Peptides of natural and synthetic sources are compounds operating in a wide range of biological interactions. They play a key role in biotechnological applications as both therapeutic and diagnostic tools. They are easily synthesized thanks to solid-phase peptide devices where the amino acid sequence can be exactly selected at molecular levels, by tuning the basic units. Recently, peptides achieved resounding success in drug delivery and in nanomedicine smart applications. These applications are the most significant challenge of recent decades: they can selectively deliver drugs to only pathological tissues whilst saving the other districts of the body. This specific feature allows a reduction in the drug side effects and increases the drug efficacy. In this context, peptide-based aggregates present many advantages, including biocompatibility, high drug loading capacities, chemical diversity, specific targeting, and stimuli responsive drug delivery. A dual behavior is observed: on the one hand they can fulfill a structural and bioactive role. In this review, we focus on the design and the characterization of drug delivery systems using peptide-based carriers; moreover, we will also highlight the peptide ability to self-assemble and to actively address nanosystems toward specific targets.

Due to its capability to self-assemble in self-supporting hydrogels (HG) under physiological conditions, Fmoc-FF is one of the most studied ultra-short peptide. This feature pushed towards the development of novel Fmoc-FF multicomponent systems.

Short peptides or single amino acids are interesting building blocks for fabrication of hydrogels, frequently used as extracellular matrix-mimicking scaffolds for cell growth in tissue engineering. The combination of two or more peptide hydrogelators could allow obtaining different materials exhibiting new architectures, tunable mechanical properties, high stability and improved biofunctionality. Here we report on the synthesis, formulation and multi-scale characterization of peptide-based mixed hydrogels formed by the low molecular weight Fmoc-FF (N^α-fluorenylmethyloxycarbonyl diphenylalanine) hydrogelator and of the PEG₈-(FY)3 hexapeptide, containing three repetitions of the Phe-Tyr motif and a PEG moiety at its N-terminus. Mixed hydrogels were also prepared by replacing PEG₈-(FY)3 with its analogue (FY)3, without the PEG moiety. Rheology analysis confirmed the improved mechanical features of the multicomponent gels prepared at two different ratios (2/1 or 1/1, v/v). However, the presence of the hydrophilic PEG polymeric moiety causes a slowing down of the gel kinetic formation (from 42 to 18 minutes) and a decrease of the gel rigidity (G′ from 9 to 6 kPa). Preliminary in vitro biocompatibility and cell adhesion assays performed on Chinese hamster ovarian (CHO) cells suggest a potential employment of these multicomponent hydrogels as exogenous scaffold materials for tissue engineering.

Introduction: The clinical use of the antitumoral drug doxorubicin (Dox) is reduced by its dose-limiting toxicity, related to cardiotoxic side effects and myelosuppression. In order to overcome these drawbacks, here we describe the synthesis, the structural characterization and the in vitro cytotoxicity assays of hydrogels (HGs) and nanogels (NGs) based on short peptide sequences loaded with Dox or with its liposomal formulation, Doxil. Methods: Fmoc-FF alone or in combination with (FY)3 or PEG8-(FY)3 peptides, at two different ratios (1/1 and 2/1 v/v), were used for HGs and NGs formulations. HGs were prepared according to the “solvent-switch” method, whereas NGs were obtained through HG submicronition by the top-down methodology in presence of TWEEN^® 60 and SPAN^® 60 as stabilizing agents. HGs gelation kinetics were assessed by Circular Dichroism (CD). Stability and size of NGs were studied using Dynamic Light Scattering (DLS) measurements. Cell viability of empty and filled Dox HGs and NGs was evaluated on MDA-MB-231 breast cancer cells. Moreover, cell internalization of the drug was evaluated using immunofluorescence assays. Results: Dox filled hydrogels exhibit a high drug loading content (DLC=0.440), without syneresis after 10 days. Gelation kinetics (20– 40 min) and the drug release (16– 28%) over time of HGs were found dependent on relative peptide composition. Dox filled NGs exhibit a DLC of 0.137 and a low drug release (20– 40%) after 72 h. Empty HGs and NGs show a high cell viability (> 95%), whereas Dox loaded ones significantly reduce cell viability after 24 h (49– 57%) and 72 h (7– 25%) of incubation, respectively. Immunofluorescence assays evidenced a different cell localization for Dox delivered through HGs and NGs with respect to the free drug. Discussion: A modulation of the Dox release can be obtained by changing the ratios of the peptide components. The different cellular localization of the drug loaded into HGs and NGs suggests an alternative internalization mechanism. The high DLC, the low drug release and preliminary in vitro results suggest a potential employment of peptide-based HGs and NGs as drug delivery tools.

Hydrogels (HGs) are tri-dimensional materials with a non-Newtonian flow behaviour formed by networks able to encapsulate high amounts of water or other biological fluids. They can be prepared using both synthetic or natural polymers and their mechanical and functional properties may change according to the preparation method, the solvent, the pH, and to others experimental parameters. Recently, many short and ultra-short peptides have been investigated as building blocks for the formulation of biocompatible hydrogels suitable for different biomedical applications. Due to its simplicity and capability to gel in physiological conditions, Fmoc-FF dipeptide is one of the most studied peptide hydrogelators. Although its identification dates to 15 ago, its behaviour is currently studied because of the observation that the final material obtained is deeply dependent on the preparation method. To collect information about their formulation, here are reported some different strategies adopted until now for the Fmoc-FF HG preparation, noting the changes in the structural arrangement and behaviour in terms of stiffness, matrix porosity, and stability induced by the different formulation strategy on the final material.