A Study on Low-Cost, Effective, and Reliable Liquid Crystal Polymer-Based Cochlear Implant System

Abstract

The pace of technological change in implantable devices such as cochlear implants, artificial retinas, and deep brain stimulators has been relatively slow compared to that in other areas, such as memory and mobile phones. Most implantable devices, including cochlear implants, still use bulky titanium electronic packages with complex fabrication processes and wire-based electrodes which are manually fabricated by skilled workers. As a result, the cost of these devices is very high and the widespread use of these devices is limited in low- and middle income countries. Innovative approaches are essential to make implantable devices as affordable as possible while not sacrificing their performance metrics. In this study, we adopt high-performance liquid crystal polymer (LCP) as a backbone for a novel polymer-based cochlear implant. As a material for cochlear implants, LCP enables new capabilities such as miniaturization, a simpler manufacturing process, better long-term reliability, and MRI compatibility, all of which are distinct from the properties of conventional cochlear implants. Moreover, LCP also enables an extremely low-cost device based on mass production with low materials and labor costs. In this study, we report a fabrication method for the creation of a LCP-based cochlear implant system. Specifically, LCP-based electronics and packaging techniques are addressed in detail. Previous studies of LCP-based packaging use a thermally deformed package cover to secure the electronics cavity and additional laser-cut LCP bonding layers with lower melting temperatures. This method, however, requires additional metal jigs to deform the package cover, and it requires a cavity-filling material such as PDMS. We applied a recessed cavity for the electronics with the stacking of laser-cut LCP multilayers. All packaging layers are composed of the same LCP films, which have a low melting temperature. Thus, the stacked multilayer structure itself acts as a bonding layer. This packaging technology enables the device packaging with a thin credit-card shape for miniaturized, simply fabricated and less invasive devices. Implantable electronics components were also fabricated using copper-clad LCP films with PCB technology. A patterned planar coil was integrated into an LCP electronics board to replace the thick platinum coil of the conventional implant, which is located outside of the metal package. Thus, we can reduce the device dimensions and realize a more efficient receiving coil with greater uniformity. Our group has developed an atraumatic 16-channel LCP-based cochlear electrode array using MEMS technology. This electrode array was used to develop the first functional prototype of an all-LCP-based cochlear implant system. We also evaluated the effectiveness of the developed LCP-based cochlear implant. The device was implanted into an animal model and the electrically evoked auditory brainstem response was successfully measured. We also verified the MRI compatibility of the LCP-based device compared to a metal-based implant, showing that the developed device has greatly superior MRI compatibility compared to a conventional metal-based device in a 3.0-T and an ultra-high 7.0-T MRI machine. In order to enhance the long-term reliability of the LCP-based device, we developed novel leak-barrier structures which have a nanoporous surface and microscale barriers with an anti-trapezoidal cross-sectional shape. This structure increases the water leakage path length and improves the mechanical interlocking force between the polymer and the metal layer. The reliability of the leak-barrier structure was determined by accelerated lifetime soak tests (110, 95, 75 °C). Preliminary results show that both the nanoporous surface and microscale barriers make significant contributions to improving the lifetime of the polymer-based electrode array. Lastly, we conducted a manufacturing cost analysis of the developed LCP-based cochlear implant system for a better understanding of the detailed cost structure and to determine if the cost could be reduced further. Our group also has experience in the development of cochlear implant systems, including titanium packages and wire-based electrode arrays similar to those in conventional devices, and the system developed by our group had been approved by the Korean FDA. The manufacturing costs of devices developed in the past were also analyzed for a comparison with the cost of an LCP-based device. The analysis revealed that the developed LCP-based cochlear implant has a significantly lower cost with regard to the materials. Also, the manufacturing cost per unit is approximately 10 % of the cost of a titanium-based cochlear implant. Also, the LCP-based device is a batch-processable product that therefore requires less labor. Thus, the manufacturing cost is greatly reduced in proportion to the overall production. This reduction in the manufacturing cost enables disruptive opportunities with regard to the use of cochlear implants in developing countries.