Alginate Gels Structure-Thermodynamic Relationship with Water and Counterions

Microbial communities are predominantly found in biofilms, which are composed of extracellular polymeric substances (EPS). The EPS matrix is engineered and reconfigured by microbes, making it difficult to distinguish between the biotic and abiotic origins of biofilm properties. To establish this distinction, simplify models of the EPS matrix, the study uses molecular dynamic(MD) simulation to predict the nanoscale structure of a model extracellular polymeric substance (EPS) matrix and its sensitivity to interpolymer interactions and water content. Provide insight into the complex nature of alginate gelation and highlights the importance of water content and counterion type on the properties of the gel. Replica exchange molecular dynamics (REMD) were used to generate all-atom configurations of ten 3.4 kDa alginate polymers at a range of water contents and Ca−Na ratios. The primary findings suggest that the structure of hydrogels is highly sensitive to the identity of charge-compensating cations, but the thermodynamics of water within the gels are only weakly sensitive to cation identity. The study also predicts the differential enthalpy and free energy of hydration, including a short-ranged enthalpic term that promotes hydration and a longer-ranged term that promotes dehydration.