Biomimetic Diamond-like Carbon Coating on a Lumen of Small-diameter Long-sized Tube Modified Surface Uniformly with Carboxyl Group using Oxygen Plasma
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-12-16 |
| Journal | Journal of Photopolymer Science and Technology |
| Authors | Yuichi Imai, Hiroyuki Fukue, Tatsuyuki Nakatani, Shinsuke Kunitsugu, Kazuhiro Kanda |
| Institutions | Okayama University of Science, Japan Agency for Medical Research and Development |
| Citations | 4 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study details the development and characterization of a biomimetic Diamond-like Carbon (DLC) coating applied to the inner lumen of small-diameter, long silicone tubes (catheters) using a novel AC high-voltage burst plasma Chemical Vapor Deposition (CVD) method.
- Core Achievement: Successful deposition of hydrogenated amorphous carbon (a-C:H) DLC film onto the inner wall of silicone tubes (up to 400 mm length, 2 mm inner diameter).
- Biomimetic Functionalization: The DLC surface was modified using AC high-voltage burst oxygen plasma to introduce hydrophilic functional groups, specifically carboxyl (O-C=O) and C-O bonds.
- Surface Potential Control: The functionalized surface achieved a negative zeta potential (minimum -15.9 mV), mimicking biocompatible surfaces and enabling control over protein adsorption characteristics.
- Structural Classification: The deposited film was characterized as a soft, polymer-like a-C:H DLC (Hardness: 0.79 GPa; Reduced Elastic Modulus: 8.51 GPa), necessary for preventing delamination on flexible resin tubes.
- Anti-Biofilm Performance: In vitro evaluation demonstrated that the oxygen-plasma-treated DLC significantly inhibited Pseudomonas aeruginosa adhesion and biofilm formation compared to both uncoated silicone and plain DLC.
- Process Uniformity: Plasma bullet transport was confirmed using an ultra-fast camera, suggesting uniform oxygen plasma surface modification along the long tube lumen.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Film Type | a-C:H DLC | N/A | Hydrogenated amorphous carbon |
| Inner Diameter (Tested) | 2 | mm | Silicone tube lumen |
| Length (Tested) | 400 | mm | Satisfies urethral catheter requirements |
| Aspect Ratio (Achieved) | 750 | N/A | Inner diameter 2 mm, length 1500 mm (glow discharge confirmed) |
| AC Voltage (CVD/Plasma) | 5 | kV | Discharge condition |
| Offset Voltage | 2 | kV | Discharge condition |
| Frequency | 10 | kHz | Discharge condition |
| Pulse Frequency | 10 | pps | Discharge condition |
| Combined Pressure | 39 | Pa | Methane and oxygen gases |
| Hardness (HIT) | 0.79 | GPa | Nanoindentation result |
| Reduced Elastic Modulus (Er) | 8.51 | GPa | Nanoindentation result (Polymer-like carbon) |
| sp3/(sp3+sp2) Ratio | 43.9 | % | Calculated from NEXAFS analysis |
| Hydrogen Content | 35 to 36 | at.% | Determined by ERDA |
| Areal Density | 2100 to 2200 x 1015 | atoms/cm2 | Determined by RBS |
| Minimum Zeta Potential | -15.9 | mV | Achieved after 1 s O2 plasma treatment |
| O-C=O Content Increase | 1.13 to 5.38 | % | Increase after O2 plasma treatment (XPS) |
| C-O Content Increase | 9.04 to 14.40 | % | Increase after O2 plasma treatment (XPS) |
| Optimal O2 Plasma Time | 5 | s | Suggested for maximum anti-biofilm effect |
Key Methodologies
Section titled âKey MethodologiesâThe study utilized a specialized AC high-voltage burst plasma system for both DLC deposition and subsequent surface functionalization, characterized by multiple advanced analytical techniques.
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DLC Deposition:
- Silicone tubes were coated on the inner lumen using AC high-voltage methane plasma-CVD.
