Biothermal Technology Laboratory

Fracture Formation Around a 1.3 mm Cryosurgical Probe

with Thermal Insulation

Department of Mechanical Engineering

Carnegie Mellon University

Objective

To demonstrate fracture formation around a cryosurgical probe.

Methods

A prototype of a proprietary cryoprobe is applied in water. The cryoprobe is constructed as a U-shape heat exchanger with a sharp pointed tip. The cryoprobe is cooled with liquid nitrogen, supplied from a hand-held container, and pressurized with compressed air.

Observations and Comments

1. It is demonstrated that fracture formation can be prevented during cooling by reducing the cooling rate.

2. Due to a the low cooling rate in the current demonstration, no fractures were formed during cooling. However, fractures always form within seconds from the beginning of rewarming. The same observation repeated four times during the demonstrated process, when liquid nitrogen supply was stopped for 10 seconds intervals. This observation indicates that thawing is not the inverse of freezing in the solid mechanics sense.

3. During cryosurgery, results may differ from the current demonstration in water due to the fact that tissue freezing occurs over a significant temperature range, while pure water freezes at a unique temperature. Nevertheless, fracture formation in biological tissues is expected to be qualitatively consistent with the current demonstration.

Cryoprobe tube diameter = 1.3 mm

Beaker diameter = 65 mm

Four freezing periods separated by 10 sec intervals of no liquid nitrogen flow.

Elapsed time in is shown on each photo (min:sec).