Soft cationic hydrogels based on short peptide sequences for potential localized siRNA delivery

Abstract Localized gene-delivery systems represent a key enabling technology for regenerative medicine, diagnostics, and real-time monitoring of biological processes. Among biomaterial platforms, peptide-based hydrogels have attracted significant interest due to their biocompatibility, structural tunability, and ability to incorporate bioactive molecules and nucleic acids. Fmoc-diphenylalanine (Fmoc-FF) hydrogels are widely studied for these applications; however, their intrinsic mechanical rigidity and limited shear-thinning behavior may restrict their suitability for minimally invasive delivery. Here, we describe the formulation and comparative evaluation of a family of Fmoc-FF-derived tripeptide hydrogels, and examinate how subtle sequence modifications influence supramolecular assembly, mechanical properties, and nucleic acid incorporation. By introducing positively charged amino acids at the C-terminus of the Fmoc-FF scaffold and modulating terminal functionality, we investigated the relationship between molecular structure and hydrogel performance. The resulting systems formed soft hydrogels with measurable viscoelastic properties and were able to associate with siRNA through electrostatic interactions, showing sustained cargo retention. In vitro characterization indicated good cytocompatibility and structural stability of the hydrogels under the tested conditions. Non-invasive in vivo monitoring of subcutaneously injected hydrogel depots using T2-weighted magnetic resonance imaging (T 2W ) has demonstrated the feasibility of longitudinal assessment of hydrogel persistence, volume changes, resorption behavior, and qualitative indications of cellular infiltration in murine models. In agreement with these observations, in vivo studies performed in this work showed preservation of hydrogel integrity following administration, with no evidence of local toxicity or pronounced inflammatory responses within the investigated timeframe. Collectively, these findings identify Fmoc-FF-derived tripeptide hydrogels as injectable peptide-based materials capable of siRNA incorporation and non-invasive MRI monitoring, providing a basis for further investigation as localized gene-silencing delivery systems and for MRI-assisted in vivo monitoring approaches.