Understanding extracellular polymeric substances (EPS)-based hydrogel formation and properties at the nanoscale through MP-SPR and QCM-D techniques

Abstract

This work investigates the calcium-induced formation and properties at the nanoscale of hydrogels of structural extracellular polymeric substances (EPS) extracted from aerobic granular sludge (AGS) during wastewater treatment. By comparing EPS with model polymers representing the key biochemical families present in EPS—alginate for polysaccharides and bovine serum albumin (BSA) for proteins—we aim to elucidate their respective contributions to the overall hydrogel formation with calcium cations. Nanoscale characterization techniques (MP-SPR, QCM-D, and AFM) were employed to assess how divalent cations influence hydrogel formation and properties. Our findings revealed that polysaccharides played a dominant role in hydrogel formation through ionic crosslinking, as well as in hydrogel softness and water retention, while proteins contributed to the modulation of structure and viscoelasticity. The nanoscale structural analysis conducted in this study lays a valuable foundation for further understanding the macroscopic properties of EPS hydrogels, enhancing their potential applications in bio-based materials science.