BIOPRESERVATION: HEAT/MASS TRANSFER CHALLENGES AND BIOCHEMICAL/GENETIC ADAPTATIONS IN BIOLOGICAL SYSTEMS

Abstract

Biopreservation is the science of extending the shelf life (storage time) of biological systems. The scientific field of biopreservation can be broadly classified into three distinct but interrelated research areas: Cryopreservation (storage by freezing), Desiccation (storage by drying) and Freeze-Drying (storage by freezing first and then sublimating the frozen water). Although, both freeze-frying and desiccation create products that are easier to store and transport, they have not, as yet, been successfully applied to store a variety of biological specimens. However, both these technologies have been quite successfully applied in a variety of fields including pharmaceutical sciences and food industry, as demonstrated by the easy availability of shelf-stable drugs and instant mashed potatoes! On the other hand freezing storage has a long and storied history of being used to transport biological specimen, over long distances, as far back as the time of the Pharaohs. However, the lack of portable refrigeration/freezing techniques (and the inviolate second law) limited the use of cryopreservation in every-day life, until the early 19^th century. This short review will outline some of the challenges and opportunities in the fields of engineering, heat and mass transfer, biochemical and genetic adaptations in the preservation of biological systems.

Fig. 1

Master Switch Hypothesis: Hypothetical Model describing how low temperature (LT) in association with light regulates the expression of cold responsive genes. Low temperature is first perceived by putative membrane associated receptor(s) and then transmitted to the nucleus. This triggers global regulator (master switch). These transcription factors activate the promoters (red helix) of cold regulates genes (blue helix). The transcribed mRNAs are translated to different proteins that contribute to the development of freezing or cold tolerance (17).

Fig. 2

Inverse ‘U’ Curve showing the relationship between freezing velocity and cell response.

Fig. 3

Schematic drawing of the Krogh cylinder, a representation of generic tissue cell unit.

Fig. 4

Morphology of frozen (A) and vitrified (B) veins cryosubstituted at −90 °C. The structure of the frozen sample is noticeably distorted due to the presence of variable sized ice crystals. In marked contrast, the vitrified sample appears to be free of ice with the normal structural features of the tunica intima (I), the tunica media (M) and tunica adventitia (A) clearly discernible. Reproduced from Song et al. (2000).

Fig. 5

Generic supplemented phase diagram. See text, for discussion. Redrawn from Fahy et al. (1984).