How do I decide which coating to order?
Your interdisciplinary product development team should produce a project plan describing what features are needed for surface modifications on the device. For many applications that are searching for a second source of coating, there is an existing specification for coating performance describing the test methods and other requirements for the product. In general, these specifications can be described by the categories similar to those that have been shown under our product lines.
If there is no category on our products page listings to accommodate your requirements, please get in touch. We are able to make these coatings harder or softer, more resilient or less flexible by varying the resins we select.
How do I decide how much coating to order?
In most instances we would suggest that you begin your evaluations with small amounts and build experience with the viscosity, handling, pot life, and coating application/cure and performance optimization. These patented coating systems are tougher and more durable with better adhesion, but they should be understood well prior to plant introduction.
If you are doing a rough evaluation of coating utility and can flow coat from an eyedropper or dip the device into (or pull it through) the coating, then the smaller amounts should suffice. You can always order more or in larger quantities. Making the most of the coating can be a continuous improvement project. Consider the pot life of the mixed coating and geometries of the devices to be coated when deciding on mix quantities. The hydrophilic coating with the Crosslinker B added has limited shelf life, and quantities should be optimized early in the development cycle.
If you have a current reservoir that needs filling, we can discuss larger quantities than what is listed on the forms for a better economy of scale. Redesign of the coating process and tanks may be a good option, since pot life should be considered in the process design.
How do I mix my coating?
Proper mixing is key to obtaining a stable solution. Pot life on the Crosslinker A mixes can be several days, but mixes with Crosslinker B may be only 6 to 8 hours depending on the solids of the coating solution. Crosslinker B, which is used with the hydrophilic coating, absorbs water from the air and can become too high in viscosity and eventually gel after repeated opening and closings. Many customers have decided to mix the B concentrate just before use, with a co-solvent such as NMP or MEK. This eliminates the concern for hygroscopic solvents absorbing water upon opening and then reacting with the B functionality. You may opt to specify your orders for Crosslinker B Concentrate, but the premix is included in the coating kit.
More detailed instructions may be found in the Instructions for Use Page
How do I apply my mixed coating?
Mixed coatings may be applied by almost any coating method. Complex geometries and transfer efficiencies often make dipping the preferred method. Flow, spray, brush, and transfer methods— including knife over roll, gravure, and screen—may be employed. Attention to minimizing foam generation is key for many of these methods. There is no defoamer in these formulations, but foam may be suctioned off the top of a bath of coating as needed.
The Instructions for Use Page will explain in greater detail.
- I have the coating on the device. Now how do I dry/cure it?
Each coating will dry or cure a bit differently.
- Coatings without crosslinker will simply dry by evaporation of water. This can take 5 minutes at 60°C for a very thin coating, or 30 to 50 minutes for a thicker one.
- Coatings with Crosslinker A are usually cured by the evaporation of the neutralizing base in the coating, with immediate reaction of the crosslinker to the freed acid functionality. Heat can improve molecular mobility with improved ability of the polymer chains to access crosslinker groups. We would recommend temperatures of 60° to 80°C to help in the degree of cure. Excess crosslinker hydrolyzes or reacts with functional groups on the surface to innocuous, biocompatible coatings.
- Coatings using Crosslinker B are cured with time and temperature. Active hydroxyl, amide, and amine groups participate in the curing and can be contributed by the surface, the polymer, or the coating resin. Like the Crosslinker A systems, heat and time will help in the cure and subsequent hydrolysis of the residual functional groups. This may take a week or more, with properties building/optimizing over several days. Excess reactive groups will hydrolyze to a biocompatible material.
In all cases, you can accelerate drying by using a forced hot-air oven at temperatures that are suited to your substrate materials. Most of the coatings will take temperatures up to 300°F for short periods. It is recommended that you test the process you plan to use to mix, coat, and dry/cure on your device at several different ambient conditions for temperature and humidity conditions once suitable performance is obtained.
Why bother to coat?
- Performance and appearance improvements
- Bulk modification may be too expensive or additives may diminish bulk properties/integrity
- Materials are only required at the surface for attributes such as slip, therapy delivery, color, etc.
What are the advantages of water-based coatings?
Ambient/ Low-Temperature Cure
Does not require high temperatures, which could affect proteins or other heat-sensitive bioactive additives or substrates.
Usually not an issue with water-based coatings, which means that they are typically given lower plant insurance rates and are not combustible or have a flash point.
Workers love the low odor compared to conventional solvent coatings.
Water-based coatings are less hazardous to employee health and easier to handle and clean-up.
The specific heat of water is higher than most solvents customarily used, but the water will not require the ventilation for cleanrooms required with conventional solvents. This reduces the need for clean, heated/ air-conditioned (humidified) makeup air and the associated costs.
What are the specific advantages over UV coatings?
- Line-of-site cure is not an issue.
- Expensive calibration and validation of equipment for curing is not an issue.
- Oxygen inhibition and surface tackiness not an issue.
What are the specific advantages over solvent-based coatings?
- Workers appreciate the low odor and easy water wash-up of equipment.
- Easy Disposal—Please consult local and state regulations, but a dry-out/cure will usually allow placement in the trash, as is practiced with latex paints.
- Surface acceptability—No stress crazing on solvent sensitive plastics, such as polycarbonate, acrylic, polyester, urethane, etc.
- Insurance—Because these are non-flammable or non-carcinogenic solvents, lower insurance and facilities costs result.
What if the coating will not wet, beads up, or does not stick?
Surface tension is a basic science. If you do not have the surface tension of the coating below that of the surface, the coating will not wet out—never mind stick. Water has a surface tension of 73, and many low- energy surfaces have surface tensions lower than 30. So what can you do? The solution is to either increase the surface tension of the surface with plasma, corona, acid etch, priming, etc., or bring down the surface tension of the coating with the addition of solvents and/or surfactants. (We suggest the solvent route, if possible, since solvent comes out during the drying/curing phase, but the addition of materials that remain in the final coating may alter the biocompatibility test results.) The FDA has been particularly sensitive to the addition of surfactants as an extractable.
If solvent addition does not develop the adhesion, primers and/or corona and plasma are very effective. These methods often produce functional groups at the surface, which can covalently link with the topcoat. Covalent bonding will provide a more robust adhesion and durability.
How do I sterilize my coated device?
Most devices are sterilized with ETO. The humidification step may cause adhesion between hydrophilic surfaces, but these will fall apart when hydrated.
The hydrophilic polymer is susceptible to H-abstraction and subsequent addition polymerization, so care should be taken if you are considering E-beam or other high-energy methods.
Typical chemical sterilants and autoclaving are not suggested methods for achieving sterility, but short heat cures may be tolerated.
Experiment with your device and method.
Note: If you are experiencing problems with the application of these products, please contact us for coaching, or consider utilizing our engineering services to prepare initial samples for your evaluation.