Deposition of boron doped DLC films on TiNb and characterization of their mechanical properties and blood compatibility
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-01-16 |
| Journal | Science and Technology of Advanced Materials |
| Authors | Shahira Liza, Junko Hieda, Hiroki Akasaka, Naoto Ohtake, Yusuke Tsutsumi |
| Institutions | University of Malaya, Tokyo Institute of Technology |
| Citations | 30 |
| Analysis | Full AI Review Included |
6CCVD Technical Documentation: Boron-Doped Carbon Coatings for Biomedical Devices
Section titled â6CCVD Technical Documentation: Boron-Doped Carbon Coatings for Biomedical DevicesâResearch Paper Analysis: Deposition of boron doped DLC films on TiNb and characterization of their mechanical properties and blood compatibility
Executive Summary
Section titled âExecutive SummaryâThe following points summarize the key findings and value proposition of the research into boron-doped diamond-like carbon (B-DLC) for blood-contacting biomedical devices:
- Target Application: B-DLC films were developed and tested as a surface coating for TiNb alloys, a promising material for medical stents and artificial valves, focusing on mitigating thromboembolism risk.
- Key Material Achievement: Optimal hemocompatibilityâcharacterized by the lowest platelet adhesion and activationâwas achieved using B-DLC with a controlled Boron-to-Carbon (B/C) ratio of 0.03 (equivalent to 2.6 at.% B).
- Tribological Improvement: Boron doping significantly reduced friction. The optimal B-DLC film (B/C = 0.03) achieved a steady-state friction coefficient of $\mu = 0.1$, a 50% reduction compared to the undoped DLC film ($\mu = 0.2$).
- Mechanical Tuning: Boron incorporation successfully reduced the high internal stress inherent in DLC coatings by lowering the hardness (from 13.6 GPa to 10.9 GPa) and Youngâs Modulus (from 92.5 GPa to 58.8 GPa) at the optimal B/C ratio.
- Surface Wetting Control: High hydrophilicity (low water contact angle) was correlated with improved blood compatibility, driven primarily by increased polar and hydrogen-bonding components of the surface energy.
- Methodology: Films were deposited using Pulsed Plasma Chemical Vapor Deposition (PPCVD), controlling the B/C ratio by adjusting the flow rate ratio of trimethylboron (TMB) to acetylene (C2H2).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimal B/C Ratio (Biocompatibility) | 0.03 | Ratio | Achieved the least platelet activation and adhesion risk. |
| Optimal Boron Atomic Content | 2.6 | at.% | Corresponds to B/C = 0.03 ratio. |
| Undoped DLC Hardness | 13.6 | GPa | Baseline measurement (Nanoindentation). |
| B-DLC (B/C=0.03) Hardness | 10.9 | GPa | Reduced stiffness beneficial for stress relief. |
| Undoped DLC Youngâs Modulus | 92.5 | GPa | Baseline measurement. |
| B-DLC (B/C=0.03) Youngâs Modulus | 58.8 | GPa | Highly decreased stiffness. |
| Friction Coefficient ($\mu$) - Optimal | 0.1 | Unitless | B-DLC (B/C = 0.03) during steady-state dry sliding. |
| Deposition Technique | PPCVD | N/A | Pulsed Plasma Chemical Vapor Deposition. |
| Pulsed Plasma Frequency | 14 | kHz | Monopolar pulsed power frequency. |
| Substrate Used (Biomedical) | TiNb (23 at.% Nb) | Alloy | Alternative material for stents due to low cytotoxicity. |
| Typical Film Thickness | 1.0 - 1.8 | ”m | Thickness range used for mechanical testing. |
| Smoothest Surface Roughness (Ra) | < 0.2 | nm | Achieved by B-DLC (B/C = 0.03). |
Key Methodologies
Section titled âKey MethodologiesâThe B-DLC films were fabricated and characterized using advanced thin-film deposition and biomedical testing protocols:
- Substrate Preparation:
- TiNb (23 at.% Nb) and Ti Grade 2 alloy discs (10 mm diameter, 1.5 mm thickness) were ground, water-milled to a mirror surface, and ultrasonically cleaned (distilled water, methanol, acetone).
- PPCVD Deposition Setup:
- A turbomolecular pump evacuated the chamber to a background pressure < 4.0 x 10-7 Pa.
- Plasma was generated using a 14 kHz monopolar pulsed power source.
- Film Recipe Control:
- Pre-Cleaning: Substrates were sputter-cleaned with Argon (Ar) plasma at 30 cm3 min-1 and a -3 kV bias for 2 hours.
- DLC Deposition: Acetylene (C2H2) was used as the carbon source (20 cm3 min-1).
- Boron Doping: Trimethylboron (B(CH3)3, TMB) was used as the boron precursor. The B/C ratio was controlled by varying the TMB flow rate (3, 10, 15 cm3 min-1) while maintaining C2H2 flow (20 cm3 min-1).
