An Inverse Shape‐Memory Hydrogel Scaffold Switching Upon Cooling in a Tissue‐Tolerated Temperature Range

Abstract

either by covalent or physical interaction) is heated above a thermal transition temperature T trans (a glass (T g ) or melting transition temperature (T m )) associated to the switching domains and deformed into a new shape. The temporary shape is obtained after cooling of the sample below T trans and release of external stress. This temporary shape is stable until it is exposed to heat and a switching temperature T sw is exceeded. If the SME is triggered, the material recovers its original shape. It is a one-way effect, meaning that the original shape will not change upon cooling. The fixation of the temporary shape is caused by the formation of temporary cross-links in addition to the netpoints of the polymer network (e.g., phase transition within a semi-crystalline matrix). Various material concepts with sophisticated functions and abilities based on this technology have been reported, [2] e.g., in triblock copolymers from poly(raclactide)-b-poly(propylene oxide)-b-poly(raclactide) dimethacrylates the classical SME functionality based on the T g of the poly(rac-lactide segments) could be combined with degradability. [3] In addition to the classical SME, materials with advanced functions such as triple-or multi-shape-effect were created. [1b,4] Similarly to classical SME, in triple-or multi-shapeeffect polymers the temporary shape is reversed by heating.SME materials have great potential in biomedical application scenarios spanning from a SMP-based self-tightening suture for wound closure up to stents or aneurysm occlusion devices. [5] Of special interest are application scenarios for minimally invasive surgery based on their capability to change shape. So far SMP became elastic when heated. It was the aim of this study to design and fabricate a cell-compatible poly mer-based network with a cooling-induced inverse SME (iSME) within a tissue-tolerated temperature range. In case of an iSME the temporary shape is stable until the material is cooled to T sw . In analogy to the SME, the iSME is a one-time, one-way effect. Once the original shape is recovered, the material does not switch back. Even if heated again, the material remains in its permanent shape obtained during cooling. In this way iSME materials differ from soft artificial muscles (actuators [6] ), who lose their shape obtained during cooling when heated. Potential applications for such a biomaterial system with an iSME are envisaged in soft tissue reconstruction where the device needs to be placed minimally invasively.Soft tissue reconstruction faces various challenges. Current clinically established approaches are based on multiple surgical Tissue reconstruction has an unmet need for soft active scaffolds that enable gentle loading with regeneration-directing bioactive components by soaking up but also provide macroscopic dimensional stability. Here microporous hydrogels capable of an inverse shape-memory effect (iSME) are described, which in contrast to classical shape-memory polymers (SMPs) recover their permanent shape upon cooling. These hyd...

Shape Memory Hydrogels for Biomedical Applications

“…Thermally responsive SMHs can be programmed to actuate when stimulated by an external thermal stimulation. Thermal activation was the first reported means of externally actuating SMPs and is still the most widely used shape-morphing approach [39][40][41][42]. Typically, thermoresponsive materials are prepared by functionalization/modification of thermoresponsive polymeric networks to allow for temporal shape-morphing.…”