Communicating macropores in PHEMA-based hydrogels for cell seeding: Probabilistic open pore simulation and direct micro-CT proof

Open macroporosity is crucial for scaffolds in tissue engineering. Porogen-templating method is an attractive approach for fabrication of macroporous hydrogels, however, the effect of shape and amount of template particles on imprinted structure has not yet been quantitatively established. We present a mathematical model for simulating the formation of paths percolating through distributed cubical particles as a function of the filling volume. The model was used to select the fraction of NaCl particles as templates for preparation of hydrogels with communicating pores. Hydrogels were prepared from 2-hydroxyethyl methacrylate (HEMA) copolymerized with 2-ethoxyethyl methacrylate (EOEMA), [2-methacryloyloxy)ethyl]trimethylammonium chloride (MOETACl) or ionizable methacrylic acid (MANa) to modulate swelling, surface and mechanical properties of gels. Micro-CT analysis of swollen samples proved a highly-interconnected pore structure. Charged hydrogels swelled more and their apparent elastic modulus G′ was below 1 kPa. For PHEMA and P(HEMA/EOEMA) hydrogels, G′ was 5 and 80 kPa, respectively. Within two-week in vitro studies, MG63 osteoblasts proliferated fastest on P(HEMA/EOEMA) showing the lowest swelling and the highest elastic modulus, whereas cell growth was impaired on positively charged P(HEMA/MOETACl). The mathematical simulation of cubical particle packing in hydrogels and micro-CT data in swollen state provided evidence of an extensive void communication in 3D.