Hydrophilic Coatings Particulate

As promised to one reader, I am putting a little bit more information here on particulates and particulate testing with regards to hydrophilic coatings.

The first thing I want to do is point you to some great information on general theory and the regulatory status of particulates for medical devices.  There is an excellent article by Susan Reynolds and Ryan Lunceford on the basics of particulate testing.  It talks about the prevalent use of USP 788, as I have done in my previous article on medical device particulates here, including some specifics on the differences between laser counting versus microscopic counting of particles.

The article is a few years old, and at that time, the AAMI was not yet finished writing its report on setting medical device particulate limits.  However, now that report is out, and you can find it here.  Personally, I found it a little vague.  It does not give any sort of concrete limits to follow, and is not any sort of draft guidance.  It is good for figuring out how to think about this when going about your own particulate tests, however.

One item touched on by both the AAMI report and the article is composition.  Specifically for hydrophilic coatings and/or lubricious coatings, these particles have characteristic identities.  Like anything else, a major consituent of particulate could be clean room dust, which originates from human skin or clothing, or other particles tracked in from the outside.  However, after abrasion, it can also be due to coating wear particulate.  In fact, one method of testing durability for a hydrophilic coating is to run it through a tortuous path test and then measure the amount of particulate in the path after multiple cycles.  For increasing number of cycles, you can track the increase in particle count.

Again, this is just an idea and not a standard.  There are no suggested limits for a test like this right now.  Everything in this field is at this point "unregulated", and we are all concerned about what the FDA will eventually do to throw a wrench in the innovation in the name of hypersensitivity. 

 

Biocoat Releases Three New Hydrophilic Coatings

Biocoat, Inc., maker of lubricious HYDAK® hydrophilic coatings introduced three new hydrophilic coatings for medical devices to its classic lineup. "HydroSleek2", the new successor to the original HydroSleek lubricious coating, with improved processing and biocompatibility. "The HydroSleek Kit" is another variation on the HydroSleek coating, which allows the product to be stored and transported under a wider array of conditions. Third, the "Hydak® T-040 Kit" is a remake of another classic, Hydak® L-110, also allowing for wider availability to Asian and European markets.

All of these coatings are based on high molecular weight Hyaluronic Acid (HA). This technology has applications among a range of fields including ophthalmology, urology, cardiology, endoscopy, and neurovascular. HydroSleek coatings have overcome the trade off between lubricity and durability seen in cross-linked coatings. Additionally, HydroSleek involves a heat-cure process so both ID and OD may be coated without the concerns surrounding UV curing.

These new products will act as Biocoat's front line solution to medical device firms seeking to reduce surface friction for their devices. Each of these new products possesses the same beneficial characteristics of the family of HYDAK® coatings, plus advancements device manufacturers have requested.

For further comments or questions, email Dr. Josh Simon, Senior Product Manager at jsimon at biocoat dot com.

Practical Challenges for Medical Device Coatings

I still plan to talk a little more about particulates as promised, but I wanted to take a break and point out an article I have out in Medical Design Technology.

The title is Practical Challenges for Medical Device Coatings, and as you may guess, it spells out some things to think about when looking at coating data. This is not just for hydrophilic coatings, but for many other kinds as well.

The full issue of Medical Design Technology is found here.  To get to my article, turn to page 24, or click on the link to the article in the Table of Contents.

I dislike these digital edition magazines becasue they hide all their content behind a single URL and that does not let you link directly to an article, nor does it let anyone get search engine credit for it.

Lubricious Coating Biocompatibility - Verification

At the request of a fan of this site, I am devoting a post to Verification of biocompatibility of lubricious hydrophilic coatings.  Next article, I might talk a little bit about particulate and give an update on that, so stay tuned.

The first thing you need to do when looking into biocompatibility for a medical device, coated or not, is think about your application and categorize it on this chart:

For most hydrophilic coatings, the application requires a Limited exposure (<24 hrs) in a Circulating Blood environment.  Therefore the chart reveals that you will need to do cytotoxicity, sensitization, irritation, systemic toxicity, in some limited circumstances genotoxicity, and finally, haemocompatibility.  If your application is different, look it up on the chart and see which tests you need.

