tribological testing (pin-on-disk, 2 x 10⁵ cycles) and advanced characterization (LSM, SEM, Raman spectroscopy, particle analysis).
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the research paper, detailing the mechanical properties of the coatings and the tribological test conditions.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| SCD/PCD Coating Thickness (tc) | 1.0 to 1.4 | µm | a-C:H:W (metals) and a-C:H (UHMWPE) coatings |
| Indentation Hardness (HIT) | 14.4 ± 1.3 to 16.1 ± 1.3 | GPa | Ti64:W and CoCr:W coatings, respectively |
| Indentation Modulus (EIT) | 148 to 153 | GPa | CoCr:W and Ti64:W coatings, respectively |
| Hardness/Modulus Ratio (HIT/EIT) | 0.097 to 0.106 | Dimensionless | CoCr:W and Ti64:W coatings (indicates compliance) |
| Critical Normal Load (Lc3) | 21 to 22 | N | Adhesion strength for CoCr:W and Ti64:W coatings |
| Average Pin Wear Reduction (Ti64:W) | 77 | % | Compared to uncoated Ti64 reference |
| Average Pin Wear Reduction (CoCr:W) | 49 | % | Compared to uncoated CoCr reference |
| Max. Total Contact Pressure (Pt,max) | 4.59 to 4.61 | MPa | Numerical EHL simulation results |
| Solid Asperity Load Share (Fa/F) | 81.3 to 81.6 | % | Coated pairings (UHMWPE:H paired with CoCr:W/Ti64:W) |
| Sliding Distance | 2 x 10⁵ | cycles | Total test duration |
| Test Temperature | 37 ± 0.2 | °C | Environmental chamber control |
| Lubricant Protein Content | 20 ± 1 | g/L | Diluted Bovine Calf Serum (BS) substitute SF |
Key Methodologies
Section titled “Key Methodologies”The experimental and numerical approach combined advanced coating deposition with rigorous tribological analysis and simulation.
- Coating Deposition: Amorphous carbon coatings were applied using Physical Vapor Deposition (PVD).
- a-C:H:W (Tungsten-doped) was deposited on metallic pins (CoCr, Ti64).
- a-C:H (pure hydrogenated) was deposited directly onto the polymeric UHMWPE disks.
- Adhesion Architecture: A thin adhesive layer of Chromium (Cr) and an intermediate layer of Tungsten Carbide (WC) were utilized to ensure high coating-substrate adhesion on the metal pins.
- Tribological Setup: Pin-on-disk tribometer operating in rotational sliding mode.
- Normal Force: 10 N.
- Sliding Velocity: 0.1 m/s.
- Total Cycles: 2 x 10⁵ cycles (2 x 10⁴ m sliding distance).
- Lubrication Environment: Artificial Synovial Fluid (SF) based on diluted Bovine Calf Serum (BCS) was used, maintained at 37 °C, simulating harsh, low-viscosity conditions typical of inflammatory joints.
- Wear Quantification: Volumetric wear rates (WV) were calculated using Light Microscopy (LM) and Laser Scanning Microscopy (LSM) measurements of wear track cross-sections, avoiding gravimetric errors due to fluid absorption by UHMWPE.
- Microstructural Analysis: Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB) cross-sectioning, and Raman Spectroscopy were used to analyze coating integrity, graphitization, and wear mechanisms.
- Particle Analysis: Wear particles were characterized according to ASTM F1877-16, measuring Equivalent Circle Diameter (ECD), Aspect Ratio (AR), and Roundness (R).
- Numerical Modeling: A 3D Elastohydrodynamic Lubrication (EHL) model based on the full-system Finite Element Method (FEM) was used to calculate pressure distribution, film height, and solid asperity contact pressure, confirming mixed lubrication conditions.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The research highlights the critical role of high-performance carbon coatings and precise material engineering in extending the service life of biomedical implants. 6CCVD’s expertise in MPCVD diamond materials offers superior alternatives and customization capabilities to advance this research.