- Adhesion Layer: A Tetramethylsilane (TMS) interlayer was used on TiNb substrates to enhance adhesion and prevent delamination.
- Mechanical and Tribological Testing:
- Nanoindentation was performed (load 0.8 mN) to determine Hardness and Youngâs Modulus, ensuring maximum indentation depth was < 10% of coating thickness.
- Ball-on-disk tribological tests were conducted using a steel ball counter face (6 mm diameter, 1 N normal load, 0.209 m s-1 sliding speed) under dry ambient conditions for 100,000 cycles.
- In Vitro Blood Compatibility Test:
- Samples were incubated in Platelet-Rich Plasma (PRP) adjusted to 1 x 105 ”l-1 platelet density for 5, 10, and 15 minutes at 37 °C.
- Platelet adhesion and activation were quantified by measuring the percentage platelet coverage area using computer-aided ImageJ analysis of optical microscopy and SEM images.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research confirms that precisely controlled boron doping in carbon-based coatings is a critical pathway for developing high-performance biomedical and tribological solutions. 6CCVD, as an expert in MPCVD diamond fabrication, is uniquely positioned to supply the advanced materials necessary to replicate and exceed these research findings.
Applicable Materials
Section titled âApplicable MaterialsâThe ideal material solution for replicating or extending this research leverages the fundamental benefits of diamondâs structure combined with controlled boron doping:
- Boron-Doped Diamond (BDD): The direct analog and superior successor to B-DLC, 6CCVDâs BDD material offers controllable conductivity, exceptional chemical inertness, and intrinsic biocompatibility. Researchers can specify BDD films (SCD or PCD) to target the optimal 2.6 at.% B concentration found in this study, ensuring stable, conductive, and highly hemocompatible surfaces for advanced biosensors or implants.
- Optical Grade Single Crystal Diamond (SCD): For applications demanding the absolute lowest friction and wear (critical in mechanical heart valves or micro-robotics), 6CCVD provides SCD films (0.1 ”m to 500 ”m thick) with superior structural quality and surface finishing.
- Ultra-Polished Surfaces: The study highlighted the importance of low surface roughness (Ra < 1 nm) for biocompatibility. 6CCVD offers state-of-the-art polishing capabilities, achieving Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring surfaces meet the rigorous nanoscale requirements for medical devices.
Customization Potential
Section titled âCustomization PotentialâThe experimental use of custom alloy substrates (TiNb) and thin film layers demands flexibility that 6CCVD is built to provide:
- Custom Dimensions and Substrate Integration: While the study used 10 mm discs, 6CCVD can supply MPCVD diamond wafers (PCD up to 125 mm) or custom-cut plates suitable for direct coating or integration onto customer-supplied substrates, including medical alloys. We offer precision laser cutting for complex geometries required in stents or micro-mechanisms.
- Precision Thickness Control: 6CCVD guarantees tight tolerance control for BDD film thickness (from 0.1 ”m up to 500 ”m), allowing engineers to precisely tune mechanical properties, such as controlling residual stress and modulus, as demonstrated to be critical in this paper.
- Advanced Metalization: While the paper used a TMS interlayer, many biomedical devices require conductive pads or complex interconnects. 6CCVD offers internal metalization services (Au, Pt, Pd, Ti, W, Cu) for BDD and SCD, enabling the fabrication of fully functional bio-electrodes and sensors directly on the diamond film.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs commitment extends beyond material supply. Our in-house PhD engineering team is available to support complex research and development projects:
- Material Selection for Biomedical Coatings: 6CCVDâs experts can assist in optimizing the Boron doping recipe in our MPCVD BDD films to specifically target the desirable mechanical (low modulus) and surface energy characteristics identified in this research for similar biomedical, tribological, and implant projects.
- Tribological Interface Design: Our team provides consultation on designing highly durable, low-friction diamond coatings for use in boundary lubricated or dry sliding environments, drawing on extensive experience in extreme operating conditions.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Diamond-like carbon (DLC) material is used in blood contacting devices as the surface coating material because of the antithrombogenicity behavior which helps to inhibit platelet adhesion and activation. In this study, DLC films were doped with boron during pulsed plasma chemical vapor deposition (CVD) to improve the blood compatibility. The ratio of boron to carbon (B/C) was varied from 0 to 0.4 in the film by adjusting the flow rate of trimethylboron and acetylene. Tribological tests indicated that boron doping with a low B/C ratio of 0.03 is beneficial for reducing friction (Ό = 0.1), lowering hardness and slightly increasing wear rate compared to undoped DLC films. The B/C ratio in the film of 0.03 and 0.4 exhibited highly hydrophilic surface owing to their high wettability and high surface energy. An <i>in vitro</i> platelet adhesion experiment was conducted to compare the blood compatibility of TiNb substrates before and after coating with undoped and boron doped DLC. Films with highly hydrophilic surface enhanced the blood compatibility of TiNb, and the best results were obtained for DLC with the B/C ratio of 0.03. Boron doped DLC films are promising surface coatings for blood contacting devices.