In the present era, there is a wide range of progress in the polymeric materials which are related to external stimuli and used in the application of robotics, biomedical engineering and optical devices. These materials are classified into two classes (1) Shape-Changing Materials in which a certain type of shape-shifting is encoded in the original material. (2) Shape-Memory materials which do not have any fixed Shape-Shifting as prepared, but allow programming of complex shape transformations. Even though we know shape shifting polymers from Decades, till now there is no proper material that is spotted on the basic molecular behaviour responsible for the materials properties, so we need to adapt them to new applications on trial-and-error approaches. The goal of this review is to highlight recent developments in reversible shape-shifting by introducing novel mechanisms, materials, and applications.
What are Shape-Shifting Polymers?
Shape-shifting material changes upon external stimuli, converting stored potential energy into motion as actuators. Polymeric Materials have been intensively explored due to their low density, high deformability and wide range of synthetic strategies in molecular design and functionalization. Shape-shifting polymers can transform under a variety of stimuli including heat, electricity, light, solvent and magnetic field.
Shape-Shifting Materials are divided into two types:
a) Shape memory polymers can be programmed to hold a particular temporary conformation which reverts to a different, permanent shape when heat is applied. To do this the temporary shape is formed within a phase transition of the polymer
Example: The glass transition where the molecules of the polymer change from a ’frozen’ glassy state to a more mobile ’rubbery’ state upon heating.
b) Shape-changing materials undergo reversible shape alterations upon various stimuli. Generally speaking, nearly all objects change their dimensions in response to minute changes in the surrounding environment.
Example: Thermal expansion and swelling.
Shape-shifting materials can perform shape variations from macroscopic to micro/nanoscales. Dynamic change in surface topologies and microstructures can affect physical properties including wetting, adhesion and propulsion effects.
The shape shifting of polymers is followed by force generation, transforming stimuli into mechanical energy. With complex designing, the samples have the ability to perform remote manipulated self-loco motions as micro robotics. By applying the concept of cyclic stimuli, the reversible deformation of bending and unbending can be altered into motions such as swimming, walking, etc.
Biomedical Devices and Artificial Muscles
Mechanically smart polymers which shift shape have large capability in biomedical applications. For example, in minimally invasive surgery, vasospasms can be prevented by specially designed shape shifting stents. The stent can be inserted or removed as thin wires and can be expanded in situ under stimuli.
This review presents a summary of different concepts of shape-shifting in polymeric materials. Demands in potential applications from micro robotics to biomedical devices require materials that are capable of reversibly actuating between sophisticated shapes, from macro to nanoscales and within a variety of environments under different stimuli. The test was met with advancement through both substance plans with artificially new materials and novel instruments and conventions that grow the uses of existing polymers. The advances show a promising future for smart materials that could change our day-to-day routine.