First, make sure that your devices are tested exactly as they are delivered clinically, i.e. coated and sterilized.  You do not want to find out that your coating is fine but when sterilized it suddenly becomes cytotoxic, for example. 

The other thing you really should do is look at each bicompatibility test and understand how it works.  Do not just send out your samples with a checklist and rely on the results without thinking. 

For example, the cytotoxicity test can be complicated, and that's one of the simplest ones.  There are different variations on the MEM Elution test.  In the first phase, the test article is submerged in a fluid to extract substances into it.  This extraction can be done at different temperatures and for different lengths of time.  Obviously a longer extraction time at a higher temperature is the toughest test.  If you think you can pass the toughest test, go for it.  If you can't, then you just need to go for the test that is acceptable to the Regulatory body you work with.  In the second phase of the MEM Elution test, the extracted solution is exposed to cells, usually L929 fibroblasts.  This extraction can be done for different lengths of time too, from 24 hrs to 72 hrs.  The longer the exposure, the tougher the test.  Extractions can also be done with polar and non-polar solvents, and the tests can be run by weight or by surface area which has a big effect on the results.  Usually for hydrophilic coatings, you want to run the test by weight.

There are also vendor differences for these tests.  For example, they use different amounts of serum in their media, and some add antibiotics to the solution and some do not. Ask your testing vendor to see the protocols.  I am not able to conclude whether or not these protocol differences influence results but I can definitely tell you that different vendors give different results.  In my experience, Toxikon is really easy to pass, almost too easy, whereas Nelson Laboratories is tougher, but very reliable.  NAMSA is somewhere in between, and Apptec is probably on the tougher side.  Again, this is just my experience.  Your mileage may vary.

Generally, you should just figure out the minimum test protocol your Regulatory body will accept, and do that.  As long as in reality your device is not harmful to humans, you can rely on the results.

 

 

 

 

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. 

 

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.

 

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?

 

Pinch Testing White Paper Released

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.

 

Coatings odds and ends - From pinch tests to trade shows

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.

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

Biocoat to exhibit hydrophilic coatings at MDM West - Anaheim 2012

As the title says, Biocoat will be exhibiting in Booth #1393 at the MDM West show in Anaheim this year from February 14th to 16th.

Feel free to reserve an appointment with me if you wish to consult about upcoming hydrophilic coating projects, or just stop by the booth and say "hi".

 

Booth #1393

5 Critical Questions to Ask About Pinch Testing Data

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. 

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.

Hydrophilic Coatings Market Misinformation - Part 2

Last week I discussed why some of the estimates that the professional market research organizations make on the size of the medical device coatings market are a bit off.  I did not want to throw everything at you at once, so this week I will continue with the topic.

There is one other area where errors are made in estimating market size.  Let us take the example of a company that has developed its own antimicrobial coating for its own use.  In fact, currently there are several such examples of companies that do this:  Edwards Lifesciences, Cook Medical, B. Braun, and Medtronic. 

These companies employ their antimicrobial coatings on their own devices and gain revenue from sales.  For any one of the examples above, the sales on a given antimicrobial device are in the millions.  The mistake made by the market researchers is adding the revenue of these devices into their market size calculation.  If Cook Medical's minocycline/rifampin line of catheters sells $100 million per year (a number which I just made up off the top of my head), the market reports will add that $100 million to the market size.

This is incorrect.  When a company produces its own antimicrobial coating only for its own devices, it is not licensing out that coating or supplying it to others in any way.  However, what if they were?  Or, what if instead of using their own coating, they licensed an antimicrobial coating from a coating vendor and paid a royalty on it?  The revenue from the licensing and royalties to the coating vendor would be the number added into Market Size for medical device coatings. 

So, my proposal is that instead of simply adding the $100 million to the market size, what the researchers should do is pretend that those coatings were licensed from a coating company and then calculate the revenue gained by the theoretical coating vendor for those coatings.  This isolates the coatings revenue from the device revenue.

Afterall, we are looking at a coatings market, not a device market, so the revenues should be separated out.  Reports that talk about coated device markets might help coated device vendors, but they require all sorts of mental rejiggering to become useful for coating companies.

When you sell house paint, do you look at the selling price of all the houses you are going to paint, or do you look at how many gallons of house paint you are going to use to paint them?