“We have recently taken on some medical tubing device-assembly work from another company but the information supplied seems to be missing some crucial points. We are having bond-strength issues when fixing a flexible PVC tube into the female port of an ABS connector.

The instruction we had was to use 100% cyclohexanone, but my feeling and internet research seems to show some form of cyclo/THF and pellet combination would perform better. Would you agree or is there a ready-made alternative available?”

In general, adding pellets (PVC) to the solvent mixture can help avoiding stress cracks and allows more flexibility in the gap design due to its gap-filling properties. So far, we have not come across a readily available mixture.

If you consider moving away from using solvent, I would suggest looking at light-curable adhesives. Dymax offers a variety of products suitable for bonding PVC to ABS. Medical grade adhesive Dymax 1161-M for instance provides strong bonds to a variety of substrates and cures within seconds upon exposure to UV and/or visible light.

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“We are looking for a medical-grade adhesive for bonding PEBAX (72D MED) tubing to latex nature rubber. We need shore hardness of a UV adhesive below 50D after cured. What is the best adhesive for this application? Also, which pre-surface treatment is suitable for PEBAX?

We also need a medical-grade adhesive for bonding PEBAX (72D MED) tubing to a colored ABS hub. Which fast setting adhesive is suitable for this?”

Latex nature rubber can typically be bonded with cyanoacrylates, also referred to as Super Glue. The Dymax medical grade 222 series cyanoacrylates might be a good place to start.

For bonding PEBAX I would suggest looking at Dymax 208-CTH-F, which is a medical grade, light-curable adhesive with shore D55. To combine PEBAX with latex or colored ABS, light-curable adhesives might not be suitable due to low adhesion to latex and problems with light curing through the colored ABS hub. Therefore, a cyanoacrylate is most likely the adhesive of choice.

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“I’m looking for a UV-curable adhesive to bond polyolefin surfaces (cyclic olefin polymer), 100 cm² max size. The surfaces could be pre-treated (primer, plasma). What adhesive/primer do you recommend?”

Bonding to COC is very difficult due to its low surface energy. Surface treatment has not shown big improvements. Since the demand of bonding COC is growing, adhesive suppliers are working on new adhesives that can handle such difficult surfaces.

You can contact Dymax with your specific inquiry to see if they have new products in their pipeline that fit your needs.

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“Is there a UV-curable, medical-grade (safe to use in the body) biodegradable adhesive of any kind on the market right now? If not, would it be possible to formulate the adhesive?”

Dymax does not presently pursue implantable applications for our adhesives, and we are unaware of any adhesive on the market that would be biodegradable. Consequently, we cannot comment on the feasibility of such a product.

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“I want to find an epoxy that can bond two pieces of polycarbonate materials and be sterilized using autoclave. We tried using epoxy 353ND from Epoxy Technology but it is very difficult to cure completely, and after the sterilization process, the epoxy failed.”

Similar to light-curable adhesives, polycarbonate is usually not suitable for repeated autoclaving cycles. If a strong bond between the two pieces of polycarbonate is achieved, 1-5 cycles may be possible without damaging the adhesive and the polycarbonate.

There are several light-curable adhesives for polycarbonate available that are also approved for medical applications. One example is Dymax 1161-M, which I recommend for further testing with your application.

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“We are observing a cracking problem in the bonding of a PVC tube and component of PC-144R with a 50% Cyclohexanone + 50% Tetrahydrofuran solvent mixture. Please suggest an alternative solvent for bonding the above component. Also describe why the polycarbonate is showing cracks when used with aforementioned solvents.”

There are cases where the PC tends to crack upon contact to attacking chemicals like ketones (Cyclohexanone, MEK) , ethers, and esters (Tetrahydrofuran):

1. Applied stress due to joint design: when both parts are pushed into each other putting them into tension. To resolve, we recommend changing the design.
2. Residual stress due to the molding process: when the molded PC does not cool down consistently. An annealing step (time and temperature to be determined) will relieve residual stress.

I would recommend looking at the possibility of stress within the Polycarbonate and make changes to design and/or process accordingly.

You can also look into switching to a light-curable adhesive, which is typically less harsh to Polycarbonate. For bonding PVC to PC, Dymax has a variety of products if you are interested exploring this path further.

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“I am looking for an adhesive that can be used to bond tubes made of flurorocarbons (PVDF and FEP) to a titanium connector. This connection needs to withstand repeated autoclave sterilization at 134° celsius. Do you have any recommendations?”

Fluoropolymers such as PVDF, FEP, and PTFE (Teflon) are very difficult to adhere to. The only way to overcome this is by using a chemical etch solution. Two possible suppliers are www.actontech.com or www.fluorocarbon.co.uk. Both web sites also offer a variety of information regarding this topic.

The etching process removes a layer of fluorine atoms from the surface and allows oxygen and hydrogen from the atmosphere to attach, which enables adhesives to bond to it. The next challenge is the required resistance to repeated autoclave cycles. We recommend trying a two-part or heat-curable epoxy from Masterbond or Epoxy Technology.

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“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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“We are looking for a good adhesive to pot Nitinol or Titanium wire into a hole in a Noryl device. The hole is 0.156″, while the wire is 0.125″. We are looking for an adhesive that can stand up to re-sterilization using various methods of sterilization including autoclave and EtO, and that will also fill the gaps well. Can you recommend an adhesive?”

If the number of sterilization cycles is limited to a few you may be able to utilize a light-curable adhesive for your application. Dymax 1128A-M is a medical-grade adhesive that cures with UV and visible light, and exhibits good adhesion to a variety of metals. Adhesion to the Noryl will have to be tested.

If more than 10 cycles of autoclave sterilization are required then the best choice of adhesive will be either a heat-curable or two-part epoxy. Masterbond and Epotec offers a variety of materials that are medical grade and suitable for repeatable sterilization.

Adhesives, Medical 1128A-M, medical grade adhesives, metal bonding, nitinol bonding, noryl bonding

“Can you suggest a medium-viscosity adhesive that is well suited for metal-to-metal bonding?”

“We are currently using Dymax 1184-M, M-B, and V for most applications. However, we’ve found out that they are not well suited for bonding metal to metal, partly because the cured hardness is too high and partly because the UV light cannot penetrate through metal seams.”

For metal-to-metal joints I would suggest looking at traditional epoxies rather than light-curable acrylates.

Epotec and Master Bond Inc. offer epoxies in medical-grade versions. There is an old article that describes the impact of Sterrad low-temperature hydrogen-peroxide-gas plasma on several adhesives. The article, along with the results, can be viewed at: http://www.mddionline.com/article/compatibility-medical-devices-and-materials-low-temperature-hydrogen-peroxide-gas-plasma.

According to the results in the article, some two-part epoxies from Epotec have a moderate compatibility with Sterrad.

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