Research Centre "E. Piaggio", University of Pisa, Largo Lucio Lazzarino 1, 56122 Pisa, Italy; Department of Information Engineering, University of Pisa, Via Girolamo Caruso 16, 56122 Pisa, Italy.
Research Centre "E. Piaggio", University of Pisa, Largo Lucio Lazzarino 1, 56122 Pisa, Italy.
J Mech Behav Biomed Mater. 2019 Jan;89:162-167. doi: 10.1016/j.jmbbm.2018.09.031. Epub 2018 Sep 21.
The aim of this study was to identify a method for modifying the time-dependent viscoelastic properties of gels without altering the elastic component. To this end, two hydrogels commonly used in biomedical applications, agarose and acrylamide, were prepared in aqueous solutions of dextran with increasing concentrations (0%, 2% and 5% w/v) and hence increasing viscosities. Commercial polyurethane sponges soaked in the same solutions were used as controls, since, unlike in hydrogels, the liquid in these sponge systems is poorly bound to the polymer network. Sample viscoelastic properties were characterised using the epsilon-dot method, based on compression tests at different constant strain-rates. Experimental data were fitted to a standard linear solid model. While increasing the liquid viscosity in the controls resulted in a significant increase of the characteristic relaxation time (τ), both the instantaneous (E) and the equilibrium (E) elastic moduli remained almost constant. However, in the hydrogels a significant reduction of both E and τ was observed. On the other hand, as expected, E - an indicator of the equilibrium elastic behaviour after the occurrence of viscoelastic relaxation dynamics - was found to be independent of the liquid phase viscosity. Therefore, although the elastic and viscous components of hydrogels cannot be completely decoupled due to the interaction of the liquid and solid phases, we show that their viscoelastic behaviour can be modulated by varying the viscosity of the aqueous phase. This simple-yet-effective strategy could be useful in the field of mechanobiology, particularly for studying cell response to substrate viscoelasticity while keeping the elastic cue (i.e. equilibrium modulus, or quasi-static stiffness) constant.
本研究旨在寻找一种不改变弹性成分而改变凝胶时变粘弹性的方法。为此，我们制备了两种常用于生物医学应用的水凝胶：琼脂糖和丙烯酰胺，将它们溶解在浓度逐渐增加（0%、2%和 5%w/v）的葡聚糖水溶液中，从而增加溶液的粘度。我们使用相同溶液浸泡的商业聚氨酯海绵作为对照，因为与水凝胶不同，这些海绵系统中的液体与聚合物网络的结合很差。使用基于不同恒应变速率压缩试验的ε-dot 方法来表征样品的粘弹性。实验数据符合标准线性固体模型。在对照中，增加液体的粘度会导致特征松弛时间（τ）显著增加，瞬时（E）和平衡（E）弹性模量几乎保持不变。然而，在水凝胶中，E 和 τ 都观察到显著降低。另一方面，正如预期的那样，E-粘弹性松弛动力学发生后平衡弹性行为的指标-被发现与液相粘度无关。因此，尽管由于液相和固相之间的相互作用，水凝胶的弹性和粘性成分不能完全解耦，但我们表明可以通过改变水相的粘度来调节其粘弹性行为。这种简单有效的策略在机械生物学领域可能很有用，特别是在研究细胞对基质粘弹性的响应时，可以保持弹性线索（即平衡模量或准静态刚度）不变。
