Nöchel Ulrich, Behl Marc, Balk Maria, Lendlein Andreas
Institute of Biomaterial Science and Berlin-Brandenburg Center for Regenerative Therapies (BCRT) and ‡Joint Laboratory for Biomaterials and Regenerative Medicine, Helmholtz-Zentrum Geesthacht , Kantstr. 55, 14513 Teltow, Germany.
ACS Appl Mater Interfaces. 2016 Oct 19;8(41):28068-28076. doi: 10.1021/acsami.6b09581. Epub 2016 Oct 10.
Shape-memory hydrogels enable directed movements of a specimen in response to temperature, whereby crystallizable switching segments incorporated as side chains resulted in constant degrees of swelling during the shape-memory cycle. Here we report about hydrogels exhibiting a thermally induced triple-shape effect that allows complex movements of soft materials with two almost independent shape changes. Potential applications for those soft triple-shape materials are two-step self-unfolding devices or temperature-sensitive hydrogel actuators, for example, smart valves for flow rate control in aqueous media. Series of hydrogels with two different hydrophobic crystallizable switching segments were prepared. The degrees of swelling of the triple-shape hydrogels were not affected for different shapes or temperatures, which avoided in this way interferences on the shape shifts. During the two-step programming procedure, two distinct shapes can be implemented as reflected by shape fixity ratios of generally >50%. Structural analysis of the switching domains during the triple-shape cycle by means of X-ray scattering indicates that longer side chains gain lower orientation after deformation and that shorter side chains orient perpendicular to the hydrophilic main chain. Furthermore, it is observed that increased orientation of the switching domains is not a key requirement for adequate shape fixity and recovery ratios of the triple-shape effect in hydrogels, thus longer side chains can be utilized as switching segments in other shape-memory hydrogels.
形状记忆水凝胶能够使样本响应温度进行定向运动，其中作为侧链并入的可结晶开关段在形状记忆循环期间导致恒定的溶胀度。在此，我们报道了表现出热诱导三形状效应的水凝胶，该效应允许软材料进行具有两个几乎独立形状变化的复杂运动。这些软三形状材料的潜在应用包括两步自展开装置或温度敏感水凝胶致动器，例如用于控制水性介质中流速的智能阀。制备了一系列具有两种不同疏水性可结晶开关段的水凝胶。三形状水凝胶的溶胀度不受不同形状或温度的影响，从而避免了对形状变化的干扰。在两步编程过程中，可以实现两种不同的形状，通常形状固定率>50%即可反映这一点。通过X射线散射对三形状循环期间开关域进行结构分析表明，较长的侧链在变形后取向较低，而较短的侧链垂直于亲水性主链取向。此外，观察到开关域取向的增加不是水凝胶中三形状效应具有足够形状固定率和回复率的关键要求，因此较长的侧链可作为其他形状记忆水凝胶中的开关段。
