This paper reports results of in vivo experiments that confirm the feasibility of a new minimally invasive method for tissue ablation, irreversible electroporation (IRE). Electroporation is the generation of a destabilizing electric potential across biological membranes that causes the formation of nanoscale defects in the lipid bilayer. In IRE, these defects are permanent and lead to cell death. This paper builds on our earlier theoretical work and demonstrates that IRE can become an effective method for nonthermal tissue ablation requiring no drugs. To test the capability of IRE pulses to ablate tissue in a controlled fashion, we subjected the livers of male Sprague-Dawley rats to a single 20-ms-long square pulse of 1000 V/cm, which calculations had predicted would cause nonthermal IRE. Three hours after the pulse, treated areas in perfusion-fixed livers exhibited microvascular occlusion, endothelial cell necrosis, and diapedeses, resulting in ischemic damage to parenchyma and massive pooling of erythrocytes in sinusoids. However, large blood vessel architecture was preserved. Hepatocytes displayed blurred cell borders, pale eosinophilic cytoplasm, variable pyknosis and vacuolar degeneration. Mathematical analysis indicates that this damage was primarily nonthermal in nature and that sharp borders between affected and unaffected regions corresponded to electric fields of 300-500 V/cm.

A surgical micra-robot that swims inside the human ureter is proposed to provide a novel and minimally invasive method of kidney stone destruction. Inspired by the swimming mechanisms of bacteria such as E. coli, the robot utilizes biomimetic synthetic flagella composed of multiwalled carbon nanotubes that are driven into a rotating helical shape by a micro motor. Design aspects are discussed with the focus on locomotion. The performance of the propulsion mechanism is determined through simultaneous modeling of the viscous drag on the filaments and the stress strain behavior of the nanotubes. The effects of the syntheticflagellum geometry and frequency of rotation on efficiency and swimming speed are explored. With InW of power, utilizing 100pm-Iong filaments, swimming speeds approaching I "/s are shown to be possible for a realistic design. The proposed new robot would revolutionize kidney stone destruction i f implemented, yet the design of the robot and the propulsion analysis are applicable to many other possible surgical procedures. I. INTRODUCnONThis paper presents the design of a robot that swims inside the human ureter to destroy kidney stones non-invasively. In order to accomplish this, the robot has to maneuver through the urethra and into the bladder, then enter the correct ureter and find the kidney stones. Once it has found them, it needs to he capable of destroying the stones without adverse effects to the surrounding tissue. Upon completion of its task, it must exit the body safely. The duration of the procedure should he similar to that of other stone removal techniques.The design of the robot is presented as a total system. Major functions include sensors, a power source, means of communication, control, packaging, stone destruction and propulsion. This paper primarily focuses on the design of the propulsion mechanism.Research into swimming micro-robots for in vivo applications faces many challenges, of which a means of propulsion and a power source are two primary concems. In order to design propulsion systems that work at the micro scale, it is instructive to look at how nature has accomplished this. In the Stokes flow regime present in microscopic viscous media, bacteria and spermatozoa use flagella and cilia to swim. Flagella and cilia range from 18nm to half a micron in diameter and from a few hundred nanometers in 7 n h e first two authors contributed equally: 0 ; 1~o 3 = 1~6~i~w $ i 7 . o 0 CI 2w3 IEEE 2583

The temperature-dependent impedivity of rat liver, transverse abdominal muscle and full skin was determined in vitro as a function of frequency across the temperature range 5 degrees C to 37 degrees C and from 100 Hz to 10 kHz. This study was motivated by an increasing interest in using electrical impedance tomography (EIT) for imaging of cryosurgery and a lack of applicable data in the hypothermic range. Using a controlled-temperature impedance analyzer, it was found that as the temperature is reduced the resulting increase in tissue impedivity is more pronounced at low frequencies and that the beta dispersion, resulting from cell membrane polarization, shifts to lower frequencies. With these new data a simple case study of EIT of liver cryosurgery was examined, using a finite-element model incorporating the Pennes bio-heat equation, to determine the impact of this behavior on imaging accuracy. Overestimation of the ice-front position was found to occur if the EIT system ignored the effects of the low-temperature zone surrounding the frozen tissue. This error decreases with increasing blood perfusion and with higher measurement frequencies.

Methods that can determine the extent of tissue damage in transplant organs, before the decision to transplant has been made, have the potential to improve the outcome of the procedure by preventing unfit organs from being transplanted into the patient. The raised confidence in the organ state with such a technique would also increase availability. Now restricted due to the fear of introducing a failed organ resulting from the relative lack of viability data during transport, stringent criteria for donation would relax. Electrical impedance tomography is an imaging modality that recovers the spatial variation of the complex impedivity in the body from electrical measurements made on the periphery. In this study, we apply 3D EIT with the complete electrode model to a sample conductivity distribution that might result from an organ that is losing its viability due to prolonged ischemia. The reconstructed images show that EIT has the potential to become an adjuvant method for the field of organ transplantation.