Influence of Rhamnolipids and Ionic Cross-Linking Conditions on the Mechanical Properties of Alginate Hydrogels as a Model Bacterial Biofilm

Abstract

The literature indicates the existence of a relationship between rhamnolipids and bacterial biofilm, as well as the ability of selected bacteria to produce rhamnolipids and alginate. However, the influence of biosurfactant molecules on the mechanical properties of biofilms are still not fully understood. The aim of this research is to determine the effect of rhamnolipids concentration, CaCl2 concentration, and ionic cross-linking time on the mechanical properties of alginate hydrogels using a Box–Behnken design. The mechanical properties of cross-linked alginate hydrogels were characterized using a universal testing machine. It was assumed that the addition of rhamnolipids mainly affects the compression load, and the value of this parameter is lower for hydrogels produced with biosurfactant concentration below CMC than for hydrogels obtained in pure water. In contrast, the addition of rhamnolipids in an amount exceeding CMC causes an increase in compression load. In bacterial biofilms, the presence of rhamnolipid molecules does not exceed the CMC value, which may confirm the influence of this biosurfactant on the formation of the biofilm structure. Moreover, rhamnolipids interact with the hydrophobic part of the alginate copolymer chains, and then the hydrophilic groups of adsorbed biosurfactant molecules create additional calcium ion trapping sites.

Biopolymer Composites: Synthesis, Properties, and Applications

“…This Special Issue, with a collection of eight research articles, offers representative examples of the most recent advances in the synthesis, properties and applications of biodegradable biopolymer composites. Attention has been focused on production, processing, and application of biodegradable composites prepared from polymers such as polylactic acid (PLA) [6], chitosan [7], alginate [8], natural rubber [9], and so forth, which are amongst the most promising matrices for green composites in the future.…”

“…In addition, alginate is one of the biofilm substances produced by bacteria, and alginate hydrogels are used as a model biofilm in laboratory research [14]. In this regard, alginate hydrogels containing rhamnolipids, a group of biosurfactants produced by many microorganisms such as pathogen Pseudomonas aeruginosa, have been used to investigate the existence of a relationship between rhamnolipids and bacterial biofilm [8]. The presence of rhamnolipids changes the mechanical properties of the alginate: at concentrations below the CMC, the addition of this biosurfactant decreases compression loads, while it increases at concentrations above CMC.…”