Kara N. Bocan

Carbon Nanotube Chemiresistor for Wireless pH Sensing

The ability to accurately measure real-time pH fluctuations in-vivo could be highly advantageous. Early detection and potential prevention of bacteria colonization of surgical implants can be accomplished by monitoring associated acidosis. However, conventional glass membrane or ion-selective field-effect transistor (ISFET) pH sensing technologies both require a reference electrode which may suffer from leakage of electrolytes and potential contamination. Herein, we describe a solid-state sensor based on oxidized single-walled carbon nanotubes (ox-SWNTs) functionalized with the conductive polymer poly(1-aminoanthracene) (PAA). This device had a Nernstian response over a wide pH range (2–12) and retained sensitivity over 120 days. The sensor was also attached to a passively-powered radio-frequency identification (RFID) tag which transmits pH data through simulated skin. This battery-less, reference electrode free, wirelessly transmitting sensor platform shows potential for biomedical applications as an implantable sensor, adjacent to surgical implants detecting for infection.

Adaptive Transcutaneous Power Transfer to Implantable Devices: A State of the Art Review.

Wireless energy transfer is a broad research area that has recently become applicable to implantable medical devices. Wireless powering of and communication with implanted devices is possible through wireless transcutaneous energy transfer. However, designing wireless transcutaneous systems is complicated due to the variability of the environment. The focus of this review is on strategies to sense and adapt to environmental variations in wireless transcutaneous systems. Adaptive systems provide the ability to maintain performance in the face of both unpredictability (variation from expected parameters) and variability (changes over time). Current strategies in adaptive (or tunable) systems include sensing relevant metrics to evaluate the function of the system in its environment and adjusting control parameters according to sensed values through the use of tunable components. Some challenges of applying adaptive designs to implantable devices are challenges common to all implantable devices, including size and power reduction on the implant, efficiency of power transfer and safety related to energy absorption in tissue. Challenges specifically associated with adaptation include choosing relevant and accessible parameters to sense and adjust, minimizing the tuning time and complexity of control, utilizing feedback from the implanted device and coordinating adaptation at the transmitter and receiver.

Innovation and Translation Efforts in Wireless Medical Connectivity, Telemedicine and eMedicine: A Story from the RFID Center of Excellence at the University of Pittsburgh

Translational research has recently been rediscovered as one of the basic tenants of engineering. Although many people have numerous ideas of how to accomplish this successfully, the fundamental method is to provide an innovative and creative environment. The University of Pittsburgh has been accomplishing this goal though a variety of methodologies. The contents of this paper are exemplary of what can be achieved though the interaction of students, staff, faculty and, in one example, high school teachers. While the projects completed within the groups involved in this paper have spanned other areas, the focus of this paper is on the biomedical devices, that is, towards improving and maintaining health in a variety of areas. The spirit of the translational research is discovery, invention, intellectual property protection, and the creation of value through the spinning off of companies while providing better health care and creating jobs. All but one of these projects involve wireless radio frequency (RF) energy for delivery. The remaining device can be wirelessly connected for data collection.

Tissue Variability and Antennas for Power Transfer to Wireless Implantable Medical Devices

The design of effective transcutaneous systems demands the consideration of inevitable variations in tissue characteristics, which vary across body areas, among individuals, and over time. The purpose of this paper was to design and evaluate several printed antenna topologies for ultrahigh frequency (UHF) transcutaneous power transfer to implantable medical devices, and to investigate the effects of variations in tissue properties on dipole and loop topologies. Here, we show that a loop antenna topology provides the greatest achievable gain with the smallest implanted antenna, while a dipole system provides higher impedance for conjugate matching and the ability to increase gain with a larger external antenna. In comparison to the dipole system, the loop system exhibits greater sensitivity to changes in tissue structure and properties in terms of power gain, but provides higher gain when the separation is on the order of the smaller antenna dimension. The dipole system was shown to provide higher gain than the loop system at greater implant depths for the same implanted antenna area, and was less sensitive to variations in tissue properties and structure in terms of power gain at all investigated implant depths. The results show the potential of easily-fabricated, low-cost printed antenna topologies for UHF transcutaneous power, and the importance of environmental considerations in choosing the antenna topology.

Transmission mechanisms with variable tissue properties in a paired electrode system for transcutaneous power

Wireless transcutaneous power transfer and communication has the potential to reduce the size of implantable medical devices, thereby reducing patient discomfort and minimizing the tissue area exposed to foreign material. Electromagnetic transmission mechanisms through tissue are determined by tissue structure and associated frequency-dependent tissue properties, which are significant in the design of wireless implantable medical devices. The purpose of this study was to investigate the effects of varying tissue dielectric properties on maximum power transfer to a subcutaneously implanted device in a paired electrode system designed for use in proximity to metallic orthopedic implants. The transcutaneous system including external and implanted electrode pairs was simulated at several radio frequencies (125 kHz, 1 MHz, 13.56 MHz, 403 MHz, and 915 MHz) while varying the dielectric properties of the tissue medium over a range of physiological values. Maximum power transfer was calculated to represent the best-case power gain across the range of tissue properties and frequencies, and greater achievable efficiencies were seen with higher quality factor as a function of the tissue properties. The results suggest that in the paired electrode system, utilization of capacitive coupling allows the system to function in proximity to metallic surfaces such as orthopedic implants. The results also suggest that higher power gains are possible through a choice of implant location based on expected tissue properties.

Multi-Disciplinary Challenges in Tissue Modeling for Wireless Electromagnetic Powering: A Review

Wireless electromagnetic powering of implantable medical devices is a diverse research area, with goals including replacing percutaneous wires, miniaturizing and extending the lifetime of implanted devices, enabling wireless communication, and biosensing, all while maximizing safety and efficiency of wireless power transfer. Many challenges in wireless transcutaneous powering are associated with tissue as an electromagnetic transmission medium. Tissue is lossy and variable, and safety is a concern due to absorption of electromagnetic energy in high-water-content tissue. The purpose of this overview is to summarize reported variability of tissue properties, particularly in the context of electromagnetic safety, with a focus on models of tissue that can represent variability in the design and evaluation of systems for wireless transcutaneous power transfer.