@conference {131, title = {Towards addressable wireless microstimulators based on electronic rectification of epidermically applied currents}, booktitle = {Annual International Conference of the IEEE Engineering in Medicine and Biology Society}, year = {2014}, month = {2014///}, pages = {3973 - 3976}, publisher = {IEEE}, organization = {IEEE}, address = {Chicago}, abstract = {

Electrical stimulation has been explored to restore the capabilities of the nervous system in paralysis patients. This area of research and of clinical practice, known as Functional Electrical Stimulation, would greatly benefit from further miniaturization of implantable stimulators. To that end, we recently proposed and demonstrated an innovative electrical stimulation method in which implanted microstimulators operate as rectifiers of bursts of innocuous high frequency current supplied by skin electrodes, thus generating low frequency currents capable of stimulating excitable tissues. A diode could suffice in some applications but, in order to broaden the method{\textquoteright}s clinical applicability, we envision rectifiers with advanced capabilities such as current control and addressability. We plan flexible thread-like implants (diameters \< 300 urn) containing ASICs. As an intermediate stage, we are developing macroscopic implants (diameters \~{} 2 mm) made of off-the-shelf components. Here we present a circuit which responds to commands modulated within the high frequency bursts and which is able to deliver charge-balanced currents. We show that a number of these circuits can perform independent stimulation of segments of an anesthetized earthworm following commands from a computer.

}, keywords = {Batteries, Capacitors, Electrical Stimulation, Electrodes, Implants, Microcontrollers, Rectifiers}, author = {Laura Becerra-Fajardo and Antoni Ivorra} } @article {Ivorra2011a, title = {{Remote electrical stimulation by means of implanted rectifiers.}}, journal = {PloS one}, volume = {6}, number = {8}, year = {2011}, pages = {e23456}, abstract = {

Miniaturization of active implantable medical devices is currently compromised by the available means for electrically powering them. Most common energy supply techniques for implants{\textendash}batteries and inductive couplers{\textendash}comprise bulky parts which, in most cases, are significantly larger than the circuitry they feed. Here, for overcoming such miniaturization bottleneck in the case of implants for electrical stimulation, it is proposed to make those implants act as rectifiers of high frequency bursts supplied by remote electrodes. In this way, low frequency currents will be generated locally around the implant and these low frequency currents will perform stimulation of excitable tissues whereas the high frequency currents will cause only innocuous heating. The present study numerically demonstrates that low frequency currents capable of stimulation can be produced by a miniature device behaving as a diode when high frequency currents, neither capable of thermal damage nor of stimulation, flow through the tissue where the device is implanted. Moreover, experimental evidence is provided by an in vivo proof of concept model consisting of an anesthetized earthworm in which a commercial diode was implanted. With currently available microelectronic techniques, very thin stimulation capsules (diameter \<500 {\textmu}m) deliverable by injection are easily conceivable.

}, keywords = {Animals, Electric Stimulation, Electric Stimulation: instrumentation, Electric Stimulation: methods, Electrodes, Implanted, Oligochaeta, Software}, issn = {1932-6203}, doi = {10.1371/journal.pone.0023456}, url = {http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=3151300\&tool=pmcentrez\&rendertype=abstract}, author = {Antoni Ivorra} } @article {Laufer2010, title = {{Electrical impedance characterization of normal and cancerous human hepatic tissue.}}, journal = {Physiological measurement}, volume = {31}, number = {7}, year = {2010}, pages = {995{\textendash}1009. {\textcopyright} 2010 Institute of Physics and IOP Publishing Limited.}, abstract = {

The four-electrode method was used to measure the ex vivo complex electrical impedance of tissues from 14 hepatic tumors and the surrounding normal liver from six patients. Measurements were done in the frequency range 1-400 kHz. It was found that the conductivity of the tumor tissue was much higher than that of the normal liver tissue in this frequency range (from 0.14 +/- 0.06 S m(-1) versus 0.03 +/- 0.01 S m(-1) at 1 kHz to 0.25 +/- 0.06 S m(-1) versus 0.15 +/- 0.03 S m(-1) at 400 kHz). The Cole-Cole models were estimated from the experimental data and the four parameters (rho(0), rho(infinity), alpha, f(c)) were obtained using a least-squares fit algorithm. The Cole-Cole parameters for the cancerous and normal liver are 9 +/- 4 Omega m(-1), 2.2 +/- 0.7 Omega m(-1), 0.5 +/- 0.2, 140 +/- 103 kHz and 50 +/- 28 Omega m(-1), 3.2 +/- 0.6 Omega m(-1), 0.64 +/- 0.04, 10 +/- 7 kHz, respectively. These data can contribute to developing bioelectric applications for tissue diagnostics and in tissue treatment planning with electrical fields such as radiofrequency tissue ablation, electrochemotherapy and gene therapy with reversible electroporation, nanoscale pulsing and irreversible electroporation.

}, keywords = {80 and over, Adult, Aged, Electric Impedance, Electrodes, Female, Humans, Liver, Liver Cirrhosis, Liver Cirrhosis: pathology, Liver Neoplasms, Liver Neoplasms: pathology, Liver: pathology, Male, Middle Aged}, issn = {1361-6579}, doi = {10.1088/0967-3334/31/7/009}, url = {http://www.ncbi.nlm.nih.gov/pubmed/20577035}, author = {Laufer, Shlomi and Antoni Ivorra and Reuter, Victor E and Boris Rubinsky and Solomon, Stephen B} }