Martikainen Lahja, Bertula Kia, Turunen Matti, Ikkala Olli
Department of Applied Physics, Molecular Materials Group, Aalto University School of Science, FI-00076 Espoo, Finland.
Department of Bioproducts and Biosystems, Aalto University School of Chemical Engineering, FI-00076 Espoo, Finland.
Macromolecules. 2020 Nov 24;53(22):9983-9992. doi: 10.1021/acs.macromol.0c00601. Epub 2020 Sep 14.
Inspired by the specific strain stiffening and negative normal force phenomena in several biological networks, herein, we show strain stiffening and negative normal force in agarose hydrogels. We use both pre-strain and strain amplitude sweep protocols in dynamic rheological measurements where the gel slip was suppressed by the gelation in the cross-hatched parallel plate rheometer geometry. Within the stiffening region, we show the scaling relation for the differential modulus ∝ σ, where σ is stress. The strain at the onset of stiffening is almost constant throughout the concentration range. The gels show negative apparent normal stress difference when sheared as a result of the gel contraction. The pore size of the hydrogel is large enough to allow water to move with respect to the network to balance the pressure difference caused by the hoop stress. The rheological analysis together with scanning electron microscopy suggests that the agarose gels can be described using subisostatic athermal network models where the connectivity dictates the stiffening behavior. Therefore, the simple agarose gels appear to capture several of the viscoelastic properties, which were previously thought to be characteristic to biological protein macromolecules.
受几种生物网络中特定的应变硬化和负法向力现象的启发，在此我们展示了琼脂糖水凝胶中的应变硬化和负法向力。在动态流变测量中，我们使用预应变和应变幅度扫描方案，其中在交叉阴影平行板流变仪几何结构中通过凝胶化抑制凝胶滑动。在硬化区域内，我们展示了微分模量的标度关系 ∝ σ，其中 σ 是应力。在整个浓度范围内，硬化开始时的应变几乎是恒定的。由于凝胶收缩，凝胶在剪切时表现出负的表观法向应力差。水凝胶的孔径足够大，以允许水相对于网络移动，以平衡由环向应力引起的压力差。流变学分析与扫描电子显微镜表明，琼脂糖凝胶可以用亚等静压无热网络模型来描述，其中连通性决定了硬化行为。因此，简单的琼脂糖凝胶似乎捕捉到了几种粘弹性特性，这些特性以前被认为是生物蛋白质大分子所特有的。
