NONINVASIVE DETECTION OF THERMAL-STRESS FRACTURES IN FROZEN BIOLOGICAL-MATERIALS

Thermal stress induced fractures render cryopreserved frozen tissue un usable for transplantation and cause bleeding and medical complication s during cryosurgery. It would be beneficial to know when those intern al fractures occur prior to the medical failure of the treated tissue. To this end, we introduce an acoustic emission technique for non-inva sive and instantaneous detection of the occurrence of internal fractur es during freezing of biological materials. The method employs a piezo electric element which converts the pressure waves produced by fractur es into electrical signals. The use of the technique is illustrated th rough a study of one dimensional, in vitro freezing of liver. It is sh own that while fracture formation frequency and amplitude are qualitat ively proportional to the cooling rates during freezing, the fracture formation event is stochastic and the occurrence in individual cases, unpredictable.