Plasma Treatment for Adhesion of Lubricious Hydrophilic coatings

Posted by Josh Simon on Mon, Nov 28, 2011 @ 09:18

Today's article comes to us from Drs. Demetrius Chrysostomou and James Bond from PVATepla.  It is an informative read on plasma treatment for hydrophilic coatings:

Catheters are inserted into the body for fluid drainage, duct dilation and drug/nutrient delivery.  With an invasive device the host’s health can be compromised due to tissue trauma and subsequent infection. Hydrophilic coatings are beneficial in reducing trauma damage. However, some catheter polymers can be classified ‘difficult to coat’ and the adhesion is far from optimal.  Good adhesion of the hydrophilic coating is essential. Poor adhesion could lead to shedding of the coating in vivo and increase the risk of coronary embolism.    This is where plasma can play an important role

What is plasma?

plasma

Plasma is a gas energized to a state of electrical conductivity. Chemically it is a highly reactive environment that is used to change the properties of surfaces without affecting the bulk material. Plasma is a powerful tool in solving surface preparation problems such as precision cleaning and decontamination, increasing surface wettability and adhesion promotion of functional bio-molecules and coatings. Plasma can also be used to polymerize coatings onto surfaces through a technique called Plasma Enhanced Chemical Vapor Deposition (PECVD). The main advantage of plasma as an enabling technology is that it is a clean dry process. As such there are none of the liabilities of wet chemistry, such as leaching toxic solvents.

Historical use of Primers for Surface Activation

Historically primers have been used to activate ‘difficult polymer’ surfaces. Some primers are considered hazardous.  There may be primers are highly toxic, caustic, carcinogenic and are potential leachables. The EPA and FDA review medical grade primers and the trend is to remove particular primers from the ‘safe to use list’. An example of the chemical primer used for PTFE and ePTFE is TetraEtch (a mixture of sodium, naphthalene and 1,2 – dimethoxyethane). This primer is teratogenic, toxic and caustic.  

plasma schematic

Plasma prepares the surface by molecular cleaning.  Specific chemical groups are then grafted by a second plasma step.  The surface is then exposed to the functional molecules that chemically bind to the plasma grafted moieties.

ePTFE use for medical devices

Expanded polytetrafluoroethylene (ePTFE) is a commonly used material for implant applications. It’s mechanical strength, impermeability to blood and inertness to bio fouling make ePTFE ideal for such in-vivo applications. Its flexibility aids in healing, and catheter tubing doesn’t kink very easily and generally has good compression resistance. For biomedical applications the ability to modify PTFE surfaces is important to promote interfacial biocompatibility.

 

Plasma treatment of ePTFE for binding lubricous coatings

 It is possible to graft polar functional groups to PTFE by plasma activation. These polar functional groups act as excellent anchor to covalently bond hydrophilic coatings. The PVA TePla plasma surface activation for ePTFE is an environmentally friendly alternative to primer treatment. We treat parts in a highly controlled low temperature, low pressure dry, clean gas environment such as the IoN300 catheter treating tool below.  

plasma machine

What does PVA TePla America offer?

 PVA TePla America offers a solutions based team of chemists (physical, surface, organic and bio-chemist) who will work with you or your chosen coatings company to find the very best surface treatment for you polymer. We offer free proof of process as an incentive to evaluate our plasma technology. We have clean area contract processing capability with ISO 9001:2008 certification. And we offer a full range of vacuum and atmospheric gas plasma systems. PVA TePla America is based in Corona, CA. www.pvateplaamerica.com

 

For further information contact  [email protected] (951) 415-0391

 

 

 

 

 

 

Tags: coating equipment, PVATepla, lubricious coatings, hydrophilic coating on teflon, plasma treatment

Medical Device Coating Processes

Posted by Josh Simon on Tue, Jul 05, 2011 @ 02:56
Coatings exist in multiple industries, aside from medical device coatings. In fact, there is an index of all kinds of coating methods on Wikipediathat is enlightening. When it comes to medical device coatings, I tend to think that the industry is behind on its technology, when compared with circuit board coating technology, for instance. Most of the coating processes in that index are never used in medical device manufacturing, as near as I can tell. The main reason for this is demand. Not all of those coating methods are necessary for medical devices, even though they are required for circuit boards or electronics. So, what are the most-used methods for coating medical devices?

Dip Coating

One of the most common processes for coating medical devices is dip coating. There are generally five steps to it: 1) Surface preparation/washing 2) Submersion of the device in a coating liquid (with a certain dwelling time in some instances) 3) Dip coating machineWithdrawal from the coating liquid, i.e. coating application/deposition 4) Drying and/or Curing of the coating (via heat or UV) 5) Post processing, if any. Especially with heat curing, this is a batch process. With proper equipment, the batches can be quite large, giving a decent effective throughput.

Spray Coating

Spray coat systems use a special nozzle and driver to nebulize the coating solution and apply it to the surface as a mist. Some of these systems, like the one from Sono-Tekuse ultrasound transducers to control spray droplet size, whcih can impact the thickness and quality of the coating. In general, spray coating systems can be set up as continuous processes. While they are often too slow for mass-produced electronics, they can work well for most normal medical device volumes. (Of course, that is not the case if you are in the business of medical disposables sold by the millions per week.)

Reel-to-Reel Coating

Reel-to-Reel coatings are most often seen for guide wires and films. They are usually not applicable to small intricate devices. Essentially, this method is literally what it says it is. One reel of wire or film is unravelled and travels through a resevoir of coating solution and then into an oven for drying/curing, before being rolled up onto the second reel. As far as continuous processing goes, reel-to-reel coating is effective. The trick is to align it with the idiosyncracies of a given coating. It can be difficult to make a reel go slow enough or through a big enough oven to cure a coating, for example.

Robotic Coating

This method is used mostly on complicated shapes, like stents. Tiny nozzles directed robotically can trace along struts and other structures with precision. By dialing in the viscosity of the coating solution, a set amount of coating with a set thickness can cover the surface. If all things are equal with the type of coating, this process is amenable to a continuous system.

Brush Coating

Of all methods, brush coating is most primitive. Using a brush, a skilled operator applies a coating to a surface. Since this is a manual process, there can be a lot of variability in coating quality. However, with skilled operators it can be quite acceptable. Naturally, as one may suspect, this process is not amenable to large volumes. However, it is surprising to inspect some facilities and see 300+ individuals brushing on coating at a rate of several devices per minute. It deserves some consideration.

Spin Coating

In this method, a flat surface is set onto a plate and locked down, usually with a strong vacuum or magnet. A motor then spins the surface quickly, while a droplet of coating solution is deposited at the exact center of the spinning surface. Centrifugal force instantly draws the droplet out away from the axis of rotation, causing the surface to be coated. Parameters like solution viscosity and angular velocity are important for determining coating thickness and quality. It can be difficult to produce large numbers of devices with this method.

Inevitably, there will be other methods for coating medical devices. At this time, these seem to be the most popular. Each method has inherent pros and cons, and not all methods are applicable to all devices or materials.

Tags: medical device coating, industrial coating, dip coating machine, coating equipment, medical device coatings, coatings manufacturer, industrial coatings, Dip coater, dip coating