Tailoring the Shape-Memory Performance of 2D and 3D Fabricated Semi-Crystalline PCL Networks Via Optimal Crosslinking

Photo-crosslinking is a fast and efficient approach to obtain chemically crosslinked semi-crystalline networks featuring both one-way and two-way shape-memory effect. However, the effect of photo-crosslinking parameters and fabrication method on the physical, thermo-mechanical, and shape-memory properties of these networks still has to be investigated. This paper aims to fill this gap, specifically focusing on semi-crystalline polycaprolactone (PCL) networks. In detail, the influence of key photo-crosslinking parameters -crosslinking temperature and UV light intensity- as well as the fabrication method -2D vs. 3D- were investigated. As a general trend, crosslinking above the melting temperature of PCL and selecting a high UV light intensity yielded structures with superior performance, also displaying stress-free shape-memory behavior. Conversely, crosslinking below the crystallization temperature of PCL and selecting a low UV light intensity led to reduced performance and absence of stress-free actuation. To address this limitation, a post-treatment involving additional UV exposure was introduced, which significantly improved overall performance, particularly enhancing the two-way shape-memory behavior. Interestingly, although the 3D printed samples displayed thermal properties comparable to their 2D counterparts, their shape-memory performance was significantly reduced. Overall, these findings provide practical design guidelines for engineering 2D and 3D PCL-based semi-crystalline structures with tunable physical, thermal, and shape-memory properties.