Abstract
Current antennas used for communication with implantable medical devices are connected directly to the titanium device enclosure, but these enclosures are shrinking as batteries and circuits become smaller. Due to shrinking device size, a new approach is needed that allows the antenna to extend beyond the battery pack, or to be entirely separate from it. Softer properties are needed for antennas in direct contact with body tissues. This must be achieved without compromising the high electrical conductivities and stabilities required for acceptable performance. Here, a nanocomposite based approach was taken to create soft, biocompatible antennas that can be embedded in the fat layer as an alternative to the metallic antennas used today. The nanocomposite films combine the exceptional electrical conductivity, biocompatibility, and biostability of Au nanoparticles with the mechanical compliance, biocompatibility, and low water permeability of polyurethane. Nanocomposite film synthesis utilized flocculation and vacuum assisted filtration methods. The soft antenna films display high conductivities (∼103 S/m–105 S/m), reduced Young’s moduli (∼102 MPa–103 MPa), exceptional biocompatibilities characterized by in vivo and in vitro work, and notable biostabilities characterized by accelerated degradation studies. Consequently, the nanocomposite antennas are promising for chronic in vivo performance when the conductivity is above 103 S/m.
Highlights
Implantable bioelectronics are becoming increasingly important for diagnostics and treatments of diseases, including neural electrode arrays for functional brain–computer interfaces,1 deep brain stimulators,2,3 intracranial seizure advisory systems,4 cardiac pacemakers,5 and cochlear implants.6 Wireless antennas are an essential component to implantable bioelectronic telemetry systems for monitoring the status of the medical devices and transmission of patient data.4,7,8 To perform efficiently, an antenna must be approximately half a wavelength long at its operating frequency.9–11 Common frequencies for implantable antennas are the MedRadio band (402 MHz–405 MHz), which corresponds to an antenna length of ∼6 cm while implanted in the body.12 Many MedRadio antennas are less than half a wavelength long, which is suboptimal for the antenna, but often necessary given the available space
Our objective is to develop a material that has suitable electrical and mechanical characteristics for an implantable antenna that can be embedded in the fat layer under the skin
We present highly conductive and soft Au nanocomposites developed through a vacuum assisted flocculation method for use to fabricate implantable antennas
Summary
Implantable bioelectronics are becoming increasingly important for diagnostics and treatments of diseases, including neural electrode arrays for functional brain–computer interfaces, deep brain stimulators, intracranial seizure advisory systems, cardiac pacemakers, and cochlear implants. Wireless antennas are an essential component to implantable bioelectronic telemetry systems for monitoring the status of the medical devices and transmission of patient data. To perform efficiently, an antenna must be approximately half a wavelength long at its operating frequency. Common frequencies for implantable antennas are the MedRadio band (402 MHz–405 MHz), which corresponds to an antenna length of ∼6 cm while implanted in the body. Many MedRadio antennas are less than half a wavelength long, which is suboptimal for the antenna, but often necessary given the available space. Wireless antennas are an essential component to implantable bioelectronic telemetry systems for monitoring the status of the medical devices and transmission of patient data.. An antenna must be approximately half a wavelength long at its operating frequency.. Many MedRadio antennas are less than half a wavelength long, which is suboptimal for the antenna, but often necessary given the available space. Medical devices are continually shrinking (the Utah neural array is about 4 × 4 mm2) and no longer have the space available to directly support this antenna size on the device itself. By remotely locating the primary antenna closer to the skin within the fat layer and installing a smaller, more accommodating antenna to act as a passively coupled feed, the size of the antenna is no longer limited to the size of the implantable device. Locating the antenna within the fat layer [Fig. 1(a)] takes advantage of the fat’s electrically insulating properties and eliminates the need for encapsulation of the antenna in supplementary insulating materials
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