Joe Anderson, product and promotional marketing manager at Harland, explores the role of surface preparation in the application of hydrophilic and hydrophobic coatings.
Harland
Surface preparation is a fundamental step in the manufacturing of medical devices, particularly when applying hydrophilic and hydrophobic coatings. These coatings significantly enhance the lubricity, stiction, trackability and the medical device’s ability to navigate tortuous paths. However, their effectiveness heavily relies on the quality of surface preparation. The challenge lies in addressing contaminants which can compromise a coatings ability to create a covalent bond, coating adherence and introduce defects. This article explores the importance of thorough surface preparation, and the methods involved in ensuring a clean substrate for optimal coating performance.
The impact of contaminants on coating performance
Medical devices often encounter various contaminants during manufacturing, handling, and transportation. These contaminants can interfere with the application and efficacy of hydrophilic and hydrophobic coatings. Common contaminants include:
- Grease and oils: Residual oils and greases from manufacturing processes or handling can create barriers between the device surface and the coating. This results in poor adhesion and voids, leading to peeling or flaking of the coating.
- Foreign Material (FM) and particulate: FM and particulate can settle on the device surface, causing irregularities that affect the uniformity of the coating layer. This can compromise the coating’s effectiveness and the device’s overall performance.
- Silicon oil and mould release agents: Particularly problematic in devices produced via injection moulding, silicon oil residues can create a slippery surface that hinders proper coating adhesion. This residue can be challenging to remove and, if not adequately cleaned, can lead to significant defects, voids and contamination in the batch.
- Leaching and cross-contamination: Contaminants that are not removed can leach into the chemistry pot used for coating additional devices, causing contamination across multiple devices in the lot and potentially affecting their performance and safety.
Surface preparation: key steps and methods
To ensure that coatings adhere effectively, and the devices are safe, meticulous surface preparation is essential. This involves several critical steps:
1. Cleaning the surface
a. Cleaning agents and solvents:
Solvents: Different solvents are suited to different contaminants. For example, hydrocarbons like heptane are effective in dissolving oils and greases, including silicon oil. Isopropyl alcohol (IPA) and ethanol, while less aggressive, are excellent for general residues and dust removal. Each solvent’s choice should align with the contaminant being targeted to ensure thorough cleaning.
Cleaning agents: Specialised cleaning agents may be used for persistent residues. These agents are often formulated to address specific types of contaminants and can be more effective than general solvents.
b. Cleaning techniques:
- Ultrasonic and turbulent flow cleaning: For thorough cleaning, ultrasonic cleaning can be employed. This method uses high-frequency sound waves in a solvent bath to remove contaminants from the device surface. It is particularly useful for cleaning intricate or complex geometries where manual cleaning might be insufficient. Additionally, turbulent flow cleaning can be employed to enhance the removal of contaminants, ensuring that even the most challenging surface areas are thoroughly cleaned.
- Manual cleaning: In cases where ultrasonic cleaning is not feasible, manual cleaning with appropriate solvents and brushes or cloths can be used. Care must be taken to ensure that the cleaning process does not introduce new contaminants or damage the device.
2. Selecting the right wipes
- Purpose: Lint-free polyester wipes often used for their strength and low particulate shedding are ideal for the final cleaning stage to ensure that no particles or fibres remain on the device surface. Traditional wipes may shed fibres, which can introduce additional contaminants and affect coating adhesion.
- Application: Wipe the surface gently to avoid scratching or damaging it. Use the wipes in a single direction to prevent redistributing contaminants. Multiple wipes may be needed to ensure a thoroughly clean surface.
3. Cleaning methodology
Ensure that every part of the device, including those with intricate and complex geometry, is thoroughly cleaned. Achieving this often involves employing multiple wipes and using them in various directions to cover every surface area comprehensively. Additionally, rotating the device while wiping can be an effective strategy to ensure that all surfaces, including hard-to-reach areas, are cleaned adequately. This meticulous approach helps to ensure that no residual contaminants are left behind, which is crucial for achieving optimal coating adhesion and device performance.
Ensuring effective coating application
Thorough surface preparation is essential for ensuring that substrate modification materials such as hydrophilic and hydrophobic coatings adhere effectively and deliver the desired performance. Proper preparation eliminates contaminants that could interfere with coating adhesion and functionality. To verify the effectiveness of the coating process, a representative percentage of the lot is often subjected to additional testing. This includes staining to evaluate the coating’s uniformity, visual inspection to detect any defects, and friction testing to ensure that the coating performs as intended. These steps help confirm that the coatings adhere properly and that the devices meet performance standards before they are deemed suitable for use.
Conclusion
Surface preparation is a critical and multifaceted step in the manufacturing of medical devices, especially when applying hydrophilic and hydrophobic coatings. Thorough cleaning, appropriate solvent selection, and the use of lint-free wipes are essential to ensure that the device surface is free from contaminants such as grease, foreign material, and silicon oil residues. By meticulously preparing the surface, manufacturers can achieve effective coating adhesion, enhance device performance, and ensure the safety and reliability of medical devices. This process not only improves the functionality and durability of the coatings but also mitigates the risk of cross-contamination and defects, ultimately benefiting both the manufacturer and the end-users.