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Swelling behavior of polymer hydrogels: chitosan–PVA hydrogels prepared with four cycles of freeze–thawing (a); chitosan–PVA hydrogels obtained at −80 °C with different numbers of freeze–thawing (b). In the sample abbreviation, the first number after “CP” indicates the quantity of freeze–thawing cycles, the second one indicates the temperature of freezing. Reproduced from [35], with permission from JoVE, 2021.
