Lubricity Testing - Manipulation of Data for a Smoother Outcome

Posted by Josh Simon on Thu, Jul 05, 2012 @ 04:27

I've been locked in my office all day today working on the slides for this upcoming webinar.  You can registor for it by clicking this link:

 

 Coating Pinch Test Webinar

 

Depending on how you test a hydrophilic coating, you will get different outcomes, for the same coating, and some may be "good" and others not.  Moreover, companies that sell hydrophilic coating frequently "massage" the data, usually by leaving out some particulars, to make their coatings seem more lubricious or durable than they really are.

What I aim to do here is not directly attack printed data, but rather educate the public on the proper questions to ask about data, so they can think critically about it themselves.  I will go over several different types of  lubricity and durability tests, as well as their pro's and con's, and then focus on a particularly common coating test called a Pinch Test.  From there, I will talk about how you can get different results from that test depending on how you run it, and what things you should look out for when trying to make "apples to apples" comparisons between lubricious coatings.

The slides should be informative and I at least try a little to make them entertaining as well, so come on by!

Tags: lubricious coating, Hydrophilic Coating, penton webinar, pinch tester, pinch test, hydrophilic coatings, lubricious coatings, Webinar, pinch testing

Pinch Testing White Paper Released

Posted by Josh Simon on Fri, Feb 24, 2012 @ 03:39

As promised, and not long after my last message, I present to you our newest white paper on Pinch Testing.  In its pages, you will come to understand what kinds of parameters govern the pinch test, with regard to hydrophilic coatings.

This paper is an attempt on my part to educate engineers in the field about how to choose a coating based on pinch test data.  For a few years now, I have encountered pinch test data from various companies that portray hydrophilic coatings in a durable and lubricious light.  The problem I saw with some of that data is that it was misleading.  In some instances, it did not give the conditions of the test.  Heck, it sometimes seemed like the authors of the data did not even know there were any test conditions in some cases.  They merely touted it as if it were sliced bread, but better.

That makes it rather difficult to tell the good coatings from the bad.  They are all more or less lubricous, but whether or not they can stand up to abrasion is not honestly portrayed in all cases.  It is my hope that this article would shed some light on that.

 

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Tags: Hydrophilic Coating, pinch tester, white paper, medical device development, pinch testing

Coatings odds and ends - From pinch tests to trade shows

Posted by Josh Simon on Thu, Feb 23, 2012 @ 01:46

There has been a flurry of activity this year that I am working to keep up with. 

Quite soon, I will be releasing an entire white paper based on my earlier blog article here, 5 Critical Questions to Ask About Pinch Testing. Do not worry about missing the release because you will see an announcement here, plus a press release, most likely.  From either of those sources you will be able to download the article.

We also just got back this week from the MDM West show in Anaheim, CA. With regard to hydrophilic coatings and related subjects, there was a lot of activity there.  Although I must note that Bayer's hydrophilic coating was conspicuously absent from their booth.  Maybe they finally read my blog articles on Hydrophilic Coating Market Size? There were also a few nice talks on plasma treatment of surfaces before coating, and another talk on cardiovascular-based applications by Dr. Ron Sahatjian of Medi-Solve.  To be honest, I could not attend either talk due to the traffic at my booth, and the schedule of meetings I kept that week.  If anyone wants to remark on them, feel free.

This is a little shot of the "Biocoat crew" from the show.

Biocoat Hydrophilic Coatings

Left to Right:  Dhruv Patel, Peg Beavers, Keith Edwards, Josh Simon

Tags: pinch tester, medical device development, hydrophilic coatings, MDM West, hydrophilic coating market, hydrophilic coatings blog, pinch testing, plasma treatment

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

Lubricious Coatings: Pinch Test Primer

Posted by Josh Simon on Tue, Aug 16, 2011 @ 02:30

Lubricious coatings for medical devices come from various companies, chemistries, and calibres.  Differentiating the "men from the boys" can be difficult when it comes to coatings, however.  I do go into some detail in this in my white paper on hydrophilic coatings, but here I would like to expand on one method for determining lubricity and durability: pinch testing.

Conceptually, pinch testing is exactly what it sounds like.  A coated rod, wire, or tube is literally pinched between two surfaces inside a gripper, and then a motorized unit pulls and pushes the coated item through the gripper.  The motorized unit could be a type of mechanical tester, such as an Instron, which keeps track of the force and displacement during the test.  A few cycles will yield results on coefficient of friction for the lubricious coating, and a few more cycles will determine durability.

Sounds simple, right?

Determining if a coating is durable and lubricious, in favor of, or despite all claims about the coating, requires testing on a machine such as this, yet results from different machines are almost incomparable to one another.  Here are the factors that come into play:

  • Pinch Force - What force is the gripper applying to the coated object?  Many competitors in this field will put an almost non-existent pinch force on their coatings and then show that the coatings remain lubricious over many cycles of testing.  It makes pretty graphs, but the coating is still not durable, per se.
  • Pad Material - The gripper pads are made from some material.  What material is that?  Material matters.  A soft material like silicone gives a much easier test, than say, a hard plastic.  A common trick in this industry is to run a pinch test with a silicone pad and show durability out to tens of cycles,when in actuality, if that pad was switched for something harder, like polyethylene, the coating would fail within a few cycles.
  • Pad Shape - Pad shape determines contact area.  If the gripper pads are rectangular, a large area will be contacted on the surface of the test object.  The pinch force is therefore spread out over a wider area. Again, this makes for an easier test, compared with a shape that gives a line contact area.

Granted, not all hydrophilic coatings would need to withstand forces like this.  It depends on the application.  Moreover, pinch testing (and other methods of characterizing lubricity and durability) has not been correlated to clinical function.  Rather, it is a basis for making an engineering decision on a coating. No one really knows how many cycles on a pinch tester equates to how many passes in and out of the vasculature during a surgery, for example.  Something still needs to be the basis of a decision during the design phase. Plus, which coating do you want on that neurovascular catheter?  The one that fails in 20 cycles or the one that fails in 100?

However, understanding this data is still important.  A lot of marketing material from lubricious coating companies purports great things, when in reality, the tests are customized to make the coating look good.  The best thing to do is to get a bunch of samples of coatings from a bunch of coating companies and put them ALL through the same test.  A head-to-head comparison is the way to go.

 

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Tags: lubricious coating, pinch tester, lubricious coatings, pinch testing