Biocompatibility of Al2O3-Doped Diamond-like Carbon Laparoscope Coatings

At a Glance

Metadata	Details
Publication Date	2025-04-07
Journal	Coatings
Authors	Russell L. Leonard, Amj Bull, Fan Xue, Christopher P. Haycook, Sharon K. Gray
Institutions	University of Tennessee at Knoxville, Vanderbilt University
Citations	2
Analysis	Full AI Review Included

Expert Analysis: Al₂O₃-Doped Diamond-like Carbon Laparoscope Coatings

Executive Summary

This study successfully synthesized and characterized aluminum oxide (Al₂O₃)-doped Diamond-like Carbon (DLC) thin films via Pulsed Laser Deposition (PLD) for use as transparent, antifogging coatings on laparoscopic lenses.

Core Value Proposition: The doped DLC films exhibit high transparency, excellent biocompatibility, and initial hydrophilicity, addressing the critical issue of lens fogging during minimally invasive surgery.
Optimal Composition: Films synthesized with 17.5% Al₂O₃ laser pulses demonstrated the best combination of desirable properties (transparency, lowest contact angle, highest surface energy, and acceptable wear depth).
Optical Performance: Doped films achieved exceptional transparency (up to 98% transmission across the visible spectrum), a significant improvement over the undoped DLC film.
Biocompatibility: The coatings showed excellent acute biocompatibility (NIH/3T3 cells) and hemocompatibility, with no measurable Adenosine Triphosphate (ATP) release from blood platelets, suggesting a low risk of coagulation-related adverse events.
Hydrophilicity Challenge: While plasma cleaning reduced the water contact angle to 8°, this effect was short-lived, diminishing rapidly within 48 hours, indicating that further surface optimization is required for durable antifogging performance.
Mechanical Trade-off: Doping initially increased wear depth compared to undoped DLC (7 nm), but higher doping levels (25%) improved wear resistance (10 nm), suggesting a content-dependent optimization is necessary.

Technical Specifications

Parameter	Value	Unit	Context
Deposition Method	Pulsed Laser Deposition (PLD)	N/A	Synthesis technique using ArF excimer laser.
Laser Wavelength	193	nm	ArF excimer laser.
Pulse Duration	5	ns	FWHM.
Laser Fluence	4.1	J/cm²	Focused spot size 0.06 mm².
Pulse Repetition Rate	100	Hz	Constant rate during deposition.
Deposition Pressure	< 4.0 x 10^-4	Pa	High vacuum chamber pressure.
Film Thickness Range	29.6 - 45.0	nm	Measured via white-light interferometry.
Maximum Transparency	Up to 98	%	Achieved by doped films (17.5% Al₂O₃).
Lowest Contact Angle (As-made)	32	°	Achieved at 17.5% Al₂O₃ doping.
Lowest Contact Angle (Plasma-cleaned)	8	°	Measured within 60 min of argon plasma treatment.
Maximum Total Surface Energy	70	mN/m	Achieved at 17.5% Al₂O₃ doping (polar component dominant).
Undoped Wear Depth	7	nm	Measured using Hysitron TI 980 Triboindenter (100 µN load).
25% Doped Wear Depth	10	nm	Wear resistance approaching undoped film performance.
Biostability Test Duration	40	weeks	Immersion in Simulated Body Fluid (SBF) at 37 °C.
Hemocompatibility (ATP Release)	< 0.01	nmol	Below instrument sensitivity limit (0.4% of total available ATP).
RMS Roughness (17.5% Doped)	10.0	nm	Significant increase compared to substrate (0.37 nm).
G-Peak Position (10% Doped)	1562 ± 1	cm^-1	Indicates decreased sp³ content relative to undoped film (1555 cm^-1).

Key Methodologies

The films were synthesized using Pulsed Laser Deposition (PLD) and characterized using standard material science and biomedical protocols.

Substrate Preparation:
- UV-grade Corning 7980 fused silica substrates (500 µm thick) were used.
- Cleaning involved sequential ultrasonic cleaning in acetone and methanol (10 min each), followed by a 2 min immersion in 1:1 piranha solution (H₂SO₄:H₂O₂).
Pulsed Laser Deposition (PLD):
- A multicomponent target (semiconductor-grade graphite and Al₂O₃) was used.
- Total laser pulses were held constant at 400,000.
- Dopant concentration was controlled by varying the percentage of pulses applied to the Al₂O₃ target (0% to 25%).
- Deposition was performed at a 66 mm target-to-substrate distance under high vacuum (< 4.0 x 10^-4 Pa).
Physical and Optical Characterization:
- Thickness: Measured using white-light interferometry (Keyence VK-X3050).
- Transparency: Transmission spectra recorded (400-800 nm) using spectrophotometry. Attenuation coefficients calculated via Beer-Lambert law.
- Structure: Raman spectroscopy (532 nm laser) was used to analyze D and G peaks and estimate sp³/sp² bonding ratios.
- Morphology/Roughness: Atomic Force Microscopy (AFM) in contact mode (2 µm x 2 µm scan area) was used to determine RMS roughness.
- Adhesion: Assessed via ASTM D3359 cross-hatch tape testing.
Surface Energy and Hydrophilicity:
- Contact Angle: Measured using ultrapure water and benzyl alcohol via the Krüss DSA20E Easy Drop Standard.
- Surface Energy: Calculated using the Fowkes method, separating dispersive and polar components.
- Plasma Cleaning: Argon plasma treatment (Harrick Plasma PDC-32G) for 3 min at medium RF power was used to enhance hydrophilicity temporarily.
Biomedical Testing:
- Biostability: Samples were immersed in Simulated Body Fluid (SBF) at 37 °C for 40 weeks, monitored for delamination.
- Cell Viability (Acute Toxicity): NIH/3T3 cells were incubated with the films for 24 h. Viability was quantified using modified CellTiter-Glo assays (luminescence).
- Hemocompatibility: Platelet activation was assessed by quantifying ATP release from platelet-rich plasma (PRP) after 60 min of contact.
Wear Testing:
- Wear depth was measured using a Hysitron TI 980 Triboindenter with a diamond Berkovich tip.
- An automated load function scanned a 15 µm x 15 µm area at a 100 µN load.

