Ultra-hydrophilic Diamond-like Carbon Coating on an Inner Surface of a Small-diameter Long Tube with an Amino Group by AC High-voltage Plasma Discharge
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-06-15 |
| Journal | Journal of Photopolymer Science and Technology |
| Authors | Yuichi Imai, Hiroyuki Fukue, Tatsuyuki Nakatani, Shinsuke Kunitsugu, Noriaki Kuwada |
| Institutions | Okayama University of Science, Industrial Technology Center of Okayama Prefecture |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study details the development of an ultra-hydrophilic, positively charged Diamond-like Carbon (DLC) coating applied to the inner surface of small-diameter long medical tubes using a dry, AC high-voltage plasma chemical vapor deposition (CVD) process.
- Core Achievement: Successful formation of a dense, uniform DLC film on the inner wall of polyurethane (PU) sheets encapsulated in silicone tubes.
- Surface Modification: Subsequent NH3 plasma treatment introduced amino groups (-NH2) to the DLC surface, fundamentally altering its properties.
- Ultra-Hydrophilicity: The treatment achieved a pure water contact angle as low as 12.2° (and an average of 15.6° ± 4.3° for treatments > 10 s), confirming super-hydrophilicity.
- Charge Control: The NH3 plasma treatment resulted in a strong positive zeta potential (up to 20.7 mV), contrasting sharply with the negative potential typically achieved by oxygen plasma treatment.
- Biomimetic Potential: The ability to arbitrarily control both hydrophilicity and surface potential (positive via NH3, negative via O2) allows for tailoring surface properties to inhibit thrombosis and biofilm adhesion in various medical applications.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| DLC Deposition Voltage (AC) | 5 | kV | AC High-voltage Plasma CVD |
| Offset Voltage | 2 | kV | AC High-voltage Plasma CVD |
| Frequency | 10 | kHz | Plasma Discharge |
| Deposition Gas | CH4 | N/A | DLC Film Formation |
| Gas Flow Rate (CH4/NH3) | 96.2 | sccm | Constant flow rate for deposition and treatment |
| Deposition Time (DLC) | 20 | min | DLC Film Formation |
| Working Pressure | 36.2 | Pa | Plasma CVD Process |
| Untreated PU Contact Angle | 87.3 | ° | Baseline hydrophobicity |
| Treated DLC Contact Angle | 12.2 | ° | Minimum achieved after 20 s NH3 plasma |
| Untreated PU Zeta Potential | -3.9 ± 0.5 | mV | Baseline surface charge (Negative) |
| Treated DLC Zeta Potential | 20.7 ± 4.5 | mV | Maximum achieved after 5 s NH3 plasma (Positive) |
| Surface Composition (C:N:O) | 76:15:9 | at% | Semi-quantitative XPS analysis (20 s NH3) |
| Dominant Surface Bonds | C-C, C-H | N/A | ~75% of total bonds (DLC component) |
| Polar Bonds Introduced | Amide (-NHCO-), Amino (-NH2) | N/A | Responsible for hydrophilicity and positive charge |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a dry coating technique involving AC high-voltage burst plasma deposition followed by NH3 plasma treatment to modify the DLC surface properties.
-
Experimental Setup:
- An AC high-voltage plasma CVD system was used, consisting of a voltage generator (IWATSU SG-4105) and an amplifier (NF Corporation HVA4321).
- The voltage from the generator was amplified 1000 times to achieve the required high voltage for plasma generation.
-
Sample Preparation:
- Polyurethane (PU) sheets (25 mm x 7 mm x 0.15 mm) were selected as the base material, mimicking medical tube material.
- The PU sheets were encapsulated inside silicone tubes to simulate the inner surface geometry of a small-diameter long tube.
-
DLC Deposition (CVD):
- DLC thin films were formed on the inner surface of the encapsulated PU sheets using CH4 gas plasma.
- Deposition parameters were fixed (5 kV AC, 10 kHz frequency, 96.2 sccm CH4 flow, 20 min duration). No Argon (Ar) bombardment was performed prior to deposition.
-
NH3 Plasma Treatment:
- Following DLC deposition, the surface was treated using NH3 plasma discharge.
- The NH3 gas flow rate was maintained at 96.2 sccm.
- Plasma discharge duration was varied systematically: 5 s, 10 s, 20 s, 30 s, and 60 s.
-
Surface Characterization:
- Contact Angle: Measured using 1.5 ”L of distilled water (Dropmaster 500). Results confirmed ultra-hydrophilicity (contact angle < 20°).
- Zeta Potential: Measured the electrical mobility of the fixed surface using a zeta-potential-measuring device (ELSZ-1000) and analyzed via the Mori/Okamoto formula. Polystyrene latex particles (500 nm) were used as monitors.
- Chemical Bonding State (XPS): X-ray photoelectron spectroscopy (ULVAC PHI500 VersaProbe III) was used to analyze the surface chemistry, confirming the introduction of N-containing functional groups (amino and amide).
Commercial Applications
Section titled âCommercial ApplicationsâThis technology provides a robust, dry coating solution for enhancing the biocompatibility and performance of critical medical devices, particularly those requiring controlled surface charge and extreme hydrophilicity to mitigate biological fouling.
| Industry/Product | Application Detail | Technical Benefit |
|---|---|---|
| Cardiovascular Medicine | Coronary artery stents, Artificial vascular grafts | Reduced risk of stenosis and occlusion by thrombus formation; improved hemocompatibility. |
| Urology | Ureteral stents, Indwelling catheters | Inhibition of biofilm adhesion (anti-fouling) due to ultra-hydrophilic surface and positive charge. |
| General Surgery/ICU | Small-diameter long medical tubing, High-calorie blood transfusion catheters | Uniform, dense dry coating prevents issues associated with wet coatings (delamination, non-uniformity, thick walls). |
| Biomaterials Engineering | Customized implants and devices | Arbitrary control of surface potential (positive via NH3 plasma, negative via O2 plasma) to optimize interaction with specific biological environments. |
View Original Abstract
Medical tubing includes artificial vascular grafts and catheters, each has a different purpose of use, but they both need to hydrophilize the lumen surface. Diamond-like carbon (DLC) is a dry coating technology, and its surface can be easily modified with hydrophilic functional groups. AC high-voltage plasma chemical vapor deposition has been developed for DLC deposition on the inner surface of small-diameter long tubes. In addition, oxygen plasma treatment of the DLC-deposited surface has been performed to enhance the hydrophilicity of the tube lumen and to inhibit biofilm adhesion in urinary catheters. However, the oxygen plasma treatment using silicone as the base material had only a slight inhibitory effect on biofilm adhesion, with a water contact angle of 104.4° for the DLC film and 90.6° for the DLC film, compared with oxygen plasma treatment, with an average value of 119.5° for the blank film. Recently, a new ammonia plasma treatment method has been developed, and an ultra-hydrophilic water contact angle of nearly 10° has been achieved with polyurethan (PU) as the base material. Furthermore, the zeta potential was found to be negative in oxygen plasma treatment and positive in ammonia plasma treatment, indicating that the hydrophilicity, and surface potential can be arbitrarily controlled by combining these plasmas, thereby achieving surface properties suitable for various applications.