Department 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.
Physical Chemistry and Soft Matter, Wageningen University, Stippeneng 4, WE, Wageningen 6708, the Netherland.
Water Res. 2021 Dec 1;207:117835. doi: 10.1016/j.watres.2021.117835. Epub 2021 Nov 5.
Bacterial alginate-like exopolymers (ALE) gels have been used in this work as a model for the extracellular polymeric matrix of biofilms. Aim was to relate the mechanical properties and strength of this matrix that make biofilms as persistent to cleaning as they are, to the complex cohesive molecular interactions involved. Mechanical properties of the gels as a function of CaCO concentration were investigated using dynamic and static rheology. Gels with relatively low CaCO concentrations, between 100 μmol and 300 μmol per g ALE, were found to exhibit similar viscoelastic behaviour as real biofilms, with elastic moduli between 50 Pa and 100 Pa and dissipation factors between 0.2 and 0.3. Increasing CaCO concentrations resulted in an increase of the elastic modulus up to 250 Pa, accompanied by an increase in brittleness. At a CaCO concentration of 1250 μmol per g ALE this trend stopped, probably due to disturbance of the continuous ALE network by precipitation of salts. Therefore, overdosing of Ca salts can be an adequate approach for the removal of biofouling. All gels exhibited permanent strain hardening under medium strain, and their mechanical properties showed dependency on their strain history. Even after application of an oscillatory strain with 200% amplitude that caused the gel structure to collapse, the gels recovered 65 to 90% of their original shear modulus, for the major part within the first 20 s. Recovery was slightly less for gels with high CaCO concentration. In creep tests fitted with a Burgers model with multiple Kelvin elements at least three different interactions in the ALE gels could be distinguished with characteristic retardation times in the range of 10, 100 and 1000 s. Further identification of the mechanisms underlying the gel mechanics will allow the development of targeted strategies to undermine the mechanical strength of biofouling and aid the cleaning process.
细菌海藻酸盐样胞外聚合物 (ALE) 凝胶已被用于本工作中，作为生物膜细胞外基质的模型。目的是将使生物膜具有与清洁持久性相关的这种基质的机械性能和强度，与涉及的复杂粘性分子相互作用联系起来。使用动态和静态流变学研究了凝胶的机械性能作为 CaCO 浓度的函数。发现 CaCO 浓度相对较低（每克 ALE 为 100μmol 至 300μmol）的凝胶表现出与真实生物膜相似的粘弹性行为，弹性模量在 50Pa 至 100Pa 之间，耗散因子在 0.2 和 0.3 之间。增加 CaCO 浓度会导致弹性模量增加到 250Pa，同时脆性增加。当 CaCO 浓度达到每克 ALE 1250μmol 时，这种趋势停止，可能是由于盐的沉淀干扰了连续的 ALE 网络。因此，过度投加 Ca 盐可以作为去除生物污垢的一种适当方法。所有凝胶在中等应变下都表现出永久应变硬化，并且它们的机械性能表现出对其应变历史的依赖性。即使在施加 200%振幅的振荡应变导致凝胶结构崩溃之后，凝胶在最初的 20 秒内恢复了其原始剪切模量的 65%至 90%，在很大程度上是这样。对于 CaCO 浓度较高的凝胶，恢复稍少。在用具有多个 Kelvin 元件的 Burgers 模型拟合的蠕变测试中，至少可以区分 ALE 凝胶中的三种不同相互作用，其特征延迟时间在 10、100 和 1000s 范围内。进一步确定凝胶力学背后的机制将允许开发有针对性的策略来破坏生物污垢的机械强度，并有助于清洁过程。
