Design and mechanical evaluation of additively-manufactured graded TPMS lattices with biodegradable polymer composites

Triply periodic minimal surfaces (TPMS) structures have been extensively promoted for mimicking the tissue scaffolds with interconnected pores and robust mechanical properties. To further optimize the mechanical performance, two kinds of TPMS structures including Schwarz P (P) and Gyroid (G) with uniform and different graded-thickness were designed and proposed in the current work. Biodegradable polymer composites based on poly (butyleneadipate-co-terephthalate) (PBAT) and poly (lactic acid) (PLA) were developed into fused filament fabrication (FFF) filaments. Results showed that PBAT/PLA filaments exhibited good flexibility, thermal and rheological properties and high printability. As for compressive properties, the load-bearing capacity and energy absorption (EA) of TPMS-G were superior to TPMS-P uniform structures. TPMS-G graded samples exhibited better EA capacity, whereas those of graded TPMS-P were inferior to uniform counterparts. The deformation behavior of the internal structure in graded TPMS-G and TPMS-P were examined by computed tomography (CT) scanning and reconstruction. Furthermore, tensile properties of graded and non-graded TPMS were also compared. Under tension load, results demonstrated that non-graded structure of TPMS were both stronger than the graded ones. The proposed biodegradable PBAT/PLA composite and structure design could be applied as biomedical soft scaffolds, wearable devices and resilient absorbing buffers.