Seeing the light: New applications for light curable adhesives in medtech

Peter Swanson, managing director of adhesives specialist Intertronics, discusses some of the latest formulations of UV curing adhesives used for assembling wearable medical devices.

UV curing adhesives offer significant manufacturing productivity benefits, due to their fast “on demand” curing when exposed to the correct wavelength of UV light. Several new light-curable materials have come to market that can help medtech manufacturers assemble devices more efficiently, accurately, and safely.

Due to their benefits, UV curing adhesives are growing more popular for the assembly of medical devices. There are many materials available that have passed ISO 10993 tests. Once a material is chosen, establishing a UV curing process is relatively straightforward. Light curable adhesive processes are easy to measure, control, and validate — and process repeatability and robustness are important in such a regulated sector.

Adhesives for wearables

The use of diagnostic and therapeutic medical wearable devices has hit the mainstream, as consumers manage their health through monitoring, drug delivery and pain control systems. This includes the use of continuous monitors for sleep, glucose levels and vital signs. According to Gov.uk, more than 270 million units of ear-worn devices (from hearing aids to music ear buds) and 180 million units of wristwear devices (from blood pressure monitors to step counters) are forecast to be shipped in 2023. Consumers will be using more wearable devices for communication and entertainment too, including virtual reality.

When assembling wearable devices, adhesives, encapsulants, and coatings are commonly used to bond components, protect the electronics from the environment, and to join or seal plastics or metals within the assembly. Typical applications for light curable materials include electronics encapsulation, needle to hub bonding, component edge bonding, wire and flexible circuit staking, and battery reinforcement.

When designing a wearable device, the engineer must consider whether the specified materials could cause skin sensitivity. It’s also important that the device can survive repeated use, exposure to different environments and extended periods of time on the body. These factors make adhesive selection critical.

Sometimes, the chemical isobornyl acrylate (IBOA) is found in adhesives because it is useful as a diluent or plasticiser. However, IBOA is a known skin irritant — if an adhesive containing IBOA is used in a wearable device, it has the potential to cause skin sensitivity issues if it is not fully-cured and crosslinked. TPO (2,4,6-trimethylbenzoyldiphenyl phosphine oxide) is a photo initiator and a material of concern.

For this reason, manufacturers are launching products formulated with skin sensitivity in mind. The new Dymax 2000-MW series, for instance, is the first dedicated light curable adhesive product line formulated specifically without materials of concern and common skin irritants, like IBOA and TPO. Ideally, the adhesives must meet ISO 10993-10 that verifies they are not skin sensitisers when fully cured.

The series produces strong bonds on substrates used in the industry, including low surface energy plastics, and dependable performance against moisture and thermal shock. These materials contain no solvents, so environmental impact is minimised and worker safety is enhanced. In addition, there are formulations available that include Ultra-Red fluorescent technology to enable easy and clear process validation.

Surviving repeat sterilisation

One challenge for manufacturers of medical tools like scopes, surgical instruments, dental equipment, and sensors, is ensuring the devices can cope with high heat, humidity, chemicals, and other environmental factors. The same is true of the radio frequency identification (RFID) tags, which are increasingly attached to instruments to aid inventory management and help keep track of them during procedures.

The adhesive used for RFID chip encapsulation must form extremely strong bonds to stainless steel and other metals that surgical instruments are made from, enable the tag to remain in place throughout a procedure, and to ensure safe instrument use and storage. For tools that must tolerate repeat sterilisation, the adhesive may also need to possess low water absorption properties. Instrument makers may need a product that meets certain requirements such as fast cure or certifications like ISO 10993-5.

Designed to be autoclave resistant for more than 100+ cycles, Dymax 1040-M is a UV cured adhesive that can be used to quickly bond, pot, or encapsulate RFID chips onto medical devices, tools, and vials. It features exceptional bond strength to stainless steel and aluminium substrates used in medical instruments.

The future

As the medical device market grows and changes, manufacturers are introducing products that address the needs of specific healthcare applications. Bonding and coating challenges follow. Equipped with an understanding of the latest materials and technologies on the market, and helped with implementing these into their production process, medical device companies can solve common assembly challenges while improving patient safety.