Cauterization Catheter

1
Cauterization Catheter An Advancement in
Conductive Biomaterials and Medicine C. Blyth1,
C. Fernandez1, S. Hittinger1, C. Jones1, B.
McGee1 Advisors B. Wood2, MD, T. Kam2,
MD 1Vanderbilt University, Nashville, TN 2NIH,
Bethesda, MD
Design
Introduction
Conductive Polymers

• 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. S bonds
  are fixed and unable to move, but p bonds, though
  localized as well, are not bound as tightly .
  The conjugated bonds of polyacetylene contain
  many p bonds and the electrical current that runs
  through the chain, post-electron doping, creates
  movement of p electrons through the entire
  molecule which allows the conduction of
  electricity. Metal conductors have a conductivity
  range of 104-1010 S/m. By doping polyacetylene,
  it is possible to achieve a conductivity similar
  to that of metals (107 S/m).

• 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.

• 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.

Conductive Polymer Electrode

• 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
  catheters conductive region (which could
  adversely affect the conduction).

Market Need/Problem Statement

• 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.

Filter Opening of Catheter

• 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.

Filter Connecting Joint
Heat Transfer

• Power dissipates from the catheter radially in a
  1/r2 fashion (where r is distance), assuming
  homogenous tissue in the immediate surroundings.

• Pennes Equation of Bioheat

• 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.

• Arrhenius Equation

? density of tissue or blood (kg/m3) ? 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) Qm metabolic
heat source
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.