Supramolecular hydrogels based on custom-made poly(ether urethane)s and cyclodextrins as potential drug delivery vehicles: design and characterization

The design of supramolecular (SM) hydrogels based on host-guest complexes represents an effective strategy to develop drug delivery systems. In this work, we designed SM hydrogels based on α-cyclodextrin and high-molar mass amphiphilic poly(ether urethane)s (PEUs) based on Poloxamer® 407 and differing in their chain extender. The successful formation of poly(pseudo)rotaxanes and their supramolecular interactions were chemically demonstrated. Then, self-healing (80-100% mechanical recovery) supramolecular hydrogels were developed by mixing PEU and α-cyclodextrin solutions at different concentrations. Stability in physiological-like environment and mechanical properties improved with increasing α-cyclodextrin content (9-10% w/v), meanwhile gelation time decreased. A synergistic effect of poly(pseudo)rotaxanes crystals and PEU micellar structures on gel properties was observed: the first were predominant at low PEU concentrations (1-5% w/v), while the latter prevailed at high PEU concentrations (7-9% w/v). Increasing PEU concentration led to gels with increased dissolution rate, not-fully developed networks and slight cytotoxicity, meanwhile residence time in aqueous media improved (>7 d). At low PEU concentrations (1-5% w/v), cytocompatible gels (100% cell viability) were obtained, which maintained their shape in aqueous medium up to 5 d and completely dissolved within 7 d. PEU chemical composition affected PEU/α-cyclodextrin interactions, with longer gelation time and lower mechanical properties in gels based on PEU with pendant functionalities. Gels progressively released a model molecule (fluorescein isothiocyanate-dextran) within 3-4 days with no initial burst release. We thus demonstrated the suitability of custom-made PEUs as constituent of SM hydrogels with α-cyclodextrin and the high potential of the resulting systems for drug delivery applications.