Commercial Applications

The development of transparent, durable, and biocompatible antifogging coatings has direct relevance across several high-value industries, particularly in medical devices and optics.

Biomedical Devices:
- Laparoscopes/Endoscopes: Primary application, eliminating intraoperative fogging and contamination, reducing surgical time and infection risk.
- Bronchoscopes, Cystoscopes, Laryngoscopes: Improving visual clarity in various minimally invasive procedures.
- Dental Mirrors: Maintaining clear vision during dental procedures.
- Protective Coatings: DLC’s inherent hardness and bio-inertness make it suitable for protective coatings on joint replacements and other implantable devices (Al₂O₃ is already researched for this purpose).
Optical and Consumer Products:
- Eyewear: Antifogging and scratch-resistant coatings for glasses and safety goggles.
- Camera Lenses: Preventing fogging in high-humidity or rapidly changing temperature environments.
- Transparent Electronics: Applications requiring transparent, wear-resistant, and chemically stable films.
Advanced Materials (Related to DLC/Alumina):
- High-Hardness Coatings: Utilizing the improved wear properties seen at higher doping levels for industrial tools and components.
- Dielectric Films: Leveraging the favorable dielectric properties of Al₂O₃ for microelectronics and optical windows.

View Original Abstract

Laparoscopic lens fogging and contamination pose significant challenges, leading to a reduced surgical field of view. Intraoperative cleaning to address these issues extends the surgical duration and elevates the risk of surgical site infections. The authors propose that a hydrophilic diamond-like carbon (DLC) coating would effectively mitigate fogging and fouling, thereby eliminating the requirement for intraoperative cleaning, while the scratch-resistant nature of DLC would provide additional benefits. The present study investigates the efficacy of aluminum oxide (Al2O3) as a dopant in diamond-like carbon (DLC) films for antifogging applications. The authors hypothesized that adding oxygen to the DLC matrix would increase surface energy by increased hydrogen bonding, resulting in a highly hydrophilic coating. Varying dopant concentrations were tested to observe their effects on hydrophilicity, transparency, biocompatibility, and wear properties. The doped films displayed a notable improvement in transparency throughout the visible spectrum. Plasma-cleaned samples demonstrated a substantial reduction in contact angles, achieving values less than 8°. The biocompatibility of these films was analyzed with CellTiter-Glo assays; the films demonstrated statistically similar levels of cell viability when compared to the control media. The absence of adenosine triphosphate released by blood platelets in contact with the DLC coatings suggests in vivo hemocompatibility. These films, characterized by high transparency, biocompatibility, and biostability, could be valuable for biomedical applications necessitating transparent coatings.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings15040437

References

2014 - National Trends in the Adoption of Laparoscopic Cholecystectomy over 7 Years in the United States and Impact of Laparoscopic Approaches Stratified by Age
2023 - Minimally Invasive Surgery in the United States, 2022: Understanding Its Value Using New Datasets [Crossref]
1997 - A brief history of endoscopy, laparoscopy, and laparoscopic surgery [Crossref]
2016 - Comparative analysis of techniques to prevent laparoscopic fogging [Crossref]
2003 - Does using a laparoscopic approach to cholecystectomy decrease the risk of surgical site infection? [Crossref]
2022 - Laparoscopic Lens Defogging: A Review of Methods to Maintain a Clear Operating Field [Crossref]
2017 - Visual Occlusion During Minimally Invasive Surgery: A Contemporary Review of Methods to Reduce Laparoscopic and Robotic Lens Fogging and Other Sources of Optical Loss [Crossref]
2022 - Effective cleaning of endoscopic lenses to achieve visual clarity for minimally invasive abdominopelvic surgery: A systematic review [Crossref]
2022 - Nano-Ceramic Coating: A Novel Idea to Reduce Laparoscope Lens Fogging—Experimental Study [Crossref]
2023 - Biocompatibility of antifogging SiO-doped Diamond-Like carbon laparoscope coatings [Crossref]