Interstitial ice formation in cryopreserved homografts: a possible cause of tissue deterioration and calcification in vivo.
OBJECTIVE
Cryopreserved valve homografts often fail in infants. Controversies are ongoing concerning the relative contributions of cryopreservation variables, immune responses, cellular viability, and durability of the extracellular matrix to the mode of tissue failure.


METHODS
Tissues to be examined for patterns of ice crystal distribution were cryopreserved. Tissue water was substituted with methanol and the tissues cryopreserved conventionally using dimethylsulfoxide, after which they were warmed and processed for light or electron microscopy. Selected specimens were vitrified to prevent ice crystal formation, cryopreserved, and subsequently warmed and processed for light and electron microscopy.


RESULTS
Cryosubstitution of conventionally cryopreserved heart valves, while still frozen, demonstrated extensive extracellular ice formation, with smaller crystals in the ventricularis than in either the spongiosa or fibrosa. Extracellular ice formation was prevented by vitrification, a process in which the biological system is stabilized as an amorphous solid in the absence of crystalline ice.


CONCLUSIONS
It is proposed that the extensive ice formation observed in conventionally cryopreserved heart valves may cause extracellular matrix damage that predisposes the valves to calcification. Future studies will assess the above hypothesis by comparison of conventional and ice-free (vitrification) cryopreservation methods in animal models of calcification.
Brockbank
K G
KG
Organ Recovery Systems, Inc., Port City Center, Charleston, South Carolina 29403, USA.
Lightfoot
F G
FG
Song
Y C
YC
Taylor
M J
MJ
D000818:Animals; D001021:Aortic Valve / Q000473:pathology / Q000637:transplantation; D002114:Calcinosis / Q000473:pathology*; D015925:Cryopreservation; D004195:Disease Models, Animal; D005109:Extracellular Matrix / Q000473:pathology; D006085:Graft Survival / Q000502:physiology; D006351:Heart Valves / Q000473:pathology / Q000637:transplantation*; D007053:Ice; D008854:Microscopy, Electron; D009926:Organ Preservation; D011183:Postoperative Complications / Q000473:pathology*; D012307:Risk Factors; D013552:Swine
D007053:Ice