In 2013, funding for medical research across the world had gone above $260 billion with the United States accounting for 45% of that while countries such as China and Japan increase investments significantly in these areas as well. With global research on the rise, many of the acceptable practices have come into question. Medical device manufacturing in the US is expected to reach $133 billion in 2016 and over $350 billion worldwide. Manufacturing of medical devices can be extremely demanding and to meet new technologies and regulations, industries serving medical device manufacturers must be able to keep up as well. Adhesive solutions are an integral part of medical device manufacturing and epoxy adhesives have become a preferred option. Epoxies are excellent adhesives due to their high strength, compatibility with many materials, ease of use, and moisture resistance. Many epoxy systems are also non-toxic making them a preferred choice for use in implantable medical devices.
Adhesive Selection
If you are an engineer you will ask yourself, “What kind of epoxy adhesive do I need?” Adhesive selection is an important part of designing a medical device and plays an integral role the success of the application. An ideal medical adhesive does not exist. The ideal epoxy adhesive is the one that works and meets regulatory requirements. There are many key factors to consider when selecting an epoxy. Firstly, what are the physical properties needed from the epoxy? Knowing things such as viscosity, thixotropy, cure time, hardness, and density are all important to know when choosing an epoxy. Does it need to be certified for biocompatibility? USP Class VI and ISO 10993 are both certifications for biocompatibility and may be a requirement for your application. It also may not be necessary when choosing an epoxy which opens options for products are is likely more economical. Can the epoxy withstand sterilization? In many cases, medical devices will go through sterilization such as gamma radiation and/or autoclave. The epoxy must be able to withstand these harsh processes. Most epoxies are non-nutrient which means fungus and bacterial will not grow on it.
Epoxies can be engineered to have different or enhanced properties. Thermally conductive epoxy adhesives offer higher levels of thermal conductivity, thermal impedance, and insulation than compared to standard epoxy adhesives. Different powders and fillers such as boron nitride, aluminum nitride, and aluminum oxide are added to epoxies to give thermal conductivity. Electrically conductive epoxies are also widely used in medical electronic components. Silver filled epoxy is a well-known electrically conductive epoxy used for a variety of applications including EMI/FRI shielding, solder replacement, and die attach. If your application needs conductivity it is crucial to get this information from Epoxyset to offer the best product for the application.
Application Example: Ultrasound Transducers
Ultrasound technology is vital to modern medical therapies. Medical ultrasonic transducers (probes) come in a variety of different shapes and sizes for use in making pictures of different parts of the body. The transducer may be passed over the surface of the body or inserted into a body opening. The probe itself is enclosed in polycarbonate housing with only the outer most layer exposed, known as the lens or window material. This material is generally a silicone adhesive but higher frequency ultrasound transducers may use a low modulus urethane adhesive. Behind the lens material are 3 important elements of the transducer: acoustic matching layer(s), piezoelectric element (PZT), and backing material. The PZT is generally a ceramic material due to its high conversion efficiency. Behind the PZT is the backing material. The backing material is commonly a highly engineered and specific epoxy based adhesive. In several backing materials in acoustic technology, EB-130M-1 is the base epoxy used. The EB-130M-1 is further formulated adding fillers and additives to meet certain acoustic requirements. In front of the PZT are generally a series of matching layers. The acoustic matching layer is designed to have adequate acoustic impedance value using a combination of different resin materials. One transducer can have several matching layers, all epoxy based systems. Depending on the process of applying each matching layer, there may be a lamination epoxy used between each matching layer. A popular product for lamination is EB-106 for its high strength, low viscosity, and excellent wetting capabilities.
Biocompatibility
All medical devices must be biocompatible. What is biocompatible epoxy? Epoxy that is biocompatible is an epoxy system that is made of non-toxic materials that do not irritate or damage living human tissue and do not cause physiological or immune system reactions. The United States Pharmacopeia (USP) Class VI testing is a North American certification for biocompatibility. An epoxy that has USP Class VI certification is suitable for either direct or indirect contact with a human patient. Medical devices where USP Class VI certified medical grade epoxy can be used include endoscopes, infusion pumps, catheters, transducers, and many more. These medical epoxies are also used in prosthetics and diagnostic equipment.
USP Class VI certification of an epoxy is not a guarantee the entire device is biocompatible but does assure that the epoxy itself is not a cause of a lack of compatibility. Many adhesives used in medical devices do not need or have USP Class VI certifications as either internal testing permits or engineers are familiar with products and the chemistries used.
Conclusion
Medical research is on the rise worldwide and part of that research is going into medical devices as well. In order to keep up with medical research, companies must develop new and innovative tools necessary to facilitate the growing demand. Medical epoxy adhesives continue to be a crucial aspect of medical device manufacturing. It not only is necessary for assembly work but is often crucial to the technology as shown in ultrasound transducers. Epoxy adhesives are advantageous over other chemistries such as silicones or urethanes due to its high bond strength and chemical resistance. Medical grade epoxy is generally 100% solids and contains no solvents. Biocompatibility can be necessary for applications however it is important to find out whether certification for biocompatibility is necessary. USP Class VI and ISO 10993 certifications are the widely accepted around the world for this and is common when researching epoxy.
