Project Definition • The aim of this project was to design a steerable catheter, which would enable easier access to specific blood vessels. The design would be used in the Radiology Department for improved treatment of cerebral aneurysms in the brain. Additionally, a simulated arterial system was created for catheter testing and training.
Background • Aneurysms are disorders that involve the localized widening of one or more blood vessels. It is estimated that 5% of the population has some type of aneurysm. There are no known ways to prevent aneurysms, but they are often treatable. The most common method used to treat an aneurysm is surgery. During surgery a catheter is inserted and guided into a specific blood vessel. The base of the aneurysm is closed off with clamps, sutures, coils, and other methods using catheters. Currently, catheter guidance techniques involve the use of various guide wires which can be very difficult and time consuming. The design of a steerable catheter would allow the surgeon to access hard to reach areas in less time.
Demands & Wishes • Demands • Catheter can turn up to 90° in any direction • Catheter diameter must be 1 mm in order to access arteries ranging in diameter from 2-3 mm • Perform within temperature range between 95°F and 105°F • Perform in various viscosity levels of the blood • Perform under various flow patterns and pulsatile natures of the blood • Catheter must not alter or harm the well being of the patient • Wishes • Catheter should be relatively easy to handle and maneuver • Price should be competitive with current catheters in the market
Calculations • What should the ratio of glycerol to water be to represent the viscosity of blood? • Given: • blood 4cP, m 8 mol/kg, MWGlycerol = 92 g, glycerol 1.1 g/cm3 • Solution: • Volume of glycerol = (molality)(Molecular Weight)/(Density glycerol) • = 0.669 Liters of glycerol/Liter of H2O • Determination of Reynold’s Number (Ex. S.E.D. = 5): • Given: • solution = 1.04 g/cm3, Diam. = 0.79375 cm, solution 4cP, Area = 0.495 cm2 • Solution: • Velocity (V) = Flow (Q)/ Area (A) = 47.58 cm/sec • Reynold’s Number (Re) = (solution)(V)(D)/(solution) = 982…Laminar
Catheter Models • Model I consisted of a turn-wire threaded completely through the catheter and fastened to the end about 0.5-1.0 in. down the outside of the catheter with silicon. • Model II is very similar to Model I except that the wire exits the catheter about 1 in. below the catheter tip where it is then fastened with silicon to the catheter head.
Catheter Models (cont.) • Model III followed the concept of Model II with the exception that the turn-wire floats freely outside the catheter to decrease the resistance between the wire and the catheter. To further this design, improvements must be done to guide the turn wire along the outside of the catheter. • Model IV* is currently under development, although proper materials are uncertain. The catheter design contains two types of tubing with varying stiffness connected by silicon. Again, a turn-wire is completely threaded through the catheter and attached with silicon to the catheter tip.The tube creating the catheter tip is more pliable than the other Suggestion from Dr. Bob Galloway
Catheter Models (cont.) • Model V will be created using Muscle-Wire technology. Muscle-Wire contracts when heated electrically past a threshold temperature. In this design, electrical wires attached to the Muscle-Wire run through the inside of the catheter. The Muscle-Wire is attached to the head of the catheter. Silicon will seal the head of the catheter to prevent liquid from entering.
Overview: A closed-loop system, created from a reservoir, roller pump, and surgical tubing, allows the continual flow of a water and glycerol solution (providing Newtonian fluid characteristics) simulating blood within the arterial system. The model is approximately twice the size of the actual microvasculature (IDtubing = 6.3 mm). Objectives: Test prototypes of catheter designs Create an applicable learning device to further catheter insertion and guidance techniques* Simulated Arterial System *Suggestion from Dr. Paul King
Catheter Design Feasibility of heating Muscle Wire in vivo Optimal attachment positions of turn-wire on head of catheter Appropriate materials for Model IV design Arterial Model Similarity of surgical tubing in relation to actual arterial wall stiffness Leakage at catheter insertion point Accuracy of blood flow within cerebral vasculature Uncertainties
Future Work • Follow-up on uncertainties • Continue patent search • Build and test additional prototypes • Research the possibility of marketing the simulated arterial system for catheter training purposes • GRADUATE!