- Source gas: Methane (CH4).
- Discharge parameters: 5 kV AC voltage, 2 kV offset voltage, 10 kHz frequency, 10 pps pulse frequency, and 39 Pa combined pressure.
-
Surface Functionalization (Biomimetic Modification):
- The DLC-coated lumen was treated with AC high-voltage burst oxygen plasma.
- Source gas: Oxygen (O2).
- Treatment times varied (1 s, 2 s, 5 s) to optimize the introduction of carboxyl groups (O-C=O) and control zeta potential.
-
Structural and Compositional Analysis:
- NEXAFS (Near-Edge X-ray Absorption Fine Structure): Used to determine the sp3/(sp3+sp2) ratio (43.9%) and confirm the a-C:H structure.
- RBS (Rutherford Backscattering Spectrometry): Used to determine the areal density (2100 to 2200 x 1015 atoms/cm2) and check for impurities.
- ERDA (Elastic Recoil Detection Analysis): Used to determine hydrogen content (35-36 at.%).
- XPS (X-ray Photoelectron Spectroscopy): Used to quantify the existence ratios of C-O and O-C=O bonds, confirming successful carboxyl group introduction.
-
Mechanical and Surface Property Testing:
- Nanoindentation: Measured Hardness (HIT) and Reduced Elastic Modulus (Er) to confirm the soft, flexible nature of the DLC film required for resin tubes.
- Contact Angle Measurement: Evaluated surface hydrophilicity change after plasma treatment (decreased from 119.5° to 90.6°).
- Zeta Potential Measurement: Determined the surface charge, confirming the shift to negative potential (-15.9 mV) due to carboxyl group introduction.
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In Vitro Evaluation:
- A continuous-flow system was used with artificial urine reflux.
- Pseudomonas aeruginosa (GFP-labeled) was used to evaluate anti-bacterial adhesion and anti-biofilm properties.
- Confocal laser-scanning microscopy (LSM780) and Comstat version 2 were used for biomass and biofilm thickness quantification.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology is highly relevant for medical device manufacturing, particularly where long-term indwelling and infection prevention are critical.
- Urology and Catheters:
- Long-term indwelling urinary catheters (Foley catheters).
- Ureteral stents and drainage tubes, where biofilm formation is a major cause of failure and infection.
- Vascular and Circulatory Systems:
- Small-diameter artificial vascular grafts (less than 6 mm inner diameter), where stenosis due to organic matter adhesion is a persistent issue.
- Coronary stents (potential application for functionalized DLC coatings to improve biocompatibility and reduce thrombosis).
- General Medical Tubing:
- Any flexible, small-lumen medical tubing (e.g., feeding tubes, drainage lines) requiring enhanced biocompatibility and resistance to bacterial colonization.
- Biomaterial Engineering:
- Development of surfaces that control protein adsorption characteristics by tuning the surface zeta potential, leading to improved integration with biological environments.
View Original Abstract
Silicone tubing is used in small-diameter long-sized tubes for medical applications, such as urinary catheters. However, bacteria in urine adhere to the catheters, forming colonies and biofilms and resulting in blockages and urinary tract infections. Therefore, we have reported a method of AC high-voltage plasma chemical vapor deposition to prevent bacterial adhesion by depositing diamond-like carbon (DLC) on a lumen of a silicone catheter and smoothing the surface. However, the sp3/sp2 structure of DLC on the lumen surface is unresolved, and biomimetic DLC with a functionalized surface has not been investigated. Therefore, we analyzed a flexible membrane structure that can deform as the resin tube deforms. In addition, we developed a lumen surface-modification method using an AC high-voltage burst oxygen plasma processing to bring the DLC surface closer to the in vivo environment. We succeeded in creating biomimetic DLC and introducing carboxyl groups. Using this technology, the surface functionalization of medical tube materials is biocompatible with various protein-adsorption properties.