Rheological characterisation of alginate-like exopolymer gels crosslinked with calcium
N M Pfaff1, J A Dijksman2, A J B Kemperman3
1Department of Biotechnology, TU Delft, Van der Maasweg 9, HZ, Delft 2629, the Netherland; Wetsus, European Center of Excellence for Sustainable Water Technology, Oostergoweg 9, MA, Leeuwarden 8911, the Netherland.
Water Research
|November 14, 2021
Summary
This study models bacterial alginate-like exopolymers (ALE) gels to understand biofilm matrix strength. Increasing calcium carbonate (CaCO3) concentration enhances gel stiffness but also brittleness, suggesting overdosing can aid biofouling removal.
Area of Science:
- Materials Science
- Microbiology
- Biophysics
Background:
- Biofilms are persistent due to their extracellular polymeric matrix.
- Bacterial alginate-like exopolymers (ALE) gels serve as a model for this matrix.
- Understanding matrix mechanics is key to developing effective cleaning strategies.
Purpose of the Study:
- To investigate the mechanical properties of ALE gels as a function of calcium carbonate (CaCO3) concentration.
- To correlate these mechanical properties with molecular interactions within the biofilm matrix.
- To identify potential strategies for biofouling removal based on matrix strength.
Main Methods:
- Dynamic and static rheology were employed to test ALE gels with varying CaCO3 concentrations.
- Creep tests were conducted and fitted with a Burgers model to analyze gel behavior.
- Mechanical properties including elastic modulus and dissipation factor were measured.
Main Results:
- ALE gels with 100–300 μmol CaCO3/g ALE mimicked real biofilm viscoelasticity (50–100 Pa elastic modulus, 0.2–0.3 dissipation factor).
- Increased CaCO3 concentration up to 250 Pa elastic modulus, enhancing brittleness, until salt precipitation disrupted the network.
- Gels demonstrated significant recovery (65–90%) of shear modulus after large strain deformation, with faster recovery for lower CaCO3 concentrations.
Conclusions:
- The mechanical strength and viscoelasticity of bacterial biofilms are influenced by CaCO3 concentration within the ALE matrix.
- Overdosing calcium salts may be a viable strategy for biofouling removal by disrupting matrix integrity.
- Further research into the specific molecular interactions governing ALE gel mechanics can lead to targeted anti-biofouling strategies.
