Allogeneic heart valve storage above the glass transition at -80°C

Background: Cryopreserved allogeneic heart valves are usually stored and transported below -135°C; however, such methods require expensive equipment for both storage and transportation.

Methods: In this study, vitrified porcine aortic valves were stored on either side of the cryoprotectant formulation's glass transition temperature (-119°C) at -80°C and -135°C, using a newly formulated vitrification solution (VS83) consisting of a combination of 4.65M dimethyl sulfoxide, 4.65M formamide, and 3.30M 1,2-propanediol. Three groups of valves were studied: (1) fresh; (2) VS83-preserved, stored at -80°C; and (3) VS83-preserved, stored at -135°C.

Results: Using the VS83 cryoprotectant concentration formulation, cracking was not observed during valve storage. No ice-related events were detectable during 5°C rewarming by differential scanning calorimetry. All cryopreserved tissue samples demonstrated significantly less viability than fresh samples (p<0.01). No significant viability differences were observed between the VS83-preserved groups stored at -80°C and -135°C. Material testing did not reveal any significant differences among the three test groups. Multiphoton imaging of VS83-preserved heart valves stored at -80°C and -135°C demonstrated similar collagen and elastin structures.

Conclusions: These results indicate that VS83-preserved heart valves can be stored and transported at temperatures in the vicinity of -80°C with retention of extracellular matrix integrity and material properties. The VS83 preservation of heart valves at -80°C without the need for liquid nitrogen should result in both decreased manufacturing costs and reduced employee safety hazards. Moreover, it is anticipated that low cell viability may result in less immunogenicity in vivo.