“What bonding agent would you recommend for bonding soft PVC tubing to a polycarbonate connector? This is a sterile disposable tubing set.”

For this type of application I would recommend a light-curable adhesive. Dymax 1161-M could be a good candidate due to its ability to bond dissimilar substrates like PVC and polycarbonate together. This adhesive is solvent free, resistant to EtO, Gamma or Beta sterilization, and passes ISO 10993 biocompatibility testing. Via UV and visible light, the adhesive cures on demand within seconds using Dymax UV light-curing equipment.

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"Hello, currently I am working with 2 Cal Poly professors to make monitoring operating room packs easier. Our goal is to be able to attach micro RFID tags to surgical tools so that they can be scanned and bookmarked. What type of adhesive would work best to attach these tags to surgical tools? The adhesive needs to be biocompatible and be able to undergo sterilization."

Assuming most surgical tools are stainless steel, and need to survive repeated autoclave, I would recommend looking at 2-part epoxies as your base chemistry. Options are available from Loctite, 3M, and Epoxy Technology, to name a few, and some have biocompatibility certificates on file. If the surgical tools are disposable or plastic, and only need to withstand a single autoclave cycle, EtO, or Gamma sterilization, then a light-curable acrylated urethane like the DYMAX 1120-M-UR light-curable medical device adhesive would be my first choice. Acrylated urethane light-curable adhesives have excellent adhesion, are simple to apply as a 1-part material, and cure in less than a second.

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"I have an application bonding opaque parts with a Cyanoacrylate (Super Glue Type). There is much surface area and I have a very good bond. Will Gamma Sterilization effect my bond strength?"

Most cyanoacrylates will survive 1x, 2x, and sometimes even 3x gamma sterilization without a significant impact on bond strength. Repeated Gamma sterilization will start to add additional crosslinking, which will start to reduce elongation. As most cyanoacrylates are already brittle materials (depending on the grade), the adhesive may become even more brittle. Drop tests, impact testing, or tensile testing may be a good indicator of the final impact on your bond strength.

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"We currently use a light-curable acrylated urethane adhesive to bond PVC tubing to a part molded from TPE. We are seeing the adhesive turn yellow and tacky after gamma sterilization and accelerated aging. We also observed the PVC tubing becoming harder in the bond area. These conspire to cause bond failure. The suspect is plasticizer (DEHP) leaching out of the PVC and entering the adhesive. In your opinion, is this the likely cause? Once cured, I would have expected the adhesive to be impervious to DEHP."

I agree that the suspect is the plasticizer migrating during the sterilization and accelerated aging process. Plasticizers like DEHP and BOP will often migrate with heat and time from areas of high concentration to areas of low concentration. It does not matter if the adhesive is cured or uncured. Plasticizers will in effect solvate the adhesive, and migrate into it - often causing it to change color and become gummy or tacky. Just like the plasticizers keep PVC nice and flexible in the cured state, they still migrate away from the PVC under the right conditions. In this case, they migrated into the adhesive, eventually leading to bond failures. This can be tested by subjecting the PVC tubing by itself to the same heating and accelerated aging conditions, and wiping the surface periodically throughout the process. Testing the wipe media for contamination like DEHP or BOP can give an indication of the process step that causes this migration, and how much. Instead of wiping, you can “chemically wash” the part with a proper solvent, collect the solvent, and run it through Gas Chromatography to have it analyzed. To fix the problem, we would recommend trying different PVC tubing with a less mobile plasticizer, or switching to a comparable polyurethane tubing with similar physical properties, but without the need for plasticizer. Changing the chemistry of the adhesive is possible, but a last resort in most cases.

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