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There are some principles you should pay attention to when freezing tissues. Firstly, tissues should be frozen or fixed promptly to avoid morphological distortions. Secondly, be sure to keep fresh tissues on ice and process them as quickly as possible. Thirdly, the smaller size of the sample is preferred. Fourthly, keep the sample dry and avoid too much liquid before freezing. Thawing of tissue samples should be done rapidly in a 37°C water bath. For some tissues, blood vessels, and bone, controlling the thawing speeds may reduce tissue fragility. Besides these, the cryoprotectant or process will vary according to the organ. You may find more particular methods on the reference below.