title: Anomalous diffusion of Ibuprofen in cyclodextrin nanosponge hydrogels: an HRMAS NMR study.
abstract: Ibuprofen sodium salt (IP) was encapsulated in cyclodextrin nanosponges (CDNS) obtained by cross-linking of β-cyclodextrin with ethylenediaminetetraacetic acid dianhydride (EDTAn) in two different preparations: CDNSEDTA 1:4 and 1:8, where the 1:n notation indicates the CD to EDTAn molar ratio. The entrapment of IP was achieved by swelling the two polymers with a 0.27 M solution of IP in D2O, leading to colourless, homogeneous hydrogels loaded with IP. The molecular environment and the transport properties of IP in the hydrogels were studied by high resolution magic angle spinning (HRMAS) NMR spectroscopy. The mean square displacement (MSD) of IP in the gels was obtained by a pulsed field gradient spin echo (PGSE) NMR pulse sequence at different observation times t d. The MSD is proportional to the observation time elevated to a scaling factor α. The α values define the normal Gaussian random motion (α = 1), or the anomalous diffusion (α < 1, subdiffusion, α > 1 superdiffusion). The experimental data here reported point out that IP undergoes subdiffusive regime in CDNSEDTA 1:4, while a slightly superdiffusive behaviour is observed in CDNSEDTA 1:8. The transition between the two dynamic regimes is triggered by the polymer structure. CDNSEDTA 1:4 is characterized by a nanoporous structure able to induce confinement effects on IP, thus causing subdiffusive random motion. CDNSEDTA 1:8 is characterized not only by nanopores, but also by dangling EDTA groups ending with ionized COO(-) groups. The negative potential provided by such groups to the polymer backbone is responsible for the acceleration effects on the IP anion thus leading to the superdiffusive behaviour observed. These results point out that HRMAS NMR spectroscopy is a powerful direct method for the assessment of the transport properties of a drug encapsulated in polymeric scaffolds. The diffusion properties of IP in CDNS can be modulated by suitable polymer synthesis; this finding opens the possibility to design suitable systems for drug delivery with predictable and desired drug release properties.
authors.affiliation: Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Piazza L. da Vinci 32 - 20133 Milano Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Ferro
authors.affiliation: Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Piazza L. da Vinci 32 - 20133 Milano Italy.
authors.forename: Franca
authors.initials: F
authors.lastname: Castiglione
authors.affiliation: Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Piazza L. da Vinci 32 - 20133 Milano Italy.
authors.forename: Carlo
authors.initials: C
authors.lastname: Punta
authors.affiliation: Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Piazza L. da Vinci 32 - 20133 Milano Italy.
authors.forename: Lucio
authors.initials: L
authors.lastname: Melone
authors.affiliation: CNR-ICRM, Via L. Mancinelli, 7 20131 Milano, Italy.
authors.forename: Walter
authors.initials: W
authors.lastname: Panzeri
authors.affiliation: Elettra - Sincrotrone Trieste, Strada Statale 14 km 163.5, Area Science Park, 34149 Trieste, Italy and Department of Physics, University of Trento, via Sommarive 14, 38123 Povo, Trento, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Rossi
authors.affiliation: Department of Chemistry, University of Torino, Via Pietro Giuria 7, 10125 Torino, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Trotta
authors.affiliation: Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Piazza L. da Vinci 32 - 20133 Milano Italy ; CNR-ICRM, Via L. Mancinelli, 7 20131 Milano, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Mele
keywords: HRMAS NMR spectroscopy; TEM; cross-linked polymers; cyclodextrin nanosponges; diffusion