This message goes out not so much to the customers seeking hydrophilic coatings (although they will benefit from reading this), but more to the companies that make them poorly and market them as something otherwise. This is not a direct accusation at any company in particular, but guilty parties will know who they are. This is me calling you out.
Here is my beef: I see it commonly. A hydrophilic coatings company will "whip up" a coating and put it on the market. Putting it on the market is not a problem. "Whipping it up" is, especially when the company goes on to make all kinds of ridiculous marketing claims about it, many of them patently false or unproven. I wish the Federal Trade Commission (FTC) would take a look at some of these claims, honestly. As a generic example, "XXXX is the most lubricious coating available." or "XXX enhances the design features of any device." These sorts of claims often come from companies that never show testing data beyond 10 cycles. Anyone can do that. Essentially, these claims are made without any meaningful data to back them up.
This is just one example. Others exist. Another example is when companies take a hydrophilic coating, dump an antimicrobial into it and mix it together and just because it mixes successfully the company touts the coating as an "antimicrobial hydrophilic coating".
So, why do I have a problem with these practices? Two reasons: a client can really hose itself by going to one of these companies and then finding the coating is completely untested and probably never would have worked in its application. Time is wasted. Second, it ruins it for the other hydrophilic coatings companies that do the right thing and put their coatings through extensive verification testing BEFORE putting them on the market. Coatings that are done right have a better chance of success because their vendors are more knowledgeable of how they will perform under certain applications.
Now let me get specific. In my opinion, for a coating to be released to market for use in medical devices, the vendor must have some idea that it will work in at least some intended applications, and most medical applications have certain things in common like shelf-life determination and sterilization. That means certain tests need to be conducted on the coating before trying to release it to market:
1) Lubricity and durability baseline - What is the coefficient of friction and how many cycles can the coating withstand initially after applying to a surface? Sure, you can show 10 cycles with a tiny normal force, but know that the best coatings out there can bury you if you do that.
2) Lubricity and durability after sterilization - If you are going to say your coating is sterilizable, then you darn well better actually sterilize it and see if it is. For every method you claim, you need to do a test for it: Gamma-irradiation, Ethylene Oxide, Autoclaving, Other, etc. How much lubricity/durability does it lose?
3) Lubricity and durability after Aging AND Sterilization - It's nice if your coating can be sterilized every which way, but what happens if you sterilize it and then stick it on a shelf for three years? Will it function after that?
These are just some items to look at. Other things could include a knowledge of what substrates work best with the coating, an Arrhenius Plot of degradation at different temperatures, a study of the coating solution aging characteristics, and more. That is what it means to know a little about a coating, but barely scratches the surface.
Antimicrobial coatings have it worse. Probably 90% of the antimicrobial hydrophilic coatings out there are untested. Their creators just mixed them up and got them to mix successfully and put them right out into the field. If I were a buyer, I'd be scared. What is the release profile of the antimicrobial from the coating? What is the primary method by which it kills? What organisms does it target? For how many days does it release? Most importantly, does the addition of the antimicrobial affect any of the other four things I talked about above: lubricity, durability, sterilizability, and aging of the coating? What happens if you store the coating solution containing the antimicrobial? Remember, the "product" sold by the hydrophilic coating company is usually a bottle of liquid coating solution, not a dry coating on a finished device. Has the hydrophilic coating company done sufficient shipping tests, aging, and pot life characterization of its product? The answer for most of these companies is a resounding "NO", and that is why I am not pleased, on one hand.
On the other hand, the companies that are doing this right, but taking a little longer to get to market, will have a business 5 years from now.
As a guest blogger at Medical Design & Diagnostic Industry's blog, I have posted an article on the challenges of hydrophilic coatings for drug delivery.
Go over there and read the latest blog post on hydrophilic coatings for drug delivery.
A press release in Medical News Today
talks about a new type of possible antimicrobial coating in the form of positively charged short chain peptides. In a nutshell, the article talks about the possibilities of immobilizing these peptides onto the surface of a medical device, to create a medical device coating, so they stay active and continue to act against microorganisms. My question is: Since they are peptides, would they set off a chronic immune response at the surface? Depending on the type of implant, that may not be desirable.
Nevertheless, as was discussed at the last BioInterface meeting
, the concept of creating a surface that inhibits bacterial colonization and formation of biofilms is a good one. It is unclear to me upon reading the article if the peptides inhibit biofilm formation or if they are actively bacteriocidal. If they are bacteriocidal, it would be interesting to know what kind of half-life they have at the surface, i.e. how long they remain active. The drawbacks of releasing antibacterial agents from surfaces is that they eventually run out and the local concentration of antimicrobial agent can drop below the minimum inhibitory concentration (MIC) thereby promoting drug resistance. Immobilizing an antimicrobial agent on the surface could get around this, depending on how long it stays active.
I wonder if a surface like this could be combined with other agents that inhibit bacterial attachment?
A post at devicelink.com reports positive financial results and growth outlook for Cook Medical. This company uses a patented combination of minocycline and rifampin antibiotics, licensed from Baylor University, on its catheter products for reduced incidence of catheter-associated infection. See the story here.