1. Cauterization Catheter – An Advancement in Conductive Biomaterials and Medicine C. Blyth 1, C. Fernandez 1, S. Hittinger 1, C. Jones 1, B. McGee 1 Advisors: B. Wood 2, MD, T. Kam 2, MD 1 Vanderbilt University, Nashville, TN; 2 NIH, Bethesda, MD Catheter Use  It has become possible to create a catheter able to cauterize tissue in highly vascularized regions of the body utilizing flexible materials in a cost effective and practical manner to help minimize blood loss. RF Cauterization  RF Cauterization is the process by which heat is applied to tissue, denaturing the proteins within, consequently preventing fluid loss at that site. Radio-frequency (RF) ablation is cauterization where high energy is administered in the form of radio waves by way of micro- electrodes. This energy creates frictional movement of ions which heats the tissue, denaturizing local proteins which causes coagulation. Market Need/Problem Statement IntroductionConductive Polymers Market Need  With nearly 100,000 radiofrequency ablations of tumors performed yearly and RF generators available in every operating room in the USA, there is a market need for cauterizing catheter systems in percutaneous image guided therapies by interventional radiologists. Current angio-seal devices which are used to close blood vessels after percutaneous access from catheterization are sold in the millions each year. The use of a cauterizing catheter would be more time and cost efficient. Patients taking anticoagulation medicines are at an increased risk using biliary and nephrostomy tubes because vessels might be struck during operation and pseudoaneurysm could result. Problem Statement  A catheter must be designed that is capable of conducting an RF from the generator to the tissue enabling tissue cauterization, yet it must still provide its basic function. Flexibility and biocompatibility as well as an uncomplicated, efficient and cost effective method are important characteristics.  Conductivity is created when electrons not bound to atoms are free to move. For plastics or polymers to become conductive, they must have bonding that allows for the movement of electrons. Polyacetylene (shown below) has conjugated double bonds.  Prior to doping, this polymer has limited conductivity. Doping is the process of adding or removing electrons from the compound creating free electrons through the polymer. Running an electrical field through this new polymer enables free electrons to move. The “doped” polyacetylene consequently obtains a conductivity close to that of well known conductors such as silver and copper (see figure below).  The double bonds of the conductive polymers are responsible for free electron movement. Σ bonds are fixed and unable to move, but π bonds, though localized as well, are not bound as tightly. The conjugated bonds of polyacetylene contain many π bonds and the electrical current that runs through the chain, post-electron doping, creates movement of π electrons through the entire molecule which allows the conduction of electricity. Metal conductors have a conductivity range of 10 4 -10 10 S/m. By doping polyacetylene, it is possible to achieve a conductivity similar to that of metals (10 7 S/m).  Doped polyacetylene is the conductive polymer in the catheter design and will be insulated by polyurethane. Both materials are biocompatible and cost effective. In addition to polyacetylene, polythiophene can be doped and used as a conductive polymer. Therefore, our prototype testing will include two catheters: one catheter will test the effectiveness of polyacetylene and the other polythiophene. The electronic difference between doped and undoped polythiophene is shown below. http://nobelprize.org/nobel_prizes/chemistry/laureates/2000/public.html  Power dissipates from the catheter radially in a 1/r 2 fashion (where r is distance), assuming homogenous tissue in the immediate surroundings. Design  The implanted end of the catheter has an exposed section of conductive polymer that acts as an electrode transmitting the RF waves to the surrounding tissue. The cylindrical shape ensures flush contact with the tissue. This cylindrical design provides an approximately even dissipation of power.  The outer ring of the catheter, in cyan, is insulating polymer. The inner section of the filter opening, in red, is solely made of conducting polymer while the inner portion of the catheter body is surrounded by insulating polymer preventing transduction of RF through the catheter body. The inner insulation also prevents any contamination or buildup on the catheter’s conductive region (which could adversely affect the conduction). Heat Transfer  The connecting joint is threaded so that it can establish a secure connection with the figures above and below. The piece is visualized in the complete structure in the far left performing its stabilizing operation.  This final section enables a secure connection of the conducting polymer to the RF generator source. The source has a male three prong connection that would closely mate with a female port on this bottom end of this piece. It is important to note only conducting polymer is exposed to maximize the amount of transmitted RF waves. Conductive Polymer Electrode Filter Opening of Catheter Filter Connecting Joint Connecting Joint to RF source Acknowledgement: The authors wish to thank Dr. Wood, Dr. Kam, and Dr. Guion at the NIH for their support, advice and assistance. We would also like to thank Dr. King at Vanderbilt for his instruction.  Pennes Equation of Bioheat  Arrhenius Equation  = density of tissue or blood (kg/m 3 )  = tissue state coefficient  = blood perfusion coefficient (sec -1 )  = probability of cell death at time step t (%) C = heat capacity ( J/ kg m) k = heat conduction coefficient ( W/ K m) Q m = metabolic heat source