New frontiers in cyclodextrin-based nanosponges : from synthesis to physical investigation

Cyclodextrin-based nanosponges (CDNS) are a versatile class of cross-linked polymers able to generate hydrogels. CDNS are prepared by polycondensation between cyclodextrins (CDs) and suitable cross-linkers. The reaction leads to the formation of a three dimensional network, showing both hydrophilic and hydrophobic nano-sized cavities where different species can be encapsulated and selectively released. The protocol of synthesis for these materials is still incomplete due to random distribution between CD and cross-linker and to the difficulty to standardize the reaction process. For this reason, the first part of my research focused on the study and the optimization of the synthesis of CDNS in order to define once at all the ideal operative conditions. The new materials were in-deep investigated and the results were published into two papers: “Direct evidence of gel-sol transition in cyclodextrin-based hydrogel as revealed by FTIR-ATR spectroscopy” (Soft Matter 2014, 10, 2320-2326) and “Glass-like dynamics of new cross-linked polymeric systems: behavior of the Boson peak” (J. Non-Crys. Sol. 2014, DOI 10.1016/j.jnoncrysol.2014.01.016). In the second part of my work I faced the study of paramagnetic CDNS from their synthesis to their characterization. In order to introduce a paramagnetic aspect into CDNS, maintaing the metal-free character of these soft materials, which represents a key aspect for biocompatibility, the CDs were functionalized with a nitroxyl radical (TEMPO) and then reacted with an appropriate crosslinker. The introduction of a paramagnetic feature has different advantages. First, it is possible to obtain an additional characterization of CDNS through Electron Spin Resonance (ESR), which allows to identify paramagnetic moieties as probes and, hence, to define the real cross-linking degree and the structural conformation. Then, it suggests the possibility to follow drug delivery in specific diseased areas via magnetic resonance imaging. Finally, it allows to design an anti-oxidant material: TEMPO is a stable radical and it is able to modulate the level of reactive oxygen species.