A Novel Transplantable Epidermal Cell Sheet Noninvasively Harvested from Thermoresponsive Cell Culture Dishes without Proteolytic Enzymes

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To develop new technology for harvesting transplantable cultured epithelium without dispase treatment, human keratinocytes were plated on culture dishes grafted with a thermoresponsive polymer, poly(N-isopropylacrylamide). The grafted dish surfaces are slightly hydrophobic above 32℃, but reversibly change to hydrophilic below this temperature. According to the method of Rheinwald and Green, keratinocytes proliferated and made a multilayer on the grafted surfaces at 37℃, as on the nongrafted culture dishes. The multilayered keratinocyte sheets were detached from the grafted surfaces only by reducing temperature to 20℃ without need for dispase. No cell remnants were observed on the dishes. Such cell sheet detachment was not observed on nongrafted dishes. Immunoblotting of harvested keratinocyte sheets revealed that dispase treatment disrupted E-cadherin and laminin 5, while these molecules remained intact in the keratinocyte sheets harvested by only reducing temperature from the grafted dishes. Transmission electron microscopy revealed that desmosomes were destroyed in dispase treatment but retained in low-temperature treatment. Use of thermo-responsive dishes was examined as a new tool for tissue engineering to achieve the preparation of artificial epithelium for cell transplantation as well as for the investigation of intact multilayered keratinocyte sheets. After the transplantation experiments with atymic rats, we have just started the clinical application of tissue-engineered epidermal cell sheets.