Peptide-based hydrogels represent promising systems for the sustained release of different types of drugs (i.e. cargoes), ranging from small molecules to biologicals [1]. Aiming at subcutaneous injection, which is a desirable parenteral administration route [2], we herein focus on physically crosslinked systems possessing thixotropic behaviour [3]. More specifically, in this study we evaluated the impact when elongating the amphipathic hexapeptide hydrogelator H-FQFQFK-NH₂ 1 [4] to the corresponding dodecapeptide H-FQFQFKFQFQFK-NH₂ 2, aiming at increased intermolecular interactions.

First, the hydrogels have been characterized at the microscopic and macroscopic level by cryogenic transmission electron microscopy (cryo-TEM) analysis and dynamic rheometry. Unique to this study is the elucidation of the in vivo properties of both hydrogels, after subcutaneous injection in mice. Nuclear SPECT/CT imaging revealed a significantly improved in vivo stability for hydrogel 2, which consequently led to a more prolonged release of encapsulated peptide cargoes. While no direct link could be made with the mechanical properties of the hydrogels before injection, rheological analysis on the post in vivo injection hydrogel residue suggested a possible influence of the subcutaneous environment. Finally, the effectiveness of hydrogel 2 as sustained release platform was demonstrated for a therapeutically relevant analgesic peptide, using the hot-plate test as acute thermal pain model. Altogether, this simple structural modification could provide a solid basis for reaching longer durations of action upon use of these soft biomaterials.