Tissue tek

Two 4-mm skin punch biopsies are taken under local anesthesia, including one from active psoriatic skin and one from clinically healthy skin neighboring the psoriatic biopsy area with a minimum distance of 2 cm from the psoriasis biopsy. The biopsy locations have the same priority for body sites as the skin swabs. After collection, biopsies are immediately cut in two parts and processed separately for RNA sequencing and immunohistochemistry.
Biopsies for RNA sequencing are placed directly into RNAprotect Tubes (QIAGEN), which are stored at 4°C overnight and thereafter at −80°C. RNA is isolated from biopsies, and its quality is assessed using the 2100 Bioanalyzer (Agilent). Sequencing libraries are prepared using SureSelect XT RNA Direct (Illumina) for samples with an RNA integrity number (RIN) score >8 and are sequenced at the Genomics Core Facility at Icahn School of Medicine at Mount Sinai.
Biopsies for immunohistochemistry are placed into a cryomold (Tissue Tek, Sakura Finetek) with optimal cutting temperature (OCT) solution (Tissue Tek, Sakura Finetek) that is subsequently snap-frozen with liquid nitrogen and immediately stored at −80^°C. OCT samples are cut, mounted, fixed, and stained with hematoxylin and eosin, and with antibodies to selected target antigens using standard immunohistochemical techniques.

Two amputated fins of each group (n = 2) were gently placed into a cryomold (TissueTek®; Sakura Finetek Europe B.V., Alphen aan den Rijn, the Netherlands) and were totally covered with Optimal Cutting Temperature (OCT) compound (TissueTek®). The compounds were indirectly frozen using liquid nitrogen, covered with aluminum foil and stored at −21°C until used. The blocks were cut into 30‐μm‐thick slices, perpendicular to the bony rays' direction of growth, at −21°C, with a microtome CM3050 S (Leica Microsystems GmbH, Wetzlar, Germany), as described.⁽³⁴⁾ The used thickness is over the minimum standard accepted to submicron analyses.⁽³⁵⁾ The sliced samples were fixed in properly labeled microscope glass slides and the excess of OCT was washed using phosphate‐buffered solution (PBS) with pH of ~7.4, formulated as described by Chazotte.⁽³⁶⁾ One of the cross‐sectioned samples was used in the surface roughness analysis, whereas the other was used for mechanical evaluation.

Tumor and normal mucosal samples were obtained from operative specimens after gross evaluation by a pathologist. The tissue samples were placed in separate standard Cryomolds (Tissue Tek, Sakura Finetek, Torrance, CA) which were filled with OCT (optimal cutting temperature) compound (Tissue Tek, Sakura Finetek, Torrance, CA) and placed in liquid nitrogen. The frozen tissue samples were stored in a −80°C freezer.