Additive Manufacturing Protocol for Production of Complex and Oscillating POSS-Based 4D Structures

Two-way shape memory polymers (2WSMPs) are a fascinating class of materials with the unique ability to revert between two distinct shapes in response to external stimuli. Upon exposure to a specific stimulus, such as heat or humidity, the polymer undergoes a reversible transition, enabling it to switch back and forth between the two shapes. This dynamic behavior of 2WSMPs opens up a wide range of potential applications in fields like medicine, aerospace, soft robotics, and smart textiles.<br/>In this study, complex and high-performance 2WSMPs actuators were manufactured for the first time via direct ink writing (DIW) additive manufacturing (AM) technique of crosslinked poly Oligomeric Silsesquioxanes (PolyPOSS) thermoset applied on a Kapton film. For this purpose, a fused filament fabrication (FFF) 3D printer was converted into a DIW 3D printer.<br/>Initially, physical parameters such as PolyPOSS gelation time at various temperatures, as well as its wetting ability on Kapton substrates were investigated. Then, PolyPOSS printing parameters were meticulously investigated, and ideal printing parameters were identified while establishing a unique printing protocol for thermoset polymers.<br/>Parameters such as printing speed, volumetric flow rate, layer height, and layer width were investigated, and the results were confined and evaluated according to a single printing index developed uniquely for this purpose. A set of printing parameters that yields the lowest printing index, i.e., the most unified printed lines, was identified. The optimal line distance to print a uniform layer was then tested. After obtaining a satisfactory first layer, an additional set of printing parameters, this time for a second layer, was established.<br/>Finally, various complex 2WSMP actuators were printed. The actuators’ response to various temperatures, gripping abilities, and unique as well as oscillating shape memory behaviors was recorded.<br/>We thus showed that using AM allows complex 2WSMP structures to be produced in a manner that would be nearly impossible with conventional casting manufacturing methods.