36. An engineering perspective on toxicity

Abstract

Toxicity plays a central role in cryopreservation, whether it be toxicity of added cryoprotectants or of naturally occurring salts and other solutes concentrated in the unfrozen solution by ice formation. Toxicity may be studied from the viewpoint of biochemical mechanisms—understanding what molecule, pathway, or structure is “poisoned”. However, an engineering perspective on toxicity is extremely relevant to cryopreservation. The toxicity of compounds to cells is concentration, temperature, and exposure-time dependent. Understanding the cryoprotectant exposure that a cell deep within a tissue experiences in a given loading/removal protocol requires an understanding of permeation/efflux kinetics with time. The dependence of toxicity on temperature can be used to advantage in designing cryopreservation strategies. Finally, even without knowledge of toxicity mechanisms, cryoprotectant toxicity and toxicity interactions can be modelled with empirical equations for use in protocol design. Our research group has explored these issues. The developed engineering approaches to toxicity were critical in design of a protocol to cryopreserve intact full-thickness human articular cartilage on a bone base (as required for transplantation) with high chondrocyte viability, metabolic activity and function.