Novel non-cytotoxic alginate–lignin hybrid aerogels as scaffolds for tissue engineering

This paper presents a novel approach towards the production of hybrid alginate-lignin aerogels. The key idea of the approach is to employ pressurized carbon dioxide for gelation. Exposure of alginate and lignin solution containing calcium carbonate to CO₂ at 4.5 MPa resulted in a hydrogel formation. Various lignin and CaCO₃ concentrations were studied. Stable hydrogels can be formed up to 2:1 (w/w) alginate-to-lignin ratio. Upon substitution of water with ethanol, gels were dried in supercritical CO₂ to produce aerogels. Aerogels were characterized in terms of bulk density, specific surface area and pore volume. To introduce macroporosity, the CO₂ induced gelation was supplemented with rapid depressurization (foaming process). Porosity, mean pore size and interconnectivity in the macroporous range were assessed by micro-CT. Young’s modulus of alginate-lignin aerogels was measured in both dry and wet state. Cell studies revealed that alginate-lignin aerogels are non-cytotoxic and demonstrate good cell adhesion properties making them attractive candidates for a wide range of applications including tissue engineering and regenerative medicine.