Monolithic Encapsulation of Implantable Neuroprosthetic Devices Using Liquid Crystal Polymers

Flexible polymers have gained much attention in the development of low cost, magnetic resonance compatible, and nonfragile implantable medical devices. However, efficacy of the conventional polymer encapsulations containing hybrid interfaces is limited due to their relatively high moisture absorption and unstable interfacial adhesion in aqueous environments. As an alternative, we report on a monolithic encapsulation platform for neuroprosthetic devices using liquid crystal polymers (LCPs), which have a very low degree of moisture absorption (<;0.04%) and a fusion bondable interface. This platform offers monolithic encapsulation by fusion bonding of the hemispherical LCP package lids and LCP-based microelectrode arrays. The package lids were fabricated by thermoforming of the LCP films to provide the desired shape and size for encasing the electronic components and wireless telemetry coils. Fusion-bonded LCP encapsulations were evaluated using electrical leakage current measurements during in vitro soak tests. The measurements were done in both 37°C and 75°C phosphate-buffered saline (PBS) solution and showed that LCP encapsulation was superior and more reliable in PBS than polyimide and parylene-C encapsulations. In addition, LCP-based monolithic encapsulation provided reliable electrical insulation for more than 300 days in both 37°C and 75°C PBS solution.