Selection of an optimal cryoprotectant for long-term storage of human tendon allografts

Introduction. Tendon grafts are widely demanded in reconstructive plastic surgery. Allogeneic tendons potentially have a number of advantages. However, the method of long-term storage of allogeneic tendons has not been optimized to date. Aim. Selection of an optimal cryoprotectant for the storage of human tendon allografts at ultra-low temperatures, which allows preserving the native tissue structure. Material and methods. We studied M. tibialis anterior tendon grafts taken from tissue donors. Endocellular/penetrating cryoprotectants (dimethyl sulfoxide, polyethylene glycol-400, glycerol) and exocellular/non-penetrating cryoprotectants (glucose solution, albumin solution) were used in the cryopreservation process. Tendon mechanical properties were evaluated using rupture and stretching-shear test, the general morphology of tendons, topography, dense and integrity of collagen fibers, preservation of cellular elements were microscopically evaluated. Results. Histological analysis showed that the safety of collagen and elastin fibers differed depending on the cryoprotectant used. At the same time, micro-fractures of collagen fibers were microscopically detected in all the experiments. In the presence of dimethyl sulfoxide, polyethylene glycol-400 and their combination the structure of collagen fibers and cells did not undergo visible changes compared to the control, whereas in all the experiments with non-penetrating cryoprotectants the topography and orientation of the fibers were clearly disturbed, deformation of many cells in the tendons was also observed. Conclusions. Cryoprotectants based on dimethyl sulfoxide, polyethylene glycol and their combinations allowed us to preserve the structural integrity of allogeneic tendons. Non-penetrating cryoprotectants did not effectively preserve the integrity of collagen fibers and cells in the tendons and cannot be recommended for cryopreservation.