Verification of Lubricious Coatings on Medical Devices
I have hinted much on this blog about ways to go about verifying hydrophilic coatings on medical devices. When I speak of "verification", I am talking about the first "V" in "V&V", i.e. the Verification step in Design Controls that may or may not precede a Validation step, depending on the device. As you may quickly realize, speaking about specific verification steps for any device is a huge task, because verification is nothing more and nothing less than confirming that design inputs = design outputs. Does your device prototype meet specification? Since every device in the world has different specifications, it is impossible to come up with ways that apply to all devices.
However, for lubricious coatings there are some general themes that pop up which are widely applicable, even though specific verification tests may vary per device.
In all but rare cases, if you are coating a device, you want the coating to stick, at least for a while. You may not care if the coating ultimately resorbs, or you might care. However, in most cases, you would not be satisfied if the coating flaked off and left material behind in the body. Thus, some sort of adhesion test is necessary. For flat surfaces, ASTM D3359-78 may be appropriate. This is known as the "tape test". Modifications to this test would be necessary for curved or irregular surfaces. Adhesion can also be tested with a pinch test indirectly.
If using a lubricious coating, you obviously want it to be slipperier than a device without the coating. Thus, your verification process will require some testing of lubricity against a control, and/or to your spec. Pinch testing is also an option for this, and you can click on the button below to get an article that goes into details on that. There are also other tests you can rig up, such as an anatomical model for sliding your coated article through it and measuring force or ease of insertion/withdrawal. The pinch test paper mentions four major kinds of lubricity tests. However, the limitation of most lubricity tests is that they do no correlate to clinical use. Despite this limitation, they can still be a good basis for making an engineering decision.
Most sterilization testing involves bioburden analysis, i.e. making sure that you get a 4-log kill (or whatever your spec states). The other thing to think about is how the sterilization method will affect your coating, so you will need to do coating performance tests after sterilization, as well as before (if that is still relevant to you). Performance testing can be the same type of tests mentioned above for Adhesion and Lubricity.
Once you have a favored set of tests and output variables, such as lubricity via pinch testing, or adhesion via tape test, you can keep using those tests over and over for environmental effects, such as Aging. Does your coating remain lubricious after aging? This can be accelerated aging, but make sure the conditions of acceleration do not adversely affect the coating. For example, if your coating is sensitive to water vapor, do not run an aging study at 100% Relative Humidity, because it will not correlate with real time.
Transportation and Handling
How will people treat your lubricious coating on the road, in the doc's office, during shipping, at the patients' houses? The first step is to do a shipping study. Send the coated article somewhere and test its performance. Make sure it stands up. From there, you can gradually get more nasty by subjecting it to harsher environments, mimicing the trunk of a sales rep's car on a hot day in Puerto Rico, for instance. Again, you will be using your preferred performance output variables.
Differences in testing will be dictated by what your device actually is. Is it an IOL Cartridge? Is it a Jamshidi needle? Is it a coronary guidewire?
Also, this list is by far not exhaustive. I have not even mentioned things like biocompatibility and particulate testing. I wonder if I should make several parts to this post?