Active implants: encapsulation to protect the technology

Active implants are among the most important inventions of the past 50 years. Many manufacturers will once again showcase their products at the COMPAMED 2018 trade fair. But what is the best way to protect the sensitive technology in pacemakers, hearing aids and other devices?

In 1958, Åke Senning implanted the first pacemaker ever to help his patient Arne Larsson. In terms of its construction, the device resembled our modern defibrillators with one key difference: to protect the technology, it was previously installed in a shoe polish tin and then cast in epoxy resin. Inventor Earl Bakken didn’t take into consideration that polymers can absorb water. The plastic subsequently absorbed water, causing the technology to be destroyed by corrosion within a mere two days. Nowadays, encapsulations with hermetic seals are crucial for active implants.

Materials under consideration must have high permeability to avoid corrosion of the technology. That is why glass, ceramics, and metal are currently being used for the application. Having said that, corrosion protection is not the only important aspect. Materials must also be resilient, biocompatible and electrically insulating. Each material has its own pros and cons.

Most implants today are encapsulated in metal because it can withstand high mechanical stress. However, since they also corrode themselves, they need an alloy. The most commonly used metals are stainless steel, Elgiloy, niobium and tried and tested titanium. They ensure that the used metals become biocompatible and don’t poison the human body. What makes titanium so unique are his super-insulating properties. It ensures electrical insulation for encapsulation as the third important necessary characteristic.

Fewer implant manufacturers use ceramic housings for their technology, even though they have excellent electrical insulation characteristics, are biocompatible and inexpensive. What’s more, they have an advantage over metal housings: they don’t block communication with the outside world. This allows manufacturers to create ever-smaller and less complex implants because there is no need to add an external housing for a receiver coil. Yet there is one major drawback: ceramics break more easily. High stress causes cracks and can lead to fracture. Nevertheless, these housings are perfect for applications such as cochlear implants since they are primarily for children and must, therefore, be very small.

Glass is the material that absorbs the least amount of body fluid. Just like ceramics, it breaks easily and is also broken down by liquid - like a piece of broken glass in a river. Implant stability is compromised as a result. That's why electrical implants rarely have glass encapsulations.

Metal likely continues to be the reigning champion of encapsulation systems in the future. When it comes to stability, ceramics and glass are simply unable to compete. Ceramic encapsulations will gradually disappear from the market in the future and will only be used for certain implants. Thanks to new innovations, glass encapsulations might be found in more applications in the future. Having said that, neither ceramics nor glass are able to ascend the iron throne of encapsulation anytime soon.