Dental and Orthopedic Applications for Hydrophilic Coatings

Posted by Josh Simon on Wed, Dec 21, 2011 @ 02:53

I am not going to say this is a hopeless cause, because there could always be that device out there that could benefit from a slippery hydrophilic coating that I have not seen yet.  However, if you think about dental and orthopedic applications in relation to hydrophilic coatings and/or lubricious coatings, I am generally not enthusiastic when approached by these companies.

Mainly, what I am thinking about right now are bone screws and plates for bone repair, and dental implants for prosthetic dentistry.  To analyze this, I want you to ask yourself what sorts of environmental conditions are these devices exposed to?

Essentially, these are implantable medical devices, so everything I said in my previous article on implantable hydrophilic coatings applies. That is to say that polymeric hydrophilic coatings will degrade or be abraided off during insertion.  A hydrophilic coating made from your typical polyurethane, polyacrylic, pvp, or hyaluronan would not have the strength to withstand those shear forces.  A research version of a titanium-based hydrophilic coating exists which might be good for this sort of application, except that it has no commercial sales that I can find, and could literally be years or a decade away from commercialization.  This also means that I cannot find anything about its mechanical or frictional properties.  Thus, for now, we are stuck with polymeric coatings.

Even more strangely, I recently got a call from an entrepreneur seeking to coat a calcium phosphate-based bone void filler with hydrophilic hyaluronan.  Unfortunately, he could not tell me why.  Everything I know about bone growth into scaffolds tells me this should not be done because if you inhibit clotting in the porous matrix, you can inhibit formation of the fibrin matrix that eventually houses the osteoblasts that will eventually lay down bone.  More thought needs to be put into some of these applications.

If instead you are thinking about temporary disposable instruments, like a replaceable tip for a knee scope, or a minimally invasive surgical canula, you may be in luck.  Devices that are disposable and not implanted might indeed benefit from a lubricious hydrophilic coating.


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Tags: lubricious coating, Hydrophilic Coating, dental, orthopedics, hydrophilic coatings, lubricious coatings, hyaluronic acid, hyaluronic acid coating

Implantable Hydrophilic Coatings

Posted by Josh Simon on Mon, Nov 21, 2011 @ 03:59

In a previous blog post on permanent hydrophilic coatings, I noted that really all hydrophilic coatings have some sort of bioerosion, degradation, and/or resorption rates in vivo.  For most coatings of this nature, those rates are high, which means they are not always suitable for implantation.

Honestly, that's a rather broad and general statement about the utility of implantable hydrophilic coatings.  In reality it goes back to a question I like to ask a lot on this blog:  What is your application?

Let me break that out into some more specific thought questions:

What kind of device do you want to coat?

WHY do you want to coat it?

Do you want it to be slippery?  Non-thrombogenic?  Closely associated with water to prevent fogging or misting?

Given your answer to the question above, exactly WHEN do you want the coating to possess those properties during the life of the device?  Pre-implantation? During implantation?  During explantation?  The whole time?

Given that last answer, how long is that time period?  Minutes?  Hours?  Days?  Weeks?  Forever?

In many cases, for example in the case of an implantable cardiac pacemaker, surgeons may be complaining that it is difficult to squish the leads into place during the procedure.  A lubricious coating might help with that.  However, once the device is implanted, who cares about what happens to the coating as long as it is biocompatible?  Or maybe I should ask:  do you care what happens?

If you do care, then you need to ask yourself why.  Is there some other function a slippery, non-thrombogenic, water-loving coating will serve a purpose after implanting that pacemaker?

Most of the time, when clients come to me asking for permanent hydrophilic coatings, it actually turns out that they do not need them to be permanent.  They just need them to fulfil a temporary role, which the coating can do easily, and then when it goes away it is of no consequence.


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Tags: advanced coating, lubricious coating, medical device coating, Hydrophilic Coating, biomaterials, hydrophilic coatings, lubricious coatings, non-thrombogenic coating

Hydrophilic Coatings at MDM Minneapolis 2011

Posted by Josh Simon on Wed, Nov 09, 2011 @ 02:56

The guys at Medical Design Technology filmed me while I was at our booth for the MDM Minneapolis show this past week giving a lubricious hydrophilic coating demonstration.


I want to especially thank Mr. Sean Fenske, Editor-In-Chief at MDT magazine for doing this.

Tags: lubricious coating, Hydrophilic Coating, hydrophilic coatings, coating video

Hydrophilic Coatings vs. Hydrophobic Coatings

Posted by Josh Simon on Fri, Oct 14, 2011 @ 09:02

An article I wrote for Med-Tech Innovation back in April that covers the crucial differences between hydrophilic and hydrophobic coatings is now open to the public.  Until now it was somewhat paywalled behind a free subscription.  So, if you have not yet looked at it, head over there and take a look now!


