Implantable medical devices packaging

Biocompatible materials that have been successfully used for implantable medical device packaging include titanium and its alloys, noble metals and their alloys, biograde stainless steels, some cobalt-based alloys, tantalum, niobium, titanium-niobium alloys, Nitinol, MP35N (a nickel-cobalt-chromium-molybdenum alloy). 

The medical device packaging manufacturers have had to deal with continuous innovation from their customers. In the past 10 years, we have seen the rapid expansion of new generation devices such as stents, complex implants, prefilled syringes, heart valves and devices incorporating powered components, eg, pacemakers. In most cases, a vital part of the functionality of the packaging is the need to provide a secure and protective media and systems to achieve assured long-term pack sterility. 

Technology Advances and Challenges in Hermetic Packaging for Implantable Medical Devices... 

Implantable medical devices have been widely used to restore body functions, improve the quality of life, or save lives. Experts estimate that 8 to 10 percent of all Americans (some 20 million to 25 million people) [1], or about 1 in 17 people in industrialized countries [2], carry some form of implanted device. Many medical devices, such as the implantable cardiac defibrillator, cochlear implant, artificial vision prosthesis, neuromuscular microstimulator, and the like contain sophisticated electronic circuits. Such long-term implantable medical devices are susceptible to damage by body fluids over time. Hermetic packaging is required to protect the electronic circuitry of the implant from the harsh environment of the human body. 

Biocompatibility is the first thing that the packaging engineer should consider when designing a hermetic package for an implantable medical device, as it is the package that makes direct contact with body tissue. It is critical that implantable medical devices do not elicit any undesirable local or systemic effects in the human body. In addition, the package materials should be stable and must be able to withstand attack from a harsh ionic body environment. 

A small heat-affected zone can be achieved with laser welding, which is particularly critical for the miniaturized implantable medical device, where too much heating or the close proximity of the heating zone might cause damage to the components inside the package. 

For many applications it is desirable that the implantable medical devices remain benign in the subject for the rest of the subject s life to avoid a secondary removal surgery. The intent is to leave the implanted neuromuscular microstimulator in the subject s body for the rest of his/her lifetime, which could be up to 80 or more years [15]. The cochlear implant is now the treatment of choice for children with profound and severe congenital and neonatal hearing loss [84, 85]. The long-term stability of the package for both of these devices is very important. 

An implantable medical device is not only exposed to the harsh environment of the human body, but also to the electrical potential or current that is generated by the implantable medical device itself [7]. Corrosion is one of the major degradation mechanisms affecting the lifetime of metal packages used in medical implants in the body. The corrosion process will induce adverse biological reactions in the body and can lead to mechanical failure of the implants. The packaging materials or construction must eliminate the corrosion risk in the body in both passive and active conditions. 

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