From its earliest use in orthodontic arch wires to its more-recent dominant role in cardiovascular implants such as stents, endografts, and filters, nitinol possesses unique properties that have made it the material of choice for a variety of medical applications. The vast majority of medical applications take advantage of nitinol’s unusual superelastic properties.

While conventional engineering materials typically have an elastic limit much less than 1% strain, nitinol can experience fully recoverable strains up to 8%. This capability allows a properly designed nitinol component to radically transform its shape during service, fueling the trend toward minimally invasive procedures. For example, a nitinol stent may be designed to be delivered through a 2-mm sheath and expand to support a 10-mm vessel. Similarly, an endoscopic instrument may be delivered through a 15-mm instrument, expand to 60 mm to retrieve a specimen, and then collapse to exit through a similarly sized port.

In short, if a medical component must be delivered in a compressed state and then become an expanded shape, nitinol is likely to offer design advantages unavailable with other materials.

An information sheet from Ineos Nova lists various solvents such as cyclohexanone, cyclohexanone/tetrahydrofuran, cyclohexanone with various medical-grade acrylic polymers dissolved in the solvent for added strength, and various other combinations.

Solvent grades are typically not listed as medical grade or FDA approved but rather by the purity level of the solvent. Obtaining the solvent of choice with the highest purity (99.9% or higher) would limit the potential of leaching chemicals into the water. Sigma Aldrich or Alpha Aesar both provide small quantities of these solvents in various grades for evaluation purposes. Methyl ethyl ketone is an alternative solvent system. However, because of their odor, flammability, and explosive-material storage requirements, using solvents requires special handling and is carefully monitored by the EPA. Dispensing systems such as those offered by Tecnoideal are options to limit operator exposure.

If you want to consider a solvent-free adhesive, looking at a one-part light-curable adhesive such as Dymax’s 1161-M is possible if you can get visible light to the bond line (the nonopaque parts). Alternatively, a two-part urethane or epoxy from companies such as Epoxy Technology or 3M (to name two options) can be considered. These alternatives can provide a bond almost as strong as that provided by a solvent and with fill gaps in the molded ABS bond lines. In addition, they are much more environmentally friendly.