ABSTRACT
Current generation left ventricular assist devices (LVADs) are powered by a percutaneous driveline. The high prevalence of driveline infections has motivated the development of transcutaneous energy transfer (TET) systems which eliminate driveline associated complications by wirelessly delivering power across the skin. Destination therapy (DT) requires long-term reliable operation of the TET electronics suggesting the use of hermetic packaging techniques as used in all other chronically implanted devices. TET coils dissipate heat during operation and in order for the technology to be suitable for patient use, sufficient power must be delivered while maintaining temperatures at levels deemed safe. The heating of a TET system designed for DT which uses hermetic packaging technology was evaluated in silico and in vivo. A numerical model was used to evaluate the temperature of the TET coils. The TET system was fabricated and assessed in vivo using an ovine model. The receiving coil was implanted subcutaneously in a sheep and the transmission coil placed in contact with the skin and concentric to the implanted coil. Temperatures of the system were measured using sensors fixed to the surface of the coils. Numerical modeling indicated that the maximum temperatures of the primary and secondary coil surfaces were 38.13°C and 38.41°C, respectively, when delivering 10 W continuously. Stable temperatures were observed in vivo after 70 minutes and the maximum skin and implant surface temperatures were 37.73°C and 38.31°C, respectively. This study showed that a hermetic, chronically implantable TET system is thermally safe when continuously delivering 10 W of power, sufficient to power modern LVADs.
Subject(s)
Energy Transfer , Equipment Design , Heart-Assist Devices , Animals , Electric Power Supplies , Female , Models, Animal , Sheep , Skin , TemperatureABSTRACT
Implanted electronics require protection from the body's fluids to avoid moisture induced failure. This study presents an injection molded liquid crystal polymer (LCP) package to protect active implantable devices for chronic applications, such as in optogenetic research. The technology is applied and assessed through a custom package for a fully implantable optogenetic stimulation system, built on a versatile telemetry system that can incorporate additional stimulating and recording channels. An adapted quasi-steady state model predicts the lifetime of an enclosure, where the definition of the lifetime is the time before the internal relative humidity (RH) reaches a time constant, or 63%RH, a conservative limit to minimize the risk of corrosion. The lifetime of the LCP optogenetic device is 94 days, and can be extended to 326 days with the inclusion of 5% w/v silica gel desiccant. Samples of the LCP optogenetic device containing humidity sensors testing in saline at 38 °C support the RH change predictions. Desiccants inside the implant enclosure can store permeating moisture and prolong the life expectancy of LCP-based implants to years or decades. The results of this study demonstrates the feasibility of providing reliable protection for chronic optogenetic implants, and the technology can be transferred to other applications as an easily-manufactured, cost-effective, radiofrequency compatible alternative to hermetic packaging for chronic studies.
