194 Chapter 6 of FSEs was comparable to that of ex vivo human skin. These models are therefore useful for the study of skin development and wound healing using a uniform dermal component without the need for animal models. Further development of the FSEs could include the addition of various immune cells, which would allow further study of inflammatory processes and testing of novel therapeutics. MATERIALS AND METHODS Isolation of keratinocytes and fibroblasts See Supplementary Table 1 for the contents of the culture media. Healthy skin samples were obtained from adult patients who underwent elective surgery at the Departments of Surgery or Plastic and Reconstructive Surgery of the Red Cross Hospital. Eleven skin tissue samples were used, originating from abdominal, leg, or arm reconstructions wherein excess skin was removed (donor age: 43.8 ± 11.7 years old; donor sex: 72.7% female). These samples were collected in the period between January 2021 and July 2021. Consent for the use of these anonymized, post-operative residual tissue samples was received through the informed opt-out protocol of the Red Cross Hospital, which was in accordance with the national guidelines (https://www.coreon.org/ accessed on 23 November 2020) and approved by the institutional privacy officers. Subjects were actively informed of this procedure and were able to easily withdraw at any point. Splitthickness samples of 0.3 mm were harvested using a dermatome (Aesculap AG & Co. KG, Tuttlingen, Germany). The epidermis was separated from the dermis using forceps after incubating the harvested skin samples in 0.25% dispase (Gibco) at 37 °C for 45 min. For fibroblast isolation, the dermal part of the split skin was cut into small pieces and submerged into a 0.25% collagenase (Roche)/0.25% dispase solution at 37 °C for 2 h. After addition of 1 mM EDTA/PBS to inhibit collagenase, the cell suspension was poured through a 500 µm cell strainer and centrifuged for 10 min at 360 × g. The cell pellet was resuspended in culture medium (Supplementary Table 1) and poured through a 70 µm cell strainer and cultured at 37 °C and 5% CO2. For keratinocyte isolation, the epidermis was transferred into 0.05% trypsin and incubated for 20 min at 37 °C. The cell suspension was poured through a 70 µm cell strainer and centrifuged for 10 min at 110 × g. Next, the cell pellet was washed in culture medium and centrifuged for 10 min at 160 × g. The cell pellet was then resuspended in CellnTec-07S culture medium, and keratinocytes were transferred onto a 1 µg/cm2 collagen-type-IV-coated culturing flask at 37 °C and 5% CO2. Full skin equivalent models De-epidermalized dermis (DED; European Tissue Bank BISLIFE, Beverwijk, The Netherlands), MatriDerm® (thickness 3 mm; MedSkin Solutions Dr. Suwelack AG, Billerbeck, Germany), and Mucomaix® (thickness 3 mm; Matricel GmbH, Hertzogenrath,
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