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 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 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.
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
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