Typical medical device applications which use UV curing adhesives include needles and cannulas, reservoirs, tube sets and catheters. Manufacturers find that using UV light curing technology results in production efficacy and an increase in productivity. Peter Swanson, managing director of adhesives specialist Intertronics, explains the benefits of LED UV curing technology to medical device manufacturers.
When assembling a medical device, it is critical that processes are reliable, consistent and are able to be validated. For bonding parts, UV light curing adhesives perform well against these criteria. They are single part systems and come in a range of viscosities, facilitating precise, repeatable dispensing, both in quantity and location. Curing is fully completed in seconds and within a controlled process window, meaning that immediate on-line quality assurance (QA) checks are possible. Understanding and managing process variables is key for a robust procedure, as mandated by the industry.
The benefits of LED UV curing
For decades, UV curing was most often achieved using light from mercury-based arc lamps, which generate broad spectrum UV light. Newer technology, LED-based UV lamps are growing in popularity, offering a number of benefits over broad spectrum lamps. Traditional arc-based lamps have warm up and cool down periods, which means that they are left on throughout a shift, the exposure being regulated by mechanical shutters. LED-based UV lamps are instant on-off, and consequently are only on when needed, use much less operating power and have no moving parts. They have no bulbs to replace and generate less heat, which may allow manufacturers to work with more sensitive substrates.
Of particular significance to medical device manufacturers is that LED UV lamps have a very stable intensity output over time. The output from broad spectrum UV arc lamps deteriorates significantly with time; in order to maintain a validated minimum curing dose, frequent UV intensity measurements are required (using a radiometer) and either the bulb is recurrently changed, or a production adjustment is made. The introduction of a stable, LED-based UV lamp precludes these process complications, and removes a troublesome manufacturing variable.
Choosing the right adhesive
In conjunction with the take up of LED UV curing lamps, state-of-the-art adhesives are formulated to cure with the LED’s characteristic narrow spectral output. LED-curable adhesives will react to the limited range of wavelengths to give appropriate and expected cured properties. This may not be the case with adhesives which have not been designed to be cured with LED, where cured properties may differ from datasheet values. In both cases, comprehensive testing on production parts will be needed.
Medical device manufacturers will want to consider selecting adhesives that pass ISO 10993 or USP Class VI testing, which indicates that they are non-toxic. In addition, the adhesive will need to withstand the required sterilisation process, for example ethylene oxide (EtO). Intertronics supplies a wide range of ISO 10993-tested UV-curable adhesives that can withstand sterilisation. Opting for one of these biocompatible adhesives will help the device to pass toxicity testing later on.
The choice of adhesive will be substrate dependent; an adhesive which adheres well to, say, PVC may not adhere well to stainless steel. Ensuring good adhesion to all of the substrates may be even more challenging in medical device manufacturing, where some less common plastics are used, e.g. polyether ether ketone (PEEK). A capable supplier will be familiar with industry-specific substrates and have appropriate adhesives for evaluation. In some cases, plasma surface treatment can be used to improve adhesion to low surface energy polymers.
Medical device manufacturers can take advantage of the expedited inspection and QA allowed by the very fast cure of UV adhesives, either in-process or at the end of the line. Some formulations have colour-change capability; they change colour or go clear when cured. Strong fluorescence under black light, either blue or red, is another useful inspection feature.
Choosing the right UV curing system
LED-based UV curing lamps are readily available in both suitable wavelengths (from 365nm to 405nm), and power outputs sufficient for even high-speed production. They range from lamps generating small spots of a few millimetres diameter to large area floods, and can be hand-held, configured for benchtop use, or designed for use in automation or conveyors. They compare favourably with their broad-spectrum arc lamp antecedents, with high intensity spot lamps able to generate over 30W/cm2 of UV curing light.
There is no room for inconsistencies or variability in medical device manufacturing. Adhesives which have been designed to be cured with UV light generated from LED curing lamps can bring reproducible and dependable bonding to your production.
