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

• Ca-crosslinked alginate–lignin aerogels are prepared by CO2 induced gelation and supercritical drying.
• Foaming by expansion of carbon dioxide is used to obtain aerogels with dual porosity.
• Alginate–lignin aerogels possess good cell adhesion properties.
• Alginate–lignin aerogels do not compromise cell viability.

This paper presents a novel approach toward 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 aqueous alkali solution containing calcium carbonate to CO2 at 4.5 MPa resulted in a hydrogel formation. Various lignin and CaCO3 concentrations were studied. Stable hydrogels could be formed up to 2:1 (w/w) alginate-to-lignin ratio (1.5 wt% overall biopolymer concentration). Upon substitution of water with ethanol, gels were dried in supercritical CO2 to produce aerogels. Aerogels with bulk density in the range 0.03–0.07 g/cm3, surface area up to 564 m2/g and pore volume up to 7.2 cm3/g were obtained. To introduce macroporosity, the CO2 induced gelation was supplemented with rapid depressurization (foaming process). Macroporosity up to 31.3 ± 1.9% with interconnectivity up to 33.2 ± 8.3% could be achieved at depressurization rate of 3 MPa/min as assessed by micro-CT. Young's modulus of alginate–lignin aerogels was measured in both dry and wet states. Cell studies revealed that alginate–lignin aerogels are non-cytotoxic and feature good cell adhesion making them attractive candidates for a wide range of applications including tissue engineering and regenerative medicine.

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