Engineering Multiscale Porosity in Starch–Hydroxyapatite Aerogels and Aerogel-like Xerogels

• Evaporative drying conditions led to xerogels with aerogel-like properties. • Starch–hydroxyapatite xerogels show 0.3–0.5 cm 3 /g density, 15–55 m 2 /g surface area. • Hydroxyapatites particles’ dispersion within starch porous phase is homogeneous. • Structures with hierarchical porosity were produced by 3D printing. Porous starch materials with various shapes, morphologies and properties were prepared via starch dissolution, retrogradation, solvent exchange and drying either with supercritical CO 2 (named “aerogels”) or vacuum drying (named “xerogels”). Evaporative drying was carried out under conditions allowing production of aerogel-like xerogels. The properties of porous starch materials were controlled by starch concentration, retrogradation time and type of non-solvent. They possessed low density (0.25 – 0.45 g/cm 3 ) and specific surface area up to 120 m 2 /g. In view of the potential application of starch materials as bone substitutes, hydroxyapatite (HA) beads were added to starch solutions, and starch-HA composite xerogels were produced and characterized. All materials were highly porous, nanostructured and with interconnected pores. They displayed density of 0.3–––0.55 g/cm 3 , specific surface area up to 55 m 2 /g, chord modulus between 9 and 20 MPa and demonstrated no cytotoxicity. Microtomography and SEM images revealed homogeneous dispersion of HA within starch continuous porous phase. Structures with hierarchical porosity were produced by 3D printing, with pores’ walls based on starch-HA composite xerogels.