The medical device industry which produces a large number of products (from surgical gloves to artificial joints to imaging devices), driven by innovation and new technologies, has become one of the largest markets in the healthcare sector.[1] The explosion in the sophistication and application of devices makes it possible to help improve human health in ways unimaginable just a few years ago.

All of these devices are intended to be used in the treatment, mitigation, diagnosis and/or prevention of diseases and abnormal physical conditions, but all are manufactured from non-natural materials, e.g. silicone, latex rubber, metals, ceramics, synthetic plastics, etc. and are often hydrophobic and non-slippery.

The introduction of foreign objects into the patient’s body may not only cause pain and discomfort but also increase the risk of injury, infection, and even life-threatening and therefore friction-reducing surface-modification using lubricious polymer coating technologies has been used for decades to facilitate the insertion and placement of devices (e.g. stents, catheters, bioabsorbable scaffolds, guidewires and other products) within the body. Ophthalmology is another area where such coatings have proven extremely beneficial – in the delivery of intraocular lenses, for example, as the delivery cartridges used to place the lenses must employ slippery surfaces to reduce damage.

Depending on the specific design and performance requirements of the device, one coating technology may outperform another in terms of application and efficiency.

Hydrophilic coating technologies by using appropriate hydrophilic polymers which are polar and ionic, are able to absorb water and become slippery in aqueous environments and thus have low coefficients of friction, deliver lubricious, abrasion resistant, non-thrombogenic, and biocompatible surfaces; whilst hydrophobic coatings use nonpolar, water repellent molecules (or do not absorb water) and are thus less slippery than hydrophilic coatings in aqueous media.

Hydrophilic coating technologies creating water-attracting surfaces make polymeric devices fluid-responsive by either physically depositing lubricious polymers on the surface or by chemically grafting hydrophilic polymers onto the surface via covalent bonds. In order to enhance the adhesion of coating layer on substrate surface, several activation techniques, e.g. heat, UV, plasma or coronal treatments will normally be applied. Chemical bonding is a key to improve the durability as well as prevent delamination of hydrophilic coating from coated surfaces. The lubricity and water retention properties of hydrophilic coatings reduce the force required to manipulate endovascular medical devices during interventional procedures. They can minimize the friction between coated devices and tissues up to 100 times as compared to uncoated surface. This dramatically helps reduce the risk of damage to blood vessel walls, prevent vasospasm, and allow navigation in tortuous vascular pathways and lesions inaccessible. Besides, hydrophilic coatings on medical devices can create an interface that the human immune system does not recognize as artificial, significantly reducing the risk of multi-problems.[2]

For devices and instruments that become fouled with fluids or tissue debris, hydrophobic coatings show a super performance in keeping surgical tools cleaner thanks to its repellency to fluids, which makes blood, urine, or tissue sheets slide off easily, as well as reduces risks of contamination and infections in patients.[3]

Although there are numerous benefits of using lubricious coatings for medical device applications, they do have some drawbacks. One of these challenges is the separation of the polymer coat during an interventional procedure. This delamination occurs when the coating integrity or chemical bond holding the polymer coat to the surface or base coat layer is weak. The physical/chemical bonds break, causing the polymer coat to delaminate and “flake” or “peel” away from the device and enter the bloodstream.[4]

Spray coating uses a nozzle and controller to spray a coating solution onto the surface as a mist. Ultrasonic transducers may be used to control spray droplet size, which affects the thickness and quality of the coating.

Spin coating is another technique to apply thin films to substrates. The process is quick and easy to produce homogeneous films (from a few nanometers to several microns in thickness); however, it can only be used for flat surfaces.