BIOCOMPATIBLE CARBON NANOLAYERS FOR COATING LENSES
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-06-30 |
| Journal | LĂ©kaĆ a technika - Clinician and Technology |
| Authors | Petr PĂsaĆĂk |
| Institutions | Czech Technical University in Prague |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Value Proposition: Diamond-Like Carbon (DLC) layers fabricated via Pulsed Laser Deposition (PLD) offer superior wear resistance and tribological performance for spectacle lens coatings compared to standard commercial multi-layer treatments.
- Wear Resistance Achievement: The optimized DLC-3 layer achieved the lowest final friction coefficient (0.099) among all tested lenses, attributed to the formation of a protective graphitic slip layer during friction testing.
- Mechanical Durability: The DLC-3 coating remained visibly undamaged after tribological testing (1 N load, 10 m path), demonstrating high hardness sufficient to cause damage to the Chromium steel testing ball.
- Optical Trade-off: While mechanically superior, the DLC coating resulted in a reduction of average visible transmittance (400-750 nm) by approximately 15% compared to typical commercial lenses (90 ± 5%).
- Process Optimization: Transmittance was found to be directly dependent on the laser energy density used during PLD; higher energy density resulted in higher transmittance in the visible spectrum.
- Biocompatibility: The study reinforces previous findings that DLC is a suitable, biocompatible material for ophthalmic optics, including spectacle, contact, and intraocular lenses.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | CR39 | - | Spectacle lenses base material |
| Deposition Method | Pulsed Laser Deposition (PLD) | - | Used KrF Excimer Laser |
| Laser Wavelength (λ) | 248 | nm | KrF Excimer Laser |
| Pulse Duration (Ï) | 20 | ns | Laser pulse time |
| Target Material | High purity graphite | - | Source for DLC film |
| Base Vacuum | 5 x 10-4 | Pa | Coating system pressure |
| Ambient Gas | Argon (Ar) | - | Deposition atmosphere |
| Ambient Pressure | 0.25 | Pa | Deposition pressure |
| Optimized Energy Density (DLC-3) | 10 | J·cm-2 | Parameter yielding best mechanical results |
| Approximate Thickness (DLC-3) | 40 | nm | Optimized layer thickness |
| Commercial Lens Transmittance (Avg) | 90 ± 5 | % | Average T (400 nm to 750 nm) |
| DLC Coated Lens Transmittance (Avg) | ~75 | % | Average T (400 nm to 750 nm) |
| Lowest Final Friction Coefficient (DLC-3) | 0.099 | - | Measured at end of 10 m path (1 N load) |
| Highest UV Cut-off Wavelength | 422.0 | nm | Observed for UV+420 BlueCut 1.5 SHMC lens |
| Tribological Test Load | 1 | N | Maximum load used for wear testing |
| Tribological Test Length | 10 | m | Total path length for Pin-on-Disk test |
| Testing Ball Material | Chromium steel (Ac 100 Cr6) | - | 6 mm diameter ball |
Key Methodologies
Section titled âKey Methodologiesâ- Substrate Cleaning: CR39 spectacle lenses were prepared by ultrasonic cleaning in ethanol, followed by air drying.
- PLD Setup: DLC films were deposited using a KrF excimer laser (λ = 248 nm, Ï = 20 ns) focused onto a high purity graphite target. The lens substrate was positioned 45 mm from the target.
- Deposition Environment: Films were grown at room temperature under an argon ambient pressure of 0.25 Pa, following evacuation to a base vacuum of 5 x 10-4 Pa.
- Parameter Variation: Four distinct DLC films (DLC-1 to DLC-4) were created by varying the laser energy density (4 to 12 J·cm-2) and the number of pulses (1,000 to 8,000), resulting in thicknesses ranging from 40 nm to 150 nm.
- Optical Analysis: Transmittance spectra were acquired using a UV-VIS spectrophotometer (Shimadzu UV-2600) covering the range of 200 nm to 1100 nm to determine average transmittance and short-wavelength cut-off.
- Tribological Testing: Wear resistance and friction coefficient were measured using a Pin-on-Disk Tribometer (TRB3 - Anton Paar) in dry conditions.
- Mechanical Test Parameters: A 6 mm diameter Chromium steel ball was used, moving at 5.03 cm·s-1 over a total length of 10 m, under applied loads of 0.25 N and 1 N.
- Damage Assessment: Post-test damage to both the lens surface and the testing ball was visually evaluated using a microscope at 100x magnification.
Commercial Applications
Section titled âCommercial Applicationsâ- Ophthalmic Lens Protection: Direct application of DLC as a highly durable, scratch-resistant coating for spectacle lenses, replacing or augmenting existing Hard Multi-Coatings (HMC) and Super Hydrophobic Multi-Coatings (SHMC).
- Advanced Contact and Intraocular Lenses (IOLs): Utilizing DLCâs high biocompatibility and non-degrading nature to coat IOLs and contact lenses, minimizing pathological changes and antigen reactions post-operation.
- UV/Blue Light Filtering Optics: Development of DLC layers with optimized sp3 content or doping to control the short-wavelength cut-off, providing superior protection against UV and high-energy blue light (analogous to the UV+420 BlueCut lenses).
- Low-Friction Biomedical Surfaces: Application of DLC coatings to medical instruments or implants requiring stable, low coefficients of friction and high wear resistance, benefiting from the self-lubricating graphitic slip layer formation.
- Antimicrobial Coatings: Integration of doped DLC (e.g., silver dopation mentioned) to create antibacterial surfaces for lenses and implants, protecting against calcification and microbial adhesion.
View Original Abstract
As previous studies indicated, diamond-like carbon (DLC) layers exhibit outstanding biocompatible properties. Additionally, due to high hardness and high transmittance in infrared and visible parts of spectra it is possible to utilize for application ophthalmic optics. DLC layers are suitable for coating of spectacle lenses, contact lenses and even intraocular lenses. In this paper, we focused on transmittance and wear resistance of different commercially available spectacle lenses with surface modification and lenses with DLC layer. The lens transmittance depends on base material and its surface modification. Commercially manufactured lenses exhibit usual transmittance of 90±5%, while transmittance of DLC coated lenses was lower by 15%. Wear resistance is strongly dependent on surface modification. The results of DLC layers were similar or better than commercially manufactured lenses with surface modification.