Keywords: AA; acrylic acid; CS; chondroitin sulfate; CSF; cerebrospinal fluid; DHMPA; 2,2-bis(hydroxymethyl)-propionic acid; DST; disuccinimidyl tartrate; EDC; 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide; FDA; U.S. Food and Drug Administration; GRF; gelatin-resor