Transient Anomalous Diffusion MRI Measurement Discriminates Porous Polymeric Matrices Characterized by Different Sub-Microstructures and Fractal Dimension

Marco Palombo; Andrea Barbetta; Cesare Cametti; Gabriele Favero; Silvia Capuani

doi:10.3390/gels8020095

Transient Anomalous Diffusion MRI Measurement Discriminates Porous Polymeric Matrices Characterized by Different Sub-Microstructures and Fractal Dimension

Gels. 2022 Feb 4;8(2):95. doi: 10.3390/gels8020095.

Authors

Marco Palombo^{1

2}, Andrea Barbetta³, Cesare Cametti⁴, Gabriele Favero⁵, Silvia Capuani^{6

7}

Affiliations

¹ Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Maindy Road, Cardiff CF24 4HQ, UK.
² School of Computer Science and Informatics, Cardiff University, Maindy Road, Cardiff CF24 4HQ, UK.
³ Chemistry Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy.
⁴ Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy.
⁵ Department of Environmental Biology, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy.
⁶ National Research Council-Institute for Complex Systems (CNR-ISC) c/o, Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy.
⁷ CREF, Museo Storico Della Fisica e Centro Studi e Ricerche Enrico Fermi, 00185 Rome, Italy.

Abstract

Considering the current development of new nanostructured and complex materials and gels, it is critical to develop a sub-micro-scale sensitivity tool to quantify experimentally new parameters describing sub-microstructured porous systems. Diffusion NMR, based on the measurement of endogenous water's diffusion displacement, offers unique information on the structural features of materials and tissues. In this paper, we applied anomalous diffusion NMR protocols to quantify the subdiffusion of water and to measure, in an alternative, non-destructive and non-invasive modality, the fractal dimension d_w of systems characterized by micro and sub-micro geometrical structures. To this end, three highly heterogeneous porous-polymeric matrices were studied. All the three matrices composed of glycidylmethacrylate-divynilbenzene porous monoliths obtained through the High Internal Phase Emulsion technique were characterized by pores of approximately spherical symmetry, with diameters in the range of 2-10 μm. Pores were interconnected by a plurality of window holes present on pore walls, which were characterized by size coverings in the range of 0.5-2 μm. The walls were characterized by a different degree of surface roughness. Moreover, complementary techniques, namely Field Emission Scanning Electron Microscopy (FE-SEM) and dielectric spectroscopy, were used to corroborate the NMR results. The experimental results showed that the anomalous diffusion α parameter that quantifies subdiffusion and d_w = 2/α changed in parallel to the specific surface area S (or the surface roughness) of the porous matrices, showing a submicroscopic sensitivity. The results reported here suggest that the anomalous diffusion NMR method tested may be a valid experimental tool to corroborate theoretical and simulation results developed and performed for describing highly heterogeneous and complex systems. On the other hand, non-invasive and non-destructive anomalous subdiffusion NMR may be a useful tool to study the characteristic features of new highly heterogeneous nanostructured and complex functional materials and gels useful in cultural heritage applications, as well as scaffolds useful in tissue engineering.

Keywords: anomalous diffusion; dielectric spectroscopy; diffusion NMR; fractal dimension; porosity; porous polymeric matrices; sub-diffusion.

Abstract

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