If you are referring to implantable artificial hearts, we have to pass. Dymax adhesives have not been tested for prolonged or permanent implantation and are only intended for short-term use (<29 days) or single-use disposable device applications. We do not authorize their use in long-term implant applications.

Polymerized MD medical device adhesives are biocompatibility tested in accordance with ISO 10993 and/or USP Class VI standards. ISO 10993 is a newer, internationally accepted standard. The current Dymax test protocol for medical adhesives is based on the following standards:

• ISO 10993-4: hemolysis

• ISO 10993-5: cytotoxicity

• ISO 10993-6: implantation for 14 days

• ISO 10993-10: intracutaneous use

• ISO 10993-11: systemic toxicity

Older Dymax adhesives have been tested in accordance with USP Class VI, which covers systemic toxicity, intracutaneous, and a seven-day implantation test. When comparing both standards, USP Class VI is included in and covered by ISO 10993.

First of all, I would like to refer you to an earlier exchange in “Ask the Experts” regarding the inhibition of cure.

CRC Brakleen is a very strong cleaning agent that contains tetrachloroethylene and dichloromethane or ketone (depending on the packaging used). As you already noticed, these are chemicals that easily remove the tacky layer, but they also dissolve the cured adhesive. If oxygen inhibition cannot be avoided, the tacky layer should be removed using an isopropyl alcohol (IPA) wipe. IPA is less aggressive than CRC Brakleen and is commonly used for this purpose. We would always recommend a wipe rather than a soak.

If contamination has been ruled out, delamination is most likely related to uneven stresses within the adhesive joint. I suggest that you look at the adhesive choice, viscosity, bond gap, and curing process.

Is the adhesive and its viscosity appropriate for this application and the bond gap? UV-light-curing adhesives shrink during the curing process and may pull away from the surface to which they have less adhesion. The larger the bond gap, the more likely we will see air bubbles or delamination. In such cases, I would try an adhesive with less shrinkage or a filled, higher-viscosity adhesive. Suitable products from Dymax are 1180-M and 1180-M-T-UR, which is the higher-viscosity version for larger bond gaps.

You mentioned that you tried a longer curing time. Did you also explore curing with different intensities? I would recommend that you try a shorter light exposure at a higher intensity and a longer exposure at a lower intensity.

Do you cure the adhesive from the top or from the side? If you cure from the side and use a UV spot lamp equipped with one or two light guides, there is a risk of introducing uneven stress due to the shrinkage of the adhesive. The areas not directly exposed to the light often exhibit delamination, or you see air bubbles in the bond joint. In such cases, I would recommend that you use a three- or four-splitted light guide instead.

There are a few light-curable silicones on the market that are nonacidic. They cure quickly and exhibit low outgassing properties. One of them is Dymax Cure-Point 9440, a fast-curing UV silicone potting material that adheres to a variety of substrates.

The tensile strength and cohesion strength of most UV silicones on the market is very low, and although they may stick well to substrates, a bonded joint can usually be taken apart easily. The larger the surface area, the more suitable these products are for bonding or lamination applications.

In general, it is very difficult to adhere materials to FEP. It has very similar properties to Teflon (PTFE), which is known for its antisticking surface. Due to the design of your part, you may achieve sufficient bond strength, especially if the capillary is inserted deep into the FEP tube and the adhesive can flow deep inside the bond gap. If you prefer a light-curable adhesive, I would start trials with Dymax 1180-M (medical grade) or 3013 (industrial grade).

Before making a final adhesive recommendation, however, a few more aspects need to be considered:
• The length of the bond area.
• The bond-gap size (outer diameter capillary versus inner diameter FEP tube).
• The forces and temperature to which the part will be exposed when in use.
• The medical-grade adhesive needed.
• Optical properties.

If you need higher bond strength, there is an option to chemically etch FEP. By using a sodium naphthanate solution, the surface of the FEP can be modified so that most common adhesives can be used. This etch, however, creates a darker layer on the surface, so that the clear properties of the FEP are no longer available.

When ASP introduced Sterrad low-temperature hydrogen peroxide gas plasma, they tested many UV-curing adhesives and epoxies from different suppliers. The results showed that many adhesives were compatible and did not exhibit any material damage after 200 cycles. But some products were not compatible with this sterilization method. The article with the results can be viewed here.

Since this article is more than 10 years old, some products may not be available anymore, but it is a helpful guide to identifying the most suitable product.

On occasion, full cure via UV/visible light can be achieved using opaque polypropylene hubs. Depending on the color and thickness of the polypropylene, some light from the side can transmit through the plastic and polymerize the UV/visible adhesive.

The largest portion of the adhesive is usually cured from the top. However, due to limitations in the depth of cure of most UV/visible adhesives, I would recommend keeping the length/depth of the bond joint to a minimum and molding the annular rings near the top of the hub. Suitable UV/visible light–curable products include Dymax 1180-M-SV04 and 1-20777, which are medium viscosity and will not flow deep into the hub. Low-viscosity products such as Dymax 1161-M or 1162-M can be used if the design of the bond joint prevents these materials from flowing too deeply into the hub.

In order to achieve short curing times, I would recommend using a high-intensity UV lamp such as Fusion F300, which is a focused-beam lamp, or Dymax Blue Wave 200, which is a spot lamp that can be equipped with multiwand light guides.

A silicone sealant/adhesive (Pt curable) or silicone pressure-sensitive/lamination adhesive would be good options to evaluate. A PSA such as Dow Corning’s Q2-7406 (solvent based, peroxide cure) would be applied to the Mylar film using a drawdown bar or Mayer rod. The solvent would be driven off at 65°C for 2 minutes, and then the PSA would be cured at 150°C for 2 minutes. Then the ABS would be applied.

You could also devolatilize the solvent, apply the film and uncured PSA to the ABS, and then cure at 150°C in more of a lamination-type application. If a lower temperature is required, platinum curable DC 7657 and Syl-Off 4000 catalyst could be mixed and then cured between 80° and 130°C (after driving off the solvent).

For a solvent-free option, DC 2013/Syl-Off 4000 would be a good option.

It is very difficult to achieve strong adhesion to polyethylene, which is a polyolefin. A common method to overcome this issue is to pretreat the surface via corona discharge, gas plasma, flame treatment, or priming. These methods typically increase the surface energy of the substrate and the potential to adhere to it. Utilizing any of these pretreatment methods will open up the choice of possible adhesive products. To bond surface-treated polyethylene to wood, plastic, or metal, you can use a cyanoacrylate (RX-50 from Pacer), epoxy (Master Bond EP21), or polyurethane (Master Bond EP30D12).

The right adhesive choice for you is dependent not only on the dimension, design, and substrates you are trying to assemble but also the environment the device/item is being subjected to. Is it being used indoors with no contact to moisture or outdoors with consistent contact to water? For a dry environment, a cyanoacrylate might be the right choice, whereas an epoxy might be better for a moist environment.

Colored light-curable acrylated urethane adhesives are usually custom-made and therefore hard to find. In order to find a product that will meet your specific needs (colored, medical grade, adhesion to specific substrates), you should contact the adhesive supplier of your choice.

In general, it is possible to add dyes to acrylated urethanes and to achieve ISO/FDA approval. Typically, each formulation is tested to ensure full compliance. The cured properties are usually not impacted; the only area of concern is the ability to achieve a full cure, since some colors can inhibit the light-curing process.