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Fracture Formation Around a Cryosurgical Probe

The development of thermo-mechanical stress is inherent to phase-change processes typical to cryosurgery. When the level of stress reaches the strength of the material, structural destruction follows, with fracture formation as its most dramatic outcome. In the context of cryosurgery, fracture formation at the solid state may result in unexpected injury and excessive bleeding in the cryotreated area after thawing.

The objective in this study is to demonstrate fracture formation in typical conditions to cryosurgery, but in pure water, which enables visualization of the fracturing process. Actual results during cryosurgery may differ as tissue freezing occurs over a significant temperature range, while pure water freezes at a unique temperature. Nonetheless, fracture formation in biological tissues is expected to be qualitatively consistent with the current demonstration.

Fractures tend to form during cooling as well as during rewarming, however the rate of fracture formation is much more dramatic during rewarming. It is possible to prevent fracture formation during cooling by reducing the rate of cooling. However, we could not prevent fracture formation at the onset of rewarming, regardless of the experimented thermal protocol.

This study uses a proprietary cryoprobe, in the shape of a U-tube heat exchanger with a sharp pointed tip. The cryoprobe is cooled with liquid nitrogen, supplied by a hand-held container, and pressurized with compressed air. Some pictures show simple tubes rather than a cryoprobe, to demonstrate that the process is not unique to the specific cryoprobe design.

Pictures gallery:

• Fracture formation around a 1.3 mm cryoprobe

• Fracture formation around a 2.2 mm cryoprobe

• Fracture formation around a 1.3 mm cryoprobe with thermal insulation

• Fracture formation around a 1.3 mm cryoprobe at low cooling rates

• Fracture formation around a 1.3 mm cryogenic tube

• Fracture formation around a 2.2 mm cryogenic tube

• Fracture formation around three 1.3 mm cryoprobes

• Fracture formation around three 1.3 mm cryoprobes with thermal insulation

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