Gelatin-methacrylarloyl (GelMA): A mixture of gelatin and methacrylic acid that is suspended in saline and combined with a photoinitiator. When exposed to ultraviolet light, the photoinitiator causes the methacrylic acid to cross-link the gelatin, causing it to instantly solidify and keep its shape. Imagine if warm Jello was instantly cooled and unable to melt again unless exposed to a much higher temperature.