Verification of Lubricious Coatings on Medical Devices

Posted by Josh Simon on Wed, Mar 21, 2012 @ 10:43

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. 

 

Adhesion

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.

Lubricity

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.

 

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Sterilization

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.

Aging

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?

 

Tags: medical device, medical device coating, lubricity, medical device development, medical device coatings, hydrophilic coatings, lubricious coatings, lubricity testing

5 Critical Questions to Ask About Pinch Testing Data

Posted by Josh Simon on Thu, Jan 26, 2012 @ 04:54

Pinch testing data can be used to make or break a lubricious hydrophilic coating.  It can also be used to lie.  When you see any graph depicting lubricity and durability for a coating, it is time to stop and take a breath before absorbing the data.  Ask yourself about the nature of the test used to get the information. 

pinch tester

Some hydrophilic coatings can be painted as amazingly slick and durable, but when put to a rigorous test, not so much.  Others shine and duke it out among the top.  I will soon be publishing a white paper demonstrating how differences in testing methods can make big variations in friction outcomes.  Below is a preview table of the 5 questions to ask yourself whenever you view friction data for a lubricious coating.

Question

Issue

For what Load does the current data display?

Tests using lower loads can give the appearance of a durable coating.

What is the pinch pad material used in the test?

Soft pinch pad materials are easier on the coating, and can portray favorable results.

What is the substrate material used in the test?

Soft substrates are easier on the coating, and can portray favorable results.

Was the test conducted under saline, pure water, or dry?

For medical devices, performance in saline is most clinically relevant, but dry or pure water performance can be used to artificially portray a coating in a positive or negative light, compared to actual in vivo performance.

How many cycles are displayed in the test data?

Low cycle numbers may not show a difference between two coatings, or be used to sidestep durability issues.

Tags: lubricious coating, medical device coating, pinch tester, medical device coatings, lubricious coatings, pinch testing, lubricity testing