A tiny drop of heat tolerant medical device grade cyanoacrylate adhesive (e.g. LOCTITE® 4014™, LOCTITE® 4310™ or LOCTITE® 4311™) can be used to coat the seeds in the slots. Use just enough glue to barely surround each seed. Note: these medical device grade adhesives are very expensive.
NOTE: The type 4014 glue is cured via atmospheric moisture whereas the type 4310 and 4311 are cured using both humidity and UV light to accelerate the curing process.
From the LOCTITE® 4014™ technical data sheet:
- LOCTITE® 4014™ is designed to provide fast room temperature fixturing and is also suitable for applications where heat resistance is required. Suitable for use in the assembly of disposable medical devices.
- Typical curing performance: Under normal conditions, the atmospheric moisture initiates the curing process. Although full functional strength is developed in a relatively short time, curing continues for at least 24 hours before full chemical/solvent resistance is developed.
- Effects of Sterilization: In general, products similiar in composition to LOCTITE® 4014™ subjected to standard sterilization methods, such as EtO and Gamma Radiation (25 to 50 kiloGrays cumulative) show excellent bond strength retention. LOCTITE® 4014™ maintains bond strength after 1 cycle of steam autoclave. It is recommended that customers test specific parts after subjecting them to the perferred sterilization method. Consult with Loctite® for a product recommendation if your device will see more than 3 sterilization cycles.
Let the cyanoacrylate dry overnight. If the humidity is very low, put a bowl of water near by. The cyanoacrylate glue hardens very quickly when trapped between two surfaces. The reaction is caused by the condensed water vapour on the surfaces. The water comes from the surrounding air, so the air humidity is a factor that affects bonding capabilities.
The curing reaction starts at the surface of the bonded material and develops towards the centre of the bond. Because of this, thick seams or large blobs of glue may harden less satisfactorily than surface-to-surface bonds with good fit. In a thick blob of glue, a polymerisation reaction may stop before it reaches the centre of the blob. A rule of thumb is that seams thicker than 0,25 mm should be avoided. Thick seams will also take longer time to cure.
To remove the glue and release the seeds, simply soak the plaque in a small beaker (e.g. 100 mL size) of acetone for about an hour. The cyanoacrylate will disolve and the seeds will fall out of the plaque to the bottom of the beaker. The acetone can optionally be captured and used for leak testing the seeds.