Cryopreservation of cultured periosteum: Effect of different cryoprotectants and pre-incubation protocols on cell viability and osteogenic potential

Evidence has accumulated that periosteal cells have a great potential to regenerate bone. We have demonstrated that cultured periosteum (CP) in membrane form is an effective device to regenerate alveolar bone. To increase the availability of CP in a clinical environment, an effective cryopreservation protocol for CP has been developed. In this study, three different cryoprotectants (Me2SO, glycerol, and ethylene glycol) were used. The effect on cell viability of pre-incubation temperature, pre-incubation time, and agitation during incubation was investigated. Samples were stored at −196 °C for 10 days. Cell viability was assessed by a colorimetric cell viability assay using a tetrazolium salt, and the assay results were confirmed by confocal laser scanning microscopy after staining with a combination of calcein AM and ethidium homodimer-1. The activity of the cells after thawing was assessed by alkaline phosphatase assay. To assess the osteogenic potential of cryopreserved CP, the CP was grafted to calvarial defects in athymic rats. The greatest cell viability was obtained in the group equilibrated at 37 °C for 30 min with Me2SO, under agitation, showing 63.3 ± 10.5% recovery. After cryopreservation, the cell growth of surviving cells was identical when Me2SO was used as a cryoprotectant. Alkaline phosphatase (ALP) activity was maintained in the groups cryopreserved with Me2SO and glycerol. The transplantation experiment showed that the calvarial defects were completely closed by grafting cryopreserved CP, which demonstrates that the osteogenic property of CP was well maintained. An efficient cryopreservation protocol for CP has been developed and this will provide a convenient and effective treatment option for bone regeneration in clinics.