Protecting vital medical implants with epoxies

Mike Hodgin, director of strategic applications, Meridian Electronics Division discusses enabling and protecting vital medical implants with epoxies.

Meridian

The human body is a hostile environment for medical implants. Gastric acid, sweat, synovial fluid, saliva, blood, mucus, cerebrospinal fluid, and others, create a highly corrosive “bio-broth”. To ensure medical implants are secured or that sensitive electronics stay protected from this harsh environment, liquid epoxy resins (LER) are the only practical answer.

Epoxy Technology Inc. (ETI), a brand of Meridian Adhesives Group, has pioneered the biocompatibility of epoxy adhesives for medical-grade use in a broad range of applications, including orthopaedic, dental, vascular and electronic implants since the 1980s.

Epoxies, which are two-part polymer resins, are naturally resistant to the acidic electrolyte chemistry found in bodily fluids and will not degrade over time, since long-term implant stability is always paramount. Low viscosity is another advantage and makes ETI’s EPO-TEK formulations easier to shape by allowing for liquid injection moulding. Processing at less than 60˚C also allows a polymerisation process at low temperatures (close to room temperature), whereas thermoplastics and other thermosets require a higher respective melt or curing temperature. Depending on the application, higher temperatures can result in Li-ion battery failure.

Of the 25 biocompatible formulations in the EPO-TEK line, many have been developed over the last 10 years and are used with medtech for surgical and therapeutic procedures.

EPO-TEK MED-301 is certified to meet ISO 10993 biocompatibility standards; this ensures that the material does not induce cytotoxicity or other adverse biological reactions. The resin has a low viscosity, which is advantageous for moulding applications. It allows for easy filling of moulds and creates detailed, precise implant structures.

MED-301 exhibits strong resistance to chemicals and bodily fluids, ensuring that the moulded implants remain stable and do not degrade over time when exposed to the body’s environment.

An epoxy that offers flexibility in curing schedules allows for customisation based on the specific needs of the moulding process and the design of the implant. The material is also compatible with various sterilisation methods, including EtO, gamma radiation, and E-beam, without compromising its properties.

EPO-TEK MED-301 is ideal for orthopaedic implants for structural assembly of parts, such as screws, plates, and joint replacements. It is also used in dental implants to mould crowns, where detailed crown geometries and long-term stability are required. For electronics within implants, MED-301 is also used in the encapsulation of devices such as pacemakers or neurostimulators, protecting sensitive components from the body’s environment.

Another example from ETI is EPO-TEK MED-H20S, silver-filled, electrically conductive epoxy commonly used in applications requiring strong electrical connectivity, such as medical implants, including pacemakers.

In pacemakers, MED-H20S interconnects with a quartz crystal oscillator semiconductor chip that functions with the precision of an atomic clock to keep the pacemaker working with precise regularity. To achieve desired conductivity and adhesive strength of MED-H20S, careful attention is paid to the curing process. Thorough validation testing is also required to ensure the material performs reliably under the specific conditions of the implant's environment. Given its combination of high electrical conductivity, strong adhesion, and biocompatibility, EPO-TEK MED-H20S is well-suited for the demanding requirements of pacemaker manufacturing, contributing to the device's overall performance and longevity.

MED-H20S, is used in pacemakers to create reliable electrical connections between the different electronic components, such as bonding wires, SMDs, and diodes.

Epoxy adhesives such as those developed by Epoxy Technology Inc. (ETI) play a crucial role in enhancing the longevity and performance of medical implants by providing biocompatible, corrosion-resistant, and durable solutions. Whether for structural assembly in orthopaedic devices, encapsulation of sensitive electronics, or ensuring electrical conductivity in life-saving equipment like pacemakers, ETI's EPO-TEK line of adhesives—including MED-301 and MED-H20S—demonstrates the adaptability and reliability required to meet the stringent demands of modern medical technology. As the field of medical implants continues to advance, these epoxy solutions ensure that critical devices remain effective and protected within the body's challenging environment.