Biopolymer aerogels: Structural and functional tailoring of starch/sodium alginate networks

Abstract

This study explores the synthesis, structural, and functional properties of starch/sodium alginate aerogels prepared via two-step and multi-step solvent exchange methods, with and without calcium chloride (CaCl₂) crosslinking. Fourier-transform infrared (FTIR) spectroscopy confirmed that both polymers were incorporated in an aerogel matrix, while Brunauer–Emmett–Teller (BET) analysis revealed that the preparation method and composition of initial polymer solution had a significant influence on surface area and porosity. Specifically, the surface area ranged from 4 to 132 m²/g, with multi-step solvent exchange producing aerogels with higher surface area and porosity. Scanning electron microscopy (SEM) showed that multi-step solvent exchange produced more homogeneous aerogel structures, while the two-step method was more effective for sodium alginate-rich aerogels. Mechanical testing revealed that crosslinked aerogels achieved a maximum stress force of up to 12 MPa, significantly higher than non-crosslinked aerogels, which showed a maximum stress of 9 MPa. Swelling studies in PBS buffer (pH 7.4) indicated that the equilibrium swelling degree (SD_eq) increased with sodium alginate content, with values ranging from 330 to 656 % for sodium alginate-rich samples, due to carboxyl group dissociation, whereas non-crosslinked samples, particularly those with higher sodium alginate content, dissolve in PBS buffer. Neat starch aerogels exhibited lower swelling behavior, with SDeq values around 300 %, and were largely unaffected by the addition of the crosslinker. These findings highlight the tunable structural, mechanical, and swelling properties of starch/sodium alginate aerogels, making them promising candidates for numerous applications such as drug delivery and environmental remediation applications.