Investigation of morphology associated with biporous polymeric materials obtained by the double porogen templating approach

Doubly porous polymeric materials were prepared from 2-hydroxyethyl methacrylate (HEMA) through the double porogen templating approach. One such approach required the use of a macroporogenic agent, i.e., NaCl particles, and a porogenic solvent. To this purpose, sieved NaCl particles of different size ranges were used (125–200 μm, 200–250 μm, and 250–400 μm), either sintered through Spark Plasma Sintering or non-fused, in conjunction with a porogenic solvent, i.e., isopropanol. After removal of both porogens, the resulting biporous scaffolds were finely characterized in terms of porosity by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and nitrogen sorption porosimetry. All the obtained results indicated higher porosity ratios and specific surface areas for doubly porous materials prepared from SPS-mediated sintering of macroparticles, thus demonstrating the crucial role of macroporogen packing on the resulting porosity features. Indeed, a higher compaction of NaCl particles generated fewer interstitial voids between adjacent inorganic particles and thus afforded a higher porosity (87% porosity ratio) in the resulting porous material as compared to the corresponding analogue prepared from non-sintered NaCl particles (80% porosity ratio). A complementary 3-D imaging of the microstructure by means of laboratory X-ray computed microtomography (μCT) but also synchrotron μCT analysis qualitatively confirmed these findings. The macroporogen size was also considered to be a crucial parameter regarding the porosity features, as increasing macroporogen sizes were notably associated with increasing porosity ratios. Finally, swelling of those mono- and biporous materials was investigated. The interconnection in the higher porosity level was notably evaluated, and it was observed that the water uptake of biporous PHEMA scaffolds comprising an interconnected higher porosity level can be as high as ~ 2500%.