Tags: lubricious coating, Hydrophilic Coating, hydrophobic coating, hydrophilic coatings, lubricious coatings

Leachables vs. Extractables - Hydrophilic Coating Considerations

Posted by Josh Simon on Mon, Sep 26, 2011 @ 10:00

The Qmed blog has an insightful article on differentiating between leachables and extractables in medical devices.  Though the article does not specifically mention lubricious hydrophilic coatings, it is still an important consideration. 

Something to know:  All hydrophilic coatings contain multiple ingredients, some of which are not completely bound within.  Even crosslinked coatings that purport to be chemically resistant still contain unreacted products from whatever reactions are used in the crosslinking.  The article at Qmed makes us aware that these sorts of leftovers can either leach out or be extracted out, and there is a difference.

The author notes that leaching occurs under "normal" conditions of use, i.e. what will come out of your coating when you place it in the body at 37C for some length of time?  Extraction is what happens during exaggerated conditions, i.e. what will come out of the coating at 50C in an acidic water bath, or an oil bath?

Extractables can give clues to what the leachables might be.  They can also tell you how stable your material is, chemically.  The presence of an extractable is not necessarily a show-stopper.  Unwanted leachables might be harder to explain, however.  Either way, both of these things will make up part of the larger picture of biocompatibility for your material.


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Tags: lubricious coating, medical device coating, Hydrophilic Coating, biomaterials, medical device development, medical device coatings, hydrophilic coatings, lubricious coatings, FDA regulation of coatings, extractables, leachables

Hydrophilic Coatings Webinar Available Online

Posted by Josh Simon on Fri, Sep 23, 2011 @ 02:11

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An archive of the webinar we recently announced on hydrophilic and hydrophobic coatings is now available to everyone for download.  Please stop by and grab the file and listen to it.

Click here to download the hydrophilic coatings webinar.

The webinar was sponsored by Biocoat and Specialty Coating Systems. Half of the presentation by Josh Simon is actually about hydrophilic coatings and the second half by Lonny Wolgemuth talks about hydrophobic coatings. Remember, hydrophilic means "water loving". Hydrophobic means "water fearing". The webinar sets the record straight on which is which and why you would want to use some in specific applications.

For both coatings, lubricity is discussed, i.e. how slippery they are respectively, as well as some basic mechanical properties and medical device applications. 

All in all, I am told this is a pretty good overview of coatings, and it is a nice place to start if you are just beginning your research on this area for possible future products or medical devices. 


Tags: advanced coating, lubricious coating, medical device coating, Hydrophilic Coating, hydrophobic coating, Biocoat, parylene, coatings companies, coating company, business of hydrophilic coating, coating manufacturer, biomaterials, basecoat, durability, durability testing, coating cost, coating costs, Specialty Coatings Systems, medical device coatings, hydrophilic coatings, lubricious coatings, coatings customers, coatings manufacturer, coatings supplier

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

Hydrophilic Coatings on PTFE

Posted by Josh Simon on Mon, Aug 08, 2011 @ 10:39

I have posted an entry as a Guest Blogger on Medical Design Magazine's Perspectives blog.  To understand more about why you would not want to coat a hydrophilic coating with TeflonĀ®, see my article on coating PTFE.


Teflon structure

Tags: lubricious coating, hydrophilic coatings, lubricious coatings, Teflon, hydrophilic coating on PTFE, hydrophilic coating on teflon, hydrophilic coatings blog

A Lubricious Coating That Has Dry Lubricity

Posted by Josh Simon on Tue, Jun 14, 2011 @ 11:04

Here is another question that comes up sometimes:  Do you have a coating that is lubricious when dry?

dry lubricityMore often than not, these questions come from non-medical professionals who want to use the coating for a piece of machinery, rather than a biomaterial which interacts with a living system.  In other cases, the device is for a machine that is used as part of a medical device that has moving parts.

The easiest answer to this question is "no", because hydrophilic coatings accomplish their mechanism through formation of hydrogels on a microscopic level, which closely associate electrostatically with water and lower friction.

The more precise answer is actually a question:  What do you mean by lubricious?  How slippery is slippery enough?  Ok, that is two questions.

Let's put things into perspective and talk about coefficient of friction on a surface.  The coefficient of friction of teflon is about 0.2 to 0.3.  The coefficient of friction of ice is about 0.01 to about 0.1.  The coefficient of friction for most hydrophilic coatings for medical devices ranges from 0.01 to about 0.1 also.  Some hydrophobic coatings like Parylene have coefficients of friction ranging from 0.25 to about 0.4.

If you want a coating that has a coefficient of friction in the 0.01 to 0.05 range while dry, you are basically out of luck. You may want to try a lubricant like silicone oil.  On the other hand, if friction in the range of 0.2 to 0.3 is ok for you, then you want teflon or parylene.  The drawback there is that these are hydropobic not hydrophilic.

In some cases, there are hydrophilic silicones that can have coefficients of friction around 0.2.

Tags: lubricious coating, Hydrophilic Coating, parylene, hydrophilic coatings, lubricious coatings, silicone spray, dry lubricity