Applicable Materials
Section titled “Applicable Materials”The amorphous carbon (DLC) coatings studied provide excellent tribological performance. However, for applications demanding the highest possible hardness, chemical inertness, and thermal stability, 6CCVD’s MPCVD diamond materials offer a significant performance leap.
| Research Requirement | 6CCVD Material Solution | Key Advantage |
|---|---|---|
| High Wear Resistance (DLC) | Optical Grade Polycrystalline Diamond (PCD) | Vickers Hardness > 80 GPa (significantly harder than DLC), ensuring minimal wear in boundary lubrication. |
| Extreme Durability | High Purity Single Crystal Diamond (SCD) | Ideal for high-stress pin components, offering ultimate material purity and defect control. |
| Electrochemical Sensing (Future Work) | Boron-Doped Diamond (BDD) | Provides metallic conductivity and superior electrochemical stability for potential in-situ monitoring of implant health. |
Customization Potential
Section titled “Customization Potential”The success of the DLC coatings relied on precise thickness control (1.0-1.4 µm) and specialized intermediate layers (Cr/WC). 6CCVD excels in providing the necessary material customization for complex biomedical architectures.
- Custom Dimensions and Thickness: 6CCVD offers custom SCD and PCD plates/wafers up to 125 mm in diameter, with precise thickness control from 0.1 µm up to 500 µm (SCD/PCD) or 10 mm (Substrates). This capability allows for the fabrication of large-area components required for TKA simulators.
- Advanced Metalization Services: The paper utilized Cr and W intermediate layers for adhesion. 6CCVD provides in-house metalization capabilities including:
- Adhesion Layers: Ti, W (Tungsten), Cr.
- Contact Layers: Au, Pt, Pd, Cu.
- We can replicate or optimize the multi-layer adhesion stacks necessary to bond diamond films securely to metallic substrates like CoCr and Ti64.
- Precision Polishing: The research identified that high surface roughness (Ra) of the coated specimens increased friction. 6CCVD directly addresses this limitation:
- We guarantee ultra-low surface roughness (Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD), ensuring optimal tribological performance and minimizing friction in mixed lubrication regimes.
Engineering Support
Section titled “Engineering Support”The transition from DLC to MPCVD diamond requires expert knowledge in material science and tribology.
6CCVD’s in-house PhD engineering team specializes in material selection and optimization for demanding applications, including biotribology and high-wear systems. We can assist researchers in transitioning from DLC to superior MPCVD diamond materials for similar Total Knee Arthroplasty (TKA) projects, ensuring optimal coating compliance, adhesion, and surface finish for reduced wear and friction.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Diamond-like carbon coatings may decrease implant wear, therefore, they are helping to reduce aseptic loosening and increase service life of total knee arthroplasties (TKAs). This two-part study addresses the development of such coatings for ultrahigh molecular weight polyethylene (UHMWPE) tibial inlays as well as cobalt-chromium-molybdenum (CoCr) and titanium (Ti64) alloy femoral components. While the deposition of a pure (a-C:H) and tungsten-doped hydrogen-containing amorphous carbon coating (a-C:H:W) as well as the detailed characterization of mechanical and adhesion properties were the subject of Part I, the tribological behavior is studied in Part II. Pin-on-disk tests are performed under artificial synovial fluid lubrication. Numerical elastohydrodynamic lubrication modeling is used to show the representability of contact conditions for TKAs and to assess the influence of coatings on lubrication conditions. The wear behavior is characterized by means of light and laser scanning microscopy, Raman spectroscopy, scanning electron microscopy and particle analyses. Although the coating leads to an increase in friction due to the considerably higher roughness, especially the UHMWPE wear is significantly reduced up to a factor of 49% (CoCr) and 77% (Ti64). Thereby, the coating shows continuous wear and no sudden failure or spallation of larger wear particles. This demonstrated the great potential of amorphous carbon coatings for knee replacements.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
Section titled “References”- 2018 - Knee replacement [Crossref]
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- 2014 - Ceramic femoral component fracture in total knee arthroplasty: An analysis using fractography, fourier-transform infrared microscopy, contact radiography and histology [Crossref]
- 1999 - A review of metallic, ceramic and surface-treated metals used for bearing surfaces in human joint replacements [Crossref]
- 2007 - Characterisation of wear particles produced by metal on metal and ceramic on metal hip prostheses under standard and microseparation simulation [Crossref]
- 2019 - Cross-Linked Versus Conventional Polyethylene for Long-Term Clinical Outcomes After Total Hip Arthroplasty: A Systematic Review and Meta-Analysis