The goal of hydrophilic coating testing and validation is to measure durability and performance: how well the given coating reduces friction, how firmly it bonds to the substrate, how evenly it wets, and what it may release into the body.
Hydrophilic coating quality is assessed based on several key features: lubricity, adhesion, antimicrobial properties, biocompatibility, and sterilization compatibility. The goal is to measure durability and performance. Or, simply put, how well the given coating reduces friction, how firmly it bonds to the substrate, how evenly it wets, and what it may release into the body. Nowadays, most medical device coatings are specified in numbers. Each of those numbers has to come from a repeatable standard test, which is why hydrophilic coatings for medical devices cannot be qualified on formulation chemistry alone.
At Hydromer®, Inc. we aim to prove three things before a hydrophilic coated device reaches a patient. The hydrophilic coating should be lubricious enough to protect the tissue it passes through, durable enough to last the full procedure, and clean enough to meet biocompatibility requirements. A gap in any one of them creates risk for the patient, the device maker, and the coatings partner. That said, coating testing methods are well established. Each one answers a different question about how the coating will behave once it is applied to the device.
Key Takeaways
- Validation is measured, not assumed: Friction, adhesion, wettability, particulates, and extractables are each confirmed through a dedicated test, and a good result in one does not substitute for the others.
- Lubricity and durability are judged together: A coating that slides well on the first pass but wears away after a few cycles has not passed performance testing.
- Hydrophilicity has its own measurement: Wettability and friction are related but not the same property, so both are tested separately.
- Particulate and extractables analysis is now expected: Coated devices that contact blood or tissue are increasingly evaluated for what they may shed or leach, not only for how they perform.
5 Essential Tests for Validating Hydrophilic Coatings for Medical Devices
1. Friction Testing
Friction testing measures the force needed to pull a coated device between two wet, clamped pads at a set load. It reports the result as a coefficient of friction (CoF). Repeating the pull on the same sample shows how much lubricity is lost as the coating wears. The CoF remains the first performance number most engineers ask for.
Four more tests cover what friction alone cannot provide.
2. Adhesion Testing
Adhesion testing evaluates how strongly the coating bonds to the substrate. Common methods include the ASTM D3359 tape test, wet rub or abrasion, and dye staining to reveal bare spots.1 A coating that delaminates during handling or inside the vessel fails, regardless of how low its COF reads.
3. Performance Testing
Coating performance testing combines lubricity and durability. This method cycles the coated device through repeated passes and logs the COF each time. The goal of this testing is to confirm the coating still performs at the end of the procedure, not only at the start.
4. Wettability Testing
Measuring hydrophilicity quantifies how readily the coating wets, most often through water contact angle on a goniometer using ASTM D7334. A well-formed hydrophilic coating should sit at the low end of that scale.2 Readings taken along the length of the device show whether coverage is uniform, and a water break test or dye stain exposes gaps that a single reading would miss.3
5. Particulates and Extractables Testing
Particulate and extractables analysis identifies what and how much the coating may shed or leach during use.
Coating separation from intravascular devices draws close regulatory attention, so this analysis is commonly expected for blood-contacting products.4,5
Hydromer®, Inc. Hydrophilic Coatings and Analytical Testing Services
Hydromer® is a leader in hydrophilic medical device coatings. In addition to our full line of coating formulations, we also offer a wide range of coating services. For example, we evaluate lubricity and durability on our own friction testing systems and provide specialized analytical testing as a contract service. These are done under an ISO 13485:2016 certified quality system at an FDA-registered facility. Let us coat your device and put the numbers in front of you before you commit to a coatings partner.
Request a free coated sample and run it through your own protocol, or talk to a coatings engineer about the test conditions, acceptance criteria, and standards that apply to your device.
Editorial & Technical Review Board
To ensure the highest standards of engineering precision and scientific accuracy, this article was reviewed, validated, and approved by:
- Mike Torti, Chief Executive Officer
- Anthony Millan, Senior Technical Product Manager
- Paul McCue, Vice President – International Business Development
FAQs
Hydrophilic coating performance is validated through repeated friction testing on the same sample, with the coefficient of friction logged at every pass. Adhesion checks after sterilization and accelerated aging, along with simulated-use runs through a tortuous path model, complete the validation.
Particulate testing flushes the coated device under simulated use, then sizes and counts the particles released. Extractables testing pulls chemical species out of the coating with solvents. It matters because anything a coating sheds or leaches can reach the patient directly.
Hydrophilicity is measured through water contact angle on a goniometer, where a water droplet is placed on the coated surface, and the angle at its edge is read. Readings taken at several points along the device confirm that the coating covers the surface uniformly.
References
Click to see all (5) industry and peer-reviewed sources.
- ASTM D3359-23, Standard Test Methods for Rating Adhesion by Tape Test, ASTM International, West Conshohocken, PA, 2023. DOI: 10.1520/D3359-23. https://store.astm.org/d3359-23.html
- ASTM D7334-08(2022), Standard Practice for Surface Wettability of Coatings, Substrates and Pigments by Advancing Contact Angle Measurement, ASTM International, West Conshohocken, PA, 2022. DOI: 10.1520/D7334-08R22. https://store.astm.org/d7334-08r22.html
- ASTM F22-21, Standard Test Method for Hydrophobic Surface Films by the Water-Break Test, ASTM International, West Conshohocken, PA, 2021. DOI: 10.1520/F0022-21. https://store.astm.org/f0022-21.html
- AAMI TIR42:2021, Evaluation of particulate associated with vascular medical devices, Association for the Advancement of Medical Instrumentation, Arlington, VA, 2021. DOI: 10.2345/9781570207877. https://array.aami.org/doi/10.2345/9781570207877
- U.S. Food and Drug Administration, Intravascular Catheters, Wires, and Delivery Systems with Lubricious Coatings – Labeling Considerations, Guidance for Industry and Food and Drug Administration Staff, October 10, 2019. https://www.fda.gov/media/113951/download
