4D direct ink writing of body temperature-responsive triple-shape memory scaffolds for bone tissue engineering

Four dimensional printing of shape memory polymers (SMPs) holds significant promise for addressing irregular bone defects. The incorporation of SMPs with the ability to adopt multiple shapes greatly enhances the performance of 4D-printed scaffolds. These smart scaffolds not only provide crucial structural support but also actively interact with cells to promote and enhance regenerative processes. In this study, we successfully developed novel triple-SMPs with two distinct transition temperatures (T_g= 34 °C andT_m= 56 °C). By melt blending biocompatible thermoplastics, including polycaprolactone, thermoplastic polyurethane, and Poly (lactic-co-glycolic acid) (PLGA), at different weight ratios, we achieved over 90% shape recovery ratios during two sequential recovery processes. Shape memory tests revealed that the weight ratio of PLGA in the polymer composition influenced the shape fixity and shape recovery of programmed structures at body temperature. Subsequently, the developed SMPs were utilized for 4D direct ink writing printing of smart bone scaffolds. The SMPs exhibited excellent printability, enabling successful printing at 220 °C and 200 kPa, resulting in 3D-printed scaffolds with uniform and interconnected pore distribution, ensuring structural integrity. Furthermore, the 4D-printed scaffolds demonstrated outstanding degradability, biocompatibility, and mechanical properties comparable to human trabecular bone. This work presents a robust and feasible approach for 4D printing of triple-shape memory bone scaffolds, offering a promising solution for complex irregular